Administration of muscimol into the posterior hypothalamus reduces hyperthermia induced by hippocampal neostigmine injection

Abstract

The firing rate of the sympathetic nerves innervating interscapular brown adipose tissue (IBAT), IBAT and colonic temperatures ( T IBAT and T C) and oxygen (O 2) consumption were monitored in urethane-anesthetized male Sprague–Dawley rats. These variables were measured for 40 min before (baseline values) and 40 min after an injection of neostigmine (5×10 −7 mol in 1 μl of saline) into the hippocampus and a bilateral administration of a GABA a-agonist, muscimol (28 ng in 0.5 μl of saline, per side) into the posterior hypothalamus. The same variables were recorded in other rats, but the muscimol was replaced by saline. Control animals were used with muscimol or saline alone. The results show an increase of sympathetic firing rate, T IBAT, T C and O 2 consumption after neostigmine injection. Muscimol significantly reduces this enhancement. The findings suggest that hippocampus controls the sympathetic and thermogenic activation induced by neostigmine through an influence on GABAergic tone of the posterior hypothalamus.