Central Sleep Apnea in Patients With Coronary Heart Disease Taking P2Y12 Inhibitors

ABSTRACT

Central sleep apnea (CSA) is common in patients with heart failure. Recent studies link ticagrelor use with CSA. We aimed to evaluate CSA prevalence in patients with coronary heart disease (CHD) and whether ticagrelor use is associated with CSA. We reviewed consecutive patients with CHD who underwent a polysomnography (PSG) test over a 5-year period from 3 sleep centers. We sampled patients who were on ticagrelor or clopidogrel during a PSG test at a 1:4 ticagrelor:clopidogrel ratio. Patients with an active opioid prescription during PSG test were excluded. Age, left ventricle (LV) dysfunction, and P2Y12 inhibitor use were included in a multivariate logistic regression. A total of 135 patients were included with 26 on ticagrelor and 109 on clopidogrel (age 64.1 ± 11.4, 32% male). High CSA burden (12%) and strict CSA (4.4%) were more common in patients on ticagrelor than in those on clopidogrel (27% vs. 8.3% and 10.0% vs. 1.8%). Ticagrelor use (vs. clopidogrel) was associated with high CSA burden (OR 3.53, 95% CI 1.04-12.9, P = 0.039) and trended toward significance for strict CSA (OR 6.32, 95% CI 1.03-51.4, P = 0.052) when adjusting for age and LV dysfunction. In an additional analysis also adjusting for history of atrial fibrillation, ticagrelor use and strict CSA became significantly associated (OR 10.0, 95% CI 1.32-117, P = 0.035). CSA was uncommon in patients with CHD undergoing sleep studies. Ticagrelor use (vs. clopidogrel) was associated with high CSA burden and trended toward significance for strict CSA.

Delayed esophageal anastomotic complication and ramucirumab therapy: A case report

Current NCCN guidelines for second-line therapy in recurrent or metastatic esophago-gastric cancers recommend the use of VEGF inhibitors such as ramucirumab. VEGF inhibitors have been shown to be associated with gastrointestinal perforation in clinical trials and late colorectal anastomotic leaks in a few case reports. Here, we present a case of late esophageal anastomotic leak in a patient receiving ramucirumab. Case information was obtained from our institution's electronic medical records. The patient was found to have T4N1M0, poorly differentiated invasive adenocarcinoma and subsequently received neoadjuvant chemoradiation followed by hybrid Ivor-Lewis esophagectomy 6 weeks later. He recovered well with no leak or perioperative complications. The patient had disease progression 9 months postoperatively on CT and PET imaging. Sixteen months after surgery he began paclitaxel and ramucirumab and 16 weeks after ramucirumab initiation, he was found to have an esophago-pulmonary fistula in the region of the anastomosis. Biopsies were negative for recurrence at the anastomosis. He died one week later from progressive pneumonia despite stenting. In conclusion, this is the only known report of delayed esophageal anastomotic complication associated with ramucirumab. VEGF inhibitor therapies such as bevacizumab have been associated with late (greater than 3 months postoperative) colorectal anastomotic complications including fistulas and leaks. Risk factors that have been associated are perioperative radiotherapy and history of early postoperative leak. These findings raise concern whether VEGF inhibitor therapy should be used in post-esophagectomy patients with recurrence if these rare but catastrophic events are likely to be terminal.

Sleep time and efficiency in patients undergoing laboratory-based polysomnography

STUDY OBJECTIVES

Sleep quality in patients studied with laboratory-based polysomnography may differ from sleep quality in patients studied at home but remains clinically relevant and important to describe. We assessed objective sleep quality and explored factors associated with poor sleep in patients undergoing laboratory-based polysomnography.

METHODS

We reviewed diagnostic polysomnography studies from a 10-year period at a single sleep center. Total sleep time (TST) and sleep efficiency (SE) were assessed as markers of sleep quality. Poor sleep was defined as TST ≤ 4 hours or SE ≤ 50%. Multivariable analysis was performed to determine associations between objective sleep quality as an outcome and multiple candidate predictors including age, sex, race, body mass index, comorbidities, severity of obstructive sleep apnea, and central nervous system medications.

RESULTS

Among 4957 patients (age 53 ± 15 years), average TST and median SE were 5.8 hours and 79%, respectively. There were 556 (11%) and 406 (8%) patients who had poor sleep based on TST and SE, respectively. In multivariable analysis, those who were older (per 10 years: 1.48 [1.34, 1.63]), male (1.38 [1.14,1.68]), and had severe obstructive sleep apnea (1.76 [1.28, 2.43]) were more likely to have short sleep. Antidepressant use was associated with lower odds of short sleep (0.77 [0.59,1.00]). Older age (per 10 years: 1.48 [1.34, 1.62]), male sex (1.34 [1.07,1.68]), and severe obstructive sleep apnea (2.16 [1.47, 3.21]) were associated with higher odds of poor SE.

CONCLUSIONS

We describe TST and SE from a single sleep center cohort. Multiple demographic characteristics were associated with poor objective sleep in patients during laboratory-based polysomnography.

CITATION

Harrison EI, Roth RH, Lobo JM, et al. Sleep time and efficiency in patients undergoing laboratory-based polysomnography. J Clin Sleep Med. 2021;17(8):1591-1598.

0840 Sleep Quality in Clinically Indicated In-Laboratory Polysomnography

Introduction

Few studies have explored how patients sleep or what characteristics might be predictive of poor sleep during clinically-indicated polysomnography (PSG) in an in-laboratory setting.

Methods

We reviewed clinically indicated diagnostic PSG studies completed over a 10-year period in a single academic sleep center. Total sleep time (TST) and sleep efficiency (SE) were used as proxies for sleep quality. Patients were categorized as normal or poor sleepers based on TST <4 hours or SE <50%. Multivariate linear and logistic regression analyses were performed to determine factors associated with sleep quality while controlling for demographics, medications, comorbidities and measures of sleep.

Results

We included 4957 patients, who were mostly female (58.9%), middle-aged (52.9 y), Caucasian (69.3%), and overweight or obese (91.3%). 3682 patients (74.2%) were diagnosed with sleep apnea (Apnea Hypopnea Index(AHI)>5/hr).

Average TST was 5.75±1.43 hours (Interquartile range [IQR] = 4.94 - 6.73) and average SE was 75.1%±16.1% (IQR=66.9 - 87.2). TST and SE were lower for males compared to females (5.48 vs 5.93 hr, p<0.001; 73% vs 77%, p<0.001). In multivariable analysis, older age (TST: OR = 1.04, 95% CI:[1.03,1.05]; SE: OR = 1.04, 95% CI:[1.04,1.05]), male sex (TST: 1.38,[1.14,1.68]; SE: 1.34,[1.07,1.68]), normal body habitus (TST: 1.47,[1.02,2.08]; SE: 1.51,[1.01,2.27]) and a higher AHI (TST: 1.02,[1.02,1.03]; SE: 1.02,[1.003,1.03]) were significantly associated with being a poor sleeper for both TST and SE. Antidepressant use was associated with poor sleep for TST (0.77, [0.59,1]), but not for SE (0.98, [0.73,1.3]).

Conclusion

Sleep quality during the in-laboratory PSG differed by sex, age and presence of sleep apnea. Sleep quality during in-lab PSG is thought to be compromised by obtrusive monitoring and an unfamiliar environment, but average sleep quality may be higher than expected for patients in the laboratory. Future studies should consider examining in-lab sleep quality in different patient populations.

Support

N/A

1052 Continuous Blood Pressure Monitoring In Sleep

Introduction

Abnormal nocturnal blood pressure(BP) such as non-dipping or nocturnal hypertension(reverse-dipping) represents a potent marker for cardiovascular risks. Standard cuff-based ambulatory nocturnal BP measurement yields limited data points potentially resulting in imprecise results, especially compared to continuously recorded BP. We hypothesized nocturnal BP based on periodic measurement would be different from true average beat-to-beat based BP.

Methods

We prospectively enrolled patients undergoing clinically indicated in-lab polysomnography, both CPAP and non-CPAP studies, for sleep apnea evaluation. Nocturnal BP was continuously monitored beat-to-beat by a noninvasive Caretaker™ device, which uses the Pulse Decomposition Analysis(PDA) algorithm. We compared BP recorded at 30-minute intervals with average BP continuously recorded over 30 minutes, both recorded by Caretaker™. We also looked at the differences between recording spot and continuous BP from an awake or sleeping state and BP variability(SD) based on continuously recorded BP. Using first 30 min as a reference, we determined dipping status (dipping: 10-20% reduction, level: 0-10% reduction, riser: any increase) by the two methods.

Results

A total of 18 patients were recruited(male:11, mean age:52.2). Among a total of 261 periodic BP measurements, 60 (30.0%) were obtained while awake. Mean nocturnal SBP by periodic BP measurement was higher compared with beat-to-beat-derived average BP(135.6mmHg[24.2] vs. 131.5[20.3], p<0.0001). The difference between the two methods remained similar when continuous BP was derived from sleep vs. awake period(4.5mmHg[3.1] vs. 7.7[9.9], p=0.202). BP variability was more pronounced during awake compared with sleep period(6.7mmHg[8.1] versus 3.95[7.5], p=0.047). 8 patients were dippers by spot check measurement, but 11 were dippers by continuous BP.

Conclusion

Standard ambulatory periodic nocturnal BP recording may not yield true sleep BP patterns due to its spot-check nature and lack of sleep-awake information, which leads to inaccurate dipping measurements. Incorporation of beat-to-beat continuous BP measurement can provide more accurate and meaningful nocturnal BP information.

