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

Lesion of the ventromedial nucleus of the thalamus blocks acute cocaine-induced changes in striatal glutamate

A single injection of cocaine increases extracellular glutamate in the rat dorsolateral striatum 1 day after the acute cocaine was administered (McKee and Meshul, 2005). However, the nuclei that facilitate this increase in striatal glutamate remain unknown. We hypothesized that the cocaine-induced increase in striatal glutamate was produced by activation of the ventromedial (VM) nucleus of the thalamus via the thalamo-corticostriatal or thalamostriatal pathways. First, rats received an electrolytic lesion of the VM. One day after a single cocaine or vehicle injection, extracellular glutamate was measured in the dorsolateral striatum using in vivo microdialysis. The motor thalamus lesion blocked the cocaine-induced increase in striatal glutamate and reduced extracellular glutamate to the level of the vehicle-treated group. This study shows a critical role for the VM nucleus of the thalamus in mediating the effects of cocaine on extracellular glutamate levels in the rat dorsolateral striatum.

Apomorphine-induced alterations in striatal and substantia nigra pars reticulata glutamate following unilateral loss of striatal dopamine

We have reported time-dependent changes in extracellular glutamate within the striatum at 1 and 3 months following a unilateral lesion of the nigrostriatal pathway using the neurotoxin, 6-hydroxydopamine (6-OHDA) (Meshul, C.K., Emre, N., Nakamura, C.M., Allen, C., Donohue, M.K., Buckman, J.F., 1999. Time-dependent changes in striatal glutamate synapses following a 6-hydroxydopamine lesion. Neurosci. 88, 1-16.). The aim of the present study was to determine the effects of such a lesion on glutamate within the substantia nigra pars reticulata (SN-PR) and the effect of subchronic administration of the dopamine D-1/D-2 agonist, apomorphine, on extracellular glutamate within both the striatum and the SN-PR using in vivo microdialysis. One month after the lesion, there is an increase in extracellular glutamate within the striatum and apomorphine treatment leads to a further increase. Within the SN-PR, a loss of striatal dopamine leads to a decrease in extracellular glutamate, while apomorphine treatment leads to a further decrease in nigral glutamate. Three months after a 6-OHDA lesion, there is a decrease in extracellular striatal glutamate, with apomorphine administration leading to essentially no further change in glutamate. The loss of striatal dopamine increased extracellular glutamate within the SN-PR while apomorphine administration resulted in a decrease in extracellular glutamate back to the value observed in the control group. The data suggests that the increase in striatal glutamate 1 month following a 6-OHDA lesion alone or following subchronic apomorphine is consistent with the hypothesis that a decrease in glutamate within the SN-PR leads to activation of the thalamo-cortico-striatal pathway. The decrease in striatal glutamate 3 months after a nigrostriatal lesion is also consistent with the observed increase in extracellular glutamate within the SN-PR, thus leading to a decrease in output of the thalamo-cortico-striatal pathway.

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.

Nicotine alters striatal glutamate function and decreases the apomorphine-induced contralateral rotations in 6-OHDA-lesioned rats

The overall goal of this study was to determine the effects of subchronic nicotine (0.4 mg/kg) treatment for 7 or 14 days on striatal glutamate function in both naïve and in 6-hydroxydopamine (6-OHDA)-treated rats in which the nigrostriatal dopamine pathway was lesioned. In lesioned animals, the effect of nicotine on apomorphine-induced contralateral rotations was also assessed. In naïve rats, once daily nicotine administration for 7 or 14 days resulted in a decrease and then an increase, respectively, in the basal extracellular level of striatal glutamate compared to the saline-treated group. Ultrastructurally, 14-day treatment with nicotine resulted in an increase in the density of striatal glutamate immunolabeling within nerve terminals making an asymmetrical synaptic contact compared to the saline-treated group. In 6-OHDA-lesioned animals, coadministration of nicotine with apomorphine or nicotine alone for 7 days resulted in an increase in the density of nerve terminal glutamate immunolabeling, compared to the apomorphine- or saline-treated groups. However, coadministration of nicotine with apomorphine for 14 days resulted in a decrease in the density of nerve terminal glutamate immunolabeling compared to the nicotine-treated group. Following subchronic treatment of 6-OHDA-lesioned rats with apomorphine for 7 or 14 days, there was an increase in the number of apomorphine-induced contralateral rotations compared to the saline treated group. There was a decrease in the number of apomorphine-induced contralateral rotations in the group coadministered nicotine with apomorphine for 7 or 14 days compared to the apomorphine treated group. The data suggests that in this 6-OHDA lesion model of Parkinson's disease, treatment with nicotine may be useful in counteracting the increased behavioral effect (i.e., contralateral rotations) observed after treatment with a dopamine agonist, such as apomorphine.

