Chronic neuroleptic treatment in rats produces persisting changes in GABAA and dopamine D-2, but not dopamine D-1 receptors

Region-specific and dose-specific effects of chronic haloperidol exposure on [3H]-flumazenil and [3H]-Ro15-4513 GABAA receptor binding sites in the rat brain

Postmortem studies suggest that schizophrenia is associated with abnormal expression of specific GABAA receptor (GABAAR) α subunits, including α5GABAAR. Positron emission tomography (PET) measures of GABAAR availability in schizophrenia, however, have not revealed consistent alterations in vivo. Animal studies using the GABAAR agonist [3H]-muscimol provide evidence that antipsychotic drugs influence GABAAR availability, in a region-specific manner, suggesting a potential confounding effect of these drugs. No such data, however, are available for more recently developed subunit-selective GABAAR radioligands. To address this, we combined a rat model of clinically relevant antipsychotic drug exposure with quantitative receptor autoradiography. Haloperidol (0.5 and 2 mg/kg/day) or drug vehicle were administered continuously to adult male Sprague-Dawley rats via osmotic mini-pumps for 28 days. Quantitative receptor autoradiography was then performed postmortem using the GABAAR subunit-selective radioligand [3H]-Ro15-4513 and the non-subunit selective radioligand [3H]-flumazenil. Chronic haloperidol exposure increased [3H]-Ro15-4513 binding in the CA1 sub-field of the rat dorsal hippocampus (p<0.01; q<0.01; d=+1.3), which was not dose-dependent. [3H]-flumazenil binding also increased in most rat brain regions (p<0.05; main effect of treatment), irrespective of the haloperidol dose. These data confirm previous findings that chronic haloperidol exposure influences the specific binding of non-subtype selective GABAAR radioligands and is the first to demonstrate a potential effect of haloperidol on the binding of a α1/5GABAAR-selective radioligand. Although caution should be exerted when extrapolating results from animals to patients, our data support a view that exposure to antipsychotics may be a confounding factor in PET studies of GABAAR in the context of schizophrenia.

A Focused Update on Tardive Dyskinesia

Tardive dyskinesia (TD) is a delayed and potentially irreversible motor complication following chronic exposure to centrally acting dopamine receptor antagonists, mainly of the class of antipsychotics drugs. New generations of antipsychotic drugs reduced its mean prevalence to 20%, but it continues to mar the drug experience and social integration in a significant fraction of patients. The underlying molecular cascade remains elusive, explaining in part why TD management is so often difficult. Protocol variations between experimental laboratories and inter-species differences in the biological response to antipsychotic drugs have added layers of complexity. The traditional dopamine D2 receptor supersensitivity hypothesis was revisited in an experimental nonhuman primate model. Findings in the striatum revealed a strong upregulation of D3, not D2, receptors specific to dyskinetic animals, and indirect evidence suggestive of a link between overactivation of glycogen synthase kinase-3β signaling and TD. New effective vesicular monoamine transporter type 2 inhibitors alleviating TD have been approved in the USA. They were integrated to an emerging stepwise treatment algorithm for troublesome TD, which also includes consideration for changes in the current antipsychotic drug regimen and recognition of potentially aggravating factors such as anticholinergic co-medications. These advances may benefit TD.

Neurochemical and behavioral features in genetic absence epilepsy and in acutely induced absence seizures

The absence epilepsy typical electroencephalographic pattern of sharp spikes and slow waves (SWDs) is considered to be due to an interaction of an initiation site in the cortex and a resonant circuit in the thalamus. The hyperpolarization-activated cyclic nucleotide-gated cationic I h pacemaker channels (HCN) play an important role in the enhanced cortical excitability. The role of thalamic HCN in SWD occurrence is less clear. Absence epilepsy in the WAG/Rij strain is accompanied by deficiency of the activity of dopaminergic system, which weakens the formation of an emotional positive state, causes depression-like symptoms, and counteracts learning and memory processes. It also enhances GABAA receptor activity in the striatum, globus pallidus, and reticular thalamic nucleus, causing a rise of SWD activity in the cortico-thalamo-cortical networks. One of the reasons for the occurrence of absences is that several genes coding of GABAA receptors are mutated. The question arises: what the role of DA receptors is. Two mechanisms that cause an infringement of the function of DA receptors in this genetic absence epilepsy model are proposed.

Effects of benzodiazepine treatment on cortical GABA(A) and muscarinic receptors: studies in schizophrenia and rats

Changes in cortical γ-aminobutyric acid A (GABA(A)) receptors and muscarinic receptors have been reported in schizophrenia, a disorder treated with antipsychotic drugs and benzodiazepines. As there is a reported functional relationship between the GABAergic and cholinergic systems in the human central nervous system we have investigated whether there are changes in the GABA(A) and muscarinic receptors in the cortex of subjects from APD-treated subjects with schizophrenia and whether changes were different in subjects who had also received benzodiazepine treatment. We failed to show any strong correlations between changes in GABA(A) and muscarinic receptors in the CNS of subjects with schizophrenia. We showed that subjects with schizophrenia treated with benzodiazepines had lower levels of muscarinic receptors; which was not the case in rats treated with APDs, benzodiazepines or a combination of both drugs. Further, the benzodiazepine binding site, but not the muscimol binding site, was decreased in the parietal cortex of subjects with schizophrenia independent of benzodiazepine status at death. These data would therefore support our previously stated hypotheses that changes in the cortical cholinergic and GABAergic systems are involved in the pathophysiology of schizophrenia.

Antipsychotic drugs: comparison in animal models of efficacy, neurotransmitter regulation, and neuroprotection

Various lines of evidence indicate the presence of progressive pathophysiological processes occurring within the brains of patients with schizophrenia. By modulating chemical neurotransmission, antipsychotic drugs may influence a variety of functions regulating neuronal resilience and viability and have the potential for neuroprotection. This article reviews the current literature describing preclinical and clinical studies that evaluate the efficacy of antipsychotic drugs, their mechanism of action and the potential of first- and second-generation antipsychotic drugs to exert effects on cellular processes that may be neuroprotective in schizophrenia. The evidence to date suggests that although all antipsychotic drugs have the ability to reduce psychotic symptoms via D(2) receptor antagonism, some antipsychotics may differ in other pharmacological properties and their capacities to mitigate and possibly reverse cellular processes that may underlie the pathophysiology of schizophrenia.

