Inactivation of neuronal function in the amygdaloid region reduces tail artery blood flow alerting responses in conscious rats

Abstract

Few studies have investigated whether neuronal function in the amygdaloid complex is necessary for the occurrence of the cardiovascular response to natural (unconditioned) environmental threats. In the present investigation in conscious unrestrained Sprague-Dawley rats we inactivated neuronal function in the amygdaloid complex acutely (bilateral muscimol injections) or chronically (unilateral or bilateral ibotenic acid injections) and measured the effect on sudden falls in tail artery blood flow elicited by non-noxious salient stimuli (sympathetic cutaneous vasomotor alerting responses, SCVARs). After acute bilateral injection of vehicle (200nl Ringer's solution) the SCVAR index was 81 ± 2%, indicating that tail blood flow was reduced by 81% in response to the salient stimuli. After acute bilateral injection of muscimol (1 nmol in 200 nl of Ringer's solution) into the amygdaloid complex the SCVAR index was 49 ± 5%, indicating that tail blood flow was reduced by 49% in response to the salient stimuli (p<0.01 versus vehicle, n=7 rats for vehicle and 6 for muscimol). One week after unilateral ibotenic acid lesions, the SCVAR index was 68 ± 3%, significantly less than 90 ± 1%, the corresponding value after unilateral injection of vehicle (p<0.01, n=6 rats in each group). After bilateral ibotenic acid lesions the SCVAR index was 52 ± 4%, significantly less than 93 ± 1%, the corresponding value after bilateral injection of vehicle (p<0.001, n=6 rats in each group). Ibotenic acid caused extensive neuronal destruction of the whole amygdaloid complex, as well as lateral temporal lobe structures including the piriform cortex. Our results demonstrate that the amygdaloid complex plays an important role in mediating the tail artery vasoconstriction that occurs in rats in response to the animal's perception of a salient stimulus, redirecting blood to areas of the body with more immediate metabolic requirements.

Brown adipose tissue thermogenesis contributes to emotional hyperthermia in a resident rat suddenly confronted with an intruder rat

“…Our present study and our earlier investigations in rabbits and rats (6,14,36,63,64) demonstrate that salient or emotional events also vigorously reduce thermoregulatory cutaneous blood flow, and this is also the case in humans (6,13,16,22). Emotional hyperthermia also occurs in humans, as first convincingly demonstrated by Renbourn (48).…”

Cybersickness provoked by head-mounted display affects cutaneous vascular tone, heart rate and reaction time

“…When the measures were performed several hours later, it appeared that several subjects from the "high" group moved to the "low" group and vice versa, and authors suggested that in humans finger blood flow tends to follow a "all or none" pattern rather than gradual changes [5]. While we were unable to identify any other studies where finger temperature of finger blood flow were assessed for relatively long (several hours) periods, blood flow in thermoregulatory vascular beds in animal (ear pinna artery in rabbits and tail artery in rats) is controlled in exactly this way: it remains either predominantly high or predominantly low for extended periods of time [27,45]. Mechanistically this could be explained by the likelihood that arterio-venous anastomoses abundantly present in all three vascular beds and involved in heat dissipation are either mainly opened or mainly closed.…”

Central mechanisms regulating coordinated cardiovascular and respiratory function during stress and arousal

“…In contrast, such nonnoxious brief stimuli evoke only small and transient increases in arterial pressure and little or no changes in blood flow to the mesenteric, renal, and hindlimb vascular beds (109,162), indicating that the sympathetic outflow to the cutaneous vascular bed is rather selectively activated by mild alerting stimuli. Consistent with this, alerting stimuli in humans reliably increase cutaneous sympathetic activity (156).…”

“…In animals, brief alerting stimuli such as an unexpected noise or light will evoke immediate autonomic and respiratory responses, characterized by strong cutaneous vasoconstriction and respiratory activation (17,18,84,109,161). In contrast, such nonnoxious brief stimuli evoke only small and transient increases in arterial pressure and little or no changes in blood flow to the mesenteric, renal, and hindlimb vascular beds (109,162), indicating that the sympathetic outflow to the cutaneous vascular bed is rather selectively activated by mild alerting stimuli.…”

“…Later, Blanchard and Blanchard (15) showed that this was due specifically to lesions of the amygdaloid complex. More recently, it has been shown that inhibition of neurons in the amygdaloid nuclei by microinjection of muscimol greatly reduces both the cutaneous vasoconstrictor and respiratory responses evoked by brief alerting stimuli such as noise or light (18,109,162). Furthermore, lesions of the amygdaloid complex also reduce the hindlimb vasodilation and mesenteric vasoconstriction that are evoked by a more prolonged threatening stimulus (65).…”