Intervention with exercise restores motor deficits but not nigrostriatal loss in a progressive MPTP mouse model of Parkinson's disease

Many studies have investigated exercise therapy in Parkinson's disease (PD) and have shown benefits in improving motor deficits. However, exercise does not slow down the progression of the disease or induce the revival of lost nigrostriatal neurons. To examine the dichotomy of behavioral improvement without the slowing or recovery of dopaminergic cell or terminal loss, we tested exercise therapy in an intervention paradigm where voluntary running wheels were installed half-way through our progressive PD mouse model. In our model, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is administered over 4 weeks with increased doses each week (8, 16, 24, 32-kg/mg). We found that after 4 weeks of MPTP treatment, mice that volunteered to exercise had behavioral recovery in several measures despite the loss of 73% and 53% tyrosine hydroxylase (TH) within the dorsolateral (DL) striatum and the substantia nigra (SN), respectively which was equivalent to the loss seen in the mice that did not exercise but were also administered MPTP for 4 weeks. Mice treated with 4 weeks of MPTP showed a 41% loss of vesicular monoamine transporter II (VMAT2), a 71% increase in the ratio of glycosylated/non-glycosylated dopamine transporter (DAT), and significant increases in glutamate transporters including VGLUT1, GLT-1, and excitatory amino acid carrier 1. MPTP mice that exercised showed recovery of all these biomarkers back to the levels seen in the vehicle group and showed less inflammation compared to the mice treated with MPTP for 4 weeks. Even though we did not measure tissue dopamine (DA) concentration, our data suggest that exercise does not alleviate motor deficits by sparing nigrostriatal neurons, but perhaps by stabilizing the extraneuronal neurotransmitters, as evident by a recovery of DA and glutamate transporters. However, suppressing inflammation could be another mechanism of this locomotor recovery. Although exercise will not be a successful treatment alone, it could supplement other pharmaceutical approaches to PD therapy.

Effect of intermittent washout periods on progressive lesioning of the nigrostriatal pathway with 1-methyl-2-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

We have previously reported that a progressively increased dose of MPTP over the course of 4 weeks induces the gradual impairment of the nigrostriatal dopamine (DA) pathway and several behaviors [Goldberg et al. (in press) Neuroscience]. To our knowledge, this is the first report of specific behavioral deficits correlated with discrete thresholds of DA loss in this pathway. In that study, MPTP was administered 5 d/wk, with behavioral and tissue analysis being carried out 3 days following the final injection at each dose. However, in order to better represent long-term progressive neurodegeneration the present study introduced a washout period of 10 days between each increased dose of MPTP. This implementation also controlled for any transient de-activation of tyrosine hydroxylase (TH), the enzyme that catalyzes synthesis of DA, caused by MPTP-induced oxidative stress which has been suggested following acute administration of the toxin [Smeyne and Jackson-Lewis (2005) Brian Res Mol Brain Res 134:57-66]. Additionally, by the end of the previous study, there was an ultimate decrease of 62% in the mean number of TH-labeled neurons/section in the substantia nigra pars compacta (SNpc) and a 74% decrease in caudate putamen (CPu) TH optical density with continuous MPTP. In the present study, we find that the washout periods lead to a final 79% decrease in the mean number of TH-labeled SNpc neurons/section, and a similar 74% decrease in CPu TH following the 32 mg/kg MPTP dose. Additionally, a dose-dependent decrease was observed in the mean number of SNpc TH-ir neurons/section in the current study which was not seen in the continuous MPTP protocol. These results suggest that a washout period following each increased MPTP dose allows for observation of continued cell death that might occur during the week following MPTP administration, and for therapeutic interventions to be applied at any of several stages during progressive neurodegeneration.

Dopaminergic and behavioral correlates of progressive lesioning of the nigrostriatal pathway with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

A number of neurotoxin- and gene-based rodent models of acute neurodegeneration of nigrostriatal dopamine (DA) neurons are used to study Parkinson's disease (PD). The rapid degeneration achieved by many of these current models limits the capacity of the model to develop pathogenic mechanisms and display the various stages of motor degradation representative of the human Parkinsonian condition. Chronic rodent models have been the only ones to reproduce these characteristics, yet do not show correlated progress of DA loss with multiple stepwise behavioral deficits as seen in humans. In the present study, we have developed a progressive model of increasing DA loss and motor dysfunction via progressively increased administration of the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), in the C57Bl/6J mouse. Mice were administered a daily (5 d/wk) dose of MPTP that increased weekly over the course of 4 weeks (4 mg/kg, 8 mg/kg, 16 mg/kg and 32 mg/kg). Each treatment group was tested for exploratory and motor behavioral changes after every week leading up to their final dose, as well as changes in tyrosine hydroxylase immunoreactivity (TH-ir) of the substantia nigra pars compacta (SNpc) and caudate putamen (CPu). We detected a 24% decrease in the mean number of TH-ir SNpc neurons/section after 1 week, and a 62% decrease after 4 weeks as compared to the vehicle group. CPu TH-ir began at a 35% loss after 1 week and increased to a 74% loss after 4 weeks compared to the vehicle group. CPu DA content showed an initial decrease of 20% after 1 week, and a final decrease of 70% following week 4 versus the vehicle group. Free-standing rears (versus wall-assisted rears, in a cylinder), decreased from 35% to 8% of total rears as the dose of MPTP increased from 4 mg/kg to 32 mg/kg, respectively. However, motor impairment as measured by a Parallel Rod Activity Chamber test was not significant until week 4 at 32 mg/kg compared to the vehicle group. The present study is the first to show stepwise progression of behavioral deficits which correlate with gradual dopaminergic decline in the nigrostriatal pathway. This progressive lesioning regiment may be appropriate for future investigation of pathogenic mechanisms and various intervention therapies in PD.

Impaired glutamate homeostasis and programmed cell death in a chronic MPTP mouse model of Parkinson's disease

The pathogenesis of Parkinson's disease is not fully understood, but there is evidence that excitotoxic mechanisms contribute to the pathology. However, data supporting a role for excitotoxicity in the pathophysiology of the disease are controversial and sparse. The goal of this study was to determine whether changes in glutamate signaling and uptake contribute to the demise of dopaminergic neurons in the substantia nigra. Mice were treated chronically with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and probenecid or vehicle (probenecid or saline alone). Extracellular levels of glutamate in the substantia nigra were substantially increased, and there was an increase in the affinity, but no change in the velocity, of glutamate transport after MPTP/probenecid treatment compared to vehicle controls. In addition, the substantia nigra showed two types of programmed death, apoptosis (type I) and autophagic (type II) cell death. These data suggest that increased glutamate signaling could be an important mechanism for the death of dopaminergic neurons and trigger the induction of programmed cell death in the chronic MPTP/probenecid model.

l-dopa-induced reversal in striatal glutamate following partial depletion of nigrostriatal dopamine with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

We have reported that 1 month following acute (20mg/kg x 4) or subchronic (30 mg/kg/day x 7d) administration of the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, there is an increase or decrease, respectively, in the extracellular level of striatal glutamate as determined by in vivo microdialysis [Robinson S, Freeman P, Moore C, Touchon JC, Krentz L, Meshul CK (2003) Acute and subchronic MPTP administration differentially affects striatal glutamate synaptic function. Exp Neurol 180:73-86]. The goal of this study was to determine the effects of treatment with l-dopa (15 mg/kg) for 21 days on striatal glutamate starting on day 8 after the first dose of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine was administered to mice. Following acute administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, the increase in extracellular striatal glutamate due to lesion of the nigrostriatal pathway was completely reversed to a level below that found in the vehicle-treated group after l-dopa treatment. Subchronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment resulted in a decrease in striatal extracellular glutamate that was reversed to the level close to that observed in the vehicle-treated group. There was no change in the density of nerve terminal glutamate immunolabeling associated with the synaptic vesicle pool, suggesting that the alterations in extracellular glutamate most likely originated from the calcium-independent pool. There was a similar decrease in the relative density of tyrosine hydroxylase immunolabeling, a marker for dopamine terminals, within the dorsolateral striatum in both the acute and subchronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated groups that had been administered l-dopa. There was a decrease in the relative density of immunolabeling within the dorsolateral striatum for the glutamate transporter, GLT-1, following acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment in the groups administered either vehicle or l-dopa. There was no change in GLT-1 immunolabeling following subchronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. The results demonstrate that the reversal in the extracellular level of striatal glutamate following l-dopa treatment in both the acute and subchronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated groups is not due to changes in either striatal dopamine nerve terminals or in the density of the glutamate transporter, GLT-1.

