Effects of alpha-adrenergic blocking agents on stereotyped behavior induced by apomorphine in rats

1. The effects of alpha-adrenergic blocking agents on stereotyped behavior induced by apomorphine in rats were studied. 2. Pretreatment of rats with 5 and 10 mg/kg of phenoxybenzamine or phentolamine displaced the dose-response curves for apomorphine-induced stereotypy to the left in a dose dependent manner. The ED50 for apomorphine was reduced from 1.92 +/- 0.38 (mean +/- SEM) to 0.63 +/- 0.08 by 10 mg/kg phenoxybenzamine and from 1.92 +/- 0.38 to 0.61 +/- 0.10 by 10 mg/kg phentolamine. 3. These results support the view that the expression of dopaminergic-induced stereotyped behavior is dependent on noradrenergic activity in the central nervous system.

Effects of withdrawal from long-term barbital treatment on open-field behaviour and seizure susceptibility of rats

Rats withdrawn from long-term barbital treatment were tested both for their activity in an open-field and for their sensitivity to convulsant stimuli. Barbital withdrawal induced a significant increase on locomotion and rearing frequency. Drug removal also made the rats more sensitive to convulsions elicited by sound and maximal electroshock. A positive correlation was found between locomotion plus rearing frequency and audiogenic-induced seizures 3, 4 and 5 days after barbital withdrawal. The results show that exploratory behaviour evaluated through the open-field method can be used as a reliable method to show barbital withdrawal in rats. Taken together, the results suggest that long-term barbital treatment might develop a supersensitivity state, in noradrenergic neurons in the central nervous system.

A quantitative study of cholinergic-dopaminergic interactions in the central nervous system

The effects of cholinergic (Ach) and anti-Ach drugs on stereotyped behavior induced by apomorphine administration were studied quantitatively. Dose-response curves were constructed to apomorphine and the horizontal shifts of the experimental curves induced by the different treatments were measured at the level of ED50 of apomorphine. Treatment with both atropine sulfate and scopolamine hydrobromide induced a leftward displacement of the dose-response curve; physostigmine and oxotremorine displaced the curve to the right. Changes in stereotypy were not observed after atropine methyl nitrate. It is concluded that the activity of acetylcholine-containing neurons may exert a modulatory influence on dopaminergic systems.

The effects of scopolamine pretreatment on stereotyped behavior induced by apomorphine in rats withdrawn from long-term haloperidol administration

1. The effects of scopolamine on intensity of stereotyped behavior induced by the ED50 dose of apomorphine in controls and in animals withdrawn from long-term haloperidol treatment were studied. 2. Doses of 1.0 and 3.0 microgram/kg of scopolamine increased apomorphine-induced stereotypy in both groups. However, this increase was smaller in the haloperidol-treated than in the control animals. 3. These data support the hypothesis that long-term administration of haloperidol may produce a change not only in dopaminergic but also in central cholinergic receptor sensitivity.