Treatment with haloperidol and diazepam alters GABA(A) receptor density in the rat brain

A significant body of data suggests that GABA(A) receptors are altered in the CNS of subjects with schizophrenia. However, subjects with schizophrenia are treated with antipsychotic drugs and, in some cases, antipsychotic drugs and benzodiazepines. It has therefore been suggested that the changes in GABA(A) receptors in the CNS of subjects with schizophrenia are due to such drug treatments. Surprisingly, there appear to be no studies to determine the effect of a combined antipsychotic-benzodiazepine treatment on GABA(A) receptors. We therefore measured both the GABA binding site ([3H]muscimol) and the benzodiazepine binding site ([3H]flumazenil) in the CNS of rats treated with either haloperidol, diazepam or a combination of the two drugs. The main findings of our study are that treatment with diazepam or the combination of diazepam and haloperidol results in regionally selective increases GABA binding sites but treatment with haloperidol alone decreases the GABA binding site in the thalamus but increases these sites in the hypothalamus. By contrast, treatment with diazepam, haloperidol and a combination of the two drugs resulted in widespread decreases in the number of benzodiazepine binding sites in the rat CNS. The notable exception to this outcome was increased numbers of benzodiazepine binding sites in the frontal cortex of rats that had received diazepam. Our data suggests that there are complex changes in the GABA(A) receptor following treatment with haloperidol, diazepam or a combination of these drugs. This outcome may be relevant to the therapeutic benefits of using both drugs in conjunction early in the treatment of a psychotic episode.

Long-acting injectable risperidone compared with zuclopenthixol in the treatment of schizophrenia with substance abuse comorbidity

OBJECTIVE

This study aimed to compare the efficacy of long-acting risperidone and zuclopenthixol in subjects with schizophrenia and substance abuse.

METHOD

A total of 115 subjects with schizophrenia and substance use disorders were enrolled for an open, randomized, controlled, 6-month follow-up study. Fifty-seven subjects were selected for treatment with long-acting injectable risperidone, while another 58 were treated with zuclopenthixol-depot.

RESULTS

Long-acting risperidone patients presented fewer positive urine tests (8.67 compared with 10.36, P = 0.005), showed improved scores on the Positive and Negative Syndrome Scale, and showed better compliance with the Substance Abuse Management program. The use of long-acting risperidone and less severe dependence explained the outcome at the end of the follow-up.

CONCLUSIONS

Long-acting injectable risperidone was more effective than zuclopenthixol-depot in improving substance abuse and schizophrenia symptoms in subjects with dual diagnosis.

Alterations in striatal neuropeptide Y system activity of rats with haloperidol-induced behavioral supersensitivity

The study was conducted to determine whether the expression of behavioral supersensitivity induced by haloperidol (HAL) administered once daily (2 mg/kg i.p.) for 14 days is associated with the alterations in activity of neuropeptide Y (NPY) system in the striatum (caudate-putamen) and nucleus accumbens. Dopamine supersensitivity was tested by measurement of locomotor activity and stereotyped behavior after administration of the dopamine D2/D3 receptor agonist quinpirole (1 mg/kg i.p.) on day 1, 3 and 7 after HAL withdrawal. Neuropeptide Y-like immunoreactivity (NPY-LI) was determined in the striatum and nucleus accumbens isolated 6 h after quinpirole injection on day 1, 3 and 7 after the end of HAL treatment. NPY mRNA was quantified in these structures on day 7 after HAL withdrawal. HAL increased spontaneous locomotor activity and prevalence of rearing, grooming and head-down sniffing. At the same time, striatal NPY-LI increased progressively from the reduced level found on day 1 of haloperidol withdrawal. NPY mRNA remained unchanged. In saline-treated rats, quinpirole enhanced locomotion, rearing, and induced intense head-down sniffing and oral activity. These behavioral effects were accompanied by a decrease in striatal NPY-LI. NPY mRNA was slightly increased. HAL treatment altered response to quinpirole, namely it increased locomotion, intensified oral activity and reduced rearing and head-down sniffing. The second and the third quinpirole injection decreased NPY-LI levels. NPY mRNA was unchanged. In the nucleus accumbens, apart from a decrease in NPY-LI on day 1 after the last haloperidol dose, the level of NPY-LI and NPY mRNA in any experimental group did not differ from the control value. The presented results suggest that the alterations in the activity of the striatal but not nucleus accumbens NPY system contribute to adaptive changes induced by long-term haloperidol treatment and may be of significance to the motor hyperactivity induced by intermittent stimulation of postsynaptic dopamine D2 receptors.

Measurement of dopamine D2-like receptors in postmortem CNS and pituitary: differential regional changes in schizophrenia

In situ radioligand binding with autoradiography and anti-human dopamine D(2) receptor antibodies with Western blots have been used to measure the density of dopamine D(2)-like receptors in the caudate-putamen and pituitary from schizophrenic subjects who did or did not have residual antipsychotic drugs in their tissue at death. There was a significant decrease in the Ki for haloperidol displaceable [(125)I]iodosulpride binding in the pituitary (p < 0.01) and caudate-putamen (p < 0.05) from subjects with schizophrenia with residual drugs in their tissue. There was a significant decrease in the density of [(125)I]iodosulpride in the pituitary (p < 0.001) and a strong trend to a decrease in binding in the caudate-putamen (p = 0.055) from subjects with schizophrenia. By contrast, [(3)H]spiperone binding was decreased in the caudate-putamen (p < 0.05) with a trend to decreased binding in the pituitary (p = 0.07) from subjects with schizophrenia. There was no difference in the density of dopamine D(2) receptors in the caudate-putamen from subjects with schizophrenia (p = 0.31). All the findings on receptor densities were independent of drug status. [(125)I]iodosulpride binds to the dopamine D(2&3) receptors. We have shown that there is no change in the dopamine D(2) receptor in the caudate-putamen from subjects with schizophrenia and therefore, these data would be consistent with there being a decrease in the dopamine D(3) in the caudate-putamen from subjects with schizophrenia. Since dopamine D(3) receptors are absent or present at low concentrations in the pituitary, our data would suggest the dopamine D(2) receptor is decreased in that tissue from schizophrenic subjects.