Differential regulation of the growth-associated proteins GAP-43 and superior cervical ganglion 10 in response to lesions of the cortex and substantia nigra in the adult rat

Investigation of the elements underlying synapse replacement after brain injury is essential for predicting the neural compensation that can be achieved after various types of damage. The growth-associated proteins superior cervical ganglion-10 and growth-associated protein-43 have previously been linked with structural changes in the corticostriatal system in response to unilateral deafferentation. To examine the regulation of this response, unilateral cortical aspiration lesion was carried out in combination with ipsilateral 6-hydroxydopamine lesion of the substantia nigra, and the time course of the contralateral cortical molecular response was followed. Unilateral cortical aspiration lesion in rats corresponds with an upregulation of superior cervical ganglion-10 mRNA at 3 and 10 days post-lesion, and protein, sustained from three to at least 27 days following lesion. With the addition of substantia nigra lesion, the response shifts to an upregulation of growth-associated protein-43 mRNA at 3 and 10 days post-lesion, and protein after 10 days. Nigral lesion alone does not alter contralateral expression of either gene. Likewise, motor function assessment using the rotorod test revealed no significant long-term deficits in animals that sustained only nigrostriatal damage, but cortical lesion was associated with a temporary deficit which was sustained when nigrostriatal input was also removed. Growth-associated protein-43 and superior cervical ganglion-10, two presynaptic genes that are postulated to play roles in lesion-induced sprouting, are differentially upregulated in corticostriatal neurons after cortical versus combined cortical/nigral lesions. The shift in contralateral gene response from superior cervical ganglion-10 to growth-associated protein-43 upregulation and associated behavioral deficit following combined cortical and nigral denervation suggest that nigrostriatal afferents regulate cortical lesion-induced gene expression and ultimate functional outcome.

Time-dependent changes in extracellular glutamate in the rat dorsolateral striatum following a single cocaine injection

Acute cocaine administration has been shown to alter dorsal striatal plasticity [Proc Natl Acad Sci USA 87 (1990) 6912; Brain Res Bull 30 (1993) 173] and produce long-term neurochemical changes [Pharmacol Biochem Behav 27 (1987) 533]. To date, the effects of acute cocaine on extracellular glutamate and nerve terminal glutamate immunolabeling in the rat dorsolateral striatum have not been reported. To investigate cocaine-induced changes in extracellular glutamate, in vivo microdialysis was carried out in the dorsolateral striatum of rats 1-14 days after receiving a single injection of either vehicle or 15 mg/kg cocaine. There was an increase in the group injected with cocaine 1 day prior to measuring extracellular glutamate as compared with the control group. The group injected with cocaine 3 days prior to the microdialysis session had decreased extracellular glutamate levels. Furthermore, extracellular glutamate remained attenuated 14 days after acute cocaine treatment. Striatal glutamate decreased in the cocaine-treated rats after calcium removal, suggesting that cocaine-induced changes in extracellular glutamate were partially calcium-dependent. The density of nerve terminal glutamate immunolabeling was measured using immunogold electron microscopy in the contralateral striatum of the same rats that had been acutely treated with cocaine or vehicle. There were no changes in the density of glutamate immunolabeling within identified nerve terminals making an asymmetrical (excitatory) synaptic contact 1, 2, 3, or 14 days after acute cocaine exposure as compared with the control groups. Hence, these alterations in extracellular glutamate did not result from changes in glutamate immunolabeling within the synaptic vesicle pool. In addition, no changes in glutamate immunolabeling were found in rats that received cocaine 2 h previously or were withdrawn after 1 week of cocaine administration. The results demonstrate that a single injection of cocaine produces biphasic, time-dependent changes in extracellular glutamate in the rat dorsolateral striatum.

Nerve terminal glutamate immunoreactivity in the rat nucleus accumbens and ventral tegmental area after a short withdrawal from cocaine

Cocaine administration has been shown to alter glutamate transmission in numerous studies. Using quantitative electron microscopic immunogold labeling, our laboratory has previously reported that nerve terminal glutamate immunoreactivity is transiently altered following cocaine administration. The present study was undertaken to examine presynaptic nerve terminal glutamate immunoreactivity at shorter time points after withdrawal from cocaine. Animals received saline or cocaine for 7 days followed 3 days later by a cocaine or saline challenge. Most (>75%) cocaine-challenged animals had a heightened locomotor response to cocaine compared to the first day of cocaine and were considered behaviorally sensitized. One day after the challenge, glutamate immunogold-labeling was quantified in nerve terminals making asymmetrical synaptic contacts within the core and shell of the nucleus accumbens and ventral tegmental area. A single dose of cocaine did not alter the density of presynaptic nerve terminal glutamate immunoreactivity in the nucleus accumbens (NAc) or ventral tegmental area (VTA). The density of nerve terminal glutamate immunoreactivity in the shell, but not the core, was significantly increased in the animals receiving repeated cocaine. In the VTA the density of nerve terminal glutamate immunoreactivity did not change in the cocaine-sensitized group, but was significantly increased in the nonsensitized group. The finding that repeated cocaine treatment increased glutamate nerve terminal immunolabeling within the nucleus accumbens shell, but not the core, supports the hypothesis that glutamate synapses in the core and shell are differentially sensitive to repeated cocaine administration. Overall, our study does not support a role for changes in presynaptic glutamate in the development of behavioral sensitization.

The effects of acute or repeated cocaine administration on nerve terminal glutamate within the rat mesolimbic system

Cocaine administration alters glutamate function within several brain regions. Using quantitative electron microscopic immunocytochemistry, the present study investigated the effect of repeated intermittent cocaine (resulting in behavioral sensitization) or acute cocaine administration on the density of glutamate immunogold labeling within nerve terminals. Rats were treated daily with saline or cocaine for 7 days. Following a 14-day withdrawal animals were challenged with saline or cocaine. On the challenge day, most (75%) animals that received cocaine repeatedly showed a heightened locomotor response to cocaine compared to the first day of cocaine administration, and were considered behaviorally sensitized.Three days after the challenge, glutamate immunogold labeling was quantified in nerve terminals making asymmetrical synaptic contacts within the core and shell of the nucleus accumbens, ventral tegmental area and medial prefrontal cortex. There was a decrease in such labeling in the nucleus accumbens in the group receiving acute cocaine. Locomotor activity was positively correlated with glutamate immunolabeling within nerve terminals in the nucleus accumbens core only for the cocaine-sensitized group. Nerve terminal glutamate immunolabeling in the nucleus accumbens core, but not the shell, was increased in the non-sensitized compared to the cocaine-sensitized group. In the ventral tegmental area, glutamate immunolabeling was significantly higher in the cocaine-sensitized compared to the acute cocaine group. In the prefrontal cortex, there were no significant differences in glutamate immunogold labeling between treatment groups. This study indicates that acute cocaine administration significantly decreases nerve terminal glutamate immunoreactivity in the nucleus accumbens. We suggest that sensitization results in differential changes in the nucleus accumbens core versus the shell, and may alter presynaptic mechanisms regulating glutamate release or re-uptake in the core.

Blockade of NMDA receptors by MK-801 reverses the changes in striatal glutamate immunolabeling in 6-OHDA-lesioned rats

A lesion of the dopamine (DA)-containing nigrostriatal pathway with 6-hydroxydopamine (6-OHDA) results in an increase in the density of nerve terminal glutamate immunolabeling and in the mean percentage of asymmetrical synapses containing a discontinuous postsynaptic density [Meshul et al. (1999) Neuroscience 88:1-16]. Similar alterations in striatal glutamate synapses have been reported following blockade of striatal DA D-2 receptors with subchronic haloperidol treatment [Meshul et al. (1994) Brain Res 648:181-195]. The haloperidol-induced change in glutamate synapses was blocked by coadministration of the N-methyl-D-aspartate (NMDA) noncompetitive receptor antagonist MK-801. In order to determine if blockade of NMDA receptors could alter the density of nerve terminal glutamate immunolabeling following a 6-OHDA lesion of the nigrostriatal pathway, MK-801 was administered to lesioned animals for 14 days. In addition, the number of apomorphine-induced contralateral rotations was determined prior to and following the administration of MK-801. MK-801 administration reversed the increase in the density of nerve terminal glutamate immunolabeling due to a 6-OHDA lesion. There was a small but significant decrease in the number of apomorphine-induced contralateral rotations following administration of MK-801 compared to the number of rotations prior to treatment with the NMDA antagonist. These results demonstrate that blockade of postsynaptic NMDA receptors affects the density of presynaptic glutamate immunolabeling and that this change in nerve terminal glutamate density is associated with a decreased behavioral response to direct DA receptor stimulation. Whether the effect of MK-801 is directly on the striatum or acts through other excitatory pathways of the basal ganglia remains unclear.

