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

Chronic treatment with D2-antagonist haloperidol leads to inhibitory/excitatory imbalance in striatal D1-neurons

Striatal dysfunction has been implicated in the pathophysiology of schizophrenia, a disorder characterized by positive symptoms such as hallucinations and delusions. Haloperidol is a typical antipsychotic medication used in the treatment of schizophrenia that is known to antagonize dopamine D2 receptors, which are abundantly expressed in the striatum. However, haloperidol's delayed therapeutic effect also suggests a mechanism of action that may go beyond the acute blocking of D2 receptors. Here, we performed proteomic analysis of striatum brain tissue and found more than 400 proteins significantly altered after 30 days of chronic haloperidol treatment in mice, namely proteins involved in glutamatergic and GABAergic synaptic transmission. Cell-type specific electrophysiological recordings further revealed that haloperidol not only reduces the excitability of striatal medium spiny neurons expressing dopamine D2 receptors (D2-MSNs) but also affects D1-MSNs by increasing the ratio of inhibitory/excitatory synaptic transmission (I/E ratio) specifically onto D1-MSNs but not D2-MSNs. Therefore, we propose the slow remodeling of D1-MSNs as a mechanism mediating the delayed therapeutic effect of haloperidol over striatum circuits. Understanding how haloperidol exactly contributes to treating schizophrenia symptoms may help to improve therapeutic outcomes and elucidate the molecular underpinnings of this disorder.

Subcortical neuromorphometry in schizophrenia spectrum and bipolar disorders

BACKGROUND

Disorders within the schizophrenia spectrum genetically overlap with bipolar disorder, yet questions remain about shared biological phenotypes. Investigation of brain structure in disease has been enhanced by developments in shape analysis methods that can identify subtle regional surface deformations. Our study aimed to identify brain structure surface deformations that were common across related psychiatric disorders, and characterize differences.

METHODS

Using the automated FreeSurfer-initiated Large Deformation Diffeomorphic Metric Mapping, we examined volumes and shapes of seven brain structures: hippocampus, amygdala, caudate, nucleus accumbens, putamen, globus pallidus and thalamus. We compared findings in controls (CON; n = 40), and those with schizophrenia (SCZ; n = 52), schizotypal personality disorder (STP; n = 12), psychotic bipolar disorder (P-BP; n = 49) and nonpsychotic bipolar disorder (N-BP; n = 24), aged 15-35. Relationships between morphometric measures and positive, disorganized and negative symptoms were also investigated.

RESULTS

Inward deformation was present in the posterior thalamus in SCZ, P-BP and N-BP; and in the subiculum of the hippocampus in SCZ and STP. Most brain structures however showed unique shape deformations across groups. Correcting for intracranial size resulted in volumetric group differences for caudate (p < 0.001), putamen (p < 0.01) and globus pallidus (p < 0.001). Shape analysis showed dispersed patterns of expansion on the basal ganglia in SCZ. Significant clinical relationships with hippocampal, amygdalar and thalamic volumes were observed.

CONCLUSIONS

Few similarities in surface deformation patterns were seen across groups, which may reflect differing neuropathologies. Posterior thalamic contraction in SCZ and BP suggest common genetic or environmental antecedents. Surface deformities in SCZ basal ganglia may have been due to antipsychotic drug effects.

Elevated Excitatory Input to the Nucleus Accumbens in Schizophrenia: A Postmortem Ultrastructural Study

