Oral Presentation Neuropathophysiology - an ISH satellite 2012

Psychological or emotional stressors evoke powerful autonomic and behavioural responses. The autonomic response to acute psychological stressors is mediated by the sympathetic nervous system and the neuroendocrine system. Although such responses increase the probability of survival in the face of threatening stimuli, they can also lead to acute cardiovascular disorders, such as cardiac arrhythmias. In humans, it is believed that repeated stress-evoked cardiovascular responses leads normotensive subjects to essential hypertension. Thus, acute psychological stress is an important risk factor for hypertension and other cardiovascular disorders. The autonomic response to the stress such as air-jet stress is mediated via the hypothalamic areas, especially the dorsomedial hypothalamic nucleus (DMH) and the perifiornical area (PeF). Inhibition of the DMH or PeF reduces the pressor response and tachycardia evoked by some psychological stressors. In addition, the midbrain periaqueductal grey (PAG) also plays a crucial role in mediating physiological responses to the stress.

On the other hand, these areas (DMH, PeF and PAG) are also essential brain centres of “fight and flight” defensive reaction that accompanies an excitatory cardiovascular response. Indeed, activation of neurons in the areas evoked concomitant increases in arterial pressure, heart rate and sympathetic nerve activity that are very similar to the cardiovascular response evoked by the stress. Therefore, it is well recognized that the cardiovascular response to the stress is a part of the defensive reaction to survive.

Neurons in the rostroventral medulla (RVM) and in the medullary raphe are important components of the descending pathways that mediate the cardiovascular responses to the stress. Neurons in the medullary raphe directly mediate the sympathetic cardiac components of the DMH-evoked response and the stress, while the sympathetic vasomotor component of the DMH activation is primarily mediated via the RVM neurons directly or indirectly. Neurons in the DMH and in the PAG do not have direct projection to the sympathetic preganglionic neurons in the spinal cord, and the descending pathway from the DMH to the spinal sympathetic outflow includes synapses with neurons in medullary nuclei and possibly other brain regions, such as the PAG. However, there are conflicting observations as to whether the descending cardiovascular pathway from the DMH includes a synapse in the PAG. The sympathetic excitatory mechanism and the descending pathways that mediate the cardiovascular response during the stress are still unclear. In this talk, I shall discuss the brain neuronal networks of the cardiorespiratory response evoked by acute psychological stressors.