Incidence and risk factors of omicron variant SARS-CoV-2 breakthrough infection among vaccinated and boosted individuals

Background

SARS-CoV-2 vaccines have been shown to be safe and effective against infection and severe COVID-19 disease worldwide. Certain co-morbid conditions cause immune dysfunction and may reduce immune response to vaccination. In contrast, those with co-morbidities may practice infection prevention strategies. Thus, the real-world clinical impact of co-morbidities on SARS-CoV-2 infection in the recent post-vaccination period is not well established. We performed this study to understand the epidemiology of Omicron breakthrough infection and evaluate associations with number of comorbidities in a vaccinated and boosted population.

Methods and Findings

We performed a retrospective clinical cohort study utilizing the Northwestern Medicine Enterprise Data Warehouse. Our study population was identified as fully vaccinated adults with at least one booster. The primary risk factor of interest was the number of co-morbidities. Our primary outcome was incidence and time to first positive SARS-CoV-2 molecular test in the Omicron predominant era. We performed multivariable analyses stratified by calendar time using Cox modeling to determine hazard of SARS-CoV-2. In total, 133,191 patients were analyzed. Having 3+ comorbidities was associated with increased hazard for breakthrough (HR=1.2 CI 1.2-1.6). During the second half of the study, having 2 comorbidities (HR= 1.1 95% CI 1.02-1.2) and having 3+ comorbidities (HR 1.7, 95% CI 1.5-1.9) were associated with increased hazard for Omicron breakthrough. Older age was associated with decreased hazard in the first 6 months of follow-up. Interaction terms for calendar time indicated significant changes in hazard for many factors between the first and second halves of the follow-up period.

Conclusions

Omicron breakthrough is common with significantly higher risk for our most vulnerable patients with multiple co-morbidities. Age related behavioral factors play an important role in breakthrough infection with the highest incidence among young adults. Our findings reflect real-world differences in immunity and exposure risk behaviors for populations vulnerable to COVID-19.

Nutritional needs, resources, and barriers among unhoused adults cared for by a street medicine organization in Chicago, Illinois: a cross-sectional study

BACKGROUND

Those experiencing houselessness rely on obtaining food from community organizers and donations. Simultaneously, the houseless face disproportionally high rates of medical conditions that may be affected by diet including diabetes, hypertension, and hyperlipidemia. There is limited literature on the resources and barriers of the houseless community regarding optimal nutrition from an actionable perspective. Further, less data is available on how street medicine organizations may best impact the nutrition of the unhoused they serve. Elucidating this information will inform how organizational efforts may best support the nutrition of the houseless community.

METHODS

In partnership with the medical student-run organization, Chicago Street Medicine, at Northwestern University Feinberg School of Medicine, twenty adults experiencing houselessness in Chicago, Illinois participated in the cross-sectional study. A 10-item survey was verbally administered to characterize the participants' daily food intake, food sources, barriers, resources, and nutritional preferences and needs. All data was directly transcribed into REDCap. Descriptive statistics were generated.

RESULTS

Individuals consumed a median of 2 snacks and meals per day (IQR: 1-3). No participant consumed adequate servings of every food group, with only one participant meeting the dietary intake requirements for one food group. Participants most often received their food from donations (n = 15), purchasing themselves (n = 11), food pantries (n = 4), and shelters (n = 3). Eleven of nineteen participants endorsed dental concerns as a major barrier to consuming certain foods. Twelve participants had access to a can opener and twelve could heat their meals on a stove or microwave. Seven had access to kitchen facilities where they may prepare a meal. Approximately half of participants had been counseled by a physician to maintain a particular diet, with most related to reducing sugar intake.

CONCLUSION

Most houseless participants were unable to acquire a balanced diet and often relied on organizational efforts to eat. Organizations should consider the chronic health conditions, dentition needs, and physical resources and barriers to optimal nutrition when obtaining food to distribute to the unhoused.

Multidisciplinary providers' perspectives on engaging young black, gay, bisexual and other men who have sex with men living with HIV in mental health care services

Young Black gay, bisexual, and other men who have sex with men (YB-GBMSM) living with HIV are at high risk for psychological stressors and comorbidities. We sought to gain the perspectives of multidisciplinary providers (including HIV care, mental health care, and social service providers) on their experiences with engaging YB-GBMSM in mental health care within comprehensive HIV primary care centers that included both types of services on-site. We conducted qualitative in-depth interviews with fifteen providers in two clinics, and analyzed the qualitative data using a thematic analysis approach. Our participants described high levels of need for mental health services among YB-GBMSM living with HIV, due to psychological challenges related to living with HIV as well as other frequently occurring life stressors. At the same time, barriers to accessing these services were identified, with mental health stigma, under-recognition of symptoms and confidentiality concerns being the most commonly cited. Strategies to improve mental health service uptake in light of these needs and barriers were discussed, including re-framing of mental health services, addressing logistical barriers, and utilization of a biopsychosocial perspective.