Oral dyskinesias and histopathological alterations in substantia nigra after long-term haloperidol treatment of old rats

The pathophysiologic basis of tardive dyskinesia remains unclear, but several lines of evidence suggest that persistent neuronal changes in the basal ganglia produced by oxidative stress or glutamate toxicity may play a role, especially in the elderly. In the present study we examined whether histopathological alterations in substantia nigra are related to oral dyskinesia in a rodent model of tardive dyskinesia. Haloperidol decanoate (38 mg/kg/4 weeks) was administered to young (8 weeks) and old (38 weeks) rats for a total period of 28 weeks, and the development of vacuous chewing movements (VCM) was observed. Rats with high and low levels of VCM and saline-treated controls were analyzed for histopathological alterations. Reduced nerve cell number and atrophic neurons were prominent features in the substantia nigra of old rats with high levels of VCM. Some alterations were also present in the substantia nigra of the old rats with low levels of VCM and young rats with high VCM levels, but these were significantly less affected than the high VCM rats. These results show that the development of haloperidol-induced oral dyskinesias in old rats is associated with histopathological alterations in the substantia nigra. This suggests that nigral degeneration induced by neuroleptics may contribute to the development of persistent VCM in rats and possibly irreversible tardive dyskinesia in humans.

The vacuous chewing movement (VCM) model of tardive dyskinesia revisited: is there a relationship to dopamine D(2) receptor occupancy?

Tardive dyskinesia (TD) is a late side effect of long-term antipsychotic use in humans, and the vacuous chewing movement (VCM) model has been used routinely to study this movement disorder in rats. Recent receptor occupancy studies in humans and rats have found that antipsychotics given in doses which lead to moderate levels of D(2) receptor blockade can achieve optimal clinical response while minimizing the emergence of acute motor side effects. This suggests that clinicians may have been using inappropriately high doses of antipsychotics. A review of the existing VCM literature indicates that most animal studies have similarly employed antipsychotic doses that are high, i.e. doses that lead to near complete D(2) receptor saturation. To verify whether the incidence or severity of VCMs would decrease with lower antipsychotic doses, we conducted initial experiments with different doses of haloperidol (HAL) given either as repeated daily injections or as depot injections over the course of several weeks. Our results demonstrate that (1) the incidence of VCMs is significantly related to HAL dose, and (2) significant levels of VCMs only emerge when haloperidol is continually present. These findings are consistent with the possibility that total D(2) occupancy, as well as 'transience' of receptor occupation, may be important in the development of late-onset antipsychotic-induced dyskinetic syndromes.

Chronic haloperidol-induced alterations in pallidal GABA and striatal D(1)-mediated dopamine turnover as measured by dual probe microdialysis in rats

Using dual probe microdialysis, assessment of extracellular neurotransmitter levels in the corpus striatum and globus pallidus was performed in ovariectomized and gonadally intact female, Sprague-Dawley rats following chronic (24 weeks) oral haloperidol administration. Vacuous chewing movements, an animal analog of orofacial dyskinesia, were also recorded at several time points during haloperidol administration and throughout the dialysis sampling session. Basal GABA levels were significantly elevated in the globus pallidus of haloperidol-treated rats compared with vehicle animals. Injection of the dopamine D(1) agonist dihydrexidine (3mg/kg, s.c.) decreased striatal dopamine levels in both vehicle and haloperidol-treated rats, with a larger decrease seen in haloperidol-treated rats. Furthermore, dihydrexidine reduced striatal 3,4-dihydroxyphenylacetic acid and homovanillic acid levels only in haloperidol-treated rats. Gonadal status had no effect on any neurochemical measure. Vacuous chewing movements were significantly elevated in haloperidol-treated groups by the sixth week of treatment, with higher counts seen in gonadally intact rats. Vacuous chewing movements were significantly elevated above baseline in all groups following dihydrexidine, with no differential effect of prior haloperidol treatment or gonadal status. These results indicate a tonic increase in pallidal GABA levels and a hypersensitivity of D(1)-mediated striatal dopamine and dopamine metabolite decreases following chronic haloperidol treatment. While not found to be correlated with neurochemical measures, the heightened vacuous chewing movements in gonadally intact vs ovariectomized rats may serve as a model of hormone-mediated differences in neuroleptic-induced oral dyskinesia.

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.

Regional brain changes in [3H]SCH 23390 binding to dopamine D1, receptors after long-term haloperidol treatment: lack of correspondence with the development of vacuous chewing movements

Localized alterations in brain D1 receptors have been suggested to play a role in the development of vacuous chewing movements (VCMs) in rodents after long-term neuroleptic treatment. In the present study [3H]SCH 23390 binding to D1 receptors in basal ganglia and other brain regions was examined in rats showing high or low VCM levels after 21 weeks of treatment with haloperidol decanoate (HAL). D1 binding was significantly decreased in the caudate-putamen of HAL-treated rats, compared with vehicle-treated controls (- 18%, P < 0.001). However, this decrease occurred equally in treated rats showing high or low levels of VCMs. No changes were observed in any other brain region examined, including various subdivisions of the substantia nigra pars reticulata. D1/D2 binding ratios were significantly decreased in HAL-treated as compared to vehicle controls in all regions examined, with the exception of the olfactory tubercle. However, no differences in D1/D2 ratios between high VCM and low VCM subgroups were detected. Correlations between frequency of VCMs and D1 binding, D2 binding or D1/D2 binding ratios across brain regions were generally modest (< 0.5). These results confirm the ability of long-term haloperidol to induce selective decreases in D1 binding in specific brain areas, but fail to provide evidence for a possible role of altered D1 receptor binding in the development of oral dyskinetic syndromes after long-term neuroleptic treatment.