Oral dyskinesias and morphological changes in rat striatum during long-term haloperidol administration

RATIONALE

Neuroleptic-induced oral dyskinesias in rats, a putative analogue to human tardive dyskinesia, may be due to increased glutamate release within the striatum. This may lead to excitotoxic degeneration and, as a consequence, persistent motor side effects.

OBJECTIVES

To investigate whether alterations in glutamatergic synapses within the striatum are associated with the development of neuroleptic-induced oral dyskinesia.

METHODS

Haloperidol was administered for 20 weeks, and rats with high and low levels of vacuous chewing movements (VCM) were analyzed for morphological changes with electron microscopy at three time points.

RESULTS

At week 8, the high VCM rats had a larger nerve terminal area and lower density of nerve terminal glutamate immunoreactivity than the other groups. After 18 weeks of treatment, the nerve terminal area was increased relative to controls in both the high and low VCM groups. After discontinuation of treatment, there were no significant morphological differences between the groups, but the level of VCM was still significantly increased in the high VCM group.

CONCLUSIONS

These results show that striatal glutamatergic transmission is affected during haloperidol treatment and the nerve terminal area and the density of nerve terminal glutamate immunoreactivity are important in determining the VCM response to haloperidol treatment. This indicates that increased glutamatergic synaptic activity in the striatum contributes to the development of human tardive dyskinesia.

Dopamine D4 receptor-deficient mice display cortical hyperexcitability

The dopamine D(4) receptor (D(4)R) is predominantly expressed in the frontal cortex (FC), a brain region that receives dense input from midbrain dopamine (DA) neurons and is associated with cognitive and emotional processes. However, the physiological significance of this dopamine receptor subtype has been difficult to explore because of the slow development of D(4)R agonists and antagonists the selectivity and efficacy of which have been rigorously demonstrated in vivo. We have attempted to overcome this limitation by taking a multidimensional approach to the characterization of mice completely deficient in this receptor subtype. Electrophysiological current and voltage-clamp recordings were performed in cortical pyramidal neurons from wild-type and D(4)R-deficient mice. The frequency of spontaneous synaptic activity and the frequency and duration of paroxysmal discharges induced by epileptogenic agents were increased in mutant mice. Enhanced synaptic activity was also observed in brain slices of wild-type mice incubated in the presence of the selective D(4)R antagonist PNU-101387G. Consistent with greater electrophysiological activity, nerve terminal glutamate density associated with asymmetrical synaptic contacts within layer VI of the motor cortex was reduced in mutant neurons. Taken together, these results suggest that the D(4)R can function as an inhibitory modulator of glutamate activity in the FC.

Alterations in rat striatal glutamate synapses following a lesion of the cortico- and/or nigrostriatal pathway

Ultrastructural changes within the ipsilateral dorsolateral striatum were investigated 1 month following a unilateral ablation of the rat frontal cortex (CTX), removing corticostriatal input, or injection of the neurotoxin, 6-hydroxydopamine (6-OHDA), into the substantia nigra pars compacta, removing nigrostriatal input. In addition, a combined ipsilateral cortical and 6-OHDA lesion (CTX/6-OHDA) was carried out. We find that following a CTX, 6-OHDA, or CTX/6-OHDA lesion, there was a significant decrease in the density of striatal nerve terminal glutamate immunoreactivity compared to the control group. There was also a significant increase in all three lesion groups in the mean percentage of asymmetrical synapses associated with a perforated postsynaptic density. There was a large increase within the CTX/6-OHDA-lesioned group and a smaller but still significant increase in the CTX-lesioned group in the percentage of terminals or boutons with multiple synaptic contacts (i.e., multiple synaptic boutons, MSBs), compared to either the 6-OHDA or the control group. There was no change in any of these measurements within the contralateral striatum. There was a significant decrease in the number of apomorphine-induced contralateral rotations in the CTX/6-OHDA versus the 6-OHDA-lesioned group. Animals receiving just the single CTX or 6-OHDA lesion recovered in motor function compared to the control group as measured by the Rotorod test, while the CTX/6-ODA-lesioned group recovered to less than 50% of the control level. The data suggest that following a CTX and/or 6-OHDA lesion, there is an increase in striatal glutamatergic function. The large increase in the percentage of MSBs in the combined lesion group suggests that dopamine or other factors released by the dopamine terminals assist in regulating synapse formation.

Haloperidol reverses the changes in striatal glutamatergic immunolabeling following a 6-OHDA lesion

We reported previously that 3 months following a unilateral lesion of the nigrostriatal pathway with 6-hydroxydopamine (6-OHDA), there was a decrease in the extracellular level of striatal glutamate as determined by in vivo microdialysis. This resulted in an accumulation or increase in the density of nerve terminal glutamate immunolabeling (Meshul et al., 1999). We also reported on blockade of dopamine D-2 receptors with haloperidol resulting in ultrastructural changes within the striatum consistent with increased functioning of the glutamatergic corticostriatal pathway (Meshul and Tan 1994). We hypothesized that administration of haloperidol to 6-OHDA-lesioned rats may be capable of activating the corticostriatal pathway and thereby counteracting the effects of the unilateral nigrostriatal lesion. Striatal glutamatergic function was evaluated using electron microscopy and quantitative glutamate immunocytochemistry. Starting 1 month after a unilateral lesion of the nigrostriatal pathway with 6-OHDA, haloperidol (0.5 mg/kg/d) was administered for the next 2 months. Within the dorsolateral caudate nucleus, the main area of innervation from the motor cortex, haloperidol blocked the 6-OHDA-induced increase in the density of nerve terminal glutamate immunolabeling. Within all three experimental groups (6-OHDA, haloperidol, 6-OHDA/haloperidol) there was an increase in the mean percentage of striatal asymmetrical synapses containing a perforated postsynaptic density. In addition, haloperidol treatment resulted in a reduction in the number of apomorphine-induced contralateral rotations in unilaterally 6-OHDA lesioned rats. The data suggests that the decrease in striatal glutamatergic function 3 months following a unilateral 6-OHDA lesion can be reversed by daily haloperidol treatment. This finding is discussed in terms of current therapy for Parkinson's disease. Synapse 36:129-142, 2000. Published 2000 Wiley-Liss, Inc.

Kappa opioid receptor immunoreactivity in the nucleus accumbens and caudate-putamen is primarily associated with synaptic vesicles in axons

A rabbit polyclonal antiserum, raised against a C-terminal oligopeptide of the mouse kappa opioid receptor, was used to localize the cellular distribution of kappa receptors in the dorsal and ventral striatum of rats with light and electron microscopic immunocytochemistry. Prominent, diffuse kappa receptor immunoreactivity was present in the nucleus accumbens, particularly in the shell, ventral caudate-putamen and olfactory tubercle. The density of receptor immunoreactivity decreased in more dorsal areas of the caudate-putamen. In contrast, neuronal cell bodies stained clearly in the dorsal endopiriform nucleus, claustrum and layer VI of the adjacent cerebral cortex. Observations at the electron microscopic level in the dorsomedial shell of the nucleus accumbens and caudate-putamen revealed that the kappa receptor immunoreactivity was predominantly located in axons, often associated with synaptic vesicles, remote from the terminal or preterminal area. The few terminals which were labeled made slightly more asymmetrical than symmetrical contacts and the percentage of asymmetrical contacts observed was greater in the caudate than in the accumbens. A small number of postsynaptic spines was labeled; most of them were contacted by asymmetrical terminals. No labeling was observed in dendritic shafts.Thus, the predominant localization of kappa receptor immunoreactivity in axons is consistent with its role as a major inhibitor of glutamate and dopamine release in the dorsal and ventral striatum.

Glial differences between naïve withdrawal seizure-prone and -resistant mice

BACKGROUND

Withdrawal seizure-prone (WSP) and withdrawal seizure-resistant (WSR) mice were bred in replicate (i.e., WSP-1 and WSP-2) to exhibit differences in handling-induced convulsion severity during ethanol withdrawal.

METHODS

We examined the role of the glutamatergic system in susceptibility to ethanol-withdrawal convulsions in naive mice by measuring the density of immunolabeling for several glutamate transporters and the glutamate-metabolizing enzyme, glutamine synthetase. The density of glial fibrillary acidic protein immunolabeling (a marker of glial structure) and cytochrome oxidase activity (a marker of neuronal activity) were also characterized in naive mice.