Preferences of Young Black Gay, Bisexual, and Other Men Who Have Sex with Men Regarding Integration of HIV and Mental Health Care Services

Optimization of mental health service use is critical to HIV care engagement among young Black gay, bisexual, and other men who have sex with men (YB-GBMSM). Clinic-level interventions to integrate HIV and mental health services have been proposed; however, patient perspectives on such care models are often lacking. We conducted a mixed-methods study consisting of surveys (N = 100) and qualitative in-depth interviews (n = 15) with YB-GBMSM recruited from two Ryan White-funded HIV clinics in Atlanta, Georgia. Most participants (70%) agreed that integration of HIV and mental health services was beneficial to them. Thirty-six percent (36%) desired a higher level of integration than what they perceived was currently available in their clinic setting, 51% believed their clinic was already optimally integrated, and 13% preferred less integration. In the qualitative interviews, participants discussed their support for potential integration strategies such as training HIV providers to prescribe antidepressants, closer in-clinic proximity of HIV and mental health providers, and use of patient navigators to help patients access mental health care and remind them of appointments. Perceived benefits of care integration included easier access to mental health services, enhanced overall well-being, and improved HIV care engagement. In summary, YB-GBMSM were supportive of integrating HIV and mental health services, with varying individual preferences regarding the degree and operationalization of this integration. Improving integration of mental health and HIV services, and tailoring modes of service delivery to individual preferences, has the potential to improve both general well-being and HIV care engagement in this high priority population.

Burden and Correlates of Mental Health Symptoms Among Young Black Gay, Bisexual, and Other Men Who Have Sex with Men Engaged in HIV Care in Atlanta

Mental health comorbidities are prevalent among young Black gay, bisexual, and other men who have sex with men (YB-GBMSM) living with HIV and can adversely impact HIV-related outcomes. We conducted a cross-sectional survey study with 100 YB-GBMSM recruited from two HIV care centers in Atlanta, and constructed multivariable logistic and linear regression models to examine correlates of depression, anxiety, trauma symptoms, and general well-being. In adjusted models, full-time employment was associated with fewer depressive symptoms, while HIV stigma and substance use were associated with higher levels of depressive symptoms. Younger age and full-time employment were negatively associated with severe anxiety, while HIV stigma was positively associated with severe anxiety and trauma symptoms. Trust in physicians, lower HIV stigma, full-time employment, and lack of substance use were associated with higher average general well-being scores. In conclusion, we found high frequency of depressive, anxiety, and trauma-related symptoms among this sample of YB-GBMSM living with HIV. Unemployment, substance use, and HIV stigma emerged as particularly salient correlates of psychological morbidity, suggesting a need for structural and community-level interventions to address mental health in this population.

Exploring influences on methamphetamine use among Black gay, bisexual and other men who have sex with men in Atlanta: A focus group study

BACKGROUND

Methamphetamine use is a contributor to HIV risk and poor health outcomes among gay, bisexual and other men who have sex with men (GBMSM). There is a paucity of research examining methamphetamine use and its social context specifically among Black GBMSM. We therefore sought to: (1) describe trends in methamphetamine use among Black GBMSM in Atlanta, Georgia, and (2) examine the risk environment (micro-, meso‑ and macro-level factors operating in the political, social, physical, economic, and healthcare environments) that might elevate risk for methamphetamine use in this population.

METHODS

We conducted a qualitative study consisting of eight focus groups with 54 key informants between December 2019 and March 2020. Participants represented community-based and healthcare organizations that work closely with Black GBMSM. Our thematic analysis included an iterative, team coding approach combining deductive and inductive elements.

RESULTS

Participants unanimously agreed that methamphetamine use was increasingly prevalent among Black GBMSM in Atlanta, with many describing a historical arc in which methamphetamine use - previously associated with predominantly white, affluent GBMSM - was now common among younger, lower socioeconomic status Black GBMSM. At the micro-level, participants described contributors to increasing methamphetamine use including use as a sex drug, and the interrelated burdens of stress and mental illness, housing instability, geographic mobility and poverty. At the meso‑level, participants described virtual and physical sex scenes including use of geosocial networking apps that facilitated the spread of methamphetamine use in the Black GBMSM community. At the macro-level, participants described how policies prioritizing other concerns (e.g., HIV, opioids) seemed to limit resources available for methamphetamine prevention and treatment programming.

CONCLUSION

Multi-level environmental influences are working together to elevate risk for methamphetamine use among Black GBMSM in Atlanta, with potential to adversely impact health and well-being and undermine HIV prevention and treatment efforts.

Mental Health Service Utilization Among Young Black Gay, Bisexual, and Other Men Who Have Sex with Men in HIV Care: A Retrospective Cohort Study

Young Black gay, bisexual, and other men who have sex with men (YB-GBMSM) face multiple psychosocial stressors, and are disproportionately impacted by HIV. Mental health care engagement is a promising avenue for addressing these disparities. To date, rates of mental health service utilization have not been examined specifically in this population. We conducted a retrospective cohort study among YB-GBMSM receiving care in a Ryan White-funded HIV care center that includes co-located HIV and mental health services. Of 435 unique YB-GBMSM patients, mental health concerns were identified in n = 191 (43.9%). Depressive symptoms were the most common concerns identified, followed by substance use, anxiety, and trauma. Among patients with identified mental health concerns who were not previously in mental health care, 79.1% were referred to mental health care, 56.3% set an appointment with a mental health provider, 40.5% were linked to mental health care (attended an initial visit), and 19.6% remained engaged in mental health care. Younger YB-GBMSM (age 18-24 years), who received care in a more integrated pediatric/adolescent part of the center, were more likely to have an appointment set once a concern was identified (χ² = 7.17; p = 0.007). Even in a setting with co-located HIV and mental health care services, we found significant gaps in engagement at each stage of a newly described mental health care continuum. Implications for intervention at the provider and systems levels are discussed.

