Post‐tetanic potentiation of the vascular neurogenic response in rats

Abstract

We have previously shown that, at least at frequencies of 4 Hz and above, a previous stimulation of the intramural vasoconstrictor nerves facilitates the subsequent response so that even maximal contractions can develop during periods of stimulation as short as a few seconds. In the present study the facilitating effect of a continuous nerve stimulation was quantitatively tested on 'single-twitch' responses to individual nerve impulses. Small arteries and veins (150-500 micron diameter) from rats were mounted in a myograph at known wall tension, and the intramural nerves were activated at frequencies between 0.1 and 32 Hz. After a period of continuous stimulation the single-twitch responses could be amplified 10-20 times, depending on frequency and duration of the continuous stimulation. No such amplification was observed after application of exogenous noradrenaline. The results therefore reflect a prejunctional frequency-dependent potentiating mechanism which can strongly reinforce sympathetic neuroeffector control. Furthermore, combined with previous data concerning adrenergic transmitter release, the present results seem to be more compatible with the view that the quantum of transmitter released from each varicosity upon activation is less than an entire granule.

Sympathetic transmission in small mesenteric arteries from the rat: highly calcium‐dependent at low stimulation rates

“…The response to successive trains of stimulation increased during the first 10-12 trains in 2.5 mM Ca2+. We have previously shown that this increase in response is a pre-junctional phenomenon (Nilsson 1984, Sjoblom et al 1987, Nilsson et al 1988. Reducing the calcium concentration to 1.0 mM reduced not only the amplitude of the contraction, but also the rate with which the successive responses increased.…”

Selective optogenetic control of Gq signaling using human Neuropsin

“…This may offer the possibility to investigate the mechanisms underlying the temporal superposition of contractions that have only scarcely been studied in smooth muscle tissues so far. Moreover, existing studies were largely dependent on indirect activation of smooth muscle cells via stimulation of intramural neuronal varicosities 61 – 63 .…”

Calcium dependency of the post‐stimulatory potentiation of the neurogenic response in small mesenteric arteries from the rat

“…Changes in total transmitter release, whether due to altered quanta1 release or altered probability of release, can therefore be reflected in the contractile response. We have previously shown that the post-stimulatory potentiation is a prejunctional phenomenon (Sjoblom et al 1987). The perivascular sympathetic nerves here release at least two transmitters, but the potentiation appears not to be due to a change in the ratio between the various transmitters released, since it seems to affect the adrenergic and nonadrenergic parts of the response to equal extent (Sjoblom-Widfeldt et al 1989).…”

“…With increasing frequency and number of pulses in the potentiating stimulation, the amplitude of subsequent responses is increased further (Sjoblom et al 1987), while the duration of the potentiation is only slightly affected. In other tissues, e.g.…”