Electric muscle stimulation in the spontaneously hypertensive rat induces a post-stimulatory reduction in activity: role of different opioid receptors.
We have previously shown that prolonged low-frequency muscle stimulation, inducing contractions of the gastrocnemius muscle, in conscious spontaneously hypertensive rats leads to an opioid-mediated post-stimulatory reduction in blood pressure and analgesia. In the present study we investigated whether muscle stimulation would also induce a post-stimulatory reduction in behavioural activity in the spontaneously hypertensive rats. Selective opioid receptor antagonists were used to analyse the involvement of endogenous opioids. Muscle stimulation, lasting 60 min, induced a post-stimulatory sedation that outlasted the stimulation for hours. Sniffing, locomotor activity and total behavioural activity were significantly reduced. The post-stimulatory reduction in activity was reversed back to control levels by a high dose of naloxone (15 mg kg-1 i.v.). The selective mu-receptor antagonist beta-funaltrexamine, given intracerebroventricularly before stimulation, did not influence the development of the post-stimulatory drop in activity. The delta-receptor antagonist ICI 154,129 had no effect at all on the already developed sedation, whereas MR 2266 BS, a kappa-receptor antagonist (3 mg kg-1 i.v.), completely reversed the drop in activity. These results show that muscle stimulation gives rise to an opioid-mediated post-stimulatory reduction in activity in spontaneously hypertensive rats. The results also indicate the involvement of the opioid kappa-receptor in the behavioural response.
Hoffmann
P
P
Department of Physiology, University of Gothenburg, Sweden.
Skarphedinsson
J O
JO
Thorén
P
P
D000818:Animals; D001575:Benzomorphans / Q000494:pharmacology; D004558:Electric Stimulation; D006973:Hypertension / Q000503:physiopathology* / Q000523:psychology; D008297:Male; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology*; D009132:Muscles / Q000503:physiopathology; D009270:Naloxone / Q000494:pharmacology; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology*
D001575:Benzomorphans; D011957:Receptors, Opioid; D009270:Naloxone; C027247:MR 2266; D009271:Naltrexone; C024524:beta-funaltrexamine