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 with 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.     

The relationship between dopamine D2 receptor occupancy and the vacuous chewing movement syndrome in rats

Abstract Rationale. A dose–response relationship between dopamine D₂ occupancy and acute extrapyramidal symptoms (EPS) has been well established. However, the link with the induction of tardive dyskinesia (TD) is less clear. Objectives. To ascertain the nature and extent of D₂ receptor occupancy effects on haloperidol-induced vacuous chewing movements (VCMs) in a rat model of TD. Methods. Groups of eight rats received haloperidol decanoate injections corresponding to daily doses of 0, 0.08, 0.17, 0.33, or 1 mg/kg for 10–12 weeks. VCMs were measured on a weekly basis and D₂ occupancy levels were measured in vivo using [³H]-raclopride at the end of the experiment. Results. Final VCM scores were significantly different between haloperidol doses (P=0.001). Moderate but significant correlations were found between dose and average VCM scores (r=0.69, P<0.001) and between D₂ occupancy and average VCM scores (r=0.65, P<0.001). The rats that developed the VCM syndrome (≥8 VCMs) had higher occupancies than rats that did not. Of the rats with an occupancy above 70%, 63% developed VCMs, compared with 37% of the rats with D₂ occupancy below that. Conclusions. These results indicate that chronic haloperidol induces VCMs in a dose-dependent manner, with doses leading to high D₂ occupancy increasing the likelihood of emergence of the VCM syndrome. While a certain level of D₂ occupancy may be necessary for inducing VCMs, it is not sufficient in and of itself to induce the VCM syndrome. Electronic Publication     

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 (30d) 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 attenuates the development of vacuous chewing movements induced by long-term haloperidol treatment of rats

Tardive dyskinesia (TD) is a serious side-effect of long-term treatment with neuroleptics. To investigate if TD may be a result of neuroleptic-induced excessive stimulation of striatal glutamate receptors, the effect of the anti-excitotoxic GM1 ganglioside was studied in a rat model of TD. In an acute experiment each of four groups of rats was treated with GM1 20 mg/kg SC + saline IP, saline SC + haloperidol 1.2 mg/kg IP, GM1 SC + haloperidol IP, or saline SC + saline IP. In a subsequent long-term experiment lasting 16 weeks, each of the four groups was treated as in the acute experiment, with the exception that haloperidol was injected IM as decanoate 38 mg/kg every 4 weeks, and the controls received vehicle injections. The behaviour was videotaped and scored at intervals during both experiments, including 16 weeks after cessation of the long-term treatment. Haloperidol induced a significant increase in vacuous chewing movements (VCM) and immobility both in the acute and in the long-term experiment. Other categories of behaviour (rearing, moving, sitting) were significantly affected only in the acute experiment. GM1 did not affect any of the acute behavioural effects of haloperidol, but significantly reduced VCM in the long-term experiment. The effects on VCM of haloperidol and GM1 persisted for at least 8 weeks after cessation of the long-term treatment. These results suggest that long-lasting changes in striatal function induced by excessive glutamate receptor stimulation may be a mechanism for the development of VCM in rats and perhaps also for TD in humans.     

The mitochondrial toxin 3-nitropropionic acid induces vacuous chewing movements in rats. Implications for tardive dyskinesia?

Rats were chronically treated for 4 weeks with three doses (4, 8, 12 mg/kg per day) of the mitochondrial toxin 3-nitropropionic acid (3-NP). The behaviour was videotaped at intervals during and after treatment, and vacuous chewing movements (VCM), a putative analogue to tardive dyskinesia (TD), as well as the general behaviour were scored. During treatment, 3-NP dose-dependently increased VCM and dose-dependently reduced motor activity, which is similar to the behavioural effect of long-term neuroleptic treatment. The results may support the hypothesis that neuroleptic-induced impairment of energy metabolism, a potential excitotoxic mechanism, is involved in the development of VCM in rats and probably TD in humans.     

Intermittent versus continuous neuroleptic treatment in a rat model

The treatment schedule for neuroleptic therapy is of relevance when evaluating the development of side-effects. Seventy-five rats were treated discontinuously or continuously with the predominantly dopamine D₂ receptor blocker haloperidol or the combined dopamine D₁/D₂ receptor blocker zuclopenthixol for 15 weeks. During and after treatment, a broad spectrum of behavioural parameters including vacuous chewing movements and tongue protrusions were observed. Discontinuous neuroteptic treatment as opposed to continuous neuroleptic treatment produced a significant long-lasting increase in oral activity. The changes were most pronounced in haloperidol-treated rats. The differences observed may have methodological implications for animal models of neuroleptic-induced movement disorders. Our finding are consistent with the hypothesis that pharmacological sensitization to the dyskinetic side-effects of neuroleptics develops when the drug effect is allowed to wear off between repeated administration.     