The cause of schizophrenia (SZ) is unknown and no single region of the brain can be pinpointed as an area of primary pathology. Rather, SZ results from dysfunction of multiple neurotransmitter systems and miswiring between brain regions. It is necessary to elucidate how communication between regions is disrupted to advance our understanding of SZ pathology. The nucleus accumbens (NAcc) is a prime region of interest, where inputs from numerous brain areas altered in SZ are integrated. Aberrant signaling in the NAcc is hypothesized to cause symptoms of SZ, but it is unknown if these abnormalities are actually present. Electron microscopy was used to study the morphology of synaptic connections in SZ. The NAcc core and shell of 6 SZ subjects and 8 matched controls were compared in this pilot study. SZ subjects had a 19% increase in the density of asymmetric axospinous synapses (characteristic of excitatory inputs) in the core, but not the shell. Both groups had similar densities of symmetric synapses (characteristic of inhibitory inputs). The postsynaptic densities of asymmetric synapses had 22% smaller areas in the core, but not the shell. These results indicate that the core receives increased excitatory input in SZ, potentially leading to dysfunctional dopamine neurotransmission and cortico-striatal-thalamic stimulus processing. The reduced postsynaptic density size of asymmetric synapses suggests impaired signaling at these synapses. These findings enhance our understanding of the role the NAcc might play in SZ and the interaction of glutamatergic and dopaminergic abnormalities in SZ.

Basal ganglia volume in unmedicated patients with schizophrenia is associated with treatment response to antipsychotic medication

We investigated the relationship between basal ganglia volume and treatment response to the atypical antipsychotic medication risperidone in unmedicated patients with schizophrenia. Basal ganglia volumes included the bilateral caudate, putamen, and pallidum and were measured using the Freesurfer automated segmentation pipeline in 23 subjects. Also, baseline symptom severity, duration of illness, age, gender, time off medication, and exposure to previous antipsychotic were measured. Treatment response was significantly correlated with all three regions of the bilateral basal ganglia (caudate, putamen, and pallidum), baseline symptom severity, duration of illness, and age but not gender, time off antipsychotic medication, or exposure to previous antipsychotic medication. The caudate volume was the basal ganglia region that demonstrated the strongest correlation with treatment response and was significantly negatively correlated with patient age. Caudate volume was not significantly correlated with any other measure. We demonstrated a novel finding that the caudate volume explains a significant amount of the variance in treatment response over the course of 6 weeks of risperidone pharmacotherapy even when controlling for baseline symptom severity and duration of illness.

Effect of chronic L-dopa or melatonin treatments after dopamine deafferentation in rats: dyskinesia, motor performance, and cytological analysis

The present study examines the ability of melatonin to protect striatal dopaminergic loss induced by 6-OHDA in a rat model of Parkinson's disease, comparing the results with L-DOPA-treated rats. The drugs were administered orally daily for a month, their therapeutic or dyskinetic effects were assessed by means of abnormal involuntary movements (AIMs) and stepping ability. At the cellular level, the response was evaluated using tyrosine hydroxylase immunoreactivity and striatal ultrastructural changes to compare between L-DOPA-induced AIMs and Melatonin-treated rats. Our findings demonstrated that chronic oral administration of Melatonin improved the alterations caused by the neurotoxin 6-OHDA. Melatonin-treated animals perform better in the motor tasks and had no dyskinetic alterations compared to L-DOPA-treated group. At the cellular level, we found that Melatonin-treated rats showed more TH-positive neurons and their striatal ultrastructure was well preserved. Thus, Melatonin is a useful treatment to delay the cellular and behavioral alterations observed in Parkinson's disease.

Bilateral Increase of Perforated Synapses after Unilateral Dopamine Depletion

In recent years attention has been focused on perforated synapses considering their possible involvement in synaptic plasticity in the nervous system. It has been hypothesized that an increase in the number of synapses may represent a structural basis for the enduring expression of synaptic plasticity during some events that involve memory and learning; also it has been suggested that perforated synapses increase in number after some experimental situations. The aim of this study was to analyze whether the dopamine depletion produces changes in the synaptology of the corpus striatum of rats after the unilateral injection of 6-OHDA. The findings suggest that after the lesion, both contralateral and ipsilateral striata present a significant increment in the number of perforated synapses, suggesting brain plasticity that might be an intent to recuperate the contact surface lost after endogenous or exogenous aggressions.