Support

N/A

Comparison of Neurotoxicity following Repeated Administration of L-Dopa, D-Dopa, and Dopamine to Embryonic Mesencephalic Dopamine Neurons in Cultures Derived from Fisher 344 and Sprague-Dawley Donors

Levodopa is the most efficacious and widely used symptomatic drug for Parkinson's disease (PD). There is currently, however, a great deal of interest focused on the possibility that levodopa-induced increases in dopamine (DA) turnover may increase oxidative damage derived from the breakdown of DA. Increased oxidative damage following levodopa may contribute to the progressive degeneration of remaining host nigral neurons as well as interfere with development and function of embryonic nigral neurons in neural grafting trials. There is abundant evidence that levodopa is toxic to embryonic nigral DA neurons in both cell culture and neural grafting models. These findings have prompted a number of studies on mechanisms of levodopa toxicity to identify effective means of ameliorating potential oxidative stress related to levodopa in PD. In the current study we have utilized cultures of embryonic nigral DA neurons to address the fundamental question of whether levodopa-induced toxicity is related to DA production or whether dopa itself contributes to cell death. We compared the degree of nigral DA cell death following chronic administration of: 1) levodopa (e.g.: l-dopa); 2) its less active stereoisomer d-dopa; and 3) DA. We examined the rank order of toxicity of these compounds in two species of rats, Fisher 344 (F344) and Sprague-Dawley (SD). Results indicate a toxicity profile of: DA > l-dopa > > d-dopa. In addition, although there was no difference in response of F344 and SD cultures to l-dopa, the SD cultures were significantly more susceptible to the neurotoxic effects of DA. Taken collectively, these results suggest that levodopa-induced toxicity is related primarily to DA production rather than oxidation of dopa to toxic metabolites, and that some strain related differences do exist.

Metabolic Energy Capacity of Dopaminergic Grafts and the Implanted Striatum in Parkinsonian Nonhuman Primates as Visualized with Cytochrome Oxidase Histochemistry

Histochemistry for visualization of the mitochondrial enzyme cytochrome oxidase has been used to detect cellular and regional differences in brain energy metabolism. We have examined the pattern of cytochrome oxidase (CO) staining in grafts of embryonic ventral mesencephalic tissue, and in the implanted striatum, of MPTP-treated monkeys as one index of the functional activity of grafted tissue and its influence on the host brain. Four monkeys were selected for study based on interesting variations in dopamine (DA) neuron content of their bilateral grafts as demonstrated with tyrosine-hydroxylase (TH) immunocytochemistry. The results suggest that grafts rich in DA neurons increase the metabolic activity of the implanted striatum of DA-depleted monkeys, and that this improvement of local energy metabolism is greater in the vicinity of grafts containing greater numbers of DA neurons. In addition, the pattern of CO staining within tissue transplants indicates that DA neurons exhibit the highest rate of metabolic activity among all cell types contained in the ventral mesencephalic grafts, and that the transplants receive metabolically active innervation from outside or within the grafted tissue.

Restoration of Dopamine Transporter Density in the Striatum of Fetal Ventral Mesencephalon-Grafted, but not Sham-Grafted, Mptp-Treated Parkinsonian Monkeys

Transplantation of fetal dopamine neurons to the adult striatum potentially offers a means to reverse the striatal dopamine deficiency that characterizes Parkinson's disease. Many investigations in rodents have supported the hope that neural grafting may be a useful treatment for parkinsonism. However, clinical studies have generally produced more modest improvements in motor abnormalities than observed in lower species. It is possible that the number of fetal dopamine neurons that survive transplantation is insufficient to restore dopaminergic innervation of the large human striatum to a level where striking recovery is obtained. In fact, there has been no quantitative study of graft outgrowth to indicate what portion of the dopamine-depleted striatum might be reinner-vated with present techniques. Furthermore, it has been speculated that regeneration of the host dopamine system in response to the implantation surgery may play an important role in the beneficial effects of neural grafting in primates. The present study used nine 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated parkinsonian monkeys to investigate these issues. Sham implantation procedures produced no increase in either dopamine transporter density (measured by quantitative autoradiography) or tissue dopamine concentration (measured by HPLC) in the striatum of MPTP-treated monkeys. In sham-grafted and nonimplanted MPTP-treated monkeys, the striatal dopamine concentration was reduced by 99%, based on analysis of 16 sampled sites in the caudate nucleus and putamen of each monkey. No behavioral recovery was seen in the sham-grafted and nonimplanted MPTP-treated groups. In contrast, transplantation of fetal dopamine neurons to the caudate nucleus or putamen of MPTP-treated monkeys resulted in a significant elevation of dopamine transporter density and dopamine levels in the grafted striatal nucleus. Each grafted MPTP-treated monkey received ventral mesencephalon dopamine neurons from one donor harvested during putative neurogenesis. Donor ventral mesencephalon was divided equally and implanted into six sites either in the caudate nucleus or putamen. One graft site in each monkey was examined by dopamine transporter autoradiography. In sections in which graft fibers were present, a mean of one-third of the volume of the grafted nucleus was occupied by an elevated density of dopamine transporters. This increase in dopamine transporter density was defined to be at least 5-10% of the control density. However, full behavioral recovery was not observed in the grafted MPTP-treated group. These data provide no support for the hypothesis that regeneration of the host dopamine system occurs in response to a sham implantation procedure in severely parkinsonian monkeys. The current study illustrates the power of the applied techniques for delineating the relationship between the level of host dopamine depletion, the extent of graft-induced dopaminergic restoration, and behavioral recovery.

Neural Stem Cells Implanted into MPTP-Treated Monkeys Increase the Size of Endogenous Tyrosine Hydroxylase-Positive Cells Found in the Striatum: A Return to Control Measures

Neural stem cells (NSC) have been shown to migrate towards damaged areas, produce trophic factors, and replace lost cells in ways that might be therapeutic for Parkinson's disease (PD). However, there is very little information on the effects of NSC on endogenous cell populations. In the current study, effects of implanted human NSC (hNSC) on endogenous tyrosine hydroxylase-positive cells (TH+ cells) after treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were explored in nonhuman primates. After MPTP damage and in PD, the primate brain is characterized by decreased numbers of dopamine neurons in the substantia nigra (SN) and an increase in neurons expressing TH in the caudate nucleus. To determine how implanted NSC might affect these cell populations, 11 St. Kitts African green monkeys were treated with the selective dopaminergic neurotoxin, MPTP. Human NSC were implanted into the left and right caudate nucleus and the right SN of eight of the MPTP-treated monkeys. At either 4 or 7 months after NSC implants, the brains were removed and the size and number of TH+ cells in the target areas were assessed. The results were compared to data obtained from normal untreated control monkeys and to the three unimplanted MPTP-treated monkeys. The majority of hNSC were found bilaterally along the nigrostriatal pathway and in the substantia nigra, while relatively few were found in the caudate. In the presence of NSC, the number and size of caudate TH+ cells returned to non-MPTP-treated control levels. MPTP-induced and hNSC-induced changes in the putamen were less apparent. We conclude that after MPTP treatment in the primate, hNSC prevent the MPTP-induced upregulation of TH+ cells in the caudate and putamen, indicating that hNSC may be beneficial to maintaining a normal striatal environment.

Intrastriatal Grafts from Multiple Donors do not Result in a Proportional Increase in Survival of Dopamine Neurons in Nonhuman Primates

We examined the potential for “double grafts,” i.e., grafts from two donors in each recipient, to enhance the total number of ventral mesencephalic dopamine neurons that survive grafting in adult African green monkeys. Because dopamine cell survival in grafts represents a small percentage of the total number of neurons grafted, several human clinical trials recently have employed grafts of tissue from multiple donors (e.g., from two to eight embryos per host recipient) in attempts to increase the total number of dopamine neurons that survive in grafts. Presumably, this is intended to elevate dopamine levels by providing more dopamine neurons to the damaged brain to alleviate the symptoms of parkinsonism. While well-developed grafts with several thousand dopamine neurons were found in most recipient animals, we observed a reduced total number of tyrosine hydroxylase positive neurons in the grafts in spite of the presence of some double grafts that were larger than normal. The overall growth of the grafts was impressive; some grafts were so large that they spanned the full dorsoventral extent of the caudate nucleus, probably reflecting the fact that twice as much tissue was implanted in each drop site in comparison to our standard protocol. However, some animals revealed atypical patterns of neurite outgrowth that appeared limited to the grafted tissue, and at least one monkey revealed “amorphous” grafts generally lacking in cellular structure, which suggests a possible rejection phenomenon. These findings raise questions about the use of multiple donors and suggest that the likelihood of rejection and/or cell death may be enhanced, which is of potential importance in the design of grafting strategies for clinical applications.

Phencyclidine Model of Frontal Cortical Dysfunction in Nonhuman Primates

Long-term intake of noncompetitive N-methyl-D-aspartate (NMDA)/glutamate receptor antagonists, such as phencyclidine (PCP), can simulate schizophrenia-like symptomatology in human subjects and can produce aberrant behavior in animals. The behavioral changes produced by PCP in animals have been suggested to model certain primary symptoms of idiopathic psychotic disorders, and the neurobiological substrates affected by PCP have been implicated in the pathophysiology of schizophrenia. This review considers the validity of PCP-induced behaviors in animals as a model of the human disorder, and a developing hypothesis of PCP-induced neurochemical dysfunction within the prefrontal cortex is presented. The behavioral and neurochemical effects of PCP may support the notion that altered glutamatergic/dopaminergic interactions within prefrontal cortex contribute to the cognitive dysfunction of schizophrenia.

