Effects of acetylcholine and GABA on neurons in the area postrema of Suncus murinus brainstem slices

Slices (400 microm) containing the area postrema were prepared from three Japanese house musk shrews. Data reported are from 16 representative units. Units fell into one of three separate groups with spontaneous firing rates of 36-41/s, 16-18/sec. and 6-8/sec., possibly reflecting different set points of an endogenous pacemaker. Most neurons did not respond to ionophoresis of GABA or ACh. In those that did, ACh briefly increased spike frequency in a dose-dependent manner. The firing pattern suggests that the membrane potential was depolarized strongly, coupled with an extremely large conductance increase. Bath perfusion of curare, but not atropine, inhibited the response. Ionophoresis of GABA caused strong inhibition. The data show Suncus AP contains neurons that are sensitive to nicotine and GABA and may be emetogenic.