RESULTS

We observed a significantly greater density of immunolabeling for the glial transporter, glutamate/aspartate transporter, in CA1 subfield of the hippocampus (CA1) of naive WSP-2 mice as compared to WSR-2 mice. No other significant differences were observed. However, as compared to WSR mice, naive WSP mice exhibited a trend toward (a) greater immunolabeling for the glial glutamate transporter, glutamate transporter-1, in CA3, (b) greater immunolabeling for glial-specific glutamate-metabolizing enzyme, glutamine synthetase, in CA1 (replicate-2 only), and (c) less immunolabeling for the glial structural protein, glial fibrillary acidic protein, in all brain regions tested. In contrast, no trends or significant differences in the labeling density for the neuronal transporter, excitatory amino acid carrier 1, or the neuronal activity marker, cytochrome oxidase, were observed between the selected lines.

CONCLUSIONS

These data suggest that the glutamatergic system and glia may play a pivotal role in the increased susceptibility to handling-induced convulsions observed in WSP mice.

Prolonged survival of adult rat pancreatic islets transfected with E1A-12S adenovirus

It has been reported that various mutants of the E1A-adenovirus can activate quiescent differentiated cells to start proliferating. The aim of this study was to determine whether transfection with E1A-12S could extend the life span and functionality of pancreatic islets in culture. Rat pancreatic islets were isolated and transfected with retrovirus containing the adenovirus E1A-12S, E1A-13S, or control vectors. Transfection with the retroviral E1A-13S mutant produced extensive islet necrosis compared with nontransfected islets. Islets transfected with the control E1A mutant Ad5-dl312 vector (containing no E1A-12S or E1A-13S segments) were similar to nontransfected islets in their characteristics. We found that the E1A-12S transfected islets maintained greater viability, insulin granule structure, and glucose-induced insulin responsiveness over a 6-week period compared with mock or control islets. At 6 weeks of culture, the E1A-12S transfected islets also had fewer apoptotic cells compared with nontransfected islets. These data suggest that adenovirus E1A-12S can extend the functional life span of cultured rat pancreatic islets.

Glutamate uptake in mice bred for ethanol withdrawal severity

RATIONALE

Withdrawal seizure-prone and withdrawal seizure-resistant mice were selectively bred to exhibit differences in handling-induced convulsion severity during ethanol withdrawal. The glutamatergic system has been implicated in seizure activity as well as ethanol withdrawal symptoms.

OBJECTIVE

This study assessed L-[3H]glutamate uptake into hippocampal synaptosomes prepared from withdrawal seizure-prone and- resistant mice.

METHODS

Glutamate uptake was characterized following repeated handling-induced convulsions, during acute intoxication, and during peak withdrawal following chronic ethanol exposure.

RESULTS

Hippocampal synaptosomal L-[3H]glutamate uptake did not differ between convulsion- and ethanol-naive withdrawal seizure-prone and- resistant mice. Furthermore, exposure to convulsions or to a hypnotic dose of ethanol (4 g/kg) did not alter L-[3H]glutamate uptake. However, withdrawal from 72 h of ethanol exposure significantly increased L-[3H]glutamate uptake in both mouse lines as compared to their respective ethanol-naive controls.

CONCLUSIONS

These data suggest that glutamate uptake is influenced by chronic ethanol exposure similarly in both withdrawal seizure-prone and- resistant mice. The observed increases in glutamate uptake during withdrawal may be associated with compensatory mechanisms triggered by chronic intoxication and are independent of the selected differences for withdrawal severity.

High-dose methamphetamine treatment alters presynaptic GABA and glutamate immunoreactivity

The goal of this study was to determine if high-dose methamphetamine treatment altered presynaptic immunoreactivity for the amino acid neurotransmitters GABA and glutamate within the basal ganglia. Methamphetamine (15 mg/kg every 6 h, four doses) treatment in rats resulted in severe hyperthermia and a long-lasting (four weeks) depletion of striatal dopamine content (>80%). Severe dopamine loss correlated with a decrease in the density of presynaptic immunolabeling for GABA one week post-drug, and an increase after four weeks. Although no changes were seen in presynaptic striatal glutamate immunoreactivity, there was a significant increase in the percentage of glutamate-immuno-positive terminals associated with perforated postsynaptic densities. Rats given the same dose of methamphetamine but prevented from becoming hyperthermic showed less severe dopamine depletions and a lack of ultrastructural or immunocytochemical changes. In addition, induction of hyperthermia in the absence of drug decreased immunolabeling within mitochondria, but had no effect on dopamine content, morphology or nerve terminal immunoreactivity. Altered presynaptic GABA immunolabeling and terminal size were found in both the striatum and globus pallidus, suggesting that dynamic changes occur in the striatopallidal pathway following methamphetamine-induced dopamine loss. In addition, ultrastructural changes in glutamate-positive synapses which have been correlated with increased synaptic activity were found. These results are similar to changes in GABA and glutamate synapses that follow nigrostriatal dopamine loss in 6-hydroxydopamine-lesioned animals and in Parkinson's disease, and provide the first direct evidence that methamphetamine-induced dopamine loss alters the GABAergic striatopallidal pathway. Exposure to either methamphetamine or prolonged hyperpyrexia decreased mitochondrial Immunoreactivity, indicating that hyperthermia may contribute to methamphetamine toxicity by affecting energy stores.

Time-dependent changes in striatal glutamate synapses following a 6-hydroxydopamine lesion

The goal of this study was to investigate changes in glutamatergic synapses in the striatum of rats at two different time-points following a unilateral injection of 6-hydroxydopamine into the medial forebrain bundle. One month following this lesion of the nigrostriatal pathway, there was an increase (70%) in the mean percentage of asymmetrical synapses within the dorsolateral striatum containing a discontinuous, or perforated, postsynaptic density, possibly suggesting an increase in glutamatergic activity. This was correlated, in the same brain region, with a decrease (44%) in the density of glutamate immunoreactivity within nerve terminals associated with all asymmetrical synapses and also with those terminals associated with a perforated postsynaptic density. These morphological changes were consistent with an increase (>two-fold) in the basal extracellular level of striatal glutamate, as measured by in vivo microdialysis. The density of GABA immunolabeling within symmetrical nerve terminals was increased (25%) at this one month time-period. Dopamine levels within the lesioned striatum were >99% depleted. However, at three months, while an increase in the mean percentage of striatal perforated synapses was maintained, a significant increase (50%) in the density of striatal nerve terminal glutamate immunolabeling within all asymmetrical synapses and those associated with a perforated postsynaptic density was observed. This was correlated with a small, but significant, decrease (32%) in the basal extracellular level of striatal glutamate. The density of GABA immunolabeling within nerve terminals associated with a symmetrical contact remained elevated at this three month time-period, while striatal dopamine levels remained depleted. While the density of nerve terminal GABA immunolabeling remained elevated at both the one and three month time-periods, there appeared to be a differential effect on glutamatergic synapses. The in vivo microdialysis data suggest that glutamate synapses were more active at a basal level at one month and become less active compared to the control group at the three month time-period. These data suggest that there are compensatory changes in glutamatergic synapses within the striatum following a 6-hydroxydopamine lesion that appear to be independent of the level of striatal dopamine or GABA. We propose that changes in the activity of the thalamo-cortico-striatal pathway may help to explain the differential time-course change in striatal glutamatergic synaptic activity.

Reduced glutamate immunolabeling in the nucleus accumbens following extended withdrawal from self-administered cocaine

Alterations in the density of GABA and glutamate immunolabeling within nerve terminals in the shell region of the nucleus accumbens were assessed in rats withdrawn from intravenous cocaine exposure. Four groups of rats were used: one group self-administered cocaine (0.42 mg/kg/infusion) in daily 3-h sessions for approximately 2 weeks, two additional groups received either saline or cocaine in a noncontingent fashion, and a fourth comprised a drug-naive, age-matched control group. Immunogold electron microscopy was used to quantify presynaptic terminal GABA and glutamate density within the vesicular and mitochondrial pools approximately 18 days following the last drug or saline exposure in the treatment groups. A significant 27.7% decrease in vesicular glutamate density within asymmetrical nerve terminals was observed in animals that self-administered cocaine as compared to controls. This group also showed an 18.6% decrease in vesicular nerve terminal glutamate immunolabeling as compared to animals that were administered a similar total dose of cocaine in a response-independent fashion. No significant changes in the density of nerve terminal GABA vesicular immunolabeling were observed in any groups. For both transmitters, no differences were detected in the density of immunolabeling within the presynaptic mitochondrial (i.e., metabolic) pool. These results demonstrate that glutamate density is suppressed in the shell region of the nucleus accumbens following withdrawal from 2 weeks of cocaine exposure. The findings also suggest that the motivational aspects that accompany self-administration may participate in this reduction.

