Role of Medial Amygdala in Controlling Hemodynamics Via GABA_A Receptor in Anesthetized Rats

Abstract

Experiments were conducted to determine whether the medial amygdala could control hemodynamics through the GABA receptor in anesthetized rats. Bicuculline (10-100pmol), a GABA(A) antagonist, injected into the anterior basomedial amygdala (medial amygdala) produced dose-related increases in blood pressure (BP) and heart rate (HR). Following microinjection of a 100pmol dose, plasma norepinephrine and epinephrine also rose significantly. In a group that had undergone bilateral adrenalectomy, the same dose of bicuculline into the same region of the amygdala caused similar increases in BP and HR to those produced in normal rats. Pretreatment with an intraperitoneal injection of hexamethonium prevented these responses. When bicuculline was given intravenously (100pmol) it failed to effect these cardiovascular changes. Bicuculline-induced hypertension and tachycardia were inhibited by microinjection of muscimol, a GABA agonist, into the anterior basomedial amygdala. The results thus demonstrate that the influence of bicuculline on BP and HR is through action on the anterior basomedial amygdala and direct sympathetic outflow to heart and vascular smooth muscle. There is tonic GABAergic inhibition of sympathetic outflow in the medial amygdala that plays a part in regulating hemodynamics in the limbic system.

Transcriptional Factor Aryl Hydrocarbon Receptor (Ahr) Controls Cardiovascular and Respiratory Functions by Regulating the Expression of the Vav3 Proto-oncogene

“…These effects are induced by the blockage of the tonic inhibitory GABA signaling in RVLM neurons (58). This antagonist induced the expected cardiovascular (Fig.…”

Limbic modulation of the autonomic nervous system

“…Importantly, manipulation of the synaptic transmission properties of the amygdala with the GABA A agonist, muscimol, does not produce any change in basal autonomic control but reduces the ability of the ventral hippocampus to modulate motor and autonomic output (Figure 6.7). These findings are in alignment with a previous study that investigated the role of the BMA in the haemodynamics of anaesthetised rats (Yoshida et al, 2002). In their study, injection of the bicuculline, a GABA A antagonist, into the BMA produced dose-related hypertension and tachycardia, while muscimol inhibited these effects (Yoshida et al, 2002).…”

“…However, the results obtained were not consistent, and this was attributed to differences in experimental setup, i.e., anaesthetised (Yoshida et al, 2002) versus awake (Mesquita et al, 2016) rats. Thus, there is no consensus on the inherent mechanisms but an indication of physiological interaction with brainstem autonomic control centres.…”

“…Within the amygdala, the basomedial nucleus is of particular interest because studies have demonstrated autonomic modulation by pharmacologically manipulating this nucleus (Yoshida et al, 2002;Mesquita et al, 2016). However, the results obtained were not consistent, and this was attributed to differences in experimental setup, i.e., anaesthetised (Yoshida et al, 2002) versus awake (Mesquita et al, 2016) rats.…”

Major Contribution of the Medial Amygdala to Hypertension in BPH/2J Genetically Hypertensive Mice

“…However, electric stimulation of the BLA in conscious rats and pharmacological dis-inhibition of the BLA in anesthetized rats can cause increases in BP. 29,30 Therefore, it seems unlikely that increased neuronal activity within the BLA is driving the hypotensive effect of MeAm lesions in BPH/2J mice. Another surprising finding was that comparable reductions of BP in BPH/2J mice occurred across the entire 24-hour period, which suggests that the contribution of the MeAm to elevated BP is likely mediated by a tonic pressor influence, which is independent of phasic changes in BP associated with the circadian cycle.…”