Low circulating levels of bisphenol-A induce cognitive deficits and loss of asymmetric spine synapses in dorsolateral prefrontal cortex and hippocampus of adult male monkeys

Bisphenol-A (BPA) is widely used in the manufacture of plastics, epoxy resins, and certain paper products. A majority of the population in the developed world is routinely exposed to BPA from multiple sources and has significant circulating levels of BPA. Although BPA is categorized as an endocrine disruptor with a growing literature on adverse effects, it is uncertain whether cognitive dysfunction is induced in humans by exposure to BPA. The present study examined the impact of BPA in primate brain by exposing adult male vervet monkeys for 4 weeks continuously to circulating levels of BPA that were in the range measured in studies of humans environmentally exposed to BPA. This regimen of exposure to BPA decreased both working memory accuracy and the number of excitatory synaptic inputs on dendritic spines of pyramidal neurons in two brain regions that are necessary for working memory (prefrontal cortex and hippocampus). These observed behavioral and synaptic effects were ameliorated following withdrawal from BPA. As Old World monkeys (e.g., vervets) and humans share some uniquely primate morphological, endocrine, and cognitive traits, this study indicates the potential for significant cognitive disruption following exposure of humans to BPA.

A potential compensatory role for endogenous striatal tyrosine hydroxylase-positive neurons in a nonhuman primate model of Parkinson's disease

The possibility of enhancing endogenous brain repair following neurological disorders, such as Parkinson's disease (PD), is of considerable recent interest. One such mechanism may exist in the striatum as an upregulated population of tyrosine hydroxylase (TH)-immunoreactive neurons that appear after 1-methyl-4-phenyl-1,2,3,6-tetra-hydropyridine (MPTP) lesions in nonhuman primates as well as in humans with PD. An intriguing possibility is that these endogenous neurons reflect a compensatory mechanism to mitigate the loss of striatal DA due to progressive destruction of the nigrostriatal pathway. The possibility of enhancing the number and function of this population is attractive; however, it is crucial to gain further information about these cells in order to comprehend more fully their possible therapeutic potential. The current research was designed to investigate the fate of this endogenous population in African green monkeys rendered parkinsonian by MPTP lesions. Specifically, we assessed changes in the numbers of striatal neurons expressing TH at differing stages of the toxin-induced behavioral disability and discovered a close relationship with symptom severity and striatal DA neuron numbers. Increased numbers of striatal TH-positive neurons were associated with MPTP treatment that produced parkinsonian symptoms compared to numbers of these neurons in MPTP-treated asymptomatic animals and untreated controls. Expression of striatal DA neurons peaked at the manifestation of symptoms in mild/moderate animals and remained stable in animals that were severely parkinsonian. Furthermore, in severely debilitated animals that improved after fetal dopaminergic grafts, we discovered a return to control levels of the endogenous population. Taken together, our results further support the concept that this population of DA neurons responds to variations in striatal DA tone and may serve as a compensatory mechanism to restore striatal DA levels in the context of significant depletion. Artificially manipulating this endogenous population could prove beneficial for PD treatment, especially for individuals in early disease stages.

Primate phencyclidine model of schizophrenia: sex-specific effects on cognition, brain derived neurotrophic factor, spine synapses, and dopamine turnover in prefrontal cortex

BACKGROUND

Cognitive deficits are a core symptom of schizophrenia, yet they remain particularly resistant to treatment. The model provided by repeatedly exposing adult nonhuman primates to phencyclidine has generated important insights into the neurobiology of these deficits, but it remains possible that administration of this psychotomimetic agent during the pre-adult period, when the dorsolateral prefrontal cortex in human and nonhuman primates is still undergoing significant maturation, may provide a greater understanding of schizophrenia-related cognitive deficits.

METHODS

The effects of repeated phencyclidine treatment on spine synapse number, dopamine turnover and BDNF expression in dorsolateral prefrontal cortex, and working memory accuracy were examined in pre-adult monkeys.

RESULTS

One week following phencyclidine treatment, juvenile and adolescent male monkeys demonstrated a greater loss of spine synapses in dorsolateral prefrontal cortex than adult male monkeys. Further studies indicated that in juvenile males, a cognitive deficit existed at 4 weeks following phencyclidine treatment, and this impairment was associated with decreased dopamine turnover, decreased brain derived neurotrophic factor messenger RNA, and a loss of dendritic spine synapses in dorsolateral prefrontal cortex. In contrast, female juvenile monkeys displayed no cognitive deficit at 4 weeks after phencyclidine treatment and no alteration in dopamine turnover or brain derived neurotrophic factor messenger RNA or spine synapse number in dorsolateral prefrontal cortex. In the combined group of male and female juvenile monkeys, significant linear correlations were detected between dopamine turnover, spine synapse number, and cognitive performance.

CONCLUSIONS

As the incidence of schizophrenia is greater in males than females, these findings support the validity of the juvenile primate phencyclidine model and highlight its potential usefulness in understanding the deficits in dorsolateral prefrontal cortex in schizophrenia and developing novel treatments for the cognitive deficits associated with schizophrenia.

Survival and Integration of Neurons Derived from Human Embryonic Stem Cells in MPTP-Lesioned Primates

A human embryonic stem cell (HESC) line, H1, was studied after differentiation to a dopaminergic phenotype in vitro in order to carry out in vivo studies in Parkinsonian monkeys. To identify morphological characteristics of transplanted donor cells, HESCs were transfected with a GFP lentiviral vector. Gene expression studies were performed at each step of a neural rosette-based dopaminergic differentiation protocol by RT-PCR. In vitro immunofluorescence revealed that >90% of the differentiated cells exhibited a neuronal phenotype by β-III-tubulin immunocytochemistry, with 17% of the cells coexpressing tyrosine hydroxylase prior to implantation. Biochemical analyses demonstrated dopamine release in culture in response to potassium chloride-induced membrane depolarization, suggesting that the cells synthesized and released dopamine. These characterized, HESC-derived neurons were then implanted into the striatum and midbrain of MPTP (1-methyl-4- phenyl-1,2,3,6-tetrahydropyridine)-exposed monkeys that were triple immunosuppressed. Here we demonstrate robust survival of transplanted HESC-derived neurons after 6 weeks, as well as morphological features consistent with polarization, organization, and extension of processes that integrated into the host striatum. Expression of the dopaminergic marker tyrosine hydroxylase was not maintained in HESC-derived neural grafts in either the striatum or substantia nigra, despite a neuronal morphology and expression of β-III-tubulin. These results suggest that dopamine neuronal cells derived from neuroectoderm in vitro will not maintain the correct midbrain phenotype in vivo in nonhuman primates, contrasted with recent studies showing dopamine neuronal survival using an alternative floorplate method.

Comparison of fetal mesencephalic grafts, AAV-delivered GDNF, and both combined in an MPTP-induced nonhuman primate Parkinson's model

We combined viral vector delivery of human glial-derived neurotrophic factor (GDNF) with the grafting of dopamine (DA) precursor cells from fetal ventral mesencephalon (VM) to determine whether these strategies would improve the anti-Parkinson's effects in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys, an animal model for Parkinson's disease (PD). Both strategies have been reported as individually beneficial in animal models of PD, leading to clinical studies. GDNF delivery has also been reported to augment VM tissue implants, but no combined studies have been done in monkeys. Monkeys were treated with MPTP and placed into four balanced treatment groups receiving only recombinant adeno-associated virus serotype 5 (rAAV5)/hu-GDNF, only fetal DA precursor cells, both together, or a buffered saline solution (control). The combination of fetal precursors with rAAV5/hu-GDNF showed significantly higher striatal DA concentrations compared with the other treatments, but did not lead to greater functional improvement in this study. For the first time under identical conditions in primates, we show that all three treatments lead to improvement compared with control animals.

Coordinated expression of dopamine transporter and vesicular monoamine transporter in the primate striatum during development

Several addictive or neurotoxic drugs are dependent on the dopamine transporter (DAT) and/or vesicular monoamine transporter (VMAT2) to exert their detrimental effects on dopamine neurons. For example, methamphetamine and MPTP are substrates for both DAT and VMAT2, with the ratio of DAT to VMAT2 in striatum being a determinant of the degree of toxicity inflicted by these drugs on dopamine neurons. Thus, the susceptibility of dopamine neurons to agents whose pharmacology involves DAT and VMAT2 may vary during development if the ontogeny of DAT and VMAT2 differs, and this is relevant as exposure of dopamine neurons to toxic agents during development is hypothesized to underlie some neurological or psychiatric disorders. However, the relative expression of DAT and VMAT2 has not been studied in either primate or nonprimate fetal brain, and this was addressed in the present study by measuring the binding of specific radioligands of DAT and VMAT2 to striatal membranes from nonhuman primates at mid-gestation, late-gestation, and the postnatal and adult periods. Dopamine concentration was also determined in striatal tissue from the same brains. These data indicate that in striatum of primates, unlike rodents, there is a sharp increase in DAT and VMAT2 expression after mid-gestation, with adult levels being attained at the time of birth. In addition, this study demonstrated that there is a coordinated expression of DAT and VMAT2 from the time of mid-gestation to adulthood.