Relationship of orofacial movements to behavioural repertoire as assessed topographically over the course of 6-month haloperidol treatment followed by 4-month withdrawal

Rationale Late-onset vacuous chewing movements (VCMs) arise in a significant proportion of rats treated chronically with conventional antipsychotic drugs. Given their common action to block dopamine D₂-like receptors, VCMs may be related to changes in dopaminergic function; if so, other typical dopamine-mediated behaviours might be altered also.Objective To examine this hypothesis, behavioural repertoire was studied topographically over the course of chronic treatment and withdrawal.Methods Animals were injected with haloperidol decanoate 28 mg/kg IM, or vehicle, every 3 weeks for 27 weeks, and then maintained without treatment for a further 18 weeks. Immediately before each injection and during withdrawal, VCMs and other topographies of behaviour were assessed.Results In both control and haloperidol-treated rats, exploratory behaviours declined over the study, indicating habituation effects. Conversely, VCMs emerged after 6 weeks of treatment with haloperidol and persisted after withdrawal; VCM and locomotion were not related, indicating that in treated rats, increased VCMs are not an artifact of reduced locomotion. Treated animals with VCMs evidenced increases in buccal tremor and grooming behaviour relative to those without VCMs, although no clear relationship to the emergence of VCMs was established; there were no material differences in any other topographies of behaviour.Conclusion The effect of long-term treatment with haloperidol to induce VCMs is not reflected in fundamental changes in dopamine-mediated behavioural topography but, rather, appears to affect neural mechanisms involved in orofacial movement preferentially.     

Methylazoxymethanol (MAM)-induced brain lesion and oral dyskinesia in rats

The effects of methylazoxymethanol (MAM)-induced brain lesions on vacuous chewing movements (VCM) were examined in rats given chronic haloperidol treatment (0.1 or 1 mg/kg/day) for 18 months. At the end of the experiment striatal, pallidal, and nigral activities of glutamate decarboxylase (GAD) were measured. MAM-lesioned rats had an elevated rate of VCMs compared to unlesioned controls. This effect was stable during the whole 18-month experiment. In unlesioned control rats chronic haloperidol produced a gradual increase in VCM rates, but this effect was not further exacerbated in MAM-lesioned animals. After chronic haloperidol treatment with the higher dose (1 mg/kg/day) GAD activity was reduced in substantia nigra (-20%), globus pallidus (-35%), and striatum (-26%) of unlesioned rats. MAM caused a reduction of GAD activity in substantia nigra (-29%) and globus pallidus (-29%). Chronic haloperidol did not influence these effects of MAM-induced lesion. The present results show that a MAM-induced brain lesion, in contrast to cortical ablations, cannot be used to amplify the haloperidol-induced VCM increase or influence the nigral GAD activity in a rat model for tardive dyskinesia.     

The relationship between motor effects in rats following acute and chronic haloperidol treatment

Tardive dyskinesia (TD) is a serious and sometimes irreversible side-effect to long-term neuroleptic treatment. In order to find predictors for development of TD, it would be of interest to known whether susceptibility to develop acute side-effects increases the risk of TD development. The study investigated in female Sprague-Dawley rats the relationship between haloperidol-induced acute motor effects, assessed by means of the grid test and the open field test, and the chronic motor effect assessed as vacuous chewing movements (VCM). The doses of haloperidol were 1.2, 2.4 and 4.8 mg/kg IP in the acute experiments and haloperidol decanoate 38 mg/kg per 4 weeks IM in the chronic experiment. The VCM obtained at different timepoints during the 24 weeks of chronic treatment were highly correlated. However, no correlation was found between the motor effects in the acute and the chronic experiments. The study does not indicate any connection between susceptibility to acute side-effects on neuroleptics and later development of TD.     