Bilateral nocardial endophthalmitis in a prothonotary warbler (Protonotaria citrea)

A 7-year-old captive female prothonotary warbler (Protonotaria citrea) died following chronic feather and weight loss. At necropsy, the right eye had a 2 x 2 x 1 mm corneal plaque of inspissated yellow-tan material and edema of the lower eyelid. Microscopically, both eyes exhibited diffuse, severe pyogranulomatous endophthalmitis with retinal necrosis and detachment. Numerous intralesional branching, gram-positive, beaded, filamentous bacteria formed a thick mat attached to the retinal pigmented epithelium and extending into the pecten. Bacteria were strongly acid-fast positive by Fite's stain but only occasionally acid-fast positive by Ziehl-Neelsen staining, a characteristic consistent with a Nocardia spp. Infected regions demonstrated positive in situ hybridization reactivity with a probe complementary to the 16S rRNA gene of Nocardia spp. There was no evidence of primary bacterial infection in the other organs examined.

Purine-induced alterations of dopamine metabolism in rat pheochromocytoma PC12 cells

Studies with cerebrospinal fluid from subjects with Parkinson's disease suggest that purine abnormalities may be present in this disorder. The effects of purines on dopamine metabolism have not been characterized, though adenosine is known to inhibit dopaminergic neurotransmission. In this study, dopamine, its precursor 3,4-dihydroxyphenylalanine (DOPA), and its degradation products 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) were measured in rat pheochromocytoma PC12 cells following 24-h incubation with 5, 50, and 500 microM adenosine, adenine, guanosine, guanine, hypoxanthine, xanthine, and uric acid. Incubation with adenosine increased DOPA, DOPAC, and HVA, while adenine treatment decreased DOPA. Guanosine (500 microM) decreased DOPA, dopamine, and DOPAC, while lower concentrations increased DOPAC and HVA. Incubation with guanine decreased dopamine, and xanthine decreased dopamine and DOPAC. Hypoxanthine and uric acid exerted minimal effects. These results indicate that purines exert a variety of effects on dopamine metabolism. The influence of purine metabolism on the dopaminergic deficit in the Parkinsonian brain merits further investigation.

L-DOPA does not enhance hydroxyl radical formation in the nigrostriatal dopamine system of rats with a unilateral 6-hydroxydopamine lesion

The debate about the toxicity of L-DOPA to dopaminergic neurons has not been resolved. Even though enzymatic and nonenzymatic metabolism of L-DOPA can produce hydrogen peroxide and oxygen free radicals, there has been controversy as to whether L-DOPA generates an oxidant stress in vivo. This study determined whether acute or repeated administration of L-DOPA caused in vivo production of hydroxyl radicals in striatum and other brain regions in rats with a unilateral 6-hydroxydopamine lesion of the dopaminergic nigrostriatal projections. Salicylate trapping combined with in vivo microdialysis provided measurements of extracellular 2,3-dihydroxybenzoic acid (2,3-DHBA) in striatum following L-DOPA administration systemically (100 mg/kg, i.p.) or by intrastriatal perfusion (1 mM, via the microdialysis probe). Tissue concentrations of 2,3-DHBA and salicylate were also measured in striatum, ventral midbrain, and cerebellum following repeated administration of L-DOPA (50 mg/kg, i.p., once daily for 16 days). In each instance, treatment with L-DOPA did not increase 2,3-DHBA concentrations, regardless of the nigrostriatal dopamine system's integrity. When added to the microdialysis perfusion medium, L-DOPA resulted in a significant decrease in the striatal extracellular concentration of 2,3-DHBA. These results suggest that administration of L-DOPA, even at high doses, does not induce hydroxyl radical formation in vivo and under some conditions may actually diminish hydroxyl radical activity. Furthermore, prior damage to the nigrostriatal dopamine system does not appear to predispose surviving dopaminergic neurons to increased hydroxyl radical formation following L-DOPA administration. Unlike L-DOPA, systemic administration of methamphetamine (10 mg/kg, s.c.) produced a significant increase in the concentration of 2,3-DHBA in striatal dialysate, suggesting that increased formation of hydroxyl radicals may contribute to methamphetamine neurotoxicity.

Time-dependent effects of levodopa on regional brain dopamine metabolism and lipid peroxidation

Levodopa treatment in Parkinson's disease has been suggested to contribute to disease progression through free radical generation. We compared the time course of levodopa-induced dopamine metabolism, and the resulting oxidative stress, between rat brain regions with varying dopaminergic innervation. At 1, 4, 8, and 12 h after levodopa administration (100 mg/kg), dopamine, dihydroxyphenylacetic acid, and homovanillic acid were measured in striatum and ventral midbrain, regions containing marked dopaminergic innervation, and in prefrontal cortex and cerebellum, which possess little dopaminergic innervation. Malondialdehyde, a marker of oxidative stress, was measured in additional animals. The return of dopamine and its metabolites to control concentrations tended to be slower (by 3-8 h) in cerebellum and prefrontal cortex than in dopaminergic regions. Malondialdehyde concentrations were decreased (p < 0.05) in ventral midbrain 8 h posttreatment, but increased in cerebellum 12 h posttreatment. We concluded that levodopa increases dopamine metabolism in nondopaminergic as well as dopaminergic regions, with delayed clearance of dopamine and its metabolites in nondopaminergic regions. The slower return of dopamine to control levels in nondopaminergic regions may be relevant to some of the side effects of levodopa. No support was found for the hypothesis that levodopa treatment induces oxidative stress.