Prenatal exposure to bisphenol A impacts midbrain dopamine neurons and hippocampal spine synapses in non-human primates

Prevalent use of bisphenol-A (BPA) in the manufacture of resins, plastics and paper products has led to frequent exposure of most people to this endocrine disruptor. Some rodent studies have suggested that BPA can exert detrimental effects on brain development. However as rodent models cannot be relied on to predict consequences of human exposure to BPA during development, it is important to investigate the effects of BPA on non-human primate brain development. Previous research suggests that BPA preferentially targets dopamine neurons in ventral mesencephalon and glutamatergic neurons in hippocampus, so the present work examined the susceptibility of these systems to low dose BPA exposure at the fetal and juvenile stages of development in non-human primates. Exposure of pregnant rhesus monkeys to relatively low levels of BPA during the final 2 months of gestation, induced abnormalities in fetal ventral mesencephalon and hippocampus. Specifically, light microscopy revealed a decrease in tyrosine hydroxylase-expressing (dopamine) neurons in the midbrain of BPA-exposed fetuses and electron microscopy identified a reduction in spine synapses in the CA1 region of hippocampus. In contrast, administration of BPA to juvenile vervet monkeys (14-18 months of age) was without effect on these indices, or on dopamine and serotonin concentrations in striatum and prefrontal cortex, or on performance of a cognitive task that tests working memory capacity. These data indicate that BPA exerts an age-dependent detrimental impact on primate brain development, at blood levels within the range measured in humans having only environmental contact with BPA.

Susceptibility to a parkinsonian toxin varies during primate development

Symptoms of Parkinson's disease typically emerge later in life when loss of nigrostriatal dopamine neuron function exceeds the threshold of compensatory mechanisms in the basal ganglia. Although nigrostriatal dopamine neurons are lost during aging, in Parkinson's disease other detrimental factors must play a role to produce greater than normal loss of these neurons. Early development has been hypothesized to be a potentially vulnerable period when environmental or genetic abnormalities may compromise central dopamine neurons. This study uses a specific parkinsonian neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), to probe the relative vulnerability of nigrostriatal dopamine neurons at different stages of primate development. Measures of dopamine, homovanillic acid, 1-methyl-pyridinium concentrations and tyrosine hydroxylase immunoreactive neurons indicated that at mid-gestation dopamine neurons are relatively vulnerable to MPTP, whereas later in development or in the young primate these neurons are resistant to the neurotoxin. These studies highlight a potentially greater risk to the fetus of exposure during mid-gestation to environmental agents that cause oxidative stress. In addition, the data suggest that uncoupling protein-2 may be a target for retarding the progressive loss of nigrostriatal dopamine neurons that occurs in Parkinson's disease and aging.

Asenapine effects on cognitive and monoamine dysfunction elicited by subchronic phencyclidine administration

PURPOSE

Repeated, intermittent administration of the psychotropic NMDA antagonist phencyclidine (PCP) to laboratory animals causes impairment in cognitive and executive functions, modeling important sequelae of schizophrenia; these effects are thought to be due to a dysregulation of neurotransmission within the prefrontal cortex. Atypical antipsychotic drugs have been reported to have measurable, if incomplete, effects on cognitive dysfunction in this model, and these effects may be due to their ability to normalize a subset of the physiological deficits occurring within the prefrontal cortex. Asenapine is an atypical antipsychotic approved in the US for the treatment of schizophrenia and for the treatment, as monotherapy or adjunctive therapy to lithium or valproate, of acute manic or mixed episodes associated bipolar I disorder. To understand its cognitive and neurochemical actions more fully, we explored the effects of short- and long-term dosing with asenapine on measures of cognitive and motor function in normal monkeys and in those previously exposed for 2 weeks to PCP; we further studied the impact of treatment with asenapine on dopamine and serotonin turnover in discrete brain regions from the same cohort.

METHODS

Monkeys were trained to perform reversal learning and object retrieval procedures before twice daily administration of PCP (0.3 mg/kg intra-muscular) or saline for 14 days. Tests confirmed cognitive deficits in PCP-exposed animals before beginning twice daily administration of saline (control) or asenapine (50, 100, or 150 μg/kg, intra-muscular). Dopamine and serotonin turnover were assessed in 15 specific brain regions by high-pressure liquid chromatography measures of the ratio of parent amine to its major metabolite.

RESULTS

On average, PCP-treated monkeys made twice as many errors in the reversal task as did control monkeys. Asenapine facilitated reversal learning performance in PCP-exposed monkeys, with improvements at trend level after 1 week of administration and reaching significance after 2-4 weeks of dosing. In week 4, the improvement with asenapine 150 μg/kg (p = 0.01) rendered the performance of PCP-exposed monkeys indistinguishable from that of normal monkeys without compromising fine motor function. Asenapine administration (150 μg/kg twice daily) produced an increase in dopamine and serotonin turnover in most brain regions of control monkeys and asenapine (50-150 μg/kg) increased dopamine and serotonin turnover in several brain regions of subchronic PCP-treated monkeys. No significant changes in the steady-state levels of dopamine or serotonin were observed in any brain region except for the central amygdala, in which a significant depletion of dopamine was observed in PCP-treated control monkeys; asenapine treatment reversed this dopamine depletion. A significant decrease in serotonin utilization was observed in the orbitofrontal cortex and nucleus accumbens in PCP monkeys, which may underlie poor reversal learning. In the same brain regions, dopamine utilization was not affected. Asenapine ameliorated this serotonin deficit in a dose-related manner that matched its efficacy for reversing the cognitive deficit.

CONCLUSIONS

In this model of cognitive dysfunction, asenapine produced substantial gains in executive functions that were maintained with long-term administration. The cognition-enhancing effects of asenapine and the neurochemical changes in serotonin and dopamine turnover seen in this study are hypothesized to be primarily related to its potent serotonergic and noradrenergic receptor binding properties, and support the potential for asenapine to reduce cognitive dysfunction in patients with schizophrenia and bipolar disorder.

Reduced locomotor responses to cocaine in ghrelin-deficient mice

Ghrelin, an orexigenic hormone produced by the stomach, increases food intake and enhances the locomotor and rewarding effects of cocaine. Consistent with these behavioral effects, ghrelin increases dopamine cell activity in the mesolimbic system resulting in elevated levels of dopamine release and turnover in target regions such as the ventral striatum. In the current study, we examined the psychostimulant effects of acute and daily cocaine in mice with targeted deletion of the ghrelin gene (ghrelin knockout; KO) and that of their wild-type (WT) littermates. We hypothesized that ghrelin-KO mice would be hyporesponsive to the effects of cocaine as reflected in attenuated locomotor activity following both acute and chronic injections, and that this would be correlated with striatal dopamine and dopamine metabolite concentrations. Results show that the locomotor stimulating effect of cocaine (10 mg/kg) was decreased in ghrelin-KO mice as compared with their WT littermates. In addition, repeated daily injection of cocaine resulted in gradual increases in locomotor activity in WT mice, an effect that was attenuated in ghrelin-KO mice. These behavioral effects were correlated with changes in dopamine utilization in the striatum of WT mice that were not seen in ghrelin-KO mice unless these were pretreated with ghrelin. These data suggest that ghrelin is important for normal function of the mesolimbic dopaminergic system, potentially modulating both dopamine release and reuptake.

Aged monkeys as a partial model for Parkinson's disease

Parkinson's Disease (PD) and the natural aging process share a number of biochemical mechanisms, including reduced function of dopaminergic systems. The present study aims to determine the extent that motor and behavioral changes in aged monkeys resemble parkinsonism induced by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. The behavioral and physiological changes in PD are believed to result largely from selective depletion of dopamine in the nigrostriatal system. In the present study, ten aged female monkeys were compared with three groups: 9 untreated young adult female monkeys, 10 young adult male monkeys and 13 older male monkeys that had been exposed to MPTP. Trained observers, blind as to age and drug condition and without knowledge of the hypotheses, scored the monkeys using the Parkinson's factor score (Parkscore), which has been validated by a high correlation with post mortem striatal dopamine (DA) concentrations. The aged animals had higher scores on the Parkscore compared with the young adults, with most of its component behavioral items showing significance (tremor, Eating Problems, Delayed initiation of movement, and Poverty of Movement). L-Dopa and DA-agonists did not clearly reverse the principal measure of parkinsonism. DA concentrations post mortem were 63% lower in 3 aged monkeys in the ventral putamen compared with 4 young adults, with greater reductions in putamen than in caudate (45%). We conclude that aged monkeys, unexposed to MPTP, show a similar profile of parkinsonism to that seen after the neurotoxin exposure to MPTP in young adult monkeys. The pattern of greater DA depletion in putamen than in caudate in aged monkeys is the same as in human Parkinson's disease and contrasts with the greater depletion in caudate seen after MPTP. Aged monkeys of this species reflect many facets of Parkinson's disease, but like older humans do not improve with standard dopamine replacement pharmacotherapies.

GPA protects the nigrostriatal dopamine system by enhancing mitochondrial function

Guanidinopropionic acid (GPA) increases AMPK activity, mitochondrial function and biogenesis in muscle and improves physiological function, for example during aging. Mitochondrial dysfunction is a major contributor to the pathogenesis of Parkinson's disease. Here we tested whether GPA prevents neurodegeneration of the nigrostriatal dopamine system in MPTP-treated mice. Mice were fed a diet of 1% GPA or normal chow for 4 weeks and then treated with either MPTP or saline. Indices of nigrostriatal function were examined by HPLC, immunohistochemistry, stereology, electron microscopy and mitochondrial respiration. MPTP intoxication decreased TH neurons in the SNpc of normal chow-fed mice; however GPA-fed mice remarkably exhibited no loss of TH neurons in the SNpc. MPTP caused a decrease in striatal dopamine of both normal chow- and GPA-fed mice, although this effect was significantly attenuated in GPA-fed mice. GPA-fed mice showed increased AMPK activity, mitochondrial respiration and mitochondrial number in nigrostriatal TH neurons, suggesting that the neuroprotective effects of GPA involved AMPK-dependent increases in mitochondrial function and biogenesis. MPTP treatment produced a decrease in mitochondrial number and volume in normal chow-fed mice but not GPA-fed mice. Our results show the neuroprotective properties of GPA in a mouse model of Parkinson's disease are partially mediated by AMPK and mitochondrial function. Mitochondrial dysfunction is a common problem in neurodegeneration and thus GPA may slow disease progression in other models of neurodegeneration.