Autoradiographic mapping of μ opioid receptor changes in rat brain after long-term haloperidol treatment: relationship to the development of vacuous chewing movements

Brain opioid systems modulating basal ganglia function may be involved in the development of neuroleptic-induced orofacial dyskinesias. This study examined changes in μ opioid receptors labeled with [³H]D-Ala², N-MePhe⁴, Gly-ol⁵-enkephalin ([³H]DAMGO) in 79 different brain regions of rats showing vacuous chewing movements after 21 weeks of treatment with haloperidol decanoate (HAL). Dopamine D₂ receptors labeled with [³H]raclopride were also examined in the adjacent sections of the same brains. For brain analyses HAL-treated rats were divided into a group showing high incidence of vacuous chewing movements (VCMs) and a group showing low incidence of VCMs. As expected, long-term HAL resulted in a pronounced elevation of D₂ receptors in caudate-putamen, n. accumbens, globus pallidus and olfactory bulbs (range: 27–70% increases) compared to controls. These changes were equal in magnitude in both HAL-treated groups, irrespective of the frequency of VCMs. In HAL-treated rats [³H]DAMGO was significantly decreased in several parts of the basal ganglia, including n. accumbens (−21%, P < 0.01), patchy area of the anterior caudate-putamen (−12%, P < 0.05), ventral pallidum (−27%, P < 0.01) and globus pallidus (−21%, P < 0.02). Statistically significant decreases were also seen in the subthalamic nucleus (−12%, P < 0.05) and ventrolateral thalamus (−21%, P < 0.05), both of which are targets of basal ganglia output. However, as in the case of [³H]raclopride binding, [³H]DAMGO changes were generally seen both in the High VCM and the Low VCM groups. These results confirm that long-term haloperidol leads to a decrease in μ-opioid binding in basal ganglia and related structures, similar to what is seen after 6-OHDA denervation. The observed μ-receptor binding changes may be a contribution factor, but do not appear sufficient to account for the differential development of neuroleptic-induced vacuous chewing movements. Received: 2 February 1996 / Final version: 10 June 1996     

Drugs acting at D-1 and D-2 dopamine receptors induce identical purposeless chewing in rats which can be differentiated by cholinergic manipulation

Purposeless chewing in rats was dose dependently increased by acute administration of the dopamine D-1 receptor agonist SKF 38393 (5–20 mg/kg), the D-2 receptor antagonist sulpiride (10–100 mg/kg) and the D-2 receptor agonist quinpirole (0.05–0.25 mg/kg). Only high doses of the D-1 receptor antagonist SCH 23390 (1 and 5 mg/kg) induced purposeless chewing. SCH 23390 (0.05 mg/kg) blocked SKF 38393 (20 mg/kg)-induced purposeless chewing, but had no effect on the purposeless chewing induced by sulpiride (100 mg/kg) or quinpirole (0.1 mg/kg). A dose of SKF 38393 (5 mg/kg) which did not itself induce chewing, potentiated the increase in purposeless chewing observed after administration of sulpiride (100 mg/kg). Administration of SKF 38393 (20 mg/kg) and quinpirole (0.1 mg/kg) did not induce purposeless chewing but stereotyped licking was observed. Administration of sulpiride (100 mg/kg) with quinpirole (0.1 mg/kg) produced an incidence of purposeless chewing not different from that observed when either compound was administered alone. Acute administration of the cholinergic agonist pilocarpine (0.5–4.0 mg/kg) or the cholinesterase inhibitor physostigmine (0.05–0.2 mg/kg) increased the frequency of purposeless chewing in rats. Co-administration of pilocarpine (0.5 mg/kg) with sulpiride (100 mg/kg) increased the frequency of purposeless chewing above that seen when either compound was administered alone. Co-administration of pilocarpine (0.5 mg/kg) with SKF 38393 (20 mg/kg) increased the frequency of purposeless chewing in an additive manner. Co-administration of physostigmine (0.1 mg/kg) with sulpiride (100 mg/kg) but not SKF 38393 (20 mg/kg), increased the frequency of purposeless chewing above that observed when either compound was administered alone. Quinpirole (0.1 mg/kg)-induced purposeless chewing was not affected by co-administration with either pilocarpine (0.5 mg/kg) or physostigmine (0.1 mg/kg). The anticholinergic agent scopolamine (0.1 mg/kg) blocked the purposeless chewing induced by either SKF 38393 (20 mg/kg) or sulpiride (100 mg/kg), but had no effect on the purposeless chewing induced by quinpirole (0.1 mg/kg). Contrary to previous reports, acute manipulation of D-1 or D-2 receptor function can both enhance purposeless chewing behaviour in rats. These apparently identical behaviours can be differentiated by the response to cholinergic manipulation.     

