Ventrolateral periaqueductal grey matter neurotransmission modulates cardiac baroreflex activity

Baroreflex activity is a neural mechanism responsible for short‐term adjustments in blood pressure (BP). Several supramedullary areas, which send projections to the medulla, are able to control this reflex. In this context, the ventrolateral part of the periaqueductal grey matter (vlPAG), which is a mesencephalic structure, has been suggested to regulate the cardiovascular system. However, its involvement in baroreflex control has never been addressed. Therefore, our hypothesis is that the vlPAG neurotransmission is involved in baroreflex cardiac activity. Male Wistar rats had stainless steel guide cannulae unilaterally or bilaterally implanted in the vlPAG. Afterward, a catheter was inserted into the femoral artery for BP and HR recording. A second catheter was implanted into the femoral vein for baroreflex activation. When the nonselective synaptic blocker cobalt chloride (CoCl2) was unilaterally injected into the vlPAG, in either the left or the right hemisphere, it increased the tachycardic response to baroreflex activation. However, when CoCl2 was bilaterally microinjected into the vlPAG it decreased the tachycardic response to baroreflex stimulation. This work shows that vlPAG neurotransmission is involved in modulation of the tachycardic response of the baroreflex. Moreover, we suggest that the interconnections between the vlPAG of both hemispheres are activated during baroreflex stimulation. In this way, our work helps to improve the understanding about brain–heart circuitry control, emphasizing the role of the autonomic nervous system in such modulation. Baroreflex activity is an autonomic reflex that maintains blood pressure within a narrow range of variation, insuring metabolic and respiratory supply to the whole body. In this context, this work is the first to show how the ventrolateral periaqueductal grey matter (vlPAG), a mesencephalic structure of the brain, is involved in modulation of this autonomic reflex. Our results indicate that pharmacological inhibition of the vlPAG affects the sympathetic branch of the Autonomic Nervous System. Moreover, they suggest that interconnections between the vlPAG of both hemispheres seem to be activated during baroreflex stimulation.