Cellular repair in the parkinsonian nonhuman primate brain

Parkinson disease (PD) is a neurodegenerative disorder that provides a useful model for testing cell replacement strategies to rejuvenate the affected dopaminergic neural systems, which have been destroyed by aging and the disease. We first showed that grafts of fetal dopaminergic neurons can reverse parkinsonian motor deficits induced by the toxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), validating the feasibility of cellular repair in a primate nervous system. Subsequent clinical trials in Parkinson patients showed encouraging results, including long-term improvement of neurological signs and reduction of medications in some patients. However, many experienced little therapeutic benefit, and some recipients experienced dyskinesias, suggesting a lack of regulated control of the grafts. We have since attempted to improve cell replacements by placing grafts in their correct anatomical location in the substantia nigra and using strategies such as co-grafting fetal striatal tissue or growth factors into the physiologic striatal targets. Moreover, the use of fetal cells depends on a variable supply of donor material, making it difficult to standardize cell quality and quantity. Therefore, we have also explored possibilities of using human neural stem cells (hNSCs) to ameliorate parkinsonism in nonhuman primates with encouraging results. hNSCs implanted into the striatum showed a remarkable migratory ability and were found in the substantia nigra, where a small number appeared to differentiate into dopamine neurons. The majority became growth factor-producing glia that could provide beneficial effects on host dopamine neurons. Studies to determine the optimum stage of differentiation from embryonic stem cells and to derive useful cells from somatic cell sources are in progress.

Embryonic substantia nigra grafts in the mesencephalon send neurites to the host striatum in non-human primate after overexpression of GDNF

In spite of partial success in treating Parkinson's disease by using ectopically placed grafts of dopamine-producing cells, restoration of the original neuroanatomical circuits, if possible, might work better. Previous evidence of normal anatomic projections from ventral mesencephalic (VM) grafts placed in the substantia nigra (SN) has been limited to neonatal rodents and double grafting or bridging procedures. This study attempted to determine whether injection of a potent growth-promoting factor, glial cell line-derived neurotrophic factor (GDNF), into the target regions or placement of fetal striatal co-grafts in the nigrostriatal pathway might elicit neuritic outgrowth to the caudate nucleus. Four adult St. Kitts green monkeys received embryonic VM grafts into the rostral mesencephalon near the host SN, and injections of adeno-associated virus 2 (AAV2)/GDNF or equine infectious anemia virus (EIAV)/GDNF into the caudate. Three adult monkeys were co-grafted with fetal VM tissue near the SN and fetal striatal grafts (STR) 2.5 mm rostral in the nigrostriatal pathway. Before sacrifice, the striatal target regions were injected with the retrograde tracer Fluoro-Gold (FG). FG label was found in tyrosine hydroxylase-labeled neurons in VM grafts in the SN of only those monkeys that received AAV2/GDNF vector injections into the ipsilateral striatum. All monkeys showed FG labeling in the host SN when FG labeling was injected on the same side. These data show that grafted dopaminergic neurons can extend neurites to a distant target releasing an elevated concentration of GDNF, and suggest that grafted neurons can be placed into appropriate loci for potential tract reconstruction.

Clonidine and guanfacine attenuate phencyclidine-induced dopamine overflow in rat prefrontal cortex: mediating influence of the alpha-2A adrenoceptor subtype

N-methyl-D-aspartic acid/glutamate receptor antagonists induce psychotomimetic effects in humans and animals, and much research has focused on the neurochemical and network-level effects that mediate those behavioral changes. For example, a reduction in NMDA-dependent glutamatergic transmission triggers increased release of the monoamine transmitters, and some of these changes are implicated in the cognitive, behavioral and neuroanatomical effects of phencyclidine (PCP). Alpha-2 adrenoceptor agonists (e.g., clonidine) are effective at preventing many of the behavioral, neurochemical and anatomical effects of NMDA antagonists. Evidence has indicated that a key mechanism of the clonidine-induced reversal of the effects of NMDA antagonists is an attenuation of enhanced dopamine release. We have pursued these findings by investigating the effects of alpha-2 agonists on PCP-evoked dopamine efflux in the prefrontal cortex of freely moving rats. Clonidine (0.003-0.1 mg/kg, i.p.) dose-dependently attenuated the ability of PCP (2.5 mg/kg, i.p.) to increase cortical dopamine output. The effects of clonidine were prevented by the alpha-2A subtype selective antagonist BRL-44408 (1 mg/kg, i.p.). Guanfacine, which is an alpha-2 agonist with a higher affinity for the 2A, compared with 2B or 2C, subtypes, also blocked the ability of PCP to increase dopamine efflux in the prefrontal cortex. These data indicate that alpha-2A agonists are effective at counteracting the hyperdopaminergic state induced by PCP and may play a role in their neurobehavioral effects in this putative animal model for schizophrenia.

Human neural stem cells migrate along the nigrostriatal pathway in a primate model of Parkinson's disease

Although evidence of damage-directed neural stem cell (NSC) migration has been well-documented in the rodent, to our knowledge it has never been confirmed or quantified using human NSC (hNSC) in an adult non-human primate modeling a human neurodegenerative disease state. In this report, we attempt to provide that confirmation, potentially advancing basic stem cell concepts toward clinical relevance. hNSCs were implanted into the caudate nucleus (bilaterally) and substantia nigra (unilaterally) of 7, adult St. Kitts African green monkeys (Chlorocebus sabaeus) with previous exposure to systemic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a neurotoxin that disrupts the dopaminergic nigrostriatal pathway. A detailed quantitative analysis of hNSC migration patterns at two time points (4 and 7 months) following transplantation was performed. Density contour mapping of hNSCs along the dorsal-ventral and medial-lateral axes of the brain suggested that >80% of hNSCs migrated from the point of implantation to and along the impaired nigrostriatal pathway. Although 2/3 of hNSCs were transplanted within the caudate, <1% of 3x10(6) total injected donor cells were identified at this site. The migrating hNSC did not appear to be pursuing a neuronal lineage. In the striatum and nigrostriatal pathway, but not in the substantia nigra, some hNSCs were found to have taken a glial lineage. The property of neural stem cells to align themselves along a neural pathway rendered dysfunctional by a given disease is potentially a valuable clinical tool.

Clozapine normalizes prefrontal cortex dopamine transmission in monkeys subchronically exposed to phencyclidine

The mechanism responsible for the therapeutic effects of the prototypical atypical antipsychotic drug, clozapine, is still not understood; however, there is persuasive evidence from in vivo studies in normal rodents and primates that the ability to elevate dopamine neurotransmission preferentially in the prefrontal cortex is a key component to the beneficial effects of clozapine in schizophrenia. Theoretically, such an effect of clozapine would counteract the deficient dopaminergic innervation of the prefrontal cortex that appears to be part of the pathophysiology of schizophrenia. We have previously shown that following repeated, intermittent administrations of phencyclidine to monkeys there is lowered prefrontal cortical dopamine transmission and impairment of cognitive performance that is dependent on the prefrontal cortex; these biochemical and behavioral changes therefore model certain aspects of schizophrenia. We now investigate the effects of clozapine on the dopamine projections to prefrontal cortex, nucleus accumbens, and striatum in control monkeys and in those withdrawn from repeated phencyclidine treatment, using a dose regimen of clozapine that ameliorates the cognitive deficits described in the primate phencyclidine (PCP) model. In normal monkeys, clozapine elevated dopamine turnover in all prefrontal cortical, but not subcortical, regions analyzed. In the primate PCP model, clozapine normalized dopamine (DA) turnover in the dorsolateral prefrontal cortex, prelimbic cortex, and cingulate cortex. Thus, the present data support the hypothesis that the therapeutic effects of clozapine in this primate model and perhaps in schizophrenia may be related at least in part to the restoration of DA tone in the prefrontal cortex.

Embryonic substantia nigra grafts show directional outgrowth to cografted striatal grafts and potential for pathway reconstruction in nonhuman primate

Transplantation of embryonic dopamine (DA) neurons has been tested as a therapy for Parkinson's disease. Most studies placed DA neurons into the striatum instead of the substantia nigra (SN). Reconstruction of this DA pathway could serve to establish a more favorable environment for control of DA release by grafted neurons. To test this we used cografts of striatum to stimulate growth of DA axons from embryonic SN that was implanted adjacent to the host SN in African green monkeys. Embryonic striatum was implanted at one of three progressive distances rostral to the SN. Immunohistochemical analysis revealed DA neuron survival and neuritic outgrowth from the SN grafts at 12-36 weeks after grafting. Each animal showed survival of substantial numbers of DA neurons. Most fibers that exited SN grafts coursed rostrally. Striatal grafts showed evidence of target-directed outgrowth and contained dense patterns of DA axons that could be traced from their origin in the SN grafts. A polarity existed for DA neurites that exited the grafts; that is, those seen caudal to the grafts did not appear to be organized into a directional outflow while those on the rostral side were arranged in linear profiles coursing toward the striatal grafts. Some TH fibers that reached the striatal grafts appeared to arise from the residual DA neurons of the SN. These findings suggest that grafted DA neurons can extend neurites toward a desired target over several millimeters through the brain stem and caudal diencephalon of the monkey brain, which favors the prospect of circuit reconstruction from grafted neurons placed into appropriate locations in their neural circuitry. Further study will assess the degree to which this approach can be used to restore motor balance in the nonhuman primate following neural transplantation.