Effects of haloperidol and melatonin on the in situ activity of nigrostriatal tyrosine hydroxylase in male Syrian hamsters

Haloperidol, an antipsychotic drug, was tested for its effects on the in situ activity of nigrostriatal and hypothalamic tyrosine hydroxylase, in control male Syrian hamsters and in those receiving a high daily dose of melatonin. After receiving daily ip injections (1.25 mg/kg ip) of haloperidol for 21 days, the animals were sacrificed and brain tissue collected for analysis of dopamine and metabolites by HPLC with electrochemical detection. In situ activity of tyrosine hydroyxlase (TH) activity was determined by measuring the accumulation of L-Dopa after administration of the L amino acid decarboxylase inhibitor, mhydroxybenzylhydrazine. Tissue content of dopamine and its metabolites, DOPAC and HVA, was depressed in striatum of animals receiving haloperidol, and tyrosine hydroxylase (TH) activity was significantly decreased 20-24 h after the last injection (from 1823 +/- 63 to 1139 +/- 85 pg l-dopa/mg tissue). The decrease in TH activity in striatum was significantly inhibited by daily injections of a high dose of melatonin (2.5 mg/kg ip) (from 1139 +/- 85 to 1560 +/- 116 pg L-dopa/mg tissue). In the substantia nigra and in the hypothalamus, on the other hand, haloperidol significantly increased the activity of tyrosine hydroxylase. Melatonin administration did not significantly influence TH activity in the substantia nigra, but inhibited TH activity in the hypothalamus and in the pontine brainstem. One explanation for these data is that chronic haloperidol administration in Syrian hamsters increases TH activity in hypothalamus and substantia nigra, but decreases TH activity in striatum by a mechanism involving D2 presynaptic receptors and a melatonin sensitive kinase which regulates TH phosphorylation.

Chronic haloperidol promotes corticostriatal long-term potentiation by targeting dopamine D2L receptors

Reduced glutamate-mediated synaptic transmission has been implicated in the pathophysiology of schizophrenia. Because antipsychotic agents might exert their beneficial effects against schizophrenic symptoms by strengthening excitatory transmission in critical dopaminoceptive brain areas, in the present study we have studied the effects of acute and chronic haloperidol treatment on striatal synaptic plasticity. Repetitive stimulation of corticostriatal terminals in slices induced either long-term depression or long-term potentiation (LTP) of excitatory transmission in control rats, whereas it invariably induced NMDA receptor-dependent LTP in animals treated chronically with haloperidol. Haloperidol effects were mimicked and occluded in mice lacking both D2L and D2S isoforms of dopamine D2 receptors (D2R-/-), in mice lacking D2L receptors and expressing normal levels of D2S receptors (D2R-/-;D2L-/-), and in mice lacking D2L receptors and overexpressing D2S receptors (D2L-/-). These data indicate that the blockade of D2L receptors was responsible for the LTP-favoring action of haloperidol in the striatum. In contrast, overexpression of D2S receptors uncovered a facilitatory role of this receptor isoform in LTP formation because LTP recorded from D2L-/- mice, but not those recorded from wild-type, D2R-/-, and D2R-/-;D2L-/- mice, was insensitive to the pharmacological blockade of D1 receptors. The identification of the cellular, molecular, and receptor mechanisms involved in the action of haloperidol in the brain is essential to understand how antipsychotic agents exert their beneficial and side effects.

Increased N-acetylaspartate in rat striatum following long-term administration of haloperidol