Influence of repeated levodopa administration on rabbit striatal serotonin metabolism, and comparison between striatal and CSF alterations

Parkinson's disease (PD) is characterized by decreased striatal dopamine, but serotonin (5-HT) is also reduced. Because 5-HT decreases following a single levodopa injection, levodopa has been suggested to contribute to PD's serotonergic deficits. However, in a recent study, rat striatal serotonin levels were reported to increase following 15-day levodopa administration. To address this issue, we administered levodopa (50 mg/kg) to rabbits for 5 days, then measured serotonin, its precursors tryptophan and 5-hydroxytryptophan (5-HTP), and its major metabolite 5-hydroxyindole-acetic acid (5-HIAA) in striatum and CSF. Striatal serotonin and tryptophan were unchanged, while 5-HTP and 5-HIAA increased 4- and 7-fold, respectively. CSF 5-HTP and 5-HIAA were also significantly increased. In levodopa-treated animals, 5-HTP concentrations were moderately correlated (r = 0.679) between striatum and CSF, while weak correlations were present between striatal and CSF concentrations of both serotonin and 5-HIAA. These results suggest that repeated levodopa treatment increases striatal serotonin turnover without changing serotonin content. However, levodopa-induced alterations in striatal serotonin metabolism may not be accurately reflected by measurement of serotonin and 5-HIAA in CSF.

Altered guanosine and guanine concentrations in rabbit striatum following increased dopamine turnover

The significance of guanine nucleotides and nucleosides in neurodegenerative disorders is suggested by recent reports that these molecules enhance neurite branching and astrocyte proliferation. The objective of this study was to investigate the influence of increased dopamine metabolism, produced by 5-day treatment of rabbits with reserpine (2 mg/kg) or levodopa (LD) (50 mg/kg), on striatal concentrations of guanosine, guanine, and their metabolites. Reserpine treatment decreased striatal guanosine by 41% and increased guanine by 50%, while LD decreased guanosine by 48% (all p < 0.01 vs. vehicle-treated controls). LD also increased guanine by 22% (not statistically significant). Xanthine and uric acid concentrations were unchanged. Because of the neurotrophic properties of guanosine and guanine, changes in striatal concentrations of these purines secondary to increased dopamine (DA) turnover may have relevance for survival of remaining dopaminergic neurons in Parkinson's disease (PD).

Time-dependent effects of repeated amphetamine treatment on norepinephrine in the hypothalamus and hippocampus assessed with in vivo microdialysis

The effects of repeated amphetamine (AMPH) pretreatment on norepinephrine (NE) neurotransmission in the hypothalamus and hippocampus were assessed using in vivo microdialysis. Rats were pretreated with either saline or an escalating-dose AMPH regimen (1-->10 mg/kg) over 10 consecutive days, and then were withdrawn from AMPH for either 1 day or 30 days, at which time the animals underwent two consecutive days of testing. As expected, repeated treatment with AMPH resulted in time-dependent changes in both spontaneous locomotor activity and in the psychomotor response to a subsequent challenge injection of AMPH. In addition, repeated exposure to AMPH resulted in time-dependent and regionally-specific changes in the basal concentrations of NE in dialysate, and in the NE response to an AMPH challenge. For example, AMPH pretreatment produced a persistent (at least one month) increase in the basal concentration of NE in the hippocampus, but not the hypothalamus, although the response to an AMPH challenge was altered in both structures. It is suggested that AMPH treatment produces adaptations in NE systems that far outlast the acute effects of the drug, and that these may contribute to both transient and more persistent behavioral sequelae associated with the discontinuation of chronic AMPH use.

Enduring enhancement of amphetamine sensitization by drug-associated environmental stimuli

We report on the effect of environment on amphetamine sensitization in rats with a unilateral 6-hydroxydopamine lesion of the mesostriatal dopamine system. The rats were either housed in the test environment (HOME) or exposed to it only during the treatments (NOVEL). In experiment 1, the rats received seven consecutive i.p. injections of either saline or 2 mg/kg amphetamine. After 1 wk withdrawal the rotational response to 2 mg/kg amphetamine i.p. (i.e., amphetamine challenge) was compared in saline- vs. amphetamine-pretreated animals. Although both HOME and NOVEL groups sensitized, the magnitude of sensitization was greater in the NOVEL group. In the NOVEL group there was also a greater conditioned response to drug-related cues. In experiment 2 a dose-effect curve (0.75, 1.5, 3.0 and 6.0 mg/kg amphetamine i.p.) was determined before and after six i.p. injections of 4.0 mg/kg amphetamine. Sensitization was indicated by a parallel shift to the left of the dose-effect curve in both groups, but this shift was 2.6 times greater in the NOVEL group than in the HOME group. Finally, in experiment 3, we found that environment- and sensitization-dependent differences in the psychomotor response to amphetamine were not accompanied by differences in the concentration of amphetamine in the plasma or in the striatum.