Behavioral improvement in a primate Parkinson's model is associated with multiple homeostatic effects of human neural stem cells

Stem cells have been widely assumed to be capable of replacing lost or damaged cells in a number of diseases, including Parkinson's disease (PD), in which neurons of the substantia nigra (SN) die and fail to provide the neurotransmitter, dopamine (DA), to the striatum. We report that undifferentiated human neural stem cells (hNSCs) implanted into 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated Parkinsonian primates survived, migrated, and had a functional impact as assessed quantitatively by behavioral improvement in this DA-deficit model, in which Parkinsonian signs directly correlate to reduced DA levels. A small number of hNSC progeny differentiated into tyrosine hydroxylase (TH) and/or dopamine transporter (DAT) immunopositive cells, suggesting that the microenvironment within and around the lesioned adult host SN still permits development of a DA phenotype by responsive progenitor cells. A much larger number of hNSC-derived cells that did not express neuronal or DA markers was found arrayed along the persisting nigrostriatal path, juxtaposed with host cells. These hNSCs, which express DA-protective factors, were therefore well positioned to influence host TH+ cells and mediate other homeostatic adjustments, as reflected in a return to baseline endogenous neuronal number-to-size ratios, preservation of extant host nigrostriatal circuitry, and a normalizing effect on alpha-synuclein aggregation. We propose that multiple modes of reciprocal interaction between exogenous hNSCs and the pathological host milieu underlie the functional improvement observed in this model of PD.

Prenatal cocaine exposure enhances responsivity of locus coeruleus norepinephrine neurons: role of autoreceptors

Children exposed to cocaine during gestation have a higher incidence of neurobehavioral deficits. The neurochemical bases of these deficits have not been determined, but the pharmacology of cocaine and the nature of the abnormalities suggest that disruptions in catecholaminergic systems may be involved. In the current study, we used a rat model of prenatal cocaine exposure to examine the impact that this exposure has on the locus coeruleus (LC) noradrenergic system in offspring. Pregnant rats received twice-daily i.v. injections of cocaine (3 mg/kg) or saline between gestational days 10 and 20, and progeny were tested as juveniles. Exposure to a mild stressor elevated an index of norepinephrine turnover in the prefrontal cortex and also increased Fos expression in tyrosine hydroxylase-positive LC neurons in rats exposed to prenatal cocaine but not in rats exposed to prenatal saline. No change in the number of tyrosine hydroxylase-positive neurons in the LC was observed between the two prenatal treatment groups. Specific binding of [125I]-para-iodoclonidine, a radioligand with specificity for high affinity alpha2A-adrenergic receptors, was decreased in the LC of rats exposed to prenatal cocaine compared with prenatal saline controls. As alpha2-adrenergic receptors on LC norepinephrine neurons function as autoreceptors, their down-regulation by prenatal cocaine exposure provides a plausible mechanism for the observed heightened reactivity of norepinephrine neurons in these animals. These data indicate that prenatal cocaine exposure results in lasting changes to the regulation and responsivity of rat LC norepinephrine neurons. A similar dysregulation of LC norepinephrine neurons may occur in children exposed to cocaine during gestation, and this may explain, at least partly, the increased incidence of cognitive deficits that have been observed in these subjects.

Repeated phencyclidine in monkeys results in loss of parvalbumin-containing axo-axonic projections in the prefrontal cortex

RATIONALE

Repeated exposure to the N-methyl-D-aspartate antagonist, phencyclidine, has been shown to result in biochemical and cognitive changes similar to aspects of schizophrenia. Recently, emerging evidence indicated that the symptoms of schizophrenia might result at least in part from dysfunction of local circuit neurons containing parvalbumin, including a loss of their axo-axonic projections to pyramidal neurons.

OBJECTIVES

In this report, we test if repeated exposure to phencyclidine in the primate shares this change to parvalbumin-containing cells and their axo-axonic structures.

MATERIALS AND METHODS

Eight adult male African green monkeys were treated with saline or phencyclidine (0.3 mg/kg BID x 14 days) and, after 8 days drug-free, perfused and fixed, and the principal sulcus was collected (Walker's area 46) for immunohistochemical analysis.

RESULTS

Prior treatment with phencyclidine resulted in a 40% reduction in the density of parvalbumin-containing axo-axonic structures. There was no apparent change in the lengths or laminar location of the axo-axonic projections. Additionally, there was no change in the total density or laminar location of parvalbumin-containing or calretinin-containing cell bodies in area 46.

CONCLUSIONS

These results indicate that repeated treatment with phencyclidine results in plastic changes in parvalbumin-containing local circuit neurons in the prefrontal cortex similar to that reported in schizophrenia and that these changes may contribute to the common cognitive disruption seen in both schizophrenic patients and the phencyclidine monkey model.

Apoptotic natural cell death in developing primate dopamine midbrain neurons occurs during a restricted period in the second trimester of gestation

Natural cell death (NCD) by apoptosis is a normal developmental event in most neuronal populations, and is a determinant of the eventual size of a population. We decided to examine the timing and extent of NCD of the midbrain dopamine system in a primate species, as dopamine deficiency or excess has been implicated in several disorders. Genetic or environmental differences may alter the extent of NCD and predispose individuals to neurological or psychiatric diseases. In developing rats, NCD in the midbrain dopamine system has been observed to start at the end of gestation and peak in the postnatal period. In fetal monkey brains, apoptosis in midbrain DA neurons was identified histologically by chromatin clumping in tyrosine hydroxylase-positive cells, and confirmed by TUNEL and active caspase-3 staining. A distinct peak of NCD occurred at about E80, midway through gestation in this species. We estimate that at least 50% of the population may be lost in this process. In other brains we determined biochemically that the onset of apoptosis coincides with the time of greatest rate of increase of striatal DA concentration. Thus, marked apoptotic NCD occurs in the primate midbrain dopamine system half-way through gestation, and appears to be associated with the rapid developmental increase in striatal dopamine innervation.

Prenatal exposure to cocaine is associated with increased number of spine synapses in rat prelimbic cortex

Prenatal exposure to cocaine has been associated with cognitive deficits in children and in animal models. An excess activation of pyramidal neurons in the prefrontal cortex has been proposed as a potential cause for these deficits based on previous studies. The goal of this study was to determine if prenatal exposure to cocaine was associated with an increase in the number of excitatory synapses on dendritic spines in layer II/III of the prelimbic cortex. Frontal cortex of young adult male and female rats, exposed to either saline or cocaine (3 mg/kg i.e., twice a day, embryonic day 10-20), were examined using electron microscopy and the number of asymmetric spines synapses were estimated using the physical disector method. Both male and female rats prenatally exposed to cocaine had about twice as many synapses on dendritic spines as the prenatal saline controls. The increase in number of excitatory synaptic inputs associated with prenatal cocaine exposure could contribute to the increased neuronal activation and cognitive deficits noted.

Ghrelin modulates the activity and synaptic input organization of midbrain dopamine neurons while promoting appetite

The gut hormone ghrelin targets the brain to promote food intake and adiposity. The ghrelin receptor growth hormone secretagogue 1 receptor (GHSR) is present in hypothalamic centers controlling energy metabolism as well as in the ventral tegmental area (VTA), a region important for motivational aspects of multiple behaviors, including feeding. Here we show that in mice and rats, ghrelin bound to neurons of the VTA, where it triggered increased dopamine neuronal activity, synapse formation, and dopamine turnover in the nucleus accumbens in a GHSR-dependent manner. Direct VTA administration of ghrelin also triggered feeding, while intra-VTA delivery of a selective GHSR antagonist blocked the orexigenic effect of circulating ghrelin and blunted rebound feeding following fasting. In addition, ghrelin- and GHSR-deficient mice showed attenuated feeding responses to restricted feeding schedules. Taken together, these data suggest that the mesolimbic reward circuitry is targeted by peripheral ghrelin to influence physiological mechanisms related to feeding.

Subchronic phencyclidine treatment decreases the number of dendritic spine synapses in the rat prefrontal cortex

BACKGROUND

A growing body of evidence suggests the existence of synaptic pathology in schizophrenia. Here we used the phencyclidine schizophrenia model to directly investigate at the electron microscopic level whether structural synaptic alterations are present in these animals.

METHODS

Adult male rats were treated according to our subchronic phencyclidine paradigm (5 mg/kg twice daily for 7 days, intraperitoneally). Following a one-week withdrawal period, the number of prefrontal cortical spine synapses was calculated using an unbiased electron microscopic stereological approach. The number of astroglia cells and the density of their processes was also analyzed following glial-fibrillary acidic protein immunohistochemistry.

RESULTS

Subchronic phencyclidine treatment resulted in a 41.2% decrease in the number of prefrontal spine synapses when compared to controls. This was accompanied by a 58.8% increase in astroglia process density, without significant change in the number of astroglia cells.

