Central and peripheral serotonergic control of forestomach motility in sheep

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Abstract
Sorraing, J.‐M., Fioramonti, J. & Bueno, L. Central and peripheral serotonergic control of forestomach motility in sheep. J. vet. Pharmacol. Therap. 8, 312–319. Participation of tryptaminergic receptors in the control of forestomach motility was investigated in conscious sheep using strain‐gauges and chronically implanted electrodes. Two hours after feeding the sheep, serotonin (5‐HT) was infused into the jugular vein (i.v.), or the carotid artery (i.e.), or into the lateral cerebral ventricles (i.e.v.), over a 10‐tnin period. An i.v. dose of 16 μg/kg/min abolished the cyclic propagated contractions throughout the forestomach, increased ruminoreticular tone, and induced simultaneous contractions of all the parts of the rumen. A dose of 1.6 μg/kg/min i.c. or i.v. 5‐HT inhibited phasic contractions. The effects of 5‐HT were blocked completely by i.c.v. administration of methysergide (20 μg/kg) and imipramine (200 μg/kg), and blocked partially by naloxone (25 μg/kg), but unaffected by atropine (50 μg/kg). The inhibitory effects of i.v. 5‐HT were antagonized by methysergide (200 μg/kg, i.v.) but unaffected by imipramine (2 mg/kg, i.v.) and atropine (250 μg/kg, i.v.). Only the i.v. administration of methysergide blocked the inhibition induced by i.c. infusion (1.6 μg/kg/min) of 5‐HT. It is suggested that 5‐HT exhibits an inhibitory control on forestomach phasic contractions through hypothalamic and bulbar 5‐HT receptors, and exerts peripheral excitatory effects on the tone of the rumen wall. Dr L. Buéno, Station de Pharmacologie‐Toxicologie, INRA, 180 chemin de Tournefeuille, 31300 Toulouse, France.