Effects of some depressant drugs on synaptic responses to glutamate at the crayfish neuromuscular junction

A comparison of the gastric and central nervous system effects of two substituted benzamides in normal volunteers

Eight healthy male volunteers participated in a single-blind, random allocation, crossover, comparison of intravenous metoclopramide (10 mg), the peripherally acting, gastrointestinal stimulant BRL 20627 (10 mg) and saline. The central nervous system effects were assessed by quantitative electroencephalography (EEG) and by visual analogue scales. Gastric motility and emptying were assessed by epigastric impedance. Metoclopramide increased the EEG amplitude by 10.4% (a statistically significant, P less than 0.05, effect) and increased frequencies above 22 Hz, whereas both BRL 20627 and placebo had only minor effect on the EEG frequencies and slightly decreased the EEG amplitude. Ratings on visual analogue scales showed that metoclopramide caused statistically significant (P less than 0.01 difference from placebo) restlessness and slight but significantly less (P less than 0.05 difference from placebo) feeling of happiness. Epigastic impedance changes indicated that both metoclopramide and BRL 20627 increased gastric contractile activity, but the rate of gastric emptying was not significantly altered by either drug although it tended to be shortened following metoclopramide but not BRL 20627 treatment. It is concluded that since the published animal data show that BRL 20627 has only weak dopamine antagonistic properties this study further implicates dopamine receptor blockade in the akathisia but not in the gastric effect of metoclopramide.

Aliphatic alcohols increase the decay rate of glutamate-activated currents at the crayfish neuromuscular junction

Excitatory junction currents produced by glutamate were recorded with an extracellular electrode at the excitatory neuromuscular junction of the crayfish. The currents decayed more quickly as the membrane was hyperpolarized. The direction of the voltage sensitivity of the decay phase is thus opposite to that found for acetylcholine-activated currents at the amphibian endplate. The aliphatic alcohols ethanol to octanol all increased the rate of decay of the currents. The effects of the short chain alcohols were opposite to their actions at the toad endplate, where ethanol to pentanol prolong the currents. This observation was explained in terms of the opposite direction of the voltage sensitivity in the two preparations. For each alcohol, the relationship between the half-decay time of the currents (t 1/2) and alcohol concentration was exponential. The potency of each alcohol in decreasing t 1/2 was exponentially related to carbon chain length, which would be predicted if the effects of the alcohols were directly related to their concentration in the lipid phase of the membrane. These findings are consistent with the ideas that the alcohols may alter membrane polarizability or change membrane fluidity in the vicinity of the channels.