Interactions between D1 and D2 dopamine receptor family agonists and antagonists: the effects of chronic exposure on behavior and receptor binding in rats and their clinical implications

Functional interactions between dopamine receptor subtypes may affect behavioral and biochemical responses which serve as models for neuropsychiatric illnesses and the clinical effects of drug therapy. We evaluated the effects of chronic exposure to the selective D1 receptor antagonist SCH 23390, and the selective D2 receptor antagonist metoclopramide, on spontaneous and drug-induced behavior and receptor density in rats, and then determined how these effects would be modified by concurrent administration of antagonists or agonists [SKF 38393, LY 171555 (quinpirole)] selective for the complementary receptor subtype. Administered alone, both the D1 and D2 antagonists had acute cataleptic effects to which animals became tolerant following chronic treatment, but the selective antagonists had opposing effects on spontaneous locomotor activity. Both antagonists produced equivalent, supersensitive behavioral responses to apomorphine, and resulted in an increase in D2 receptor density. Coadministration of the D1 and D2 antagonists had a synergistic effect on catalepsy, attenuated the effects on spontaneous locomotor activity observed with either drug alone, and had an additive effect on both apomorphine-induced stereotypic behavior and D2 receptor proliferation. On the other hand, when either selective antagonist was combined with the agonist selective for the complementary receptor subtype, both D2 receptor proliferation and behavioral supersensitivity were completely blocked. Combined antagonist-agonist treatments had opposing effects on the development of tolerance to antagonist-induced catalepsy. D2 - but not D1 - receptor densities were correlated with animals' behavioral responses to apomorphine. There results support and extend the notion that complex functional interactions between D1 and D2 receptor families occur within the central nervous system, and suggest that novel effects might be derived from combined administration of receptor selective agonists and antagonists.

A postmortem study of frontal cortical dopamine D1 receptors in schizophrenics, psychiatric controls, and normal controls

We tested the hypothesis that aberrant dopaminergic innervation in frontal and cingulate cortices of schizophrenic patients might be revealed by examining dopamine D1 receptor density in these brain regions. A quantitative autoradiographic assay with [3H]-SCH 23390 was performed with samples from schizophrenic patients, normal controls, neuroleptic-treated controls, and suicides. There was a significant elevation in specific binding of [3H]-SCH 23390 in the intermediate layer of the prefrontal cortex from neuroleptic-treated controls (p = .05). Elevated [3H]-SCH 23390 binding in several layers from prefrontal and cingulate cortex was observed in schizophrenic subjects, although these results did not reach statistical significance. When data from subjects who had received neuroleptics (schizophrenics and neuroleptic controls) were compared to subjects who had not received neuroleptics (normal controls and suicides), there was a significant elevation in receptor density in both the prefrontal (p = .05) and cingulate cortices (p = .03). These data suggest that elevated [3H]-SCH 23390 binding in human prefrontal and cingulate cortices may occur with chronic neuroleptic treatment, although increased receptor density that may exist as a feature of psychotic illnesses cannot be excluded.

Effect of long-term haloperidol treatment on striatal neuropeptides: relation to stereotyped behavior

Behavioral and biochemical responses to D1 and D2 dopamine (DA) agonists were used to evaluate the participation of striatal peptidergic mechanisms in the motor function alterations that attend chronic neuroleptic treatment. Rats, given haloperidol (1 mg/kg, i.c.) for 21 consecutive days, were randomly allocated to one of the following treatments: the D1 agonist SKF 38393, the D2 agonist quinpirole, their combination or saline. Stereotyped behavior and neuropeptide levels were evaluated after 5 days treatment and 4 days washout. Haloperidol increased most oral behaviors including licking, chewing and biting as well as striatal enkephalin and somatostatin levels. Subsequent treatment with SKF 38393 diminished the haloperidol-induced increase in licking and chewing; quinpirole reduced chewing behavior. The administration of both agonists together decreased chewing and biting. Neither DA agonist alone, nor their combination, reduced the haloperidol-induced increase in enkephalin levels. Both SKF 38393 and quinpirole, when given alone, tended to decrease the haloperidol-induced increase in somatostatin levels; when both D1 and D2 agonists were administered together, somatostatin levels declined significantly. These results suggest that somatostatin- but not enkephalin-containing striatal neurons contribute to the expression of haloperidol-induced stereotypies.

Subchronic administration of clozapine, but not haloperidol or metoclopramide, decreases dopamine D2 receptor messenger RNA levels in the nucleus accumbens and caudate-putamen in rats

The effects of unique profile antipsychotic drugs on dopamine D2 receptors and D2 receptor messenger RNA were assessed following subchronic administration in rats. Male, Sprague-Dawley rats were administered oral haloperidol, clozapine, metoclopramide or no drug for three weeks via their drinking water. Tissue from the medial nucleus accumbens and dorsolateral caudate-putamen was dissected and analyzed by Northern blot analysis for levels of dopamine D2 receptor messenger RNA and binding assays conducted with [3H]spiperone for dopamine D2 receptors. Haloperidol and metoclopramide, but not clozapine, significantly increased [3H]spiperone in the caudate-putamen, but not the nucleus accumbens. Clozapine significantly decreased D2 messenger RNA levels in the caudate-putamen and the nucleus accumbens, while metoclopramide and haloperidol had no significant effect in either brain region. The finding of decreased D2 receptor messenger RNA levels produced by subchronic clozapine may account for the lack of striatal D2 receptor up-regulation, which was robustly observed after subchronic haloperidol and metoclopramide. Furthermore, since haloperidol and metoclopramide have a high liability for motor side effects, the current results relate favorably to the low motor side effect profile of clozapine.

Differences in the subregional and cellular distribution of GABAA receptor binding in the hippocampal formation of schizophrenic brain

Recent postmortem studies have reported a marked upregulation of GABAA receptor binding activity in the anterior cingulate and prefrontal cortices of schizophrenic subjects. Because the hippocampal formation is a key corticolimbic region that has also been implicated by both postmortem and brain imaging studies in the pathophysiology of this disorder, the current report has sought to determine whether alterations of GABAA receptor binding might also be detected in this region from 15 normal controls and 8 schizophrenic subjects. Using a low resolution autoradiographic approach, the results show a significant increase of specific GABAA receptor binding activity in the area dentata (granule cell layer), CA4, CA3 (str. oriens, str. pyramidale), subiculum, and presubiculum of the schizophrenic group. The magnitude of the increase was greatest in CA3 and lowest in the CA1 sector. When high resolution analyses were performed on emulsion-coverslip preparations, a modest increase of binding (43%, P = 0.05) was observed on pyramidal, but not non-pyramidal neurons in sector CA1. Rather unexpectedly, GABAA binding in sector CA3 was not significantly different on pyramidal cells, but was almost three-fold higher (P = 0.015) on non-pyramidal neurons of the schizophrenic group. There was no relationship of age or the postmortem interval to the parameters showing significant changes in the schizophrenic group. Moreover, patients both with and without neuroleptic exposure showed upregulation of GABAA receptor binding activity. Taking together the rather modest increase of binding activity in CA1 and the more marked upregulation in CA3, as well as the differential changes on pyramidal neurons of CA1 vs. non-pyramidal neurons in CA3, the findings reported here are consistent with the possibility that a disturbance of brain development could have occurred either perinatally or perhaps even well into the postnatal period, and have given rise to discreet subregional and cellular alterations of disinhibitory GABAergic modulation in sector CA3 of schizophrenics. Overall, the data reported here provide further evidence that alterations of GABAergic activity may occur in the hippocampal formation of schizophrenic patients.