Dynamic measurements of cerebral pentose phosphate pathway activity in vivo using [1,6-13C2,6,6-2H2]glucose and microdialysis

Cerebral pentose phosphate pathway (PPP) activity has been linked to NADPH-dependent anabolic pathways, turnover of neurotransmitters, and protection from oxidative stress. Research on this potentially important pathway has been hampered, however, because measurement of regional cerebral PPP activity in vivo has not been possible. Our efforts to address this need focused on the use of a novel isotopically substituted glucose molecule, [1,6-13C2,6,6-2H2]glucose, in conjunction with microdialysis techniques, to measure cerebral PPP activity in vivo, in freely moving rats. Metabolism of [1,6-13C2,6,6-2H2]glucose through glycolysis produces [3-13C]lactate and [3-13C,3,3-2H2]lactate, whereas metabolism through the PPP produces [3-13C,3,3-2H2]lactate and unlabeled lactate. The ratios of these lactate isotopomers can be quantified using gas chromatography/mass spectrometry (GC/MS) for calculation of PPP activity, which is reported as the percentage of glucose metabolized to lactate that passed through the PPP. Following addition of [1,6-13C2,6,6-2H2]glucose to the perfusate, labeled lactate was easily detectable in dialysate using GC/MS. Basal forebrain and intracerebral 9L glioma PPP values (mean +/- SD) were 3.5 +/- 0.4 (n = 4) and 6.2 +/- 0.9% (n = 4), respectively. Furthermore, PPP activity could be stimulated in vivo by addition of phenazine methosulfate, an artificial electron acceptor for NADPH, to the perfusion stream. These results show that the activity of the PPP can now be measured dynamically and regionally in the brains of conscious animals in vivo.

The effects of methamphetamine and cocaine on motor behavior and extracellular dopamine in the ventral striatum of Lewis versus Fischer 344 rats

The effects of an acute systemic injection of methamphetamine (mAMP) or cocaine (COC) on motor behavior (stereotypy, locomotor activity, and rearing) and extracellular dopamine (DA) in the ventral striatum were compared in Lewis (LEW) versus Fischer 344 (F344) rats, using in vivo microdialysis in awake freely moving animals. In addition, the behavioral response to repeated mAMP injections (i.e. sensitization) was characterized in LEW and F344 rats, as was the possibility of strain differences in drug pharmacokinetics. The major findings were: (i) LEW rats showed greater behavioral activation to an acute injection of both mAMP and COC, as indicated by a shift to the left in the dose-effect curves relative to F344 rats. (ii) LEW rats were more susceptible to mAMP sensitization. (iii) An acute injection of mAMP or COC enhanced the extracellular concentration of DA to a greater extent in LEW rats, as indicated by a significant shift to the left in the dose-effect curve relative to F344 rats. (iv) Strain differences in the behavioral and neurochemical effects of these drugs were characterized largely by differences in the duration of the drug response. (v) LEW rats had higher plasma and brain levels of mAMP and COC than F344 rats, suggesting that strain differences in pharmacokinetics may contribute to strain differences in the behavioral and neurochemical effects of these drugs.

Relationship between asymmetries in striatal dopamine release and the direction of amphetamine-induced rotation during the first week following a unilateral 6-OHDA lesion of the substantia nigra

In animals with a large unilateral 6-hydroxydopamine (6-OHDA) lesion of the nigrostriatal dopamine (DA) system the traditional "rotational behavior model" states that amphetamine will induce circling behavior towards the denervated striatum (ipsiversive), that is, away from the side where there is greater amphetamine-stimulated DA release and greater DA receptor stimulation. It is puzzling, therefore, why amphetamine induces contraversive rotation in rats tested 4 days after a unilateral 6-OHDA lesion, despite a 90-95% loss of the dopaminergic input to the striatum by this time. Rats reverse their direction of amphetamine-induced rotation by 8 days post-lesion and turn in the ipsiversive direction thereafter. To try and resolve this paradox, bilateral striatal microdialysis was used to estimate the effects of amphetamine on DA neurotransmission on Day 4 and Day 8 following a large unilateral 6-OHDA lesion of the substantia nigra. On Day 4 post-lesion, amphetamine produced a moderate (around 50% of control) increase in the extracellular concentration of DA in the denervated striatum. This amphetamine-releasable pool of DA was exhausted by a single amphetamine-challenge, because a second injection of amphetamine given 3 h after the first did not produce a comparable increase in DA. It is suggested that on Day 4 post-lesion the amount of DA released by amphetamine in the denervated striatum is sufficient to produce greater DA receptor stimulation on that side, because of DA receptor supersensitivity, and this leads to contraversive rotation. On Day 8 post-lesion, amphetamine induced DA release in the intact striatum but had no effect on extracellular DA in the denervated striatum (DA was nondetectable). On Day 8, therefore, DA receptor stimulation would be greatest in the intact striatum, leading to ipsiversive rotation. In conclusion, it is suggested that the seemingly paradoxical reversal in the direction of amphetamine-induced rotation that occurs over the first week following a unilateral 6-OHDA lesion is consistent with the traditional rotational model, and is due to time-dependent changes in the ability of amphetamine to release DA in the denervated striatum.