CONCLUSIONS

Our results demonstrate a severe reduction in the number of prefrontal spine synapses in an animal model of schizophrenia. This phenomenon may contribute to phencyclidine-induced cognitive dysfunction and decreased prefrontal cellular activity observed in this model.

Uncoupling protein-2 promotes nigrostriatal dopamine neuronal function

Uncoupling protein 2 (UCP2) is known to promote neuroprotection in many forms of neurological pathologies including Parkinson's disease. Here, we examined the hypothesis that UCP2 also mediates aspects of normal nigrostriatal dopamine (DA) function. Mice lacking UCP2 exhibited reduced dopamine turnover in the striatum as measured by the 3,4-dihydoxyphenylacetic acid/dopamine (DOPAC/DA) ratio, reduced tyrosine hydroxylase immunoreactivity (TH IR) in the substantia nigra pars compacta (SNc) and reticulata, striatum and nucleus accumbens. UCP2-knockout (KO) mice also had reduced dopamine transporter immunoreactivity (DAT IR) in the SNc but not other brain regions examined. In order to determine if these biochemical deficits are transcribed into behavioural deficits, we examined locomotor function in UCP2-KO mice compared to wild-type (WT) controls. UCP2-KO mice exhibited significantly reduced total movement distance, movement velocity and increased rest time compared to wild-type controls. These results suggest that UCP2 is an important mitochondrial protein that helps to maintain normal nigrostriatal dopamine neuronal function and a reduction in UCP2 levels may predispose individuals to environmental causes of Parkinson's disease.

Development of A9/A10 dopamine neurons during the second and third trimesters in the African green monkey

Disruption in the development of dopamine-containing neurons has been postulated to underlie several CNS disorders. However, there have been no quantitative studies on the normal development of primate dopamine neurons. Thus, the fetal maturation of primate midbrain dopamine neurons was examined to establish changes that occur in the A9/A10 groups during the second and third trimesters. Eleven fetal African green monkey midbrains were immunostained for tyrosine hydroxylase (TH-ir) as a marker for dopamine neurons and quantified using stereological techniques (nucleator method). The number and size of defined dopamine neurons and the volume occupied by A9/A10 neurons increased in near linear fashion throughout the term. The estimated number of defined dopamine neurons in each hemisphere rose from approximately 50,000 at embryonic day (E) 70 to 225,000 at birth (E165), similar to the adult population. The size and the area occupied by them at birth were, however, well below the estimated adult levels. Additionally, the younger fetal midbrains had far less diversity in dopamine cell volumes compared with older fetuses and adult brains. Until midway through gestation (E81), clusters of apparently immature midbrain TH-ir cells were observed, but could not be counted. Even though the majority of cells destined to become dopamine neurons are generated in the first trimester, phenotypical maturation of A9 and A10 cell bodies continues steadily throughout gestation and extends well into the postnatal period. These data have relevance to transplantation studies that employ fetal dopaminergic grafts, and to disorders hypothesized to result from damage to developing midbrain dopamine neurons.

Alpha-2 adrenoceptor activation inhibits phencyclidine-induced deficits of spatial working memory in rats

N-methyl-D-aspartate (NMDA)/glutamate receptor antagonists, such as phencyclidine (PCP), induce behavioral abnormalities (locomotor hyperactivity, sensorimotor gating deficits, impairments of cognition) in animals that are thought to model aspects of schizophrenia. The administration of PCP increases noradrenaline transmission in the rat prefrontal cortex, a brain structure required for normal cognitive processes. Noradrenaline, in turn, works through a set of receptors that have themselves been implicated directly in NMDA antagonist-induced deficits; we recently reported that the alpha-2 agonist, clonidine, is effective at preventing PCP-induced deficits of working memory and visual attention in rats. Here, we further investigated the role for alpha-2 adrenoreceptors in the effects of PCP on spatial working memory performance. The alpha-2 agonist clonidine (0.001-0.01 mg/kg, subcutaneously (s.c.)) produced a significant amelioration of PCP-induced working memory deficits; the effects of PCP (1.0 mg/kg, s.c.), but not clonidine, were reduced in noradrenaline-depleted rats. In addition, the alpha-2A-preferring agonist guanfacine (0.05-1.0 mg/kg, s.c.) dose-dependently prevented the deficits of spatial working memory performance produced by PCP. Although the highly selective alpha-2 receptor antagonist, atipamezole (ATI), failed to affect spatial working memory on its own, at the doses studied (0.1-0.5 mg/kg, s.c.), it dramatically enhanced the working memory deficit produced by PCP. These data indicate that alpha-2 adrenoreceptors tonically inhibit PCP-induced deficits of spatial working memory, suggesting an important role for these receptors in cognitive deficits associated with NMDA receptor hypofunction.

Uncoupling protein-2 is critical for nigral dopamine cell survival in a mouse model of Parkinson's disease

Mitochondrial uncoupling proteins dissociate ATP synthesis from oxygen consumption in mitochondria and suppress free-radical production. We show that genetic manipulation of uncoupling protein-2 (UCP2) directly affects substantia nigra dopamine cell function. Overexpression of UCP2 increases mitochondrial uncoupling, whereas deletion of UCP2 reduces uncoupling in the substantia nigra-ventral tegmental area. Overexpression of UCP2 decreased reactive oxygen species (ROS) production, which was measured using dihydroethidium because it is specifically oxidized to fluorescent ethidium by the superoxide anion, whereas mice lacking UCP2 exhibited increased ROS relative to wild-type controls. Unbiased electron microscopic analysis revealed that the elevation of in situ mitochondrial ROS production in UCP2 knock-out mice was inversely correlated with mitochondria number in dopamine neurons. Lack of UCP2 increased the sensitivity of dopamine neurons to 1-methyl-4-phenyl-1,2,5,6 tetrahydropyridine (MPTP), whereas UCP2 overexpression decreased MPTP-induced nigral dopamine cell loss. The present results expose the critical importance of UCP2 in normal nigral dopamine cell metabolism and offer a novel therapeutic target, UCP2, for the prevention/treatment of Parkinson's disease.

Noradrenergic alpha-2 agonists have anxiolytic-like actions on stress-related behavior and mesoprefrontal dopamine biochemistry

Clonidine (CLON), an alpha-2 agonist, has anxiolytic-like actions on the response of mesoprefrontal dopamine (DA) neurons to aversive stimuli in addition to some fear-related behavioral responses. We hypothesized that the anxiolytic-like actions of clonidine could be mimicked by stimulation of alpha-2 receptors on the mesoprefrontal dopamine neurons. Here, we test this hypothesis using clonidine or guanfacine (GFC), another alpha-2 agonist, in a model of aversive conditioning that selectively activates the mesoprefrontal dopamine neurons. One day prior to testing with drugs, rats were conditioned to fear a soft tone by pairing it with a footshock. During testing, the animals were subjected to the tones alone after drugs were administered systemically, or by local infusion into the regions containing the cell bodies and terminals of the mesoprefrontal dopamine neurons, namely, the ventral tegmental area (VTA) and the prelimbic (PL) cortex. Systemic administration of guanfacine blocked the increase in immobility in response to the conditioned tone and prevented the stress-associated increase in dopamine turnover in the prelimbic cortex. Systemic clonidine also prevented the stress-associated increase in dopamine turnover but caused sedation preventing behavioral measures. Guanfacine was then used in all local injection studies. The local application of guanfacine into either the prelimbic cortex or the ventral tegmental area did not prevent the conditioned fear-induced increase in dopamine turnover or the increase in immobility in response to the conditioned tones. We conclude that the anxiolytic-like actions of alpha-2 agonists are not due to binding to alpha-2 receptors on the stress-sensitive mesoprefrontal dopamine neurons.

Prenatal exposure to cocaine selectively disrupts the development of parvalbumin containing local circuit neurons in the medial prefrontal cortex of the rat

Exposure to cocaine in utero can result in cognitive deficits potentially through a disruption in the inhibitory processes of the frontal cortex. One potential mechanism is through alterations in the inhibitory local circuit neurons containing the calcium-binding protein, parvalbumin. Parvalbumin-immunostaining primarily identifies 2 types of local circuit neurons: larger, rounder, axo-somal basket cells and smaller, more-spindle shaped, axo-axonic chandelier cells. Both are thought to have critical impact on the excitatory/inhibitory balance due to the proximal site of projection on pyramidal neurons. Calretinin, another calcium-binding protein, identifies a distinct sub-population of inhibitory local circuits that impinges more distally on the dendritic arbor and serves as a control population for this study. Here, we examine local circuit neurons containing either parvalbumin or calretinin in adolescent male rats (approximately 45 days old) exposed to saline or cocaine (3 mg/kg, intravenous twice a day during embryonic days 10 to 20). Prenatal cocaine exposure caused select changes in the parvalbumin, but not calretinin, containing cells in the frontal cortex. Specifically, prenatal cocaine exposure is associated with a 50% reduction in spindle-shaped parvalbumin-immunoreactive cells potentially indicating a select loss of chandelier cells or a shift to a rounder shape. Additionally, a reduction in the number of dendrites of parvalbumin-immunoreactive cells in rats exposed to cocaine in utero was noted. Other measures of both parvalbumin- and calretinin-immunoreactive cells were unchanged, including total number of cells, distribution by depth, and sizes of cells. These changes to the excitatory/inhibitory balance in the frontal cortex may contribute to the cognitive deficits associated with prenatal cocaine exposure.

