Laterality Influences Central Integration of Baroreceptor Afferent Input in Male and Female Sprague Dawley Rats

Abstract

We explored the effects of baroreceptor afferents laterality and sexual dimorphism on the expression of cardiovascular reflex responses to baroreflex activation in Sprague Dawley (SD) rats. Under urethane anesthesia, rats of either sex (total n = 18) were instrumented for left, right and bilateral aortic depressor nerve (ADN) stimulation (1-40 Hz, 0.2 ms, 0.4 mA for 20 s) and measurement of mean arterial pressure (MAP), heart rate (HR) and mesenteric (MVR) and femoral (FVR) vascular resistance. Female rats were matched for the diestrus phase of the estrus cycle. Left, right and bilateral ADN stimulation evoked frequency-dependent drops in MAP, HR, and MVR, and increases in FVR. Irrespective of sex, left and bilateral ADN stimulation as compared to right-sided stimulation mediated greater reflex reductions in MAP, HR, and MVR but not in FVR. In males, reflex bradycardic responses were greater in response to bilateral stimulation relative to both left-and right-sided stimulation. In females, left ADN stimulation evoked the largest increase in FVR. Left and bilateral ADN stimulations evoked greater reductions in MAP and MVR while left-sided stimulation produced larger increases in FVR in females compared with males. All other reflex responses to ADN stimulation were relatively comparable between males and females. These results show a differential baroreflex processing of afferent neurotransmission promoted by left versus right baroreceptor afferent inputs and sexual dimorphism in the expression of baroreflex responses in rats of either sex. Collectively, these data add to our understanding of physiological mechanisms pertaining to baroreflex control in both males and females.

Tempol Reverses the Negative Effects of Morphine on Arterial Blood-Gas Chemistry and Tissue Oxygen Saturation in Freely-Moving Rats

“…Consistent with published literature, morphine also elicited robust and sustained decreases in heart rate, which have been reported to mainly involve an increase in vagal drive to the heart (Della Puppa et al, 1989;Thornhill et al, 1989;Thurston et al, 1993). The ratio of heart rate/MAP can be taken as an index of baroreceptor reflex activity (Lewis et al, 1999;Salman et al, 2020), and our data provide evidence that morphine decreased this ratio and therefore potentially decreased the activity of the baroreflex in our rats. There is remarkably little published data as to the exact effects of morphine or any other opioid on the baroreceptor reflex system in freely-moving (nonanaesthetized) rats although the reported evidence we could find demonstrated that morphine enhances baroreceptor reflex activity in anesthetized rats (Shanazari et al, 2011) whereas it inhibits baroreflex activity in humans (Kotrly et al, 1984).…”

“…The blood pressure and heart rate values were averaged every 30 s to calculate the effects of morphine and the Tempol effects on morphine-induced cardiovascular responses. The ratios of heart rate/MAP were determined throughout the experiments to provide an index of baroreceptor heart reflex activity as described previously ( Lewis et al, 1999 ; Salman et al, 2020 ). With respect to the protocol, all rats received a slow bolus injection of morphine (10 mg/kg, IV) and after 15 min, the rats received a slow bolus injection of vehicle or Tempol at 60 or 100 mg/kg, IV.…”

The solitary nucleus connectivity to key autonomic regions in humans

“…In line with these morphological findings, the stimulation of left aortic baroreceptors exhibited a greater baroreflex response (i.e. decrease of blood pressure) than the stimulation of the right-sided receptors (Salman et al, 2020).…”

Low intensity stimulation of aortic baroreceptor afferent fibers as a potential therapeutic alternative for hypertension treatment

“…MAP and HR were derived from the arterial pressure waveform. Calculation of mesenteric (MVR) and femoral (FVR) vascular resistance were performed using the following equation 47 , 48 . …”

“…A tracheotomy was performed to facilitate spontaneous breathing. A 4–6 mm segment of the ADN was isolated distal to the point where it entered the superior laryngeal nerve and placed on bipolar silver-wire stimulating electrodes (inter-electrode distance of approximately 1 mm) and maintained uncut in mineral oil, as described previously 27 , 28 , 47 . The stimulating electrodes were then connected to a square pulse stimulator (S88 Dual Output Square Pulse Stimulator, Grass Technologies Product Group, Wisconsin, USA) using a stimulus isolation unit (Grass Instrument Co. Model PSIU6 Photoelectric Stimulus Isolation Unit, Grass Technologies Product Group, USA) to deliver monophasic electrical current.…”