Neuroleptic-induced oral dyskinesias: effects of progabide and lack of correlation with regional changes in glutamic acid decarboxylase and choline acetyltransferase activities

The development of vacuous chewing movements (VCMs), and changes in glutamic acid decarboxylase (GAD) and choline acetyltransferase (ChAT) activities in extrapyramidal nuclei were examined in rats treated chronically with neuroleptics. Animals were injected with flupenthixol (FLU) or haloperidol (HAL) decanoate for 16, 40 or 48 weeks and were then sacrificed. Another group of rats was treated with FLU or HAL for 48 weeks, and then withdrawn from the neuroleptics for 16 weeks before sacrifice. VCMs were assessed weekly, and the effects of the GABA agonist progabide on VCMs and locomotor activity were examined. GAD and ChAT activities were determined at death. The concentrations of Calbindin D_28K (CaBP) and parvalbumin (PV) were determined in rats receiving 48 weeks of neuroleptic treatment. VCMs first appeared after 8–10 weeks of neuroleptic administration, reached asymptotic rates after 18–20 weeks, and then remained stable for the remainder of the chronic drug administration period. During withdrawal, there was a steady decline in the VCM rate. The GABA receptor agonist progabide reduced VCMs and locomotor activity. Significant decreases in nigral GAD activity were observed after 40, but not after either 16 or 48 weeks of neuroleptic administration. CaBP and PV were unchanged after 48 weeks of neuroleptic treatment. In addition, ChAT activities in 16, 40 or 48 week treated animals did not show consistent changes after either neuroleptic. Chronic neuroleptic administration followed by 16 weeks of withdrawal also did not have any significant effects on GAD or ChAT activity in any of the brain areas examined. The present results demonstrate that decreases in nigral GAD activity do not occur when VCMs have reached near maximal rates. It appears, therefore, that neuroleptic-induced VCMs and decreases in nigral GAD activity are not causally related. Nevertheless, the reduction in VCMs produced by progabide suggests that impaired GA-BAergic mechanisms may be involved in the expression of these abnormal perioral movements.     

Radial-arm maze performance in rats is impaired by a combination of nicotinic-cholinergic and D2 dopaminergic antagonist drugs

Performance on the radial-arm maze depends on the integrity of both cholinergic and dopaminergic systems. We have previously found that administration of either the nicotinic-cholinergic antagonist, mecamylamine, or the muscarinic-cholinergic antagonist, scopolamine, impairs choice accuracy in the radial-arm maze. Co-administration of the dopaminergic antagonist, haloperidol, ameliorated the performance deficit caused by scopolamine but exacerbated the deficit caused by mecamylamine. Furthermore, antagonism of the effect of scopolamine is due specifically to blockade of D₁ receptors. In the present experiment behaviorally subthreshold doses of mecamylamine and the D₂ antagonist raclopride impaired maze performance when administered together. No interactive effects were observed between mecamylamine and the D₁ antagonist SCH 23390. Although several of the drug treatments studied significantly increased choice latency, an index of motor behavior, there was no perfect relationship between choice accuracy and choice latency. These data indicate that nicotinic-cholinergic and muscarinic-cholinergic systems interact selectively and differentially with D₁ and D₂ dopaminergic systems.     

Effects of ceruletide on perioral movements and the dopamine receptor-adenylate cyclase system in rats chronically treated with fluphenazine

The effects of repeated administration of ceruletide (100 µg/kg/perday, IP for 3 days) on perioral movements and the striatal dopamine receptor adenylate cyclase system were examined in rats chronically treated with fluphenazine enanthate (FPZ) (25 mg/kg IM every 3 weeks for 30 weeks) and sesame oil-treated (control) rats. After the tenth injection of fluphenazine, the rats started to display five types of perioral movements (teeth chattering, chewing, tongue protrusion, mouth opening and perioral tremors). Moreover, increases in SCH23390 binding and spiperone binding to striatal membranes were found in the FPZ-treated rats. Furthermore, dopamine receptor-coupled adenylate cyclase activity was potentiated in striatal membranes. High amplitude EMG discharges (8–10 Hz), recorded from the masseter in the FPZ-treated rats occurred concurrently with perioral tremors. Repeated ceruletide (CLT) injections abolished perioral movements, and reversed both the elevated SCH23390 binding and the dopamine stimulated adenylate cyclase (AC) activity to the control level. The effect of CLT on perioral movements, D₁ receptors and dopamine-stimulated AC activity continued for 6 days after the final CLT injection. These finding suggest that systemically administered CLT affects the D₁ receptor adenylate cyclase system and that an increase of the D₁ receptor mechanism may play an important role in the pathogenesis of tardive dyskinesia.     

