Ventral medullary organization for cardiorespiratory control

Arterial baroreceptor stimulation inhibits both arterial pressure (baro-pressure reflex) and ventilation (baro-ventilatory reflex). Regions of the ventral medulla, both near the medullary surface (VMS) and deeper in the rostral and caudal ventrolateral medulla (RVLM and CVLM respectively), are involved not only in vasomotor control and the baro-pressure reflex, but also in respiratory control. The aim of this research was to determine if these regions are also part of the pathway for the baro-ventilatory reflex.;RVLM neural structures were blocked in anesthetized dogs by unilateral focal cooling using a needle probe. The results affirmed that RVLM neural structures of the dog affect control of arterial pressure and ventilation and play a role in the baro-pressure reflex. The RVLM structures were also found to influence the baro-ventilatory reflex. Absence of detailed information regarding neural structures within the dog medulla, and technical difficulties of using the ventral approach to the medulla prompted the use of rats for further studies.;The role of neural structures adjacent to the VMS of anesthetized rats were evaluated by surface applications of various drugs (pentobarbital, nicotine, bicucculine). The results confirmed that these structures affect arterial pressure and the baro-pressure reflex, at least in part, through GABA;Neural structures in the CVLM of anesthetized rats were blocked by microinjections of excitatory amino acid antagonists. Unilateral microinjections of kynurenic acid, a non-specific glutamatergic