GABA(A) receptor modulation of temperature sensitive neurons in the diagonal band of Broca in vitro

Several regions of the brain, including the horizontal limb of the diagonal band of Broca (HDB), contain neurons that are responsive to changes in loc al temperature. These neurons are hypothesized to participate in thermoregu lation and sleep-wake control. The HDB contains a large number of gamma-ami nobutyric acid (GABA) terminals, and it has many neurons that utilize GABA as a neurotransmitter. Therefore, in this study we characterized the in vit ro effects of the GABA(A) receptor agonist muscimol (0.5, 0.25, 0.1 and 0.0 625 mu M doses) and the GABA, receptor antagonist bicuculline (3.0 and 1.0 mu M doses) on the firing rate and thermosensitivity of HDB neurons. Of the 51 neurons recorded in a submerged slice chamber, 53% were warm sensitive, 45% were temperature insensitive and 2% were cold sensitive. All neurons e xposed to bath applied muscimol exhibited reductions in both firing rate an d thermosensitivity. Muscimol induced reductions were maintained for at lea st 20 min after washout. Neurons exposed to bicuculline had no change in fi ring rate or thermosensitivity. However, after bicuculline washout there we re reductions in both firing rate and thermosensitivity. These findings sup port the hypothesis that GABA, receptor induced inhibition of HDB thermosen sitive neurons can modulate both thermoregulation and sleep-wake control. ( C) 1999 Published by Elsevier Science B.V. All rights reserved.