Inhibition of methamphetamine sensitization by post-methamphetamine treatment with SCH 23390 or haloperidol

Methamphetamine (2 mg/kg SC) increased ambulation in mice for about 3 h, with a peak effect at around 40 min after the administration, and its repeated administration induced sensitization. Both SCH 23390 (0.03 mg/kg SC) and haloperidol (0.4 mg/kg SC), dopamine D₁ and D₂ receptor antagonists, respectively, completely inhibited not only the acute stimulant effect of methamphetamine but also its sensitization when repeated methamphetamine was repeatedly combined with either of these drugs. Moreover, treatment with SCH 23390 2–5 h or haloperidol 1–5 h after each methamphetamine administration significantly antagonized methamphetamine sensitization. The maximal inhibitory effect was observed in the schedules of 3-h post-methamphetamine treatment for both drugs. However, treatments with SCH 23390 or haloperidol at 0.5 h, 6 h and 24 h after methamphetamine had no such inhibitory effect. The mice treated with SCH 23390 or haloperidol after each saline administration (the control administration for methamphetamine) did not show significant change in the sensitivity to methamphetamine. These results suggest that methamphetamine has an effect on both dopamine D₁ and D₂ receptors for several hours even after cessation of its acute stimulant effect, and that such an effect is involved in the induction of sensitization to the stimulant effect of methamphetamine on ambulation in mice.     

Chronic treatment with the D1 receptor antagonist,SCH 23390, and the D2 receptor antagonist,raclopride, in cebus monkeys withdrawn from previous haloperidol treatment

The effects of chronic treatment with dopamine (DA) D₁ and D₂ receptor antagonists were evaluated in eightcebus apella monkeys with mild oral dyskinesia after previous haloperidol treatment. SCH 23390 (D₁ antagonist) was given daily to investigate the direct behavioural effect during long-term treatment and the subsequent supersensitivity to DA agonists. Raclopride (D₂ antagonist) was investigated for comparison. All drugs were given subcutaneously. SCH 23390 and raclopride induced dystonic syndromes, catalepsy, sedation and reduced locomotor activity. The monkeys developed marked tolerance to the dystonic effect of SCH 23390, while they showed increased sensibility to the dystonic effect of raclopride. Baseline oral dyskinesia (24 h after injection) remained unchanged during D₁ antagonist treatment, while it increased during D₂ antagonist treatment. SCH 23390 induced supersensitivity to the oral dyskinesia- and grooming-inducing effects of SKF 81297 (D₁ agonist) after 9 weeks, while the subsequent treatment with raclopride induced supersensitivity to the reactivity- and stereotypy-inducing effects of quinpirole (D₂ receptor agonist) after 3 weeks. Because of the possibility of a carry-over effect (SKF 81297-induced oral hyperkinesia and grooming), other changes in raclopride-induced behaviours cannot be ruled out. The development of tolerance to the dystonic effect of SCH 23390 and the unchanged baseline oral dyskinesia during SCH 23390 treatment indicate an advantageous profile of side effects of DA D₁ receptor blockade.     

Increased dopamine receptor sensitivity in the rat following acute administration of sufentanil,U50,488H and d-Ala2-d-Leu5-enkephalin

Summary The effects of acutely administered opioid receptor agonists sufentanil, U50,488H and [d-Ala², d-Leu⁵]-enkephalin (DADL) were observed upon dopamine D₁ and D₂ binding site density in the striatum of the rat. In addition, the functional implications of opioid-induced changes in dopamine receptor sensitivity were studied using the behavioural profile elicited by apomorphine in the rat. The -agonist sufentanil (1 or 20 Erg/kg, i. p.), the -agonist U50,488H (10 mg/kg, i. p.) and DADL (1 g/animal, i. c. v.) all significantly elevated D₂ but not D₁ binding site density in rat striatum. Pretreatment with sufentanil (1 g/kg, i. p.) induced an elevation in apomorphine-induced sterotyped behaviour, but attenuated locomotor activity. Following administration of U50,488H (10 mg/kg, i. p.), both the degree of stereotypy and the intensity of the locomotor activity were enhanced. Contralateral rotation was observed in animals pretreated with DADL (1 g/animal, i. c. v.) following challenge with apomorphine. It is concluded that the opioid agonists studied induce a significant elevation in functional D₂ sites to the exclusion of D₁ sites. However, the precise mechanism by which this effect is elicited remains to be established. Send offprint requests to R. D. E. Sewell at the above address     