Time course of recovery of extracellular dopamine following partial damage to the nigrostriatal dopamine system

Partial damage to the nigrostriatal dopamine (DA) system can produce severe behavioral deficits, from which animals gradually recover. Although the compensatory neuroadaptations that contribute to recovery of function have received considerable attention, the exact role of presynaptic versus postsynaptic contributions remains unclear. For example, it has been suggested that presynaptic adaptations may not be sufficient to account for recovery of function, because compensatory increases in DA biosynthesis, metabolism, and release are maximal within 3 d following a unilateral 6-hydroxydopamine (6-OHDA) lesion, before behavioral recovery is complete. The purpose of this study was to examine another presynaptic adaptation, the normalization of extracellular DA. If this is also complete within 3 d postlesion, it, too, would be insufficient to account for the protracted time course of behavioral recovery. But if the normalization of extracellular DA proceeds more gradually, it could potentially account for the time course behavioral recovery. To address this issue, the extracellular concentration of striatal DA ipsilateral and contralateral to a unilateral 6-OHDA lesion was estimated with microdialysis, either 4 d or 3-4 weeks following the lesion. After estimating the basal extracellular concentration of DA, the ability to increase DA release further was assessed by administering an amphetamine challenge. It was found that in animals with a 6-OHDA lesion, the concentration of DA in dialysate was higher than would be predicted by the extent of DA denervation. Furthermore, in groups matched for lesion size, extracellular DA was significantly higher 3-4 weeks following a 6-OHDA lesion than 4 d following the lesion. These findings suggest that the normalization of extracellular DA may be a relatively gradual process, and therefore may be sufficient to account for the protracted time course of behavioral recovery.

Basal extracellular dopamine in the nucleus accumbens during amphetamine withdrawal: a 'no net flux' microdialysis study

The basal extracellular concentration of dopamine in the nucleus accumbens was quantified using the 'no net flux' microdialysis method, in rats undergoing withdrawal from D-amphetamine. Rats were initially pretreated with saline, or an escalating dose amphetamine regimen known to produce a robust withdrawal syndrome, and extracellular dopamine was quantified 3 or 28 days after the last pretreatment injection. There was no effect of amphetamine pretreatment on the basal extracellular concentration of dopamine in the nucleus accumbens, or on the 'in vivo recovery' of dopamine, estimated by 'no net flux' microdialysis. It is suggested that amphetamine withdrawal is not necessarily accompanied by changes in the basal extracellular concentration of dopamine in the nucleus accumbens.

A microdialysis study of ventral striatal dopamine during sexual behavior in female Syrian hamsters

Microdialysis was used to study the effects of exposure to a male hamster on extracellular concentrations of dopamine, dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindole acetic acid (5-HIAA) in the ventral striatum of ovariectomized female Syrian hamsters pretreated with either estradiol and progesterone, or a similar regimen of oil injections. The hormone-treated females showed high levels of lordosis throughout the hour of exposure to the male. In hormone-treated females, there was a rapid elevation of dialysate dopamine within the first 15 min of exposure to the male. Dialysate dopamine gradually declined over the next 45 min, though remaining significantly above baseline during the entire period of exposure to the male. None of the oil-treated females showed any indication of lordosis, and the addition of the male produced only a small increase in dopamine at 30 min, after which dopamine returned to pre-male basal levels. DOPAC, HVA, and 5-HIAA were all elevated following introduction of the male for both groups of females. These results suggest that ovarian hormones modulate the responsivity of ventral striatal dopamine to incentive stimuli associated with mating behavior in females, although extracellular levels of dopamine in the ventral striatum do not seem to be directly coupled to the display of lordosis.

On the use of multiple probe insertions at the same site for repeated intracerebral microdialysis experiments in the nigrostriatal dopamine system of rats

The effects of implantation of a dialysis probe into the striatum of awake rats on indices of dopamine (DA) and serotonin neurotransmission were assessed, first over 24 h following initial insertion of a probe, and then again following reinsertion of a probe at the same site 1 week later. It was found that the basal concentration of DA in dialysate stabilized within 20-40 min after probe implantation, although DA showed a modest decline 24 h later. There was, however, no significant difference in basal DA between two test sessions separated by 1 week. On the other hand, the basal concentrations of the DA metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid, progressively increased for 2-3 h after probe implantation and decreased markedly by 24 h later. Furthermore, in contrast to DA, the DA metabolites decreased even further after the second probe insertion. Amphetamine-stimulated DA release was also greatly attenuated following the second probe insertion, relative to the first probe insertion. Two probe insertions had only modest effects on the concentration of 5-hydroxyindoleacetic acid in dialysate, relative to the DA metabolites. It is suggested the effects of two probe insertions on DA metabolism and amphetamine-stimulated DA release described here are indicative of probe-induced damage to the nigrostriatal DA system. If this is the case, multiple probe insertions may not provide a feasible strategy for within-subjects design dialysis experiments over extended periods of time, at least in the DA system of small animals. It is suggested further that a stable basal concentration of DA in dialysate may be an especially poor indicator of the integrity of the dopaminergic input to the striatum.

The effects of four days of continuous striatal microdialysis on indices of dopamine and serotonin neurotransmission in rats

The effects of 4 days of continuous microdialysis with a small-diameter concentric-style probe on indices of striatal dopamine (DA) and serotonin neurotransmission were assessed. It was found that over 4 days of dialysis, there was a marked time-dependent decrease in the basal concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in dialysate and in amphetamine-stimulated DA release. In contrast, there was no decrease in basal DA or in the ability of cocaine to elevate the concentration of DA in dialysate over the same period of time. There were only very modest changes in dialysate levels of the serotonin metabolite, 5-hydroxyindoleacetic acid (5-HIAA), relative to the marked changes in DA metabolites. It is suggested that 4 days of continuous dialysis does not result in a non-specific decrease in diffusibility of these compounds into the dialysis probe, but that the changes are more likely due to probe-induced damage to the nigrostriatal DA system. It is also suggested that a "stable" basal concentration of DA in dialysate is an especially poor indicator of the integrity of the dopaminergic input to the striatum. The implications of these findings for within-subjects design microdialysis experiments are discussed.