Cocaine-induced changes in glutamate and GABA immunolabeling within rat habenula and nucleus accumbens

We previously reported that subchronic administration of cocaine for 5 days via slow-release pellets results in pronounced degeneration in the lateral habenula (LHB) and its primary efferent tract, the fasciculus retroflexus [Ellison (1992): Brain Res 598:353-356; Ellison and Switzer (1993): Neuroreport 5:17-20]. The lateral habenula receives both GABA and glutamate afferents. In order to test the hypothesis that the cocaine-induced degeneration of the fasciculus retroflexus may be related to changes in synaptic activity of either GABA or glutamate nerve terminals within the LHB, the density of nerve terminal immunolabeling of either neurotransmitter was quantified after 5 days of chronic drug administration followed by either 1 or 14 days off the drug. The shell of the nucleus accumbens (NACs) was also analyzed, since this area is thought to be associated with the reward aspects of addictive stimulant drug administration and was previously shown not to be associated with fiber degeneration. We found that cocaine treatment resulted in a significant decrease in the density of nerve-terminal GABA immunolabeling located within the LHB in animals taken off the drug for either 1 or 14 days, while there was no change in the density of glutamate immunolabeling. In the NACs, there was a decrease in the density of glutamate immunolabeling within nerve terminals 1 day but not 14 days after cocaine administration. There was no change in the density of GABA immunolabeling within the NACs following the 1 or 14 day-off period. These results suggest that there are long-term changes in the density of GABA immunolabeling within the LHB and that the effects seen in glutamate synapses within the NACs are transitory. The long-term decrease in GABA immunolabeling within the LHB is consistent with the hypothesis that a decrease in inhibitory synaptic activity, leading to increased excitatory influence on LHB neurons, may result in neurotoxicity and the subsequent degeneration of the fasciculus retroflexus.

Methamphetamine alters presynaptic glutamate immunoreactivity in the caudate nucleus and motor cortex

It has been suggested that methamphetamine (METH)-induced neurotoxicity requires the activation of both dopamine (DA) and glutamate (GLU) systems. To investigate the possibility that METH-induced increases in extracellular GLU, as measured by in vivo microdialysis [Nash and Yamamoto (1992) Brain Res., 581:237-243], arise from neuronal stores, postembedding immunogold electron microscopy was used to measure the density of presynaptic GLU immunoreactivity within the striatum, the shell of the nucleus accumbens, and the motor cortex. Rats were treated with METH (5 mg/kg), or an equivalent volume of saline (SAL), every 2 h for a total of four injections. No ultrastructural evidence of terminal degeneration was observed. Significant decreases in the density of nerve terminal GLU immunolabeling occurred 12 h following METH administration within the primary motor cortex and the ventrolateral caudate/putamen, and a trend towards depletion was seen within the dorsolateral caudate/putamen. Although GLU immunolabeling within the shell of the nucleus accumbens was unaffected, DA content was decreased in all regions examined 1 week following METH treatment. The lack of degeneration, coupled with a partial recovery of DA levels, suggests that moderate doses of METH may inhibit DA biosynthesis without widespread terminal loss. Furthermore, METH administration results in a decrease in presynaptic GLU that correlates both temporally and anatomically with delayed GLU overflow, suggesting that neuronally derived GLU may play a role in METH-induced neurotoxicity. However, there does appear to be a dissociation between DA loss and altered GLU immunocytochemistry within the nucleus accumbens.

Immunocytochemical analysis of glutamate and GABA in selectively bred mice

Withdrawal Seizure Prone (WSP) and Withdrawal Seizure Resistant (WSR) mice have been selectively bred for differential ethanol withdrawal handling-induced convulsions (HICs). In addition, it has been observed that WSP mice exhibit drug-naive HICs. This latter finding suggests that WSP and WSR mice differ in their susceptibility to HICs. Alterations in the glutamate and gamma-aminobutyric acid (GABA) systems have been implicated in convulsive activity and have been proposed to underlie the manifestation of ethanol withdrawal symptoms. It is therefore possible that WSP and WSR mice are genetically different with respect to their glutamatergic and/or GABAergic systems. To test this hypothesis, we have analyzed WSP and WSR mice that are both drug- and HIC-naive for differences in the density of nerve terminal glutamate and GABA immunoreactivity within the CA1 subfield of the hippocampus (CA1) and layer II of the somatosensory cortex (SSC). The major finding of this study is that drug- and HIC-naive WSP mice exhibit a significantly greater density of presynaptic glutamate immunoreactivity associated with asymmetric synapses within the CA1, but not the SSC, when compared to WSR mice. The density of GABA immunoreactivity within nerve terminals associated with symmetric synapses does not differ between the selected lines in either brain region. Since prior drug exposure and HICs cannot account for the observed differences in these naive mice, the results strongly suggest that the density of nerve terminal glutamate immunoreactivity within the CA1 is a reflection of inherent genetic differences between WSP and WSR mice. Furthermore, an elevated density of presynaptic glutamate immunoreactivity may be an underlying neurochemical correlate to increased susceptibility to drug-naive and ethanol withdrawal convulsions.

A rat model of chronic pressure-induced optic nerve damage

To develop unilateral, chronically elevated intraocular pressure in rats, episcleral veins were injected with hypertonic saline and the intraocular pressure was monitored with a Tono-Pen XL tonometer. Histologic analyses of eyes with differing degrees and durations of intraocular pressure elevation were performed to ascertain the effects of these pressures on the optic nerve. Out of 20 consecutive animals, nine had elevations of intraocular pressure following a single injection, while subsequent injections raised intraocular pressure in seven others. One eye became hypotonous. In the remaining animals, subsequent injections sufficient to raise intraocular pressure were deliberately withheld, to determine the possible direct effects of injections on the optic nerve. Mean sustained pressure elevations ranged from 7 to 28 mm Hg and the retinal vasculature remained perfused in all eyes. Optic nerve cross sections from eyes without intraocular pressure elevation appeared identical to those from uninjected eyes, while nerves from eyes with the greatest intraocular pressure rise demonstrated axonal damage that involved 100% of the neural area. Eyes with either less severe pressure elevations or shorter durations showed partial damage, ranging from 0.5% to 10.4% of the neurla area. In 70% of these nerves, damage was concentrated in the superior temporal region. Within the optic nerve head, often associated with astrocytes, axons contained abnormal accumulations of membrane-bound vesicles and mitochondria. The anterior chamber angles showed sclerosis of the trabecular meshwork with anterior synechiae, but Schlemm's canal, collector channels and aqueous veins appeared patent. Unilateral sclerosis of the trabecular meshwork produces sustained elevation of intraocular pressure in rats with optic nerve damage that in many ways resembles that seen in human glaucoma. Understanding the mechanism of nerve damage in this model may provide new insights into the pathogenesis of human glaucoma.

Effects of subchronic clozapine and haloperidol on striatal glutamatergic synapses

Subchronic treatment with haloperidol increases the number of asymmetric glutamate synapses associated with a perforated postsynaptic density in the striatum. To characterize these synaptic changes further, the effects of subchronic (28 days) administration of an atypical antipsychotic, clozapine (30 mg/kg, s.c.), or a typical antipsychotic, haloperidol (0.5 mg/kg, s.c.), on the binding of [3H] MK-801 to the NMDA receptor-linked ion channel complex and on the in situ hybridization of riboprobes for NMDAR2A and 2B subunits and splice variants of the NMDAR1 subunit were examined in striatal preparations from rats. The density of striatal glutamate immunogold labeling associated with nerve terminals of all asymmetric synapses and the immunoreactivity of those asymmetric synapses associated with a perforated postsynaptic density were also examined by electron microscopy. Subchronic neuroleptic administration had no effect on [3H] MK-801 binding to striatal membrane preparations. Both drugs increased glutamate immunogold labeling in nerve terminals of all asymmetric synapses, but only haloperidol increased the density of glutamate immunoreactivity within nerve terminals of asymmetric synapses containing a perforated postsynaptic density. Whereas subchronic administration of clozapine, but not haloperidol, resulted in a significant increase in the hybridization of a riboprobe that labels all splice variants of the NMDAR1 subunit, both drugs significantly decreased the abundance of NMDAR1 subunit mRNA containing a 63-base insert. Neither drug altered mRNA for the 2A subunit, but clozapine significantly increased hybridization of a probe for the 2B subunit. The data suggest that some neuroleptic effects may be mediated by glutamatergic systems and that typical and atypical antipsychotics can have varying effects on the density of glutamate in presynaptic terminals and on the expression of specific NMDA receptor splice variant mRNAs. Alternatively, NMDAR1 subunit splice variants may differentially respond to interactions with glutamate.

