Patterns of spontaneous unit preoptic neurosecretory cell discharges in the rainbow trout, Salmo gairdneri

Abstract

1. 1. Extracellular antidromic potentials recorded from the neurosecretory cell body were characterized by the following criteria: constant latency, the ability to follow a high frequency rate of stimulation and the collision test. 2. 2. The latency of the antidromic potentials ranged from 12 to 24ms (17.46 ± 3.10 SD) which gave a mean conduction velocity of 0.19 m/s, typical of unmyelinated nerve fibers. 3. 3. Two components could be clearly distinguished in the antidromic potential. A small “A” spike which showed constant latency and a large “B” spike with a variable latency and amplitude. A delay of 6.5 ms between the two spikes could occur and sometimes the “B” spike was blocked leaving only the “A” spike. 4. 4. Four patterns of spontaneous activity seem to emerge: Type I (26% of units, M ± SD = 0.77 ± 0.32 sp/s) corresponds to a slow and irregular pattern of activity; Type II (28% of units, M = 1.58 ± 0.47 sp/s) is hard to classify and may be related to an irregular bursting pattern of activity; Type III (28% of units, M = 2.59 ± 1.19 sp/s) corresponds to a continuous pattern of activity; Type IV (18% of units) represents a rhythmic pattern of activity with an active phase of about 3 min (M = 2.42 ± 0.90 min), a silent phase of about 4 min (M = 3.89 ± 3.02 min) and a maximal frequency of unit discharge in the range 2–18 sp/s. 5. 5. No statistical differences exist for the mean dorsal aortic pressure (DAP) between the four types of neurosecretory cell activity.