title: Effect of haloperidol on reflex activation of rat alpha-motoneurones. A possible explanation for akinesia and catalepsy?
abstract: Effects of haloperidol on rat flexor and extensor alpha-motoneurones were studied in ventral roots of laminectomized rats under halothane anesthesia. The alpha-motoneurones were activated by tetanic stimulation of low-threshold afferents (group I and II), either of the ipsilateral peroneal nerve ("flexor alpha-motoneurones") or gastrocnemius-soleus nerve ("extensor alpha-motoneurones"). Haloperidol, given in the doses of 0.075, 0.15 and 0.30 mg/kg i.p. inhibited the reflex activation of flexor alpha-motoneurones; higher doses seemed to be more effective than lower ones. Apomorphine (2 mg/kg s.c.) partially antagonized the inhibitory action of haloperidol with some latency. Higher doses of haloperidol (0.15-0.60 mg/kg i.p.) also inhibited the reflex activation of extensor alpha-motoneurones; this inhibitory effect was, at least for a short time, antagonized by apomorphine (2 mg/kg s.c.). The threshold for reflex activation both of flexor and extensor alpha-motoneurones was raised by haloperidol and lowered by a subsequent administration of apomorphine. Our results suggest that akinesia and catalepsy, induced in rats by haloperidol might be, at least in part, due to a decrease in sensitivity of alpha-motoneurones to proprioceptive stimuli.
mesh_terms: D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D002375:Catalepsy / Q000139:chemically induced* / Q000503:physiopathology; D006220:Haloperidol / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D009046:Motor Neurons / Q000187:drug effects*; D009069:Movement Disorders / Q000139:chemically induced* / Q000503:physiopathology; D051381:Rats; D012018:Reflex / Q000187:drug effects*; D013997:Time Factors
chemical_list: D006220:Haloperidol; D001058:Apomorphine