Characterization and distribution of basic fibroblast growth factor-containing cells in the rat hippocampus

Basic fibroblast growth factor (bFGF), a member of the heparin-binding growth factor family, is present in relatively high levels in the brain where it may play an important role in the maintenance, repair, and reorganization of the tissue. Although bFGF is associated mainly with astrocytes throughout most of the central nervous system (CNS), a narrow but prominent band of pyramidal neurons, which coincides with the CA2 subregion of Ammon's horn in the hippocampus, stains intensely for bFGF. In order to gain an understanding of which cells express bFGF and whether or not BFGF is a good marker for CA2 neurons, we have used a mouse monoclonal antibody directed against recombinant human bFGF to characterize the distribution and localization of bFGF expression in the hippocampus. We find that about one-quarter of the neurons in CA2 are bFGF positive, and they appear smaller and have more irregular-shaped nuclei than their unstained counterparts. In addition, all glial fibrilary acidic protein (GFAP)-positive astrocytes in the hippocampus stain for bFGF, and the distribution of these astrocytes is heterogeneous in the hippocampus. Finally, in both astrocytes and CA2 pyramidal neurons, bFGF immunoreactivity is localized primarily in the nucleus and to a lesser extent in the cytoplasm and processes of stained cells.

Correlation of vacuous chewing movements with morphological changes in rats following 1-year treatment with haloperidol

Long-term treatment with the typical antipsychotic drug, haloperidol, can lead to a sometimes irreversible motor disorder, tardive dyskinesia (TD). It has been hypothesized that increased release of glutamate due to prolonged neuroleptic drug treatment may result in an excitotoxic lesion in specific neuronal populations within the basal ganglia, leading to TD. We reported that treatment with haloperidol for 1 month results in an increase in the mean percentage of striatal asymmetric synapses containing a perforated postsynaptic density (PSD) and that these synapses are glutamatergic. Using quantitative immunocytochemistry, we found that depending on how long the animals had been off haloperidol following subchronic (30 d) treatment, there was either a decrease (1 day off) or increase (3-4 days off) in the density of glutamate immunolabeling within the presynaptic terminals of synapses with perforated PSDs. Using a rat model for TD, animals in the current study were treated for 1 year with haloperidol and spontaneous oral dyskinesias (i.e. vacuous chewing movements, VCMs) were recorded. In these long-term treated animals we wanted to determine if there was a correlation between glutamate function, as measured by changes in synapses with perforated PSDs and the density of nerve terminal glutamate immunoreactivity, and VCM behavior. In drug treated rats which demonstrated either a high or low rate of VCMs, there was a significant increase in the mean percentage of asymmetric synapses in the dorsolateral striatum with perforated PSDs in both haloperidol-treated groups compared to vehicle-treated rats. There was a small but significant increase in the density of glutamate immunolabeling within striatal nerve terminals of the high VCM group compared to the low VCM group. There was, however, no difference in the density of glutamate immunolabeling between the high VCM group compared to the vehicle-treated animals. One reason for this lack of difference was partially due to a significant increase in nerve terminal area within the high VCM group compared to either the low VCM- or vehicle-treated groups. The larger nerve terminal size in the high VCM group may be due to a small but sustained increase in glutamate neurotransmitter release with the ability of the terminal to maintain its supply of glutamate, while the terminals in the low VCM group showed evidence of glutamate depletion. This finding would be consistent with the hypothesis that increased glutamatergic activity may be associated with TD.

Activation of corticostriatal pathway leads to similar morphological changes observed following haloperidol treatment

Treatment with haloperidol, a dopamine receptor D-2 antagonist, for one month resulted in an increase in the mean percentage of asymmetric synapses containing a discontinuous, or perforated, postsynaptic density (PSD) [Meshul et al. (1994) Brain Res., 648:181-195] and a change in the density of striatal glutamate immunoreactivity within those presynaptic terminals [Meshul and Tan (1994) Synapse, 18:205-217]. We speculated that this haloperidol-induced change in glutamate density might be due to an activation of the corticostriatal pathway. To determine if activation of this pathway leads to similar morphological changes previously described following haloperidol treatment, GABA (10(-5) M, 0.5 microliters) was injected into the thalamic motor (VL/VM) nuclei daily for 3 weeks. This treatment resulted in an increase in the mean percentage of striatal asymmetric synapses containing a perforated PSD and an increase in the density of glutamate immunoreactivity within nerve terminals of asymmetric synapses containing a perforated or non-perforated PSD. Subchronic injections of GABA into the thalamic somatosensory nuclei (VPM/VPL) had no effect on the mean percentage of synapses with perforated PSDs but resulted in a small, but significant, increase in density of glutamate immunoreactivity. Using in vivo microdialysis, an acute injection of GABA (10(-5) M, 15 microliters) into VL/VM resulted in a prolonged rise in the extracellular level of striatal glutamate. The increase in asymmetric synapses with perforated PSDs and in glutamate immunoreactivity within nerve terminals of the striatum following either subchronic haloperidol treatment or GABA injections into VL/VM suggest that an increase in glutamate release may be a common factor in these two experiments. It is possible that the extrapyramidal side effects associated with haloperidol treatment may be due, in part, to an increase in release of glutamate within the corticostriatal pathway.

GM1 ganglioside administration partially counteracts the morphological changes associated with haloperidol treatment within the dorsal striatum of the rat

Haloperidol, a typical antipsychotic drug, causes an increase in the mean percentage of synapses within the situation containing a discontinuous, or perforated, postsynaptic density (PSD) following 1 month of treatment (Meshul et al. 1994). This effect is not observed with the atypical antipsychotic drug, clozapine, following subchronic administration (Meshul et al. 1992a). This morphological change is also associated with an increase in the density of dopamine D2 receptors. The synapses containing the perforated PSD are asymmetrical and the nerve terminals contain the neurotransmitter, glutamate, as demonstrated by immunocytochemistry. We have also shown that subchronic treatment with haloperidol (0.5 mg/kg per day, 30 days) results in a decrease in the density of glutamate immunoreactivity within asymmetric nerve terminals associated with perforated and non-perforated PSDs (Meshul and Tan 1994). This could be due to an increase in glutamate release, perhaps due to activation of corticostriatal synapses. Agnati et el. (1983a) reported that administration of GM1 ganglioside blocks the increase in dopamine D2 receptors following haloperidol treatment. GM1 has also been shown to attenuate the release of glutamate (Nicoletti et al. 1989). In order to determine if similar treatment with ganglioside could block the haloperidol-induced ultrastructural changes notes above, rats were co-administered GM1 (10 mg/kg per day) and haloperidol (0.5 mg/kg per day) for 30 days. We report that GM1 blocked the haloperidol-induced increase in striatal asymmetric synapses containing a perforated PSD, but had no effect on the increase in dopamine D2 receptors or the decrease in nerve terminal glutamate immunoreactivity. GM1, either alone or co-administered with haloperidol, also caused a small, but significant, increase in the density of all asymmetric synapses within the striatum. It is possible that the effect of GM1 in attenuating the haloperidol-induced change in glutamate synapses with perforated PSDs is primarily postsynaptic, since GM1 did not block the change in density of glutamate immunoreactivity within asymmetric nerve terminals.

Haloperidol-induced morphological alterations are associated with changes in calcium/calmodulin kinase II activity and glutamate immunoreactivity

Administration of haloperidol for 2 weeks causes an increase within the caudate nucleus of asymmetrical synapses associated with a discontinuous or perforated, postsynaptic density (PSD) [Meshul et al. (1992), Psychopharmacology, 106:45-52; Meshul et al. (1992), Neuropsychopharmacology, 7:285-293]. Coadministration of the N-methyl-D-aspartate noncompetitive antagonist, MK-801, with haloperidol blocked the increase in striatal synapses containing a perforated PSD [Meshul et al. (1994), Brain Res., 648:181-195]. Examination of the caudate using immuno-gold electron microscopy revealed the vast majority (90%) of asymmetrical synapses were labelled with a glutamate antibody [Meshul et al. (1994), Brain Res., 648:181-195]. The purpose of this study was to determine if there were any changes in the density of glutamate immunoreactivity within presynaptic terminals of asymmetric synapses within the striatum following treatment with haloperidol for 1 month that would correlate with the previously observed increase in synapses with perforated PSDs. We also determined the activity of striatal calcium/calmodulin kinase II (CaMK II), an enzyme known to be localized within the synaptic region, after administration of haloperidol. We report here that haloperidol causes an increase in the activity of CaMK II and a decrease in the density of immuno-gold labelling for glutamate within the nerve terminals of asymmetrical synapses containing a perforated or nonperforated PSD. These results are consistent with the hypothesis that the haloperidol-induced increase in activity of CaMK II and the increase in glutamate release, as suggested by the decrease in presynaptic glutamate immunoreactivity, may ultimately lead to an increase in the number of synapses displaying a perforated PSD. These results support the speculation that the haloperidol-induced increase in synapses containing a perforated PSD may be associated with enhanced activity at excitatory synapses.