Neonatal administration of N-omega-nitro-L-arginine induces permanent decrease in NO levels and hyperresponsiveness to locomotor activity by D-amphetamine in postpubertal rats

Nitric oxide (NO) is associated with dopamine (DA) release. Previously, we demonstrated that rats treated with a non-selective nitric oxide synthase inhibitor, N-omega-nitro-l-arginine (l-NNA) at postnatal days 4-6 (PD4-6) show increased locomotion and disrupt neuronal cytoarchitecture after puberty (PD60). Here, we investigate whether the modulation of NO production in rats at PD4-6 causes long term changes of NO system, its impact on DA innervation, and schizophrenia-like behaviors. NO levels were measured in seven brain areas at PD35, PD60, PD90, and PD120. Autoradiographic studies explored the effect of l-NNA on the expression of D₁ and D₂ receptors in the caudate-putamen (CPu) and nucleus accumbens (NAcc) at PD60. Locomotor activity was assessed at PD60 using the non-selective DA agonists, amphetamine and apomorphine, and the selective DA receptor agonist [D₂, quinpirole; D₃, 7-hydroxy-N,N-di-n-propylaminotetralin ((±)-7-OH-DPAT)]. l-NNA treatment produced decreases in NO levels in the frontal cortex, striatum, brainstem and cerebellum, while in the occipital cortex changes were observed at PD120. Hippocampus and temporoparietal cortex showed differential levels of NO. Receptor autoradiography revealed increases in D₁ receptor levels in the NAcc (shell), while decreases in D₂ receptor binding were observed in the CPu and NAcc (core). Amphetamine and quinpirole treatments resulted in increases in locomotion. In contrast, treatment with 7-OH-DPAT produced hypolocomotion at low doses, while increased locomotion was seen at the highest dose. These results show that modulation of NO levels early postnatally (PD4-6) produces long term alteration in NO levels, with possible consequences on DA transmission, and related behaviors relevant to schizophrenia.     

Cholinergic, dopaminergic and insulin receptors gene expression in the cerebellum of streptozotocin-induced diabetic rats: Functional regulation with Vitamin D3 supplementation

The study was to find out the effect of Vitamin D₃ supplementation on preventing the altered gene expression of cholinergic, dopaminergic, insulin receptors and GLUT3 gene expression in cerebellum of diabetic rats. Radioreceptor binding assays and gene expression were done in the cerebellum of male Wistar rats. Rota rod has been used to evaluate motor coordination. Our results showed a significantly increased gene expression of dopamine D2, muscarinic M1, M3, α7 nicotinic acetylcholine, insulin receptors, acetylcholine esterase, GLUT3 and Vitamin D receptor in the cerebellum of diabetic rats. There was a down-regulation of dopamine D1 receptor. Total dopamine receptor showed a decreased and total muscarinic, muscarinic M1 and M3 receptors showed an increased binding parameter, B_max. Rota rod experiment showed a significant decrease in the retention time on the rotating rod in diabetic while treatment improved retention time near to control. Vitamin D₃ and insulin treatment markedly recovered the altered gene expression and binding parameters to near control. Our study showed Vitamin D₃ functional regulation through dopaminergic, cholinergic and insulin receptors and glucose transport mechanism through GLUT3 in the cerebellum of diabetic rats which play a major role in neuroprotection in diabetes which has clinical application.     

Behavioral effects of selective and nonselective dopamine agonists on young rats after irreversible antagonism of D1 and/or D2 receptors

In general, preweanling and adult rats respond similarly when challenged with competitive dopamine (DA) agonists or antagonists. In contrast, results using a noncompetitive antagonist suggest that the D₁ and D₂ receptor systems of preweanling and adult rats differ in some critical way. To further assess this phenomenon, the behavioral effects of irreversible receptor blockade were assessed across 8 days in NPA (a nonselective DA agonist), quinpirole (a D₂ agonist), or SKF 38393 (a D₁ agonist) treated 17-day-old rat pups. The irreversible antagonist N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) did not block the locomotor activity and rearing of NPA- or quinpirole-treated rat pups, nor did EEDQ reduce SKF 38393-induced grooming. Moreover, pretreatment with EEDQ appeared to potentiate the normal increases in locomotor activity and rearing produced by NPA, but only when D₂ receptors were not protected by a previous injection of sulpiride (a D₂ antagonist). Taken together, these results are consistent with the presence of large reserves of D₁ and D₂ receptors in the preweanling rat pup.