Pinacidil induces vascular dilation and hyperemia in vivo and does not impact biophysical properties of neurons and astrocytes in vitro

Abstract

Vascular and neural systems are highly interdependent, as evidenced by the wealth of intrinsic modulators shared by the two systems. We tested the hypothesis that pinacidil, a selective agonist for the SUR2B receptor found on smooth muscles, could serve as an independent means of inducing vasodilation and increased local blood volume to emulate functional hyperemia. Application of pinacidil induced vasodilation and increased blood volume in the in vivo neocortex in anesthetized rats and awake mice. Direct application of this agent to the in vitro neocortical slice had no direct impact on biophysical properties of neurons or astrocytes assessed with whole-cell recording. These findings suggest that pinacidil provides an effective and selective means for inducing hyperemia in vivo, and may provide a useful tool in directly testing the impact of hemodynamics on neural activity, as recently predicted by the hemo-neural hypothesis.

FIGURE 1

In vivo responses to pinacidil application. (A) Cortical surface over the somatosensory cortex in a rat: yellow lines indicate course of the middle cerebral artery (MCA); purple box indicates area of subsequent analysis following pinacidil application; red outline indicates the parenchymal region. (B) Inset reveals change in MCA diameter over time (at green line in panel A); graph shows normalized changes in absorption measured in the MCA and parenchymal regions over the same time period, with the gray line indicating the onset of pinacidil application. (C) Average change in MCA diameter in rats in response to pinacidil (red) and ethanol (blue). (D) Changes in parenchymal absorbance in rats over time. (E) In mice, MCA diameter increases in response to pinacidil (red) but not ethanol (blue). (F) Changes in parenchymal absorbance in mice over time.

FIGURE 2

(A) Pinacidil at a dose of 400 μM does not show a significant effect on vessel diameters in slice (14 vessels). (B) Astrocytes depolarize slightly in response to 1% ethanol in artificial cerebrospinal fluid (ACSF). Depolarization was about 1 mV, on average (30 cells). (C) Depolarization of astrocytes in response to pinacidil and ethanol is not significant. (D, E, F) Layer 2/3 neurons showed no response to pinacidil or ethanol in input resistance, resting membrane potential, or spikes evoked by depolarizing current injection (30 cells), with no additional effect observed in response to application of pinacidil in 1% ethanol.