Effects of rating parameters on assessment of neuroleptic-induced vacuous chewing movements

Long-term administration of neuroleptics to rats produces a syndrome of vacuous chewing movements (VCMs). The validity of the VCM syndrome as a model for tardive dyskinesia (TD) in humans is unclear. This is due, in part, to inconsistencies between studies. Methods for rating VCMs have varied markedly and could account for the inconsistencies. The purpose of this study was to evaluate the importance of the different methods on VCM scores. The effects of habituation and length of rating sessions were examined in rats habituated for 2 min, 1 h, or several hours over 4 days, compared to unhabituated rats. Ratings with and without habituation were highly correlated, as were ratings from 2- and 5-min observation periods. Ratings from neuroleptic-treated rats in restraining tubes, however, were significantly correlated with unrestrained ratings only following several hours of habituation. Locomotor activity was not correlated with VCM scores. These results suggest that habituation to open cages is not an important factor in assessing VCMs. Use of restraining tubes, however, may alter scores. The lack of an habituation effect or of a relationship between activity and VCMs suggests that locomotor and oral behaviors are not necessarily in competition. Restraining rats to rate VCMs does not appear to be necessary and could alter the neurobiology of VCMs.

Oral movement patterns induced in rats by local infusions into striatum depend upon the regimen of prior neuroleptic exposure

Rats were pretreated for 11 months with vehicle or with chronic haloperidol (HAL), administered either continuously (in the drinking water) or intermittently (via weekly injections). During this time the animals were habituated to an enclosed tube and periodically monitored by a computerized video device which measured their oral movements. The rats were then withdrawn from chronic HAL and bilateral cannulae were implanted in the ventrolateral striatum (VLS) and substantia nigra (SN). One week later oral movements were observed in an open cage and then measured by the computerized video device following bilateral infusions into VLS of the muscarinic agonist pilocarpine or the dopamine D1 agonist SKF38393, or following infusions of the GABA antagonist bicuculline into SN. Agonist infusions into VLS had different effects depending upon the prior regimen of chronic HAL. Infusions of pilocarpine into VLS led to an exaggeration of the distinctive oral movement form which follows continuous HAL but an attenuation of the different oral syndrome in the intermittent chronic HAL animals. Infusions of SKF38393 into VLS had similar, but considerably smaller effects. Infusions of bicuculline into SN did not induce either effect. These results indicate differences exist in either striatum or its output circuitry in the neurochemical mechanisms which mediate the different oral movement forms induced by different chronic neuroleptic regimens.

Suppression of oro-facial movements by rolipram, a cAMP phosphodiesterase inhibitor, in rats chronically treated with haloperidol

We investigated the effects of rolipram, a selective cyclic adenosine 3',5'-monophosphate phosphodiesterase type IV inhibitor, and isobutylmethylxanthine, a nonselective phosphodiesterase inhibitor, on purposeless spontaneous chewing movements and tongue protrusions produced by 24 weeks treatment with haloperidol decanoate (25 mg/kg every 4 weeks i.m.) in rats, to examine our hypothesis that restoration of striatal cyclic adenosine 3',5'-monophosphate levels previously reduced due to dopamine D2 receptor supersensitivity, may suppress these movements. Tests were performed 8 weeks after the final injection. Haloperidol treatment significantly increased dyskinetic movements and striatal dopamine D2 receptor density compared with controls. Rolipram (0.1-1.0 mg/kg i.p.) suppressed these movements in a dose-dependent manner, whereas isobutylmethylxanthine (2 mg/kg i.p.) only slightly suppressed the syndrome and doses higher than 5 mg/kg i.p. produced other intensive movements. These results support our hypothesis and suggest that rolipram may have a therapeutic effect on tardive dyskinesia.

Neuroleptic-induced vacuous chewing movements in rodents: incidence and effects of long-term increases in haloperidol dose

Rats treated chronically with neuroleptics develop vacuous chewing movements (VCMs), similar in some respects to tardive dyskinesia (TD) in man. The VCM syndrome was used as a model of TD to examine the ability of increased neuroleptic doses to produce long-term suppression of dyskinetic movements. The incidence and persistence of the VCM syndrome in individual rats were also assessed to look for affected and unaffected subgroups. Rats were initially treated for 15 weeks and haloperidol decanoate. For the next 21 weeks, half the group received a 50-150% increase in dose while the other half continued to receive the same dose. Animals were also followed during a 28-week withdrawal period. Total VCM ratings showed a skewed distribution, with some rats exhibiting few movements while others developed marked and persistent movements. Increasing doses did not suppress VCMs, nor did they exacerbate movements during the withdrawal period. To the extent that the VCM syndrome models TD, the absence of long-term suppression of the VCM syndrome suggests that, at this dosage range, increasing depot neuroleptic doses may not be a useful long-term strategy for TD suppression.

Chronic haloperidol, but not clozapine, produces altered oral movements and increased extracellular glutamate in rats

Rats administered chronic haloperidol or clozapine in their drinking water for 6 months were monitored for changes in oral movements using a computerized video analysis system. Haloperidol-treated animals exhibited late onset increases in small amplitude oral movements and an increase in the percentage of oral movements in the 1-2 Hz range, accompanied by a decrease in oral movements in the higher frequency range (> 6 Hz) as determined by fast fourier analysis. In contrast, clozapine-treated rats showed a decrease in medium-sized amplitude oral movements, but did not demonstrate significant changes in the distribution of oral movements across frequencies. Extracellular concentrations of gamma-aminobutyric acid (GABA) and glutamate in the ventrolateral striatum were then assessed by intracranial microdialysis during oral drug administration and 3 days after drug withdrawal. Extracellular GABA and glutamate levels were not significantly different between groups during drug administration. However, 3 days after drug withdrawal, there was a significant increase in glutamate in the haloperidol-treated rats. No changes were noted for glutamate levels in clozapine-treated rats or for GABA levels in either group following withdrawal. These results confirm the atypical profile of clozapine in an animal model of tardive dyskinesia and suggest that alterations in striatal glutamatergic function follow typical, but not atypical, antipsychotic drug administration.