Time course of transient behavioral depression and persistent behavioral sensitization in relation to regional brain monoamine concentrations during amphetamine withdrawal in rats

This experiment was designed to characterize the withdrawal syndrome produced by discontiuation of treatment with escalating, non-neurotoxic doses of d-amphetamine (AMPH). AMPH withdrawal was associated with both transient and persistent changes in behavior and postmortem brain tissue catecholamine concentrations. During the first week of withdrawal rats showed a significant decrease in spontaneous nocturnal locomotor activity. This behavioral depression was most pronounced on the first 2 days after the discontinuation of AMPH pretreatment, was still evident after 1 week, but had dissipated by 4 weeks. Behavioral depression was not due to a simple motor deficit, because AMPH-pretreated animals showed a normal large increase in locomotion when the lights initially went out, but they did not sustain relatively high levels of locomotor activity throughout the night, or show the early morning rise in activity characteristic of controls. Behavioral depression was associated with the transient decrease in the concentration of norepinephrine (NE) in the hypothalamus, and a transient decrease in the ability of an AMPH challenge to alter dopamine (DA) concentrations in the caudate-putamen and nucleus accumbens. AMPH pretreatment also produced persistent changes in brain and behavior. The persistent effects of AMPH were not evident in spontaneous locomotor activity, but were revealed by a subsequent challenge injection of AMPH. AMPH pretreated animals were markedly hyper-responsive to the stereotypy-producing effects of an AMPH challenge. This behavioral sensitization was not fully developed until 2 weeks after the discontinuation of AMPH pretreatment, but then persisted undiminished for at least 1 year. It is suggested that the transient changes in brain and behavior described here may represent an animal analogue of the "distress syndrome" seen in humans during AMPH withdrawal, which is associated with symptoms of depression and alterations in catecholamine function. On the other hand, persistent behavioral sensitization may be analogous to the enduring hypersensitivity to the psychotogenic effects of AMPH seen in former AMPH addicts.

Does amphetamine preferentially increase the extracellular concentration of dopamine in the mesolimbic system of freely moving rats?

It was suggested recently that a fundamental property of drugs that are rewarding, and thus have a high potential for abuse, is that they preferentially increase the extracellular concentration of dopamine (DA) in mesolimbic structures. This hypothesis was tested here by use of microdialysis in freely moving rats to determine the effects of systemic d-amphetamine administration on the extracellular concentration of DA in the so-called "limbic" (nucleus accumbens) and "motor" (dorsolateral caudate nucleus) subdivisions of the striatal complex. Amphetamine (2.03, 4.07, or 8.14 mumols/kg) greatly increased the extracellular concentration of DA in both structures, but there was no evidence of a preferential effect in the nucleus accumbens. The two higher doses of amphetamine actually increased extracellular DA to a greater extent in the dorsolateral caudate, but there was no significant regional difference if the data were expressed as a percent of baseline. These data do not support the hypothesis that drugs of abuse preferentially increase the extracellular concentration of DA in mesolimbic structures, although other ways in which amphetamine may selectively influence mesolimbic DA activity are discussed.

The long-term effects of neurotoxic doses of methamphetamine on the extracellular concentration of dopamine measured with microdialysis in striatum

The extracellular concentrations of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) in the striatum were measured by in vivo microdialysis in freely moving rats one week after the animals were treated with neurotoxic doses of methamphetamine. Methamphetamine produced a marked depletion of striatal DA measured in postmortem tissue, and in the extracellular concentrations of DOPAC, HVA and 5-HIAA. In contrast, the resting extracellular concentration of DA in striatum was the same as in saline-pretreated controls. Furthermore, methamphetamine-pretreated rats were able to increase their concentration of extracellular DA to the same extent as controls in response to a (+)-amphetamine challenge. It is suggested that this adaptive response is probably responsible, at least in part, for the absence of obvious behavioral deficits in animals exposed to neurotoxic doses of methamphetamine.

Susceptibility to sensitization. II. The influence of gonadal hormones on enduring changes in brain monoamines and behavior produced by the repeated administration of D-amphetamine or restraint stress

Repeated amphetamine use produces an enduring sensitization of brain dopamine (DA) systems and behavior. Repeated exposure to stress can also produce sensitization, and amphetamine and stress may be interchangeable in this regard. There is, however, enormous individual variation in the susceptibility to sensitization by either stimulants or stress. The purpose of the present study was to determine if endogenous gonadal hormones contribute to individual variation in the sensitization of stereotyped behaviors, locomotion or regional brain monoamine metabolism. It was found that removal of testicular hormones by castration of male rats facilitated the behavioral sensitization produced by either repeated amphetamine treatment or repeated restraint stress, but ovariectomy of female rats was without effect. Prior exposure to amphetamine enhanced striatal homovanillic acid (HVA) levels and dihydroxyphenylacetic acid to DA and HVA to DA ratios in intact female, ovariectomized female and castrated male rats, but not gonadally-intact male rats. As a group, intact males were particularly heterogeneous because they were divisible into two neurochemically distinct subgroups based on their degree of behavioral sensitization, and the other groups were not. It is suggested that individual differences in the sensitization of brain DA systems and behavior produced by repeated exposure to amphetamine or stress may be due in part to individual differences in the concentration of a testicular hormone.

