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

The firing rate of the sympathetic nerves innervating interscapular brown a dipose tissue (IBAT), IBAT and colonic temperatures (T-IBAT and T-C) and ox ygen (O-2) consumption were monitored in urethane-anesthetized male Sprague -Dawley rats. These variables were measured for 40 min before (baseline val ues) and 40 min after an injection of neostigmine (5X10(-7) mol in mul of s aline) into the hippocampus and a bilateral administration of a GABA(a)-ago nist, muscimol (28 ng in 0.5 mul of saline, per side) into the posterior hy pothalamus. The same variables were recorded in other rats, but the muscimo l 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 r educes this enhancement. The findings suggest that hippocampus controls the sympathetic and thermogenic activation induced by neostigmine through an i nfluence on GABAergic tone of the posterior hypothalamus. (C) 2000 Elsevier Science B.V. All rights reserved.