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.

Plasticity of afferent fibers to striatal neurons bearing D1 dopamine receptors in Parkinson's disease

The loss of dopaminergic neurons in the substantia nigra provokes a plasticity of corticostriatal synapses in Parkinson's disease (PD). The corticostriatal pathway nevertheless makes synapses with neurons bearing D1 dopamine receptors (D1R) and/or D2 dopamine receptors. At the ultrastructural level, we analyzed the morphological characteristics of synapses formed by afferent fibers making asymmetric contacts with the dendritic spines of neurons identified by D1R immunoreactivity, in the striatum of control subjects and PD patients. A quantitative analysis of the morphological characteristics of the synapses and of the number of perforated synapses (considered to be very active) was performed. In PD, a 50% increase in the number of perforated synapses making contact with D1R dendritic spines was observed, whereas no change in the number of perforated synapses on non-D1R spines was observed. The change in the number of perforated synapses on D1R dendrites was associated with a slight but nonsignificant increase in the surface area of the corticostriatal afferent fibers and the surface of the mitochondria in these fibers (+29.0% and +34.6%, respectively). This suggests a hyperactivity of corticostriatal fibers in contact with D1R-bearing neurons of the direct pathway in the basal ganglia circuitry. Since stimulation of the direct pathway is thought to alleviate the clinical symptoms of PD, this suggests that the differences observed may be involved in compensatory mechanisms.

Metabolic defects caused by treatment with the tetrahydropyridine analog of haloperidol (HPTP), in baboons

Mounting evidence suggests that compromised cellular energy production is a major contributor to idiopathic and drug-induced degenerative processes. Our interest in neurotoxins have prompted us to examine in the baboon the effects of HPTP, the tetrahydropyridine dehydration product of haloperidol, on urinary chemical markers that reflect defects in mitochondrial respiration. Urinary dicarboxylic acid and conjugate profiles, similar to those seen in humans with inborn errors of mitochondrial metabolism and toxin-induced Jamaican vomiting sickness (JVS) were observed in the treated baboons. We interpret these results as evidence that HPTP and/or HPTP metabolites inhibit mitochondrial respiration in the baboon and speculate that analogous effects may occur in haloperidol-treated individuals.

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.

Presence of NMDA-type glutamate receptors in cingulate corticostriatal terminals and their postsynaptic targets

The glutamatergic projection from the anterior cingulate cortex to the medial caudate-putamen nucleus (CPN) has been implicated in motor and cognitive functions, many of which are potently modulated by activation of N-methyl-D-aspartate subtype of glutamate receptors (NMDARs). To determine the functional sites for NMDAR activation within this circuitry, we combined anterograde transport of biotinylated dextran amine (BDA) from deep layers of the rat anterior cingulate cortex with immunogold labeling of NMDAR subunit, NMDAR1, in the dorsomedial CPN. BDA-containing axons were seen in patch-like clusters in a neuropil that showed more uniform immunogold-silver labeling for NMDAR1. Electron microscopy of these regions showed that BDA-labeling was present exclusively in axons and terminals, 23% (98 of 421) of which also contained NMDAR1-immunoreactivity (IR). BDA-labeled terminals often apposed NMDAR1-immunoreactive neuronal and glial profiles. These terminals also formed asymmetric excitatory-type synapses with dendritic spines. Of 155 anterogradely labeled axon terminals forming asymmetric synapses, 34% were with NMDAR1-labeled, and 66% with unlabeled dendritic spines. These results provide ultrastructural evidence for the involvement of NMDARs in presynaptic regulation of glutamate transmission, and in postsynaptic modulation of the excitability of spiny neurons in patch-like compartments of the dorsomedial CPN. These dual NMDAR-mediated actions are likely to play a major role in the acquisition of new behaviors and reward-related processes that have been associated with cortical input to the striatal patch compartments.