N-acetylaspartate (NAA) is present in high concentrations in the CNS and is found primarily in neurons. NAA is considered to be a marker of neuronal viability. Numerous magnetic resonance spectroscopy (MRS) and postmortem studies have shown reductions of NAA in different brain regions in schizophrenia. Most of these studies involved patients chronically treated with antipsychotic drugs. However, the effect of chronic antipsychotic treatment on NAA remains unclear. In the present study, we measured NAA in brain tissue taken from 43 male Long-Evans rats receiving 28.5 mg/kg haloperidol decanoate i.m. every 3 weeks for 24 weeks and from 21 controls administered with vehicle. Determination of tissue concentrations of NAA was achieved by HPLC of sections of frozen tissue from several brain regions with relevance to schizophrenia. Chronic administration of haloperidol was associated with a significant increase (+23%) in NAA in the striatum (p<0.05) when compared to controls, with no significant changes in the other regions investigated (frontal and temporal cortex, thalamus, hippocampus, amygdala, and nucleus accumbens). NAA appears to be selectively increased in the striatum of rats chronically receiving haloperidol. This increase may reflect a hyperfunction of striatal neurons and relate to the reported increase in somal size of these cells and/or the increase in synaptic density seen in this region following antipsychotic administration. The lack of effect in other regions indicates that the well-documented NAA deficits seen in chronically treated schizophrenia patients is not an effect of antipsychotic medication and may in fact be related to the disease process.

Molecular aspects of glutamate dysregulation: implications for schizophrenia and its treatment

The glutamate system is involved in many aspects of neuronal synaptic strength and function during development and throughout life. Synapse formation in early brain development, synapse maintenance, and synaptic plasticity are all influenced by the glutamate system. The number of neurons and the number of their connections are determined by the activity of the glutamate system and its receptors. Malfunctions of the glutamate system affect neuroplasticity and can cause neuronal toxicity. In schizophrenia, many glutamate-regulated processes seem to be perturbed. Abnormal neuronal development, abnormal synaptic plasticity, and neurodegeneration have been proposed to be causal or contributing factors in schizophrenia. Interestingly, it seems that the glutamate system is dysregulated and that N-methyl-D-aspartate receptors operate at reduced activity. Here we discuss how the molecular aspects of glutamate malfunction can explain some of the neuropathology observed in schizophrenia, and how the available treatment intervenes through the glutamate system.

Antipsychotic drugs and neuroplasticity: insights into the treatment and neurobiology of schizophrenia

This paper reviews the evidence that antipsychotic drugs induce neuroplasticity. We outline how the synaptic changes induced by the antipsychotic drug haloperidol may help our understanding of the mechanism of action of antipsychotic drugs in general, and how they may help to elucidate the neurobiology of schizophrenia. Studies have provided compelling evidence that haloperidol induces anatomical and molecular changes in the striatum. Anatomical changes have been documented at the level of regional brain volume, synapse morphology, and synapse number. At the molecular level, haloperidol has been shown to cause phosphorylation of proteins and to induce gene expression. The molecular responses to conventional antipsychotic drugs are predominantly observed in the striatum and nucleus accumbens, whereas atypical antipsychotic drugs have a subtler and more widespread impact. We conclude that the ability of antipsychotic drugs to induce anatomical and molecular changes in the brain may be relevant for their antipsychotic properties. The delayed therapeutic action of antipsychotic drugs, together with their promotion of neuroplasticity suggests that modification of synaptic connections by antipsychotic drugs is important for their mode of action. The concept of schizophrenia as a disorder of synaptic organization will benefit from a better understanding of the synaptic changes induced by antipsychotic drugs.

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.

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.

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.

Failure to down regulate NMDA receptors in the striatum and nucleus accumbens associated with neuroleptic-induced dyskinesia

The syndrome of vacuous chewing movements (VCMs) in rats is similar in many respects to tardive dyskinesia (TD) in humans. Both syndromes are characterized by delayed onset of persistent orofacial dyskinesias in a sub-group of subjects chronically treated with neuroleptics. Using the rat model, we examined the role of NMDA receptor-mediated corticostriatal neurotransmission in the expression of VCMs. Rats were treated for 36 weeks with haloperidol decanoate or vehicle and then withdrawn for an additional 28 weeks. Chronic persistent VCMs were induced in one subgroup of treated animals (+VCM), but not in another group (-VCM). Rats from +VCM, -VCM groups and vehicle-treated controls were selected for post mortem studies (n = 12 to 14 per group). NMDA receptor levels were assessed using [3H]-MK-801 binding in sections from the mid-striatum and nucleus accumbens. Chronic haloperidol treatment produced a marked reduction of NMDA receptor binding levels throughout the striatum and nucleus accumbens. Post hoc comparisons demonstrated that -VCM rats had lower NMDA receptor binding levels than +VCM and vehicle-treated controls. Ventromedial striatum and nucleus accumbens core were the most affected areas. These findings suggest that down-regulation of striatal NMDA receptor binding levels may protect against the expression of neuroleptic-induced dyskinesia.

