Long-term haloperidol-treatment of mice: a change in beta-adrenergic receptor responsiveness

Evaluating early preventive antipsychotic and antidepressant drug treatment in an infection-based neurodevelopmental mouse model of schizophrenia

Current pharmacotherapy of schizophrenia remains unsatisfactory with little hope for complete functional restoration in patients once the disease has developed. A preventive approach based on intervention in the prodromal stage of the disease aiming to preserve functional integrity by halting the progress of the disease is therefore extremely attractive. Here, we investigated the effects of preventive antipsychotic or antidepressant drug treatment in a well-established neurodevelopmental mouse model of multiple schizophrenia-related abnormalities. Pregnant mice on gestation day 9 were exposed to the viral mimic polyriboinosinic-polyribocytidylic acid (2 mg/kg, intravenously) or corresponding vehicle treatment, and the resulting offspring from both prenatal treatment conditions were subjected to chronic antipsychotic (haloperidol or clozapine), antidepressant (fluoxetine), or placebo treatment during the periadolescent stage of development. The effects of the preventive pharmacotherapy on behavioral and pharmacological functions were then investigated in adulthood using paradigms relevant to schizophrenia, namely prepulse inhibition, latent inhibition, and sensitivity to psychostimulant drugs. We show that periadolescent treatment with the reference antipsychotic and antidepressant drugs can successfully block the emergence of multiple psychosis-related behavioral and pharmacological abnormalities in subjects predisposed to adult brain pathology by exposure to prenatal immune challenge. At the same time, however, our study reveals numerous negative influences of the early pharmacological intervention on normal behavioral development in control subjects. Hence, even though preventive pharmacotherapy may be beneficial in individuals with predisposition to psychosis-related brain dysfunctions, chronic antipsychotic or antidepressant drug treatment in false-positive subjects is associated with substantial risk for long-term behavioral disturbances in adulthood.

Chronic treatment with chlorpromazine, thioridazine or haloperidol increases striatal enkephalins and their release from rat brain

The aim of this paper is to study the effect of 1, 2 or 3 months' administration of chlorpromazine (CPZ), thioridazine (TDZ) (2 or 6 mg/kg) or haloperidol (HAL) (0.25 or 1 mg/kg) IP on the level of leu- and met-enkephalin (ENK) in striatum. A dose- and time-dependent increase of striatal ENK level was observed after chronic administration of the neuroleptics (NL), but 8 days after withdrawal of chronically administered NL striatal ENK was decreased. Apomorphine pretreatment significantly attenuated the elevation in ENK produced by chronic injections of NL. In perfusion fluid obtained from the lateral ventricle of animals treated 1 month with HAL a dose-dependent increase of ENK levels was observed, which was augmented by potassium ions. It is concluded that: 1) Chronic administration of neuroleptic drugs that block dopamine receptors increases the level and the release of striatal enkephalins; 2) The results support the hypothesis that activation of dopaminergic neurons tonically inhibits the synthesis of enkephalins in the striatum.

The effect of chronic haloperidol treatment on some cardiovascular parameters in cats

Blood pressure, heart rate and evoked cardiovascular reflexes were examined in cats following chronic treatment with haloperidol, at a dose of 1 mg kg-1 per day, orally for 23 days. Five days after the final dose the animals were anaesthetized and tested for their reaction to various cardiovascular stimuli and to a number of agonist and antagonist drugs, given both intravenously and into the vertebral artery. It was found that treatment with haloperidol caused hypertension in the cats, as well as a potentiation of the pressor response to bilateral carotid occlusion. The response to 30 degrees head-up tilting was also altered so that in treated cats, the blood pressure returned to normal more rapidly during the tilt. There was no difference in the heart rate of the two groups of cats, nor in the pressor response to intravenous noradrenaline or angiotensin II or to afferent brachial nerve stimulation, nor was the depressor action of bradykinin altered. Hexamethonium reduced the blood pressure in both control and treated cats to approximately the same level. Blood O2, CO2, pH and bicarbonate levels were also unaltered by the treatment, as was plasma renin activity. Of the drugs given into the vertebral artery, only noradrenaline, prazosin, ketanserin and haloperidol caused a significantly greater fall in blood pressure in treated than in control cats, while clonidine and St91 were equally effective in both groups. These results suggest that haloperidol treatment has caused a greater modulation of central alpha 1- than of alpha 2-adrenoceptors.