The neuropathological effects of antipsychotic drugs

In addition to their neurochemical effects, antipsychotic (neuroleptic) drugs produce structural brain changes. This property is relevant not only for understanding the drugs' mode of action, but because it complicates morphological studies of schizophrenia. Here the histological neuropathological effects of antipsychotics are reviewed, together with brief mention of those produced by other treatments sometimes used in schizophrenia (electroconvulsive shock, lithium and antidepressants). Most data come from drug-treated rats, though there are also some human post-mortem studies with broadly congruent findings. The main alteration associated with antipsychotic medication concerns the ultrastructure and proportion of synaptic subpopulations in the caudate nucleus. In rats, synapses and dendrites in lamina VI of the prefrontal cortex are also affected. The changes are indicative of a drug-induced synaptic plasticity, although the underlying mechanisms are poorly understood. Similarly, it is unclear whether the neuropathological features relate primarily to the therapeutic action of antipsychotics or, more likely, to their predisposition to cause tardive dyskinesia and other motor side-effects. Clozapine seems to cause lesser and somewhat different alterations than do typical antipsychotics, albeit based on few data. There is no good evidence that antipsychotics cause neuronal loss or gliosis, nor that they promote neurofibrillary tangle formation or other features of Alzheimer's disease.

Simultaneous determination of basal and evoked output levels of aspartate, glutamate, taurine and 4-aminobutyric acid during microdialysis and from superfused brain slices

A HPLC method, involving pre-column derivatisation with o-phthalaldehyde and fluorescence detection, is described. It allows the resolution of aspartate, glutamate, taurine and GABA, in a single run with detection limits of 3.2, 1.7, 1.4 and 2 fmol/microl of perfusate, respectively. It is sufficiently sensitive and rapid (15 min) for the determination "on line" of the four amino acids in perfusates obtained during in vivo microdialysis experiments. The procedure has been used to determine basal, K+ - or veratridine-stimulated release of these amino acids in different brain areas during microdialysis and from perfused tissue slices.

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.

The release of amino acids from rat neostriatum and substantia nigra in vivo: a dual microdialysis probe analysis

It has previously been demonstrated, in dual probe microdialysis studies, that stimulation of the neostriatum with kainic acid causes the release of GABA both locally within the neostriatum and distally in the substantia nigra, observations that are consistent with the known anatomy of the basal ganglia. The object of the present study was to further examine the characteristics of GABA release and to determine whether taurine, which has been proposed to be present in striatonigral neurons, has similar characteristics of release, and to examine the release of excitatory amino acids under the same conditions. To this end, dual probe microdialysis studies were carried out on freely-moving rats. The application of kainic acid to neostriatum enhanced the release of GABA, taurine, aspartate and glutamate locally in the neostriatum and distally in the substantia nigra. The distal release of each amino acid in the substantia nigra was sensitive to the administration of 6,7-dinitroquinoxaline-2,3-dione and tetrodotoxin to the neostriatum. Similarly the local release of GABA, aspartate and glutamate but not taurine was sensitive to the intrastriatal application of 6,7-dinitroquinoxaline-2,3-dione or tetrodotoxin. It is concluded that the release of taurine from the substantia nigra has similar characteristics to that of GABA and may be released from the terminals of striatonigral neurons following the stimulation of their cell bodies in the neostriatum. The release of taurine in the neostriatum however, is likely to be mediated mainly by different mechanisms and not related to neuronal activity. The release of excitatory amino acids is likely to involve indirect effects in the neostriatum and polysynaptic pathways in the substantia nigra.