Susceptibility to sensitization. I. Sex differences in the enduring effects of chronic D-amphetamine treatment on locomotion, stereotyped behavior and brain monoamines

There are sex differences in a number of behavior elicited by amphetamine (AMPH). The purpose of the present experiment was to determine if there are also sex differences in the sensitization of the locomotor activity and stereotypy produced by repeated intermittent AMPH treatment, and whether this is accompanied by sex differences in dopamine (DA) metabolism. It was found that female rats showed greater and more rapid sensitization of locomotor activity and stereotyped behavior than males. In addition, prior exposure to AMPH was associated with an elevation in resting striatal dihydroxyphenlacetic acid (DOPAC) to DA ratios in female, but not male rats, suggesting a sex difference in one neurochemical correlate of sensitization. As a group, males were more variable and heterogeneous in their response to repeated AMPH treatment, because they were divisible into two neurochemically distinct subgroups on the basis of their change in behavior and females were not. This heterogeneity may make it more difficult to identify neurochemical correlates of sensitization in males. It is suggested that there is a sex difference in the responsiveness of brain DA systems to repetitive activation, and this contributes to individual variation in the susceptibility to sensitization.

Long-lasting effects of escalating doses of d-amphetamine on brain monoamines, amphetamine-induced stereotyped behavior and spontaneous nocturnal locomotion

The repeated intermittent administration of relatively low doses of amphetamine (AMPH) produces an enduring hypersensitivity to the motor stimulant effects of AMPH (behavioral sensitization), and this is accompanied by enhanced mesotelencephalic dopamine (DA) utilization/release. In contrast, chronic treatment with very high doses of AMPH does not produce sensitization, but is neurotoxic, resulting in the depletion of brain DA (and often other monoamines). However, gradually escalating doses of AMPH provide protection against the neurotoxic effects of higher doses given later. Therefore, the purpose of the present experiment was to determine if a regimen of gradually escalating doses of AMPH, culminating in much higher doses than usually used to study sensitization, would produce neural and behavioral changes associated with AMPH neurotoxicity (DA depletion) or behavioral sensitization (increased DA utilization). Female rats were given 60 injections (2/day) of increasing (1 to 10 mg/kg) doses of d-AMPH, culminating in rats receiving 20 mg/kg/day for four consecutive days. This treatment did not deplete brain DA or serotonin, but did produce a long-lasting enhancement (at least 12 days) in striatal and nucleus accumbens DOPAC concentrations, and DOPAC/DA ratios. These neurochemical changes were accompanied by an enduring hypersensitivity to the stereotypy-producing effects of a subsequent AMPH 'challenge.' In contrast to this enhanced response to a challenge, AMPH-pretreated rats showed a marked reduction in spontaneous nocturnal motor activity. It is concluded that rats can be given escalating doses of AMPH, which mimic to some extent the AMPH 'runs' common in addicts and that this produces neural and behavioral changes consistent with the development of sensitization; not neurotoxicity.

Sex differences in the effects of gonadectomy on amphetamine-induced rotational behavior in rats

The effects of gonadectomy on amphetamine-induced rotational behavior were studied in male and female rats. Different systemic doses were used to produce equivalent brain concentrations of the drug in each group, thereby controlling for sex differences in the metabolism of amphetamine. Ovariectomy of female rats significantly attenuated amphetamine-induced rotation, whereas castration of males was without effect. The results support the idea that in females, the endogenous gonadal hormones facilitate functional activity in the mesostriatal dopamine system.

Sex differences in the effects of early experience on the development of behavioral and brain asymmetries in rats

The influence of early experience (preweaning handling) on the development of several postural/motor asymmetries (side bias in an open field, turn preference in a T-maze, amphetamine-induced rotational behavior, tail pinch-induced asymmetries) and the lateralization of brain dopamine was studied in adult male and female rats. In many cases the adult patterns of behavioral and brain asymmetries were modified by early handling in a sexually dimorphic manner. In addition, the direction of postural/motor asymmetries was very much task-dependent, especially in females. We conclude that: early experience may modify the development of behavioral and brain asymmetries; sex differences in asymmetries are very common; early handling may affect males and females differently; and different measures of postural/motor asymmetries may reflect different and multiple brain asymmetries.

Sex differences and estrous cycle dependent variation in rotational behavior elicited by electrical stimulation of the mesostriatal dopamine system

In this study electrical stimulation-induced rotational behavior was used as a behavioral index of mesostriatal dopamine (DA) activity to investigate gender and hormonal influences on the DA system. In female rats we found estrous cycle related variations in electrical stimulation-induced rotational behavior. A constant electrical stimulus produced significantly more turning on the day of estrus, than it did 24 h later, on diestrus 1. Gonadectomy attenuated contraversive rotational behavior in female, but not male rats. In contrast, ovariectomy had no effect on the ipsiversive rotational behavior produced by stimulation of the reticular formation. This evidence supports the idea that endogenous changes in gonadal hormone levels influence the functional activity of the mesostriatal DA system in a sexually dimorphic manner.

Gonadectomy attenuates turning behavior produced by electrical stimulation of the nigrostriatal dopamine system in female but not male rats

Rotational behavior induced by electrical stimulation of ascending dopamine neurons is used as a behavioral model to investigate gender and hormonal influences on extra-hypothalamic dopamine systems. Steroid hormones influence the metabolism of many dopaminergic drugs, and therefore this approach avoids the complications inherent in drug-induced behavior models of dopamine activity. We found that gonadectomy of female, but not male, rats severely attenuates electrical stimulation-induced rotational behavior. This suggests that some female gonadal steroid hormone(s) may modulate the activity of ascending dopamine neurons, while male gonadal hormones do not.