Chronic haloperidol and adrenergic receptor sensitivity in the rat

Rats were administered haloperidol (3-4 mg/kg/day) in their drinking water for 42 days, and experiments conducted on the seventh day of withdrawal. Anaesthetized haloperidol treated rats exhibited a similar mean blood pressure (BP) and heart rate (HR) response to control rats when challenged with phenylephrine (IV). When similarly pretreated rats were challenged with one of four possible doses of clonidine (IV), haloperidol treated rats were less sensitive than control rats to clonidine's hypertensive action, but there were no effects of treatment on the hypotensive (BP) effect of clonidine nor on its bradycardic effect. When one of six possible doses of tyramine was administered a similar mean BP response was seen in both treatment groups, but the positive HR response in the haloperidol-treated group was much less than in the vehicle-treated group. Atria isolated from haloperidol treated or control rats revealed a similar chronotropic response to noradrenaline and tyramine challenge. These data indicate that chronic haloperidol does not cause a generalized change in alpha-adrenergic receptor sensitivity. Nevertheless, it is clear that haloperidol has produced changes in the cardiovascular response of rats to these drugs.

BehavioraL and biochemical changes caused by muscimol in mice withdrawN from haloperidol administration

This study was designed to determine the behavioral and biochemical effects of the gamma-aminobutyric acid (GABA) agonist, muscimol, in mice withdrawn from chronic haloperidol administration. Mice received either haloperidol or vehicle In their drinking water for 35 days, after which the haloperidol was replaced with vehicle. Seven days after withdrawal from chronic treatment with haloperidol, the effect of apomorphine on the climbing behavior of haloperidol-withdrawn mice was markedly enhanced as compared to control mice that received only vehicle. Muscimol produced a dose-related reduction in the intensity of climbing behavior induced by apomorphine in both control and haloperidol-withdrawn mice. However, the inhibition of climbing behavior induced by muscimol was significantly greater in haloperidol-withdrawn animals. In addition, in haloperidol-withdrawn mice, muscimol produced a significant reduction in striatal homovanillic (HVA) levels with no change in striatal dopamine (DA) levels, suggesting a decrease in DA turnover. In support of this conclusion, muscimol decreased the disappearance of dopamine in haloperidol-withdrawn mice that were injected with alpha-methyl-p-tyrosine. Both the behavioral and biochemical effects of muscimol were blocked by the GABA antagonist, picrotoxin. These results indicate that after chronic haloperidol administration there is not only an enhanced response to dopaminergic agonists but also to GABAergic agonists.

Influence of age on the effects of chronic fluphenazine on receptor binding in rat brain

The effects of age on alterations in brain dopaminergic (spiperone), beta-adrenergic (DHA), alpha-adrenergic (WB-4101), and cholinergic (QNB) binding induced by chronic administration of fluphenazine was studied in the rat. Compared to age-matched saline controls, older-age (25 month) fluphenazine rats showed: (a) a similar percent increase in specific spiperone binding (at 0.1 nM) but a slightly smaller increase in the Bmax of spiperone binding in the striatum than younger fluphenazine-treated rats; (b) a substantially greater increase in the Bmax of DHA binding and a slightly greater increase in Bmax of WB-4101 binding in the cerebral cortex than younger fluphenazine-treated rats. There was no significant interaction of age with the effect of chronic fluphenazine on QNB binding in rat striatum.

Changes of response to dopaminergic drugs in rats submitted to REM-sleep deprivation

Three experiments were performed in order to add further support to the hypothesis that the exaggerated aggressiveness elicited by apomorphine in REM sleep deprived rats was due to a state of supersensitivity of post-synaptic dopaminergic receptors in brain. In the first experiment, REM deprived rats displayed much aggressiveness when challenged with 10 and 20 mg/kg of bromocriptine and piribedil. Thus, the intensification of responses by REM sleep deprivation is not restricted to apomorphine, as it was also obtained with two other dopaminergic agonists. In the second experiment, the association of REM deprivation with an injection of haloperidol 24 h before apomorphine administration induced still more aggressive behavior when compared to the rats that were only sleep deprived. It has been claimed that 24 h after haloperidol a state of supersensitivity to dopamine agonists occurs in the brain; therefore, it is probable that REM deprivation could also act similarly. The third experiment showed that haloperidol administered 2 h before apomorphine administration blocked the aggressive behavior in rats either submitted to REM deprivation alone or to REM deprivation plus a previous injection of haloperidol 24 h before. This also favors the proposed hypothesis. Alternative possibilities for explaining the observed hyperresponsiveness of REM deprived rats to apomorphine and other dopaminergic agonists are also analysed.