Multiple primitive neuroectodermal tumors

Primitive neuroectodermal tumors are rare, highly aggressive neoplasms that affect both sexes and occur in all age groups. They are a large group of neoplasms with neuroepithelial differentiation, including cutaneous neuroblastomas. Histopathologically they are characterized by a rather uniform population of small, dark cells, with or without Homer Wright rosettes. Immunohistochemically they stain for one or more of the reputed neural markers. Ultrastructurally they show interdigitating processes containing neurosecretory granules, intermediate filaments, and microtubules. We describe a patient with unusual multiple peripheral neuroectodermal tumors localized to the skin, with benign biologic behavior. The patient related the appearance of new lesions for several years without evidence of visceral dissemination or systemic complications. The histopathologic, immunohistochemical, and ultrastructural findings support the diagnosis of a peripheral neuroectodermal tumor.

Haloperidol-induced morphological changes in striatum are associated with glutamate synapses

Sub-chronic treatment with the typical neuroleptic, haloperidol (0.5 mg/kg/d, s.c.), but not the atypical neuroleptic, clozapine (35 mg/kg/day, s.c.), causes an increase in synapses containing a perforated postsynaptic density (referred to as 'perforated' synapses) and in dopamine (DA) D2 receptors within the caudate nucleus [46]. To determine if these perforated synapses are glutamatergic, we systemically co-administered MK-801 (0.3 mg/kg/day for 2 weeks), a non-competitive antagonist at the N-methyl-D-aspartate (NMDA) receptor-associated ion channel, and haloperidol. MK-801 blocked the haloperidol-induced increase in striatal perforated synapses, but not the haloperidol-induced increase in DA D2 receptors. Injection of MK-801 into the striatum also attenuated the haloperidol-induced increase in perforated synapses. Post-embedding immuno-gold electron microscopy using antibodies to glutamate indicated that the gold particles were localized within striatal presynaptic nerve terminals that make contact with perforated postsynaptic densities. These findings support the hypothesis that the haloperidol-induced increase in perforated synapses is regulated by the NMDA subtype of excitatory glutamate receptor. The increase in perforated synapses following administration of haloperidol, which is associated with a high incidence of extrapyramidal side effects (EPS), and the lack of a synaptic change following administration of clozapine, known to have a low frequency of EPS, suggests that glutamate synapses play a role in the motoric side effects that are observed with typical neuroleptic drug treatment.

FNA of extraskeletal myxoid chondrosarcoma: cytomorphologic, EM, and X-ray microanalysis features

Extraskeletal myxoid chondrosarcoma, an unusual soft tissue lesion which preferentially affects the extremities, is a prime candidate for "pathologist performed" fine-needle aspirates (FNA) because it preferentially affects the extremities [Enzinger and Shiraki, Hum Pathol 1972;3:421-435] and is usually an accessible lesion. Cytomorphologically, the neoplasm consists of clusters of fairly uniform cells, lacking cartilaginous differentiation, with a metachromatic matrix when stained with Diff-Quik (DQ). While subtle, this neoplasm has distinct features and must be distinguished for other neoplasms in the differential diagnosis because patient evaluation, prognosis, and therapy will vary greatly. We present a case characteristic of this tumor in which FNA derived material was subjected to light microscopy, X-ray microanalysis, and immunohistochemical studies; each modality provided data essential to the correct diagnosis.

Coadministration of haloperidol and SCH-23390 prevents the increase in "perforated" synapses due to either drug alone

Perforated synapses, which have a discontinuous density along the postsynaptic membrane, undergo changes in numbers under various experimental conditions. We have previously shown that 14-day administration of haloperidol, a typical neuroleptic which induces extrapyramidal side effects (EPS) and tardive dyskinesia (TD) in patients, causes an increase in the percentage of perforated synapses within the caudate nucleus. This increase was reversed if the animals were taken off the drug for an equal period of time (14 days). There was no effect within the nucleus accumbens. The atypical antipsychotic drug, clozapine, which when administered precipitates a very much lower incidence of EPS and TD, had no effect on the percentage of perforated synapses within either the caudate or nucleus accumbens. Because clozapine binds to both dopamine (DA) D1 and D2 receptors, it was of interest to determine if any changes in perforated synapses occurred following administration of the specific D1 antagonist, SCH-23390. Furthermore, because the action of D2 agonist may be dependent on the activation of the D1 receptor, we asked whether concomitant blockade of the D1 receptor could prevent the increase in perforated synapses due to the action of haloperidol, a drug which upregulates D2 receptors. We found that 14-day treatment with SCH-23390 (1.0 mg/kg per day) or haloperidol (0.5 mg/kg per day) caused an increase in the percentage of perforated synapses within the caudate but not the nucleus accumbens. There was a corresponding increase in DA D1 and D2 receptors in the caudate following administration of SCH-23390 or haloperidol, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of chronic intermittent haloperidol and raclopride effects on striatal dopamine release and synaptic ultrastructure in rats

The effects of chronic intermittent administration (7 months) of two neuroleptics, haloperidol (HAL) and raclopride (RAC), were compared using several different measures. Both drugs were administered weekly by subcutaneous injection at 7.0 mg/kg. Both neuroleptics consistently produced catalepsy throughout the treatment period, although HAL was generally more cataleptogenic than RAC. Assessment of dopamine (DA) release in the caudate putamen (CPu), through the use of in vivo microdialysis, showed that chronic HAL or RAC administration caused a prolonged decrease of DA release in response to a low dose of the DA D2 agonist quinpirole (0.03 mg/kg, sc). Injection of the muscarinic agonist pilocarpine (1.0 mg/kg, IP) did not have any significant within-group effects, although both neuroleptic treatment groups showed decreased DA release when compared to controls. Ultrastructural analysis of the dorsolateral CPu showed that both HAL and RAC treatment resulted in a significant increase in the number of perforated synapses, which contain a discontinuous density along the postsynaptic membrane. These results demonstrate that two different DA D2 receptor antagonists produce a similar effect on DA function and ultrastructural changes within the CPu following chronic, intermittent treatment.

Rhabdoid tumor of the skin

A tumor in the skin of a 42-year-old man was analyzed by light and electron microscopic study and immunohistochemistry. The tumor cells were large and contained eosinophilic, periodic acid-Schiff (PAS)-positive inclusions in the cytoplasm. Immunohistochemically, the neoplasm was positive for intermediate filaments, cytokeratin, vimentin, desmin, and alpha-1-antichimotrypsin, and negative for S-100 and leukocyte common antigen (LCA). Ultrastructurally, the cytoplasm and cellular processes of the cells were inundated with intermediate filaments, some of which were tightly bundled. Junctional complexes and secretory granules were absent. These features suggest a rhabdoid tumor: a malignant tumor of uncertain origin.

Effect of haloperidol and clozapine on the density of "perforated" synapses in caudate, nucleus accumbens, and medial prefrontal cortex

Perforated synapses, which contain a discontinuous density along the postsynaptic membrane, can increase or decrease in numbers following various behavioral and biochemical manipulations. We have previously established that 14-day treatment with haloperidol causes an increase in the number of perforated synapses within the caudate nucleus (dorsolateral region) but not the nucleus accumbens (Meshul and Casey 1989). This effect was reversed if the animals were withdrawn from the drug for an equivalent period of time. We have now further examined the effects of haloperidol administration, which is associated with a high incidence of extrapyramidal side effects (EPS) and tardive dyskinesia (TD), and assessed the effects of clozapine, which appears to have a lower potential for inducing EPS and TD. Administration of haloperidol for 2 weeks significantly increased the percentage of perforated synapses in the caudate, but not in the nucleus accumbens or layer VI of medial prefrontal cortex (MPCx). There was an increase in specific [125I]epidepride binding to D-2 receptors in the caudate nucleus and MPCx following haloperidol. Administration of clozapine for 2 weeks did not affect the percentage of perforated synapses in any of the three dopamine (DA)-rich regions that were examined. There was an increase in specific [3H]SCH 23390 binding to D-1 receptors and in specific [125I]epidepride binding to D-2 receptors only within MPCx following clozapine.(ABSTRACT TRUNCATED AT 250 WORDS)

Nuclear and cytoplasmic localization of basic fibroblast growth factor in astrocytes and CA2 hippocampal neurons

