Stress Adaptation in Rats Associate with Reduced Expression of Cerebrovascular Kv7.4 Channels and Biphasic Neurovascular Responses

Neurovascular coupling ensures rapid and precise delivery of O-2 and nutrients to active brain regions. Chronic stress is known to disturb neurovascular signaling with grave effects on brain integrity. We hypothesized that stress-induced neurovascular disturbances depend on stress susceptibility. Wistar male rats were exposed to 8 weeks of chronic mild stress. Stressed rats with anhedonia-like behavior and with preserved hedonic state were identified from voluntary sucrose consumption. In brain slices from nonstressed, anhedonic, and hedonic rats, neurons and astrocytes showed similar intracellular Ca2+ responses to neuronal excitation. Parenchymal arterioles in brain slices from nonstressed, anhedonic, and hedonic rats showed vasodilation in response to neuronal excitation. This vasodilation was dependent on inward rectifying K+ channel (K(ir)2) activation. In hedonic rats, this vasodilation was transient and followed by vasoconstriction insensitive to K(ir)2 channel inhibition with 100 mu M BaCl2. Isolated arteries from hedonic rats showed increased contractility. Elevation of bath K+ relaxed isolated middle cerebral arteries in a concentration-dependent and K(ir)2-dependent manner. The vasorelaxation to 20-24 mM K+ was reduced in arteries from hedonic rats. The expression of voltage-gated K+ channels, K(v)7.4, was reduced in the cerebral arteries from hedonic rats, whereas the expression of arterial inward-rectifying K+ channels, K(ir)2.1 was similar to that of nonstressed and anhedonic rats. We propose that preserved hedonic state is associated with increased arterial contractility caused by reduced hyperpolarizing contribution of K(v)7.4 channels leading to biphasic cerebrovascular responses to neuronal excitation. These findings reveal a novel potential coping mechanism associated with altered neurovascular signaling.