Search

The cardiovascular activity of neurohypophyseal peptides has been investigated in conscious trout bearing an intracerebroventricular guide cannula and a permanent intraarterial catheter. Changes in diastolic pressure, systolic pressure and heart rate were monitored during the 25-min period following intracerebroventricular or intraarterial administration of arginine vasotocin and related neuropeptides, including arginine vasopressin, oxytocin, hydrin-2, mesotocin, isotocin and conopressin-S. Intracerebroventricular injection of increasing doses of arginine vasotocin (0.62-5 pmol) induced a dose-dependent increase of diastolic and systolic pressures. The onset of the response occurred within 3-5 min after intracerebroventricular administration of arginine vasotocin and the maximal increase was reached at 10-15 min. Central administration of vasopressin and oxytocin induced a significant rise in diastolic and systolic pressures at a dose of 5 pmol while hydrin-2 only caused a significant elevation of blood pressure at a dose of 50 pmol. Central administration of mesotocin, isotocin and conopressin-S (5-500 pmol each) had no significant effect on blood pressure. No changes in heart rate occurred after intracerebroventricular injection of any of the seven neuropeptides tested. Intraarterial injection of arginine vasotocin (50 pmol) induced a significant rise in blood pressure and bradycardia. Peripheral injection of the other neuropeptides did not cause any modification of the cardiovascular activity, whatever the doses administered (5-500 pmol). The V1A receptor antagonist [d(CH2)5, Tyr(OMe)2]arginine vasopressin had no intrinsic effect on blood pressure and heart rate when injected centrally (50 pmol) or in the peripheral circulation (200 pmol). At the same doses, [d(CH2)5, Tyr(OMe)2]arginine vasopressin reduced by 50 and 66%, respectively, the increase in blood pressure evoked by intracerebroventricular (5 pmol) or intraarterial (50 pmol) injections of arginine vasotocin.(ABSTRACT TRUNCATED AT 250 WORDS)

The present investigation assessed the ability of the neurohypophysial nonapeptide arginine vasotocin (AVT) to centrally regulate the cardiovascular activity in fish. Intracerebroventricular (ICV) injection of AVT (0.4 to 50 ng/kg b.wt.) in anesthetized trout resulted in a dose-related increase in blood pressure (BP) without any consistent changes in heart rate. For doses of AVT ranging from 2 to 50 ng/kg b.wt., BP remained elevated during at least 25 min after ICV injection. Systemic (intraarterial) administration of the same doses of AVT appeared to be less efficient than ICV injection, except for the highest dose (50 ng/kg) which evoked a similar rise in BP as that observed after ICV administration. In contrast to AVT, a high concentration of neuropeptide Y (10 micrograms/kg b.wt., ICV) caused only a slight increase of BP. The results suggest that AVT acts centrally to regulate BP in fish. These data, together with the widespread distribution of AVT-immunoreactive fibers and AVT binding sites in the brain, support the notion that, in fish, AVT may play neuromodulator and/or neurotransmitter functions.

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. The latency of the antidromic potentials ranged from 12 to 24 ms (17.46 +/- 3.10 SD) which gave a mean conduction velocity of 0.19 m/s, typical of unmyelinated nerve fibers. 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. 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. No statistical differences exist for the mean dorsal aortic pressure (DAP) between the four types of neurosecretory cell activity.

This study describes a technique which allows continuous recording of MUA (Multiple Unit Activity), from the NPO (Preoptic Nucleus), DAP (Dorsal Aortic blood Pressure) and ECG (Electrocardiogram) in freely swimming rainbow trout. From the 21 trout tested, six trout (29%) clearly showed rhythmic patterns of MUA during the five post-operative days (D2-D6). The mean length of rhythmic MUA was about 18 hr (range 6-33 hr) among the six trout during the recording days. Periodic MUA occurred approximately eight times/hr and lasted about 2 min. The maximal frequency of discharges was 20-30 spikes per sec. No change occurred in the mean level of blood pressure from the first operative day to the following post-operative days, where rhythmic MUA appeared or reappeared. These results demonstrate the existence of biorhythmicity within the NPO of freely swimming trout and suggest parallel oscillations in neurohormones secretion.

Although in most vertebrate species urotensin-II (UII) is synthesized in neurons of the central nervous system, little is known regarding the physiological actions of UII in the brain. We have investigated the effects of intracerebroventricular (ICV) administration of synthetic trout UII (1, 5, and 50 pmol) on total motor activity (ACT), ventilatory frequency (VF), ventilatory amplitude (VA), and heart rate (HR) in the unanesthetized trout. ICV injection of UII increased ACT in a dose-dependent manner, and the maximal effect was observed at a dose of 5 pmol. At doses of 1 and 5 pmol, UII did not affect VF, VA, or HR. At the highest dose tested (50 pmol), UII not only increased ACT, but also significantly activated VF, VA, and HR. In contrast, ICV injection of synthetic trout angiotensin-II (5 pmol) did not produce any effect on ACT, VF, or VA, but sharply increased HR. These data provide the first evidence that UII can act centrally to induce motor activity in a nonmammalian vertebrate species. [ABSTRACT FROM AUTHOR]