Extracellular recording in rat area postrema in vitro and the effects of cholinergic drugs, serotonin and angiotensin II.
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.
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*
D010277:Parasympathomimetics; D000804:Angiotensin II; D012701:Serotonin; D004298:Dopamine