Adverse neurobiological effects of long-term use of neuroleptics: human and animal studies

Neuroleptics have revolutionized the treatment of schizophrenia and other psychoses since the early 1950s. Several adverse neurobiological effects are, however, associated with the long-term use of these agents. This article will review human and animal studies of these adverse effects, and also present some new data. Tardive dyskinesia (TD) is the most widely studied potentially persistent movement disorder resulting from long-term neuroleptic treatment, and several risk factors for TD development have been identified. Although drug-induced parkinsonism (DIP) usually disappears after the offending agent is withdrawn, a small portion of patients may have persistent parkinsonism. It is however, unclear if this is an aging-related effect. Persistent cognitive impairment associated with long-term use of typical neuroleptics has not been well documented. Atypical antipsychotics may produce improvement in cognitive performance in patients with chronic schizophrenia. MRI changes that are secondary to neuroleptics are possible, but have not yet been studied adequately. There is one unconfirmed report of neurofibrillary tangles associated with long-term neuroleptic use. A number of investigators have reported vacuous chewing movements, and neuropathologic changes following prolonged administration of neuroleptics in animals. We discuss the implications of the various reported adverse effects of long-term use of neuroleptics.

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.

Effect of a pyridinium metabolite derived from haloperidol on the activities of striatal tyrosine hydroxylase in freely moving rats

The effects of a pyridinium metabolite (HPP+) derived from haloperidol (HP) on in vivo tyrosine hydroxylation was evaluated in freely moving rats. As an index of the in vivo activity of tyrosine hydroxylase (TH), the rat striatum was perfused with NSD-1015, and extracellular 3,4-dihydroxyphenylalanine (DOPA) levels were measured. HPP+ (1 mM) gradually reduced tyrosine hydroxylation to 30% of the basal level, although the effect was less potent than 1-methyl-4-phenylpyridinium ion (MPP+). On the contrary, HPP+ at a 0.1 mM dose decreased in 5-hydroxyindoleacetic acid (5-HIAA) level, but did not affect dopamine metabolites. The present study revealed that HPP+ irreversible inhibited in vivo tyrosine hydroxylation by the same manner of MPP+. However, the neurotoxic effects of HPP+ in vivo would be selective for serotonergic over dopaminergic neurons, which distinguishes the toxic profile of this compound compared to that of MPP+.

Effects of chronic neuroleptic treatment on dopamine release: insights from studies using 3-methoxytyramine

Antipsychotic medications appear to exert their therapeutic effects by blocking D2 receptors. While D2 blockade occurs rapidly, reduction in psychotic symptoms is often delayed. This time discrepancy has been attributed to the relatively slow development of depolarization inactivation (DI) of dopaminergic neurons. The reduced firing rates associated with DI has been hypothesized to reduce dopamine release and thus psychotic symptoms. Studies assessing changes in dopamine release during chronic neuroleptic treatment, using microdialysis and voltammetry, have been inconsistent. This may be due to methodological differences between studies, the invasive nature of these procedures, or other confounds. To investigate the effects of DI on dopamine release, 3-MT accumulation, an index of dopamine release that does not involve disruption of brain tissue, was measured during acute and chronic neuroleptic treatment. These results are compared with those using other techniques. 3-MT levels remained elevated after chronic treatment, suggesting that DI does not markedly reduce release. Regulation of dopamine release during DI was examined using two techniques known to block dopamine neuronal impulse flow. 3-MT levels were markedly reduced by both, implying that DI does not alter the portion of dopamine release mediated by neuronal impulse flow. Overall, studies to date suggest that the delayed therapeutic effects of neuroleptics are not due to reductions in impulse dependent dopamine release. Recent studies using a neurodevelopmental animal model of schizophrenia have pointed to altered pre- and post-synaptic indices of dopamine neurotransmission. The results suggest that neuroleptics may exert their therapeutic effects, in part, by limiting the fluctuations in dopamine release, and raise new issues for future research.