Repeated, intermittent delta(9)-tetrahydrocannabinol administration to rats impairs acquisition and performance of a test of visuospatial divided attention

The residual neuropsychological effects of marijuana abuse in man indicate a dysfunction of the attentional/executive systems. Moreover, experimental investigations suggest that repeated, intermittent (subchronic) Delta(9)-tetrahydrocannabinol (THC), the main psychoactive ingredient of marijuana, alters neurotransmission in the frontal cortex of rats and humans, a key neural site mediating attention and executive functions. In the present studies, the acquisition and performance of a test of visuospatial attention (the lateralized reaction time task) after subchronic THC administration (10.0 mg/kg twice daily for 14 days) was examined. Rats previously administered THC showed impairments in this self-paced version of the classic multiple-choice serial reaction time task, which persisted 14 days after the final drug administration. Longer time points were not examined. These attentional impairments were transiently reversible with an acute amphetamine (0.5 mg/kg) challenge. These behavioral data demonstrate that chronic THC administration to rats induces an attentional deficit, similar to that observed in humans who abuse marijuana. Finally, amphetamine's ability to reverse the attentional impairments provides indirect evidence that monoaminergic deficits may be linked to the cognitive dysfunction.

Spatiotemporal patterns of gene expression during fetal monkey brain development

Human DNA microarrays are used to study the spatiotemporal patterns of gene expression during the course of fetal monkey brain development. The 444 most dynamically expressed genes in four major brain areas are reported at five different fetal ages. The spatiotemporal profiles of gene expression show both regional specificity as well as waves of gene expression across the developing brain. These patterns of expression are used to identify statistically significant clusters of co-regulated genes. This study demonstrates for the first time in the primate the relevance, timing, and spatial locations of expression for many developmental genes identified in other animals and provides clues to the functions of many unknowns. Two different microarray platforms are used to provide high-throughput cross validation of the most important gene expression changes. These results may lead to new understanding of brain development and new strategies for treating and repairing disorders of brain function.

Persistent and anatomically selective reduction in prefrontal cortical dopamine metabolism after repeated, intermittent cannabinoid administration to rats

Long-term abuse of delta-9-tetrahydrocannabinol (THC), the major psychoactive constituent of marijuana, produces behavioral and metabolic signs of frontal cortical dysfunction in humans; these effects persist even after short-term abstinence. Based on a preliminary finding that repeated administration of THC to rats reduces basal frontal cortical dopamine turnover (Jentsch et al. [1998] Neurosci Lett 246:169-172), we further investigated the effects of repeated administrations of THC or WIN 55,212-2 (WIN), a synthetic cannabinoid receptor agonist, on dopamine turnover in the prefrontal cortex, striatum, and nucleus accumbens. THC or WIN (twice daily for 7 or 14 days) caused a persistent and selective reduction in medial prefrontal cortical dopamine turnover; no significant alterations of dopamine metabolism were observed in the nucleus accumbens or striatum. Importantly, these dopaminergic deficits in the prefrontal cortex were observed after a drug-free period of up to 14 days. Thus, the cognitive dysfunction produced by heavy, long-term cannabis use may be subserved, in part, by drug-induced alterations in frontal cortical dopamine turnover.

Coenzyme Q induces nigral mitochondrial uncoupling and prevents dopamine cell loss in a primate model of Parkinson's disease

Parkinson's disease is characterized by dopamine cell loss of the substantia nigra. Parkinson's disease and the neurotoxin 1-methyl-4-phenyl-1,2,5,6 tetrahydropyridine may destroy dopamine neurons through oxidative stress. Coenzyme Q is a cofactor of mitochondrial uncoupling proteins that enhances state-4 respiration and eliminate superoxides. Here we report that short-term oral administration of coenzyme Q induces nigral mitochondrial uncoupling and prevents dopamine cell loss after 1-methyl-4-phenyl-1,2,5,6 tetrahydropyridine administration in monkeys.

Systemic, but not local, administration of cannabinoid CB1 receptor agonists modulate prefrontal cortical acetylcholine efflux in the rat

Drugs acting on brain cannabinoid CB(1) receptors exert complex actions on modulatory transmitters that are involved in attention and cognition; however, little is known about the precise pharmacological and anatomical mechanisms that govern these effects. Previously demonstrated effects of cannabinoids on acetylcholine (ACh) in the hippocampus prompted us to evaluate changes in the prefrontal cortex, a site associated with mnemonic and attentional functions. We utilized in vivo microdialysis, coupled with direct reverse perfusion of agents, to study the actions on cannabinoidergic drugs on ACh release within the rat frontal cortex. Systemic administration of the CB(1) receptor agonists Delta(9)-tetrahydrocannabinol (THC) or WIN 55,212-2 (WIN) dose- and time-dependently increased ACh release; these effects were blocked by pretreatment with the selective CB(1) receptor antagonist / partial inverse agonist SR141716A (SR). THC applied by reverse dialysis in the frontal cortex caused no change in ACh release, although intrastriatal infusions of THC decreased ACh efflux. These data indicate that cannabinoid agonists potentiate ACh release in the frontal cortex by activating cannabinoid receptors in brain regions other than the frontal cortex.

Axo-axonic structures in the medial prefrontal cortex of the rat: reduction by prenatal exposure to cocaine

The cognitive deficits associated with prenatal exposure to cocaine have been hypothesized to be the results of changes in the anatomy and function of the frontal cortex. In this study, pregnant dams were treated with cocaine (3 mg/kg i.v. twice a day) and the resulting adolescent (postnatal day, approximately 45) male offspring were killed for immunocytochemical determination of the total linear measure, number, location, and lengths of inhibitory GABA transporter-1 immunoreactive axo-axonic structures commonly called "candles" or "cartridges" in the medial prefrontal cortex. These inhibitory structures are the axon terminals of GABAergic cells that impinge on the initial axon segments of excitatory pyramidal neurons. We report that prenatal cocaine exposure decreased the number of these inhibitory candles. The greatest reduction of candles was observed in the ventral prelimbic cortex. Additionally, there was a subtle difference in the pattern of distribution of candles, namely the depth of the initial candle in the ventral portions of the prefrontal cortex was greater in rats exposed to prenatal cocaine. However, there was no overt change in the number of cells that were immunoreactive for the calcium-binding protein parvalbumin, an indicator of a subset of GABAergic interneurons that includes axo-axonic chandelier cells. We conclude that exposure to cocaine in utero disrupts the development of the axo-axonic cells in the prefrontal cortex and this disruption could contribute to the cognitive deficits reported with prenatal cocaine exposure.

Adaptation of monoaminergic responses to phencyclidine in nucleus accumbens and prefrontal cortex following repeated treatment with fluoxetine or imipramine

The adaptive neuronal changes that follow chronic administration of antidepressant drugs are thought to underlie clinical improvement in patient populations. Recent evidence suggests that alterations specific to N-methyl-D-aspartate (NMDA) receptors may be a final common pathway to antidepressant action. To investigate this possibility, we sought to establish the effects of chronic fluoxetine or imipramine treatment on the monoamine stimulating effect of the non-competitive NMDA antagonist phencyclidine. Male, Sprague-Dawley rats (n=9/group) were treated with saline (1 ml/kg, i.p.), imipramine (10 mg/kg, i.p.) or fluoxetine (10 mg/kg, i.p.) once daily for 14 consecutive days. After a 7-day drug-free period, animals given an acute challenge of either saline or phencyclidine (5 mg/kg, i.p.). One hour later, animals were killed, brains were removed, and the prefrontal cortex, striatum, and nucleus accumbens were dissected. Samples were assayed for the monoamines and their primary metabolites by HPLC. Repeated treatment with fluoxetine or imipramine did not alter baseline dopamine or serotonin turnover. Acute phencyclidine treatment increased prefrontal cortex and nucleus accumbens dopamine turnover in saline-treated animals (P<0.01); however, the effect in the nucleus accumbens was prevented in animals pretreated with imipramine or fluoxetine. Acute phencyclidine challenge also increased serotonin turnover in prefrontal cortex of saline- or imipramine-pretreated rats (P<0.01), though this effect was attenuated in animals pretreated with fluoxetine. Overall, the data suggest that repeated antidepressant treatment alters monoamine turnover in specific brain regions in response to blockade of NMDA receptors. The data highlight the importance of adaptive responses to NMDA receptors resulting from chronic antidepressant treatment.

Fear-like biochemical and behavioral responses in rats to the predator odor, TMT, are dependent on the exposure environment

Several laboratories have reported that exposure to predator odor can result in stress-like effects in rodents. While some laboratories have reported fear-like alterations in behavior, other laboratories, including our own, have failed to consistently observe fearful behaviors in rats exposed to the predator odor TMT. One potential contributing factor to this discrepancy is the handling of the rat and its test environment. In the current report, we examine biochemical, endocrinological, and behavioral effects of TMT in two distinct open fields: one small, familiar, and dimly lit, while the other was large, novel, and brightly lit. Only exposure to TMT in the large, novel open field resulted in fearful behavior; however, no increase in dopamine turnover was noted compared to no odor and control odor rats. As expected, the different open fields resulted in some biochemical and behavioral differences, including more horizontal locomotion and less grooming, higher serum corticosterone, and increased dopamine turnover in the ventral prefrontal cortex in the large open field. Finally, compared to the same open field controls, TMT exposure elevated rat serum corticosterone levels in both open fields and dopamine turnover in the dorsal and ventral medial prefrontal cortex and amygdala of rats only in the small, familiar open field. These results indicate that the TMT-induced biochemical activation of may occur without detectable fearful behaviors and may indicate a mechanism that prepares the animal for the expression of a fearful response if additional provocative stimuli are present.