The effects of physostigmine on synaptic transmission in the inferior mesenteric ganglion of guinea-pigs.
1. Synaptic potentials were recorded with intracellular electrodes from cells in the inferior mesenteric ganglion of the guinea-pig.2. Half-widths of the synaptic potentials recorded fell into two groups: type L cells had long synaptic potentials (11.6-15.2 msec) and low thresholds (14.6 mV mean), type S cells had short synaptic potentials (6.1-9.3 msec) and high thresholds (29.9 mV mean).3. Physostigmine (1.2 x 10(-6)M) caused a significant increase in the half-width of both types of synaptic potential.4. Physostigmine caused a significant increase in the half-width of spontaneous synaptic potentials and an increase in their amplitude.5. Repetitive preganglionic stimulation, in the presence of physostigmine, led to a marked and prolonged depolarization in all cells. In most cells repetitive spontaneous firing of action potentials was then observed. This effect was blocked by atropine (1.4 x 10(-7)M).6. The effect of atropine on the half-width in a physostigmine-treated cell was inconsistent: although synaptic potentials in some cells were slightly shortened their half-widths were always greater than the control.7. It is concluded that cholinesterase plays a role in limiting the time course of the synaptic potential, by limiting the duration of action of acetylcholine.
D000109:Acetylcholine / Q000096:biosynthesis; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D002802:Cholinesterases / Q000502:physiology; D004558:Electric Stimulation; D004566:Electrodes; D005725:Ganglia, Autonomic / Q000187:drug effects*; D006168:Guinea Pigs; D008564:Membrane Potentials / Q000187:drug effects; D008839:Microelectrodes; D009431:Neural Conduction / Q000187:drug effects*; D010830:Physostigmine / Q000494:pharmacology*; D013431:Sulfates; D013569:Synapses / Q000187:drug effects*; D013997:Time Factors
D002800:Cholinesterase Inhibitors; D013431:Sulfates; D001285:Atropine; D010830:Physostigmine; D002802:Cholinesterases; D000109:Acetylcholine