The effects of strain differences and emotional status of rats on the behavioural and neurochemical effects of chronic treatment with apomorphine

Rat climbing behavior elicited by stimulation of cerebral dopamine receptors

The experimental conditions allowing to elicit by administration of dopamine agonists a climbing behavior in rats, apparently analogous to the stereotyped cage climbing behavior previously described in mice (Protais et al. 1976), have been established. Among the various strains of rats studied i.e. Sprague-Dawley, Long Evans and Wistar, the latters were selected as the most responsive to the dopamine agonist apomorphine. However, even in the Wistar strain, only about 60% of animals responded to a test-dose of 0.4 mg/kg apomorphine by adopting in a sustained manner the typical upright position against the walls of a suitable experimental cage. Hence responsive rats were preselected 4 days before the experimental sessions and finally rated during a 60-min observation period. Increasing the test-dose of apomorphine led to a biphasic effect, the spontaneous climbing behavior being decreased at low dosage and, then, both the percentage of climbing animals and the duration of the behavior were progressively increased at higher dosages. A scoring system based on an all-or-none evaluation of the frequency of stereotyped climbing episodes over the 1 h observation period was finally adopted allowing to establish dose response curves to apomorphine and its more potent derivative N-propylnorapomorphine. Dexamphetamine (associated to L-Dopa) also produced the stereotyped climbing behavior. The latter was completely abolished in animals treated with the "atypical" antipsychotic sulpiride. The effects of lesioning various cerebral dopaminergic areas on the apomorphine-induced behavior were investigated. The response was not significantly altered following bilateral thermocoagulations of the striatum (restricted lesions), globus pallidus, nucleus interstitialis of the striae terminalis, amygdala, nucleus lateralis septi or nucleus accumbens.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of daily dose of chronic haloperidol and chronic apomorphine on behavioral hypersensitivity in the rat

Behavioral hypersensitivity in the rat consisting of increased dopamine-mediated stereotypic behaviors has been found to follow a 10-day course of treatment with the neuroleptic haloperidol as well as with the direct dopamine agonist apomorphine. The daily dose versus response relationship for chronic haloperidol indicates that a threshold daily dose exists and that behaviors increase with increasing daily dose. On the other hand, low rather than high daily doses of chronic apomorphine induce behavioral hypersensitivity and the response decreases with increasing daily dose. Prolonged functional denervation of striatal postsynaptic dopamine receptors by either neuroleptic blockade or autoreceptor stimulation may explain these findings. The results may help elucidate the relative risk of daily neuroleptic dose on tardive dyskinesia development and indicate a possible mechanism for chronic agonist-associated side effects like L-Dopa dyskinesias.

Role of adrenal medulla in morphine-induced hyperthermia through central action

The role of the adrenal glands, in morphine-induced hyperthermia was studied in normal, chemically-sympathectomized, adrenalectomized, adrenal-demedullated or splanchnicotomized rats. 2. In restrained female rats, 5 mg/kg morphine produced hyperthermia whereas 20 mg/kg and 40 mg/kg produced hyperthermia. 3. After adrenalectomy, 5 mg/kg morphine did not produce hyperthermia. 4. After adrenal-demedullation or adrenal-denervation (splanchnicotomy), 5 mg/kg morphine did not produce hyperthermia. 5. The results suggest that, in the rat, the adrenal medulla plays an important role in morphine-induced hyperthermia, and that morphine acts centrally to stimulate the medulla.

Bole of adrenals in morphine-induced hyperthermia in restrained rats

Bole of adrenals in morphine-induced hyperthermia was studied in normal, neurotransmitter antagonist-pretreated, chemical-sympathectomized, adrenalectomized or adrenal-demedullated rats. In restrained female rats, 5 mg/kg morphine produced hyperthermia whereas 20 mg/kg and 40 mg/kg produced hypothermia. Pretreatment with either phenoxybenzamine, propranolol, pentolinium or scopolamine inhibited the hyperthermia. After adrenalectomy, neither 5 mg/kg nor chronic administration of 20 mg/kg morphine produced previously demonstrated hyperthermia. After adrenal-demedullation, a dose of 5 mg/kg morphine also did not produce hyperthermia. In contrast to female rats, restrained male rats showed no significant effect on body temperature after 5 mg/kg morphine, requiring 20 mg/kg and 40 mg/kg morphine to produce hyperthermia. In adrenalectomized male rats, 20 mg/kg morphine did not produce the usual hyperthermia. The results suggest that male rats are more resistant to the hyperthermic effects of morphine than female rats and that in the rat, the adrenals, likely the medulla, play an important role in morphine-induced hyperthermia.

Two dissociable components of behavioral sensitization following repeated amphetamine administration

The acute administration of moderate to high doses (greater than 2 mg/kg) of amphetamine (AMPH) to rats produces a multiphasic behavioral response consisting of an initial period of locomotor activity followed by episodes of intense stereotyped behavior, and a period of post-stereotype locomotion. Repeated administration of the drug results in a sensitization with two components: more rapid onset of stereotypy and enhancement of the post-stereotype locomotor activity. The studies presented below provide converging evidence that the two components of the sensitization are dissociable. 1. Rats from ten different strains or suppliers all exhibited more rapid onset of stereotypy following repeated AMPH pretreatment, whereas only five of these strains or supplier groups exhibited significantly enhanced poststereotypy locomotion. 2. The time course differed for the development of these two components of the sensitization. 3. The recovery from sensitization differed for these two components of the behavioral response. Following withdrawal of the drug, post-stereotypy motor activity diminished within 2 months while the more rapid onset of stereotypy persisted for at least 3 months. These observations have particular relevance to future studies directed at specifying the biochemical substrates of the sensitization.