Fibroblast growth factors (FGFs) are known to stimulate mitogenesis in a variety of non-neuronal cell types and to support the survival in vitro of many neuronal cell types. The physiological role of FGFs in the CNS is currently not known. The present study determined the distribution in the rat CNS of a prominent member of the FGF family, basic FGF (bFGF). Immunohistochemical analysis showed that bFGF immunoreactivity was found predominantly in astrocytes throughout all regions of the CNS. In contrast, only a few neuronal populations were found to contain bFGF immunoreactivity, most prominent among them, neurons in the CA2 area of the hippocampus. This predominant localization of bFGF to astrocytes was confirmed by two other observations: (1) highly enriched cultures of astrocytes contained bFGF immunoreactivity and bioactivity, whereas highly enriched cultures of cerebral cortical neurons contained no detectable bFGF, and (2) neonatal rat cerebral cortex, which contains only a few differentiated astrocytes, also contained no detectable bFGF immunoreactivity and only low amounts of bFGF bioactivity. Immunocytochemical analysis also suggested that bFGF immunoreactivity was present in the nucleus as well as the cytoplasm of astrocytes and CA2 neurons. This nuclear localization was confirmed by EM analysis of the intracellular distribution of the immunoperoxidase reaction product. In addition, preparations of both nuclear and soluble fractions of brain extracts contained bFGF immunoreactivity and bioactivity. These data suggest that bFGF might be involved in mediating astrocytic influences on the late postnatal maturation and plasticity in the CNS, and that the nuclear localization of bFGF within astrocytes may play an important role in the differentiation of these cells. In addition, bFGF may play a similar role in a few specific neuronal populations, such as CA2 hippocampal neurons.

African Burkitt's lymphoma: case report and light and electron microscopic findings

An African Burkitt's lymphoma occurred in a 9-year-old American boy who had jaw tumors, proptosis, and abdominal masses. Histologically, the tumor consisted of a monotonous overgrowth of undifferentiated lymphocytes with a "starry sky" appearance. The differential diagnosis of African versus American form and Burkitt's lymphoma versus non-Burkitt's lymphoma is discussed.

Presynaptic ultrastructural correlates of long-term potentiation in the CA1 subfield of the hippocampus

To determine if long-term potentiation (LTP) is accompanied by changes in the ultrastructural distribution of calcium within presynaptic terminals, calcium was localized at the electron microscopic level using an oxalate/pyroantimonate histochemical technique. Following the induction of LTP at the Schaffer collateral/commissural synapses in the CA1 subfield of the rat hippocampal slice, there was a significant decrease (30%) in the percentage of synaptic vesicles containing calcium deposits. This effect could be accounted for by both a significant reduction in the average number of calcium deposit-bearing vesicles and a significant increase in the average number of synaptic vesicles per terminal profile in slices that displayed LTP. These changes persisted for at least one hour following the induction of LTP and were not observed in slices that received high-frequency stimulation in the presence of the N-methyl-D-aspartate (NMDA) receptor antagonist, 2-amino-5-phosphonovaleric acid (APV, 50 microM), which blocked LTP. These data suggest that LTP may be accompanied by long-term changes in intraterminal calcium homeostasis and the number of synaptic vesicles. These effects may be related to the reported increase in transmitter release following the induction of LTP.

Calcium channel blocker influences the density of alpha-actinin labeling at the rat neuromuscular junction

Alpha-actinin is a muscle protein located along the Z-disc. Incubation of frog muscle with the calcium ionophore, A23187, can decrease the immunogold labelling of alpha-actinin. Pyridostigmine (PYR) is an inhibitor of acetylcholinesterase, which causes disruption of Z-discs only in the region of the motor endplate. This is probably due to excess influx of calcium ions, leading to activation of proteases. Pretreating animals with the calcium channel blocker diltiazem can significantly reduce damage to the Z-discs at the motor endplate caused by PYR. It was of interest to determine whether the distribution of alpha-actinin had been altered following PYR administration and whether diltiazem could prevent those changes. There was less alpha-actinin labelling at the motor endplate compared to away from this region for all treatment groups. Animals administered diltiazem showed less labelling compared to PYR, but with no disruption of Z-discs at the motor endplate following diltiazem. Pretreatment with diltiazem reduced the incidence of Z-disc damage, but the degree of alpha-actinin labeling at the endplate was less than that seen with diltiazem alone. The greater effect seen at the endplate implies that neuromuscular activity is an important factor. The drugs may be causing a reduction in alpha-actinin labelling by different mechanisms.

Calcium channel blocker reverses anticholinesterase-induced myopathy

Inhibition of the enzyme, acetylcholinesterase (AChE), at the neuromuscular junction by pyridostigmine (PYR) results in breakdown of the postjunctional folds and dissolution of the Z-discs. It is hypothesized that excess activation of the acetylcholine (ACh) receptors by unhydrolyzed ACh results in a large influx of calcium ions. This could possibly lead to the activation of calcium-dependent proteases, resulting in the observed myopathy. Pretreatment with the calcium channel blocker, diltiazem, followed by administration of both PYR and the calcium blocker resulted in a significant reduction in the extent of muscle damage due to PYR alone. In order to ascertain whether the calcium blocker could reverse the myopathy previously induced by PYR, the AChE inhibitor was administered first, resulting in significant muscle damage, followed the next day by diltiazem. After 7 days of diltiazem treatment, with continued administration of PYR, the calcium blocker significantly reduced the myopathy at the neuromuscular junction. The results are discussed in terms of possible clinical application of diltiazem in neuromuscular diseases (i.e. muscular dystrophy).

Ultrastructural and functional evidence for the survival of corticogeniculate neurons in kainic acid-lesioned lateral geniculate nucleus

After a kainic acid lesion in the dorsal lateral geniculate nucleus of rat, retrograde axonal transport of fluorescent dyes is blocked in corticogeniculate but not in retinogeniculate neurons. This inhibition, however, can be reversed by electrical stimulation in the subcortical white matter (Woodward and Coull, Brain Research 454 (1988) 106-115). These observations suggest that retrograde axonal transport in corticogeniculate neurons is impulse-dependent and that neuronal activity in this pathway is reduced as a consequence of the lesions. To test this we examined retrograde transport of horseradish peroxidase (HRP) and cytochrome oxidase activity in the cortex of lesioned animals. Unilateral kainic acid lesions in the geniculate inhibit the retrograde transport of HRP, but this inhibition is reversed by electrical stimulation of white matter. Moreover, histochemical staining for cytochrome oxidase activity is less intense over visual cortex on the lesioned side, implying that cortical activity in intrinsic and efferent pathways is reduced as a consequence of removal of geniculate afferents. Inasmuch as the retrograde transport of HRP is dependent upon impulse activity in neurons and is thought to be mediated by synaptic vesicle recycling, these results suggest that terminals of corticogeniculate fibers survive the kainic acid lesions in the geniculate and are capable of releasing synaptic vesicles. Ultrastructural examination of lesioned geniculates strongly supports this conclusion and reveals the presence of axon terminal profiles which are filled with small round synaptic vesicles and have membrane specializations reminiscent of synaptic contacts. These terminal profiles are presumed to be of retinal and cortical origin.

Regional, reversible ultrastructural changes in rat brain with chronic neuroleptic treatment

Administration of the dopamine receptor antagonist (neuroleptic, antipsychotic), haloperidol, resulting in an increase in the number of dopamine binding sites in the striatum and nucleus accumbens, has been well established. These increases disappear following withdrawal of treatment. Ultrastructurally, we found an increase in the number of synapses containing perforated postsynaptic densities (PSDs) following haloperidol administration within the caudate nucleus but not within the nucleus accumbens. The effect in the caudate reversed following cessation of treatment. We speculate that the terminals undergoing the change are not dopaminergic but may originate from the cerebral cortex. This reversible morphological increase associated with dopamine antagonist drug therapy may be reflective of the tolerance developed to neuroleptic drug-induced extrapyramidal syndromes and/or may be associated with abnormal motor movements of tardive dyskinesia that occur following long-term treatment.

Transplanted astrocytes reduce synaptic density in the neuropil of cerebellar cultures

Cytosine arabinoside-treated neonatal mouse cerebellar cultures, devoid of granule cells and mature glia, demonstrate heterologous synapses between sprouted Purkinje cell recurrent axon collaterals and dendritic spines in the neuropil. Such cultures were transplanted with optic nerve as a source of glia, and the effect on neuropil synapses was investigated. There was a significant reduction in the number of synapses in the neuropil and an increase in the number of free dendritic spines. Many of these spines occurred in clusters, unapposed by glial processes. The effect on the synapse density was not due to a comparable increase in the area occupied by the added astrocytes or an increase in nerve terminal diameter. The results suggest that astrocytes alter the density of neuropil synapses and may also induce the sprouting of dendritic spines.