beta-endorphin and Muscle-Rigidity

A variety of behavioral tests were used to characterize the cataleptic state induced by various treatments. Besides catalepsy, posture, locomotion, rigidity and the presence of reflexive responses were assessed. Measures of analgesia and body temperature were taken. The behavioral profiles of beta-endorphin, morphine, etonitazene, haloperidol, arecoline and GABA were compared at the time maximal catalepsy scores were obtained. Results indicated that, for an equivalent degree of catalepsy, the profile of beta-endorphin was similar to that of opiates, except for changes in body temperature; beta-endorphin's profile differed markedly from that of haloperidol, arecoline and GABA. Catalepsy was less pronounced with the latter two drugs. There were similarities in the behavioral profile of haloperidol and arecoline.

Topics: Analgesia; Animals; Behavior, Animal; beta-Endorphin; Body Temperature; Catalepsy; Endorphins; Humans; Male; Morphine; Motor Activity; Muscle Rigidity; Posture; Rats; Rats, Inbred Strains

In previous studies, we had found that opioid receptors in the striatum can mediate muscular rigidity which can be recorded as a tonic EMG activity in the gastrocnemius-soleus muscle of rats. We have now tried to evaluate the type of opioid receptors mediating the EMG activity. For this purpose, opioids regarded to be selective agonists at one type of opioid receptors were injected into the striatum of unanesthesized rats. Morphine, a micro-type agonist, in the dose of 40 nmol induced a pronounced EMG activity, while 10 to 40 nmol of [D-Ala2, D-Leu5] enkephalin, a delta-type agonist, led to no or little effect, respectively. beta-Endorphin, which reacts with the epsilon -type of receptors, was completely ineffective in doses of 3 or 15 nmol. The benzomorphan compound Mr 2033-Cl, which is a kappa-type agonist, induced a moderate activity in the dose of 15 nmol; 3 nmol were ineffective. beta-Casomorphin-4 was the most potent of the drugs studied in our system, since 9 nmol induced a pronounced rigidity, which was naloxone-reversible (2 mg/kg i.p.). The doses of these opioids effective in comparison with their known in vitro potencies suggest that the rigidity is mediated by a group of striatal opioid receptors, which has some similarity to the micro-type, but also shows some differences. In contrast, haloperidol, injected either into the striatum (30 nmol) or systemically (2 mg/kg i.p.), did not induce any EMG activity, suggesting that a decrease in dopaminergic neurotransmission is not the primary mechanism inducing the rigidity. beta-LPH62-77 and beta-LPH66-77 (15 nmol) intrastritally] were also completely inactive.

Topics: Animals; beta-Endorphin; Caseins; Caudate Nucleus; Electromyography; Endorphins; Enkephalin, Leucine-2-Alanine; Enkephalins; Haloperidol; Male; Morphine; Muscle Rigidity; Peptide Fragments; Rats; Rats, Inbred Strains; Receptors, Opioid