title: Extracellular recording in rat area postrema in vitro and the effects of cholinergic drugs, serotonin and angiotensin II.
abstract: Spontaneous extracellular action potentials were recorded from rat area postrema explants in vitro for up to 6 h at 35 degrees C. Their geometric mean frequency was 4.4 +/- 1.7-11 Hz (n = 120) and they were most often recorded caudal to the obex. The frequency of spontaneously discharging units could be increased three-fold by raising the KCl concentration from 5 to 15 X 10(-3) M but a claimed non-specific excitant of neurones, L-glutamic acid at 10(-7)-10(-3) M was without effect. Carbamylcholine at 10(-9)-10(-7) M increased the frequency of spontaneous units (12/13 trials) as did 10(-7) M neostigmine sulphate (14/14 trials). The effects of carbamylcholine and neostigmine were additive and were blocked by atropine sulphate at 10(-6) M (18/18 trials). Atropine also stopped the discharge of spontaneous units while D-tubocurarine did not affect unit discharge frequency. It is suggested that units responding to cholinergic drugs have an afferent input from the dorsal vagus. A number of putative transmitters, serotonin (10(-9)-10(-7) M), angiotensin II (0.5 X 10(-10)-0.5 X 10(-9) M) and dopamine (10(-9)-10(-5) M) which on indirect grounds are thought to affect area postrema neurones, were without effect on unit discharge frequency.
mesh_terms: D000344:Afferent Pathways / Q000187:drug effects; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001933:Brain Stem / Q000187:drug effects*; D002552:Cerebral Ventricles / Q000187:drug effects*; D002831:Choroid Plexus / Q000187:drug effects; D004298:Dopamine / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects; D005110:Extracellular Space / Q000187:drug effects; D005260:Female; D008526:Medulla Oblongata / Q000187:drug effects; D010277:Parasympathomimetics / Q000494:pharmacology*; D051381:Rats; D012701:Serotonin / Q000494:pharmacology*; D009435:Synaptic Transmission / Q000187:drug effects*; D014630:Vagus Nerve / Q000187:drug effects; D014882:Water-Electrolyte Balance / Q000187:drug effects*
chemical_list: D010277:Parasympathomimetics; D000804:Angiotensin II; D012701:Serotonin; D004298:Dopamine