The distribution of dopamine D2 receptor heteronuclear RNA (hnRNA) in the rat brain

Conventional in situ hybridization methods have been useful in characterizing the anatomical distribution of cells in the central nervous system that express dopamine D2 receptor mRNA. However, due to the large size of the D2 mRNA pool, this method may be insensitive to changes in D2 gene transcription. We have developed a method of hybridizing a 35S-labelled cRNA probe to an intron in the D2 receptor gene in order to measure the amount of primary transcript or heteronuclear RNA (hnRNA) in D2-expressing cells. Introns are found uniquely in hnRNA and are thought to be short-lived intermediates. Thus, monitoring introns could represent a more direct measure of D2 gene transcription. The anatomical distribution of the D2 hnRNA is similar to the distribution of D2 mRNA in the rat brain. D2 heteronuclear RNA was found in the nuclei of cells in the caudate putamen, nucleus accumbens, hippocampus, olfactory tubercle, substantia nigra, ventral tegmental area, and zona incerta. Other regions that contain D2 mRNA, but do not demonstrate intronic signal, include the globus pallidus, prefrontal, cingulate, entorhinal, and piriform cortex, septum, and amygdala. However, these areas have low amounts of D2 mRNA and may contain levels of D2 hnRNA that are below detection. Heteronuclear RNA quantitation by solution hybridization followed by RNase protection was performed on striatum, substantia nigra, cerebral cortex, hippocampus, hypothalamus, and pituitary using a D2 intron 7/exon 8 border probe. These results corroborate the distribution of hnRNA revealed with intronic in situ hybridization. In addition, protection assays were able to detect hnRNA in areas that express low levels of D2 like the cortex, hippocampus and hypothalamus. hnRNA/mRNA ratios calculated from intron/exon border probe protection assays were not equivalent for all the tissue areas studied, indicating that transcription and/or hnRNA half lives may differ between tissues that express D2 receptors. The combined use of intronic in situ hybridization and intron/exon border protection assay as an index of D2 gene transcription and RNA processing provides more information than measuring the mRNA pool alone. It may also prove to be a more useful measure of gene regulation, allowing for evaluation of gene responses to acute treatments.

Chronic haloperidol does not alter G protein alpha-subunit levels in rats

Female Sprague-Dawley rats were administered continuous haloperidol or no drug for 32 weeks via subcutaneous silastic implants. Three days after drug withdrawal, animals were rapidly decapitated and tissue samples were analyzed for levels of G alpha subunits for Gi and Gs using immunoblotting procedures. No significant differences were seen between groups in the dopaminergic terminal regions of the medial prefrontal cortex, nucleus accumbens, or dorsolateral caudate-putamen. These results suggest that haloperidol administered in a regimen known to produce alterations in several parameters of dopamine function fails to alter the amount of receptor-linked G protein subunits in rat brain.

Regional differences in chronic neuroleptic effects on extracellular dopamine activity

The extracellular levels of dopamine (DA) and DA metabolites in the caudate-putamen (CPu) and the nucleus accumbens (NA) of rats following administration of haloperidol (HAL) decanoate and fluphenazine (FLU) decanoate for 8 months were assessed using intracranial microdialysis 1 month after final injection. Both HAL- and FLU-treated animals showed persisting plasma neuroleptic levels at time of sacrifice. Extracellular basal levels of homovanillic acid (HVA) in the CPu were significantly elevated in the FLU-treated animals, while basal levels of 3,4-dihydroxyphenylacetic acid (DOPAC) in the CPu were significantly elevated in the HAL-treated animals. Basal levels of DA and the serotonin metabolite, 5-hydroxyindoleacetic acid (5HIAA) in the CPu were not significantly different between groups. No significant between-group differences were found for basal levels of any of the analytes in the NA. Neuroleptic-treated animals showed an enhanced response to direct infusion through the dialysis probe of amphetamine (1 microM) and nomifensine (10 microM) in the CPu but not the NA. These results suggest that chronic neuroleptic treatment produces enhanced extracellular DA activity in nigrostriatal, but not mesolimbic DA pathways.

Chronic neuroleptic administration decreases extracellular GABA in the nucleus accumbens but not in the caudate-putamen of rats

The extracellular levels of gamma-aminobutyric acid (GABA) in the caudate-putamen and the nucleus accumbens of rats following administration of haloperidol decanoate, fluphenazine decanoate, or vehicle for 8 months were assessed using intracranial microdialysis. Basal levels of extracellular GABA were significantly decreased in the nucleus accumbens of both neuroleptic-treated groups while levels of GABA in the caudate-putamen were not significantly different between groups. These results provide evidence for selective chronic neuroleptic-induced effects on in vivo GABA function in different terminal regions containing dopamine receptors.

D1 and D2 receptor modulation in rat striatum and nucleus accumbens after subchronic and chronic haloperidol treatment

The antipsychotic effects of neuroleptic drugs are believed to be achieved by chronic blockade of dopaminergic transmission in the limbic system. Nevertheless, the effects of chronic (3-12 months) haloperidol administration on the dopaminergic transmission in the nucleus accumbens of rodents remains poorly understood. Studies of spontaneous locomotor activity (SLA), a behavioral measure related to limbic dopamine transmission, and of dopamine D2 receptor density in the nucleus accumbens after chronic oral haloperidol treatment have yielded conflicting results. We evaluated these indices after 8 months of parenteral administration of haloperidol decanoate. We report here that, after 8 months of parenteral treatment, SLA stays significantly decreased and D2 receptors in the nucleus accumbens exhibit the same up-regulation as in the striatum (about 50%). These results fail to support the notion of a different pattern of D2 receptor adaptation to neuroleptic treatment between the nucleus accumbens and the striatum. In contrast, dopamine D1 receptors were found to be unaffected in the nucleus accumbens but decreased in the striatum by 22% after 8 months of treatment. This observation could be relevant to the pathogenesis of tardive dyskinesia.