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.

Superior temporal gyrus and the course of early schizophrenia: progressive, static, or reversible?

Accumulating evidence suggests alterations in brain structure, especially in the prefrontal and temporal cortex, in schizophrenia. Previous studies examining the progression of brain structural alterations in schizophrenia have led to conflicting results. Morphometric studies of the superior temporal gyrus (STG) volumes were conducted in a series of neuroleptic-naive first-episode schizophrenic patients, non-schizophrenic first-episode psychotic patients, and matched healthy controls. Three-dimensional MRI scans were carried out in these subjects before and after one year of treatment. Volume reductions were seen at baseline in the left superior temporal gyrus (adjusted for intracranial volume) in both of the patient groups. Pretreatment illness duration was inversely related to the volume of the left superior temporal gyrus; this relation was confined to males. One-year follow-up MRI investigations in a smaller subset of patients suggested that the STG volume reductions may be reversible. No significant changes were noted in the STG volumes in matched healthy controls who were also scanned at baseline as well as at one-year follow-up. These findings have implications for understanding the nature of the neuropathological processes in early schizophrenia, as well as the potential impact of early treatment.

Emergence of oral and locomotor activity in chronic haloperidol-treated rats following cortical N-methyl-D-aspartate stimulation

Neuroleptic-induced orofacial movements in rats have been widely utilized as an animal model of tardive dyskinesia (TD). The present study investigated the role of the oral motor cortex in these movements by applying direct cortical stimulation in rats exposed to chronic haloperidol. Rats received depot i.m. injections of haloperidol decanoate or sesame oil vehicle every 3 weeks (10 rats per group). After 24 weeks of injections and a 3-week withdrawal period, bilateral guide cannulae were implanted into the primary oral motor cortex. After a 1-week recovery, bilateral microinfusions of saline vehicle followed by 1, 3, and 10 mM N-methyl-D-aspartate (NMDA) were given and observations of oral activity, locomotion, rearing, and grooming were recorded. Haloperidol-treated rats displayed a significant emergence of NMDA stimulated oral activity (nondirected oral movements, oral tremor, audible teeth grinding, and directed oral movements). In addition, rearing and locomotion were significantly elevated in these animals. In contrast to haloperidol-treated rats, sesame oil-treated rats showed no significant emergence of any motor activity. These results suggest that chronic haloperidol administration alters primary motor cortex efferents, and that this effect may be a factor in the manifestation of chronic neuroleptic induced motor side effects, such as TD.

Haloperidol and its tetrahydropyridine derivative (HPTP) are metabolized to potentially neurotoxic pyridinium species in the baboon

The in vivo metabolic fate of haloperidol (HP) and its tetrahydropyridine analog HPTP have been examined in the baboon to investigate the formation of potentially neurotoxic pyridinium metabolites that have been observed previously in humans. Urine samples collected from baboons treated with HPTP were shown to contain, in addition to the parent drug, the corresponding reduced HPTP (RHPTP), generated by reduction of the butyrophenone carbonyl group. RHPTP was characterized by comparison with a synthetic standard using HPLC with electrochemical detection and HPLC/MS/MS. Another compound identified by LC/MS/MS was a glucuronide metabolite of RHPTP. The HP pyridinium (HPP+) and reduced pyridinium (RHPP+) metabolites were shown to be present in urine from both HP and HPTP treated baboons by HPLC using fluorescence detection. The urinary excretion profile of HPP+ and RHPP+ in both groups was essentially identical and, in contrast to that observed in rodents, closely paralleled the profile found in humans treated with HP. These data in the baboon suggest that the metabolic processes involved in the production of the pyridinium metabolites of HP are similar to those in humans. Furthermore, the HPTP-treated baboon may be an appropriate model in which to study the role of pyridinium metabolites in the induction of tardive dyskinesia.

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.