The effects of raclopride on vacuous jaw movements in rats following acute administration

Classic neuroleptics produce a syndrome of vacuous jaw movements in rats, whereas atypical neuroleptics like clozapine do not. The present study compared the effects of repeated administration of raclopride, clozapine, haloperidol, or vehicle on vacuous jaw movements in rats over a 4-week period. Rats received an IP injection of drug once a day. On days 1, 8, 15, and 29 the rats were observed for a 5-min period by two trained observers who recorded their vacuous jaw movements. The dose-response curves at which each drug produced vacuous jaw movements are presented and discussed in terms of their predictive capabilities of early onset extrapyramidal side effects.

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.

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

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

An analysis of contemporary morphological concepts of synaptic remodelling in the CNS: perforated synapses revisited

Perforated synapses refer to a synaptic type found in the central nervous system. They are characterized by their large size and by a discontinuity of the postsynaptic density when viewed in transverse sections, and by a doughnut or horseshoe shape when viewed in en face views. Of recent morphological studies, one approach has followed their characteristics throughout development and maturity, while others have concentrated on their probable roles in activities including kindling, long-term potentiation, spatial working memory, differential rearing, and the functioning of neuroleptics. An assessment is made of the hypotheses and models that have proved determinative in the emergence of perforated synapses as being significant in synaptic plasticity. Their distribution and frequency are summarized, with emphasis on the importance of unbiased stereological procedures in their analysis. Using three-dimensional approaches various subtypes are recognized. Of these, a complex or fragmented subtype appears of especial significance in synaptic plasticity. Ideas regarding the life-cycle of perforated synapses are examined. The view that they originate from conventional, non-perforated synapses, enlarge, and subsequently split to give rise to a new generation of non-perforated synapses, is critically assessed. According to an alternative model, perforated and non-perforated synapses constitute separate populations from early in their development, each representing complementary forms of synaptic plasticity. An attempt is also made to discover whether synaptic studies on the human brain in normal aging and in Alzheimer's disease throw light on the role of perforated synapses in synaptic plasticity. The loss of synapses in Alzheimer's disease may include a loss of perforated synapses - of particular relevance for an understanding of certain neuropathological conditions.

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

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

Single preexposure to fluphenazine produces persisting behavioral sensitization accompanied by tolerance to fluphenazine-induced striatal dopamine overflow in rats

Single, previous exposure to a neuroleptic has been shown to produce long-lasting changes in various measures of behavior and neurochemistry upon subsequent drug exposure. The present study examined the effects of a single preexposure to fluphenazine (0.3 or 1.0 mg/kg) or vehicle on the effects of subsequent fluphenazine administration 15 or 30 days later. Intracranial microdialysis was used to assess changes in striatal extracellular dopamine concentrations. Animals were tested for catalepsy response on a horizontal bar test while concurrently collecting dialysis samples. Previous fluphenazine exposure produced a profound tolerance to the effects of subsequent fluphenazine at day 15 or day 30 on increasing extracellular dopamine levels. In addition, animals that had received fluphenazine on the first trial showed significant sensitization to the cataleptic effects of fluphenazine at both time points. Pretreatment with vehicle did not result in tolerance to dopamine overflow and there was only minimal evidence of cataleptic sensitization to a subsequent fluphenazine challenge. Although the tolerance to dopamine overflow may only indirectly relate to behavioral sensitization, these results support the hypothesis that significant behavioral and neurochemical alterations persist for prolonged time periods following single neuroleptic exposure.

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

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