Haloperidol-induced vacuous chewing in rats: suppression by α-methyl-tyrosine

Chronic treatment of rats with haloperidol (1 mg/kg twice daily for 4 weeks) induced repetitive vacuous chewing movements (VC), that persisted for over 72 h after haloperidol withdrawal. Haloperidol-induced VC were inhibited by the s.c. administration of the specific dopamine D1, receptor antagonist, SCH 23390 (0.025-0.100 mg/kg), in a dose-dependent manner, and were totally suppressed by an acute challenge with haloperidol (2 mg/kg i.p.) and by the dopamine synthesis inhibitor, alpha-methyl-tyrosine (AMT) (200 mg/kg i.p.). In AMT-treated rats, VC were reinstated by the administration of the selective D1 agonist, SKF 38393. The results support the hypothesis that chronic haloperidol-induced VC are mediated by dopamine acting selectively upon D1 receptors.

Neurochemical changes associated with the persistence of spontaneous oral dyskinesia in rats following chronic reserpine treatment

Rats treated chronically with reserpine develop spontaneous oral dyskinesia. The present study examined the development of the oral dyskinesia during the course of reserpine treatment, and its persistence after termination of treatment. Rats were injected with either reserpine (1 mg/kg, s.c.) or vehicle once daily for 4 days and then every other day for 6 weeks. Oral dyskinesia developed rapidly, reaching a maximal level after 3 days. It persisted at a maximal level for up to 20 days after termination of reserpine treatment, and continued to persist above control level for at least 60 days. The reserpine-treated rats also exhibited stereotypy in response to acute injection of the D1-selective agonist SKF-38393 (10 mg/kg), which was not observed in control rats. In contrast to the oral dyskinesia, this altered sensitivity to SKF-38393 returned to normal within 20 days after terminating the reserpine treatment, suggesting that these two behavioral responses involve different neural mechanisms. Quantitative autoradiographic measurement of dopamine receptor subtypes revealed that both D1 and D2 receptors were increased in the caudate-putamen (Cpu) and nucleus accumbens. Only the increase in D2 receptor density in the CPu correlated with the persistence of the oral dyskinesia; both changes persisted following termination of the reserpine treatment, and their magnitude was less at 60 days than at 1 and 20 days post-treatment. These results may have important implications for tardive dyskinesia.

Continuous cocaine administration produces persisting changes in brain neurochemistry and behavior

Rats were administered either continuous cocaine, daily injections of cocaine, continuous amphetamine, or no drug for 5 days and then given a 30 day drug-free recovery period. When subsequently tested in open field, the daily cocaine injection animals were the most hyperactive whereas the cocaine pellet animals were the most fearful. In vitro autoradiography was then utilized to examine persisting changes in receptor binding for D2 ([3H]spiperone), D1 ([3H]SCH23390), benzodiazepine ([3H]flunitrazepam), 5-HT1 ([3H]5-HT), 5-HT2 ([3H]ketanserin), and muscarinic acetylcholine (ACh) receptors ([3H]QNB; quinuclidinyl benzilate). In the amphetamine pellet animals, there were large increases in [3H]spiperone binding in several dopamine (DA)-rich regions; these were accompanied by conversely decreased [3H]SCH23390 binding. Cocaine pellet animals showed a completely different pattern, with appreciable increases in [3H]flunitrazepam binding in DA-rich areas, cortex, and amygdala but decreased [3H]QNB binding in DA-rich areas, hippocampus, and amygdala. While cocaine injection animals showed elevated [3H]spiperone binding in caudate and substantia nigra, they had generally smaller changes in most brain regions than the other drug groups. These findings replicate and extend previous reports that continuous drug administration induces long-lasting alterations in brain chemistry, but indicate that continuous cocaine has enduring effects on different neurochemical systems from continuous amphetamine.

Partial attenuation of chronic fluphenazine-induced changes in regional monoamine metabolism by D-alpha-tocopherol in rat brain

Recent evidence has suggested a role for free radicals in tardive dyskinesia. We, therefore, investigated the effects of chronic administration of fluphenazine decanoate (FLU) and/or vitamin E (VIT E) on regional monoamine metabolism in rat brain. Chronic FLU caused significant increases in dopamine (DA) in nucleus accumbens and brainstem, significant decreases in dihydroxyphenylacetic acid (DOPAC) in frontal cortex, nucleus accumbens and hippocampus and significant decreases in homovanillic acid (HVA) in nucleus accumbens, caudate-putamen and brainstem. Coadministration of FLU and VIT E normalized HVA in caudate-putamen, nucleus accumbens and brainstem as well as DOPAC in nucleus accumbens and hippocampus. Chronic FLU caused significant increases in norepinephrine (NE) levels in all regions studied. VIT E attenuated FLU-induced increases in NE levels in nucleus accumbens and hippocampus. Significant increases in serotonin (5-HT) levels occurred in nucleus accumbens and hippocampus whereas significant decreases in 5-hydroxyindole-acetic acid (5-HIAA) occurred in all brain regions after chronic FLU. Coadministration of VIT E attenuated the changes observed in hippocampal 5-HIAA but potentiated the FLU-induced increases in 5-HT in this region. Our data suggest that VIT E can attenuate some of the FLU-induced changes in monoamine metabolism. Results are discussed in relation to possible involvement of free radicals in monoamine metabolism during chronic neuroleptic use.

Repeated stressful experiences differently affect brain dopamine receptor subtypes

The binding of tritiated spiperone (D2 antagonist) and tritiated SCH 23390 (D1 antagonist), in vivo, was investigated in the caudatus putamen (CP) and nucleus accumbens septi (NAS) of mice submitted to ten daily restraint stress sessions. Mice sacrificed 24 hr after the last stressful experience presented a 64% decrease of D2 receptor density (Bmax) but no changes in D1 receptor density in the NAS. In the CP a much smaller (11%) reduction of D2 receptor density was accompanied by a 10% increase of D1 receptors. These results show that the two types of dopamine (DA) receptors adapt in different or even opposite ways to environmental pressure, leading to imbalance between them.

Striatal neurons express increased level of dopamine D2 receptor mRNA in response to haloperidol treatment: a quantitative in situ hybridization study

In the present study, quantitative in situ hybridization was used to analyse the effect of haloperidol treatment on D2 dopamine receptor gene expression in the rat caudate-putamen nucleus. Variations of D2 receptor mRNA level were studied and measured at the macroscopic level of densitometric analysis of X-ray film and at the microscopic level by counting of autoradiographic silver grains in striatal cells. Macroscopic analysis demonstrated that haloperidol treatment two times 1 mg/kg per day during seven, 14 and 21 days increased D2 receptor mRNA level in the caudate-putamen. Detailed microscopic analysis demonstrated a significant increase in D2 receptor mRNA in the two neuronal populations known to express the D2 receptor gene: medium-sized neurons previously identified as enkephalinergic neurons, and large-sized neurons previously identified as cholinergic neurons. The increase was more important in cholinergic neurons (+119%) than in enkephalinergic neurons (+54%). Haloperidol treatment did not modify the number of medium-sized enkephalinergic neurons expressing the D2 receptor mRNA. In contrast, it significantly increased the percentage of large-sized neurons containing D2 receptor mRNA (from 80 to 94%). These results demonstrate that haloperidol treatment acts at the gene level to modulate D2 receptor content in striatal dopaminoceptive neurons, and that the D2 receptor mRNA increase in postsynaptic neurons contributes to dopamine supersensitivity induced by neuroleptics in the rat. This suggests that dopamine acts trans-synaptically to control D2 receptor gene expression in target striatal neurons. These results suggest that modifications of D2 receptor gene expression may be part of the biological events that lead to the movement disorders induced by neuroleptic drugs or Parkinson's disease.

Autoradiographic analysis of regional alterations in brain receptors following chronic administration and withdrawal of typical and atypical neuroleptics in rats

Rats were administered haloperidol, clozapine, raclopride, or no drug for 28 days or 8 months. Following a 3 week withdrawal period, in vitro autoradiography was utilized to examine receptor binding for dopamine D2 ([3H]spiperone and [3H]raclopride), dopamine D 1 ([3H]SCH23390), GABA(A) ([3H]muscimol), benzodiazepine ([3H]RO15-1788), and muscarinic ACh receptors ([3H]QNB). [3H]spiperone was elevated in striatal subregions only in haloperidol-treated rats, with the largest increases seen in the 8 month duration animals. Striatal [3H]raclopride binding was increased after both short- and long-term treatment in both haloperidol and raclopride, but not clozapine-treated animals. Clozapine-treated rats showed significant increases in [3H]SCH23390 in the nucleus accumbens after 28-day administration; otherwise no changes were seen for this ligand in any other groups. Increases in [3H]muscimol binding in the substantia nigra reticulata were seen in haloperidol-treated rats after 8 month treatment. Binding of [3H]QNB and [3H]RO151788 were not significantly different from control for any of the drug-treated groups. These data suggest that persisting alterations in receptor binding are primarily seen in dopamine D2 and GABA receptors after withdrawal from chronic administration of haloperidol but not the atypical neuroleptics, clozapine and raclopride.

Pathogenesis and treatment of neuroleptic malignant syndrome

1. Neuroleptic drugs (antipsychotics) produce numerous side effects which include serious extrapyramidal symptoms consisting of akathisia, dystonia, neuroleptic malignant syndrome, parkinsonian reactions such as postural abnormality, tremor, akinesia or bradykinesia, rigidity, and tardive dyskinesia. 2. Among the complications of neuroleptic chemotherapy, the most serious and potentially fatal complication is malignant syndrome, which is characterized by extreme hyperthermia, "lead pipe" skeletal muscle rigidity causing dyspnea, dysphagia, and rhabdomyolysis, autonomic instability, fluctuating consciousness, leukocytosis, and elevated creatine phosphokinase. 3. Neuroleptic malignant syndrome should be differentiated from malignant hyperthermia, lethal catatonia, and other pathological states producing some of these same symptoms. 4. In addition to neuroleptics, malignant syndrome has been caused by thymoleptics (antidepressants), metoclopramide (antiemetic), metoclopramide combined with cimetidine, tetrabenazine, overdosage of benzodiazepine, phenelzine, dothiepin and alcohol, and amphetamine. 5. Factors leading to and/or facilitating the emergence of neuroleptic malignant syndromes are reportedly organic brain syndrome, dehydration, exhaustion, external heat load, excessive sympathetic discharge, use of long acting neuroleptics, high doses of neuroleptics, rapid dose titration with neuroleptics, abrupt discontinuation of antiparkinsonism agents, and concurrent lithium therapy. 6. Although, the pathogenesis of neuroleptic malignant syndrome is not understood completely, a blockade of dopaminergic receptors in the hypothalamus, spinal cord and striatum, an alteration of dopaminergic-serotonergic transmission in the body, an enhanced synthesis and action of prostaglandin E1 and E2, and a modification of calcium-mediated signal transduction in the body have been suggested. 7. The treatment of malignant syndrome includes immediate withdrawal of neuroleptic drugs, i.v. infusion of dantrolene, and oral administration of bromocriptine; or alternatively i.v. infusion of dantrolene and the combination of levodopa-carbidopa. 8. Other measures to enhance the therapeutic effectiveness of the aforementioned regimens are to include the use of anticholinergic drugs such as benztropine to enhance the effectiveness of bromocriptine, of lorazepam if catatonic symptoms persist, or of electroconvulsive therapy (ECT) if psychotic symptoms persist. 9. These treatments, however, must be "active" rather than "passive", in order to avert fatalities and/or unfortunate sequelae from this iatrogenic and incompletely understood disease.

Spontaneous orofacial movements induced in rodents by very long-term neuroleptic drug administration: phenomenology, pathophysiology and putative relationship to tardive dyskinesia

While understanding of the major clinical and ethical issue of tardive dyskinesia would be greatly facilitated by the development of an isomorphic or homologous animal model, particularly in rodents, this has proved to be a highly contentious issue. The literature on orofacial function in rats administered neuroleptic drugs for substantial proportions of their adult lifespan is reviewed. It reveals the emergence of late-onset orofacial movements in a number of studies, but very early-onset movements or no effect in others. Potential explanations for these discrepancies are considered, and ways of resolving such inconsistencies are suggested. The relationship of these various orofacial phenomena to dopaminergic and non-dopaminergic function, and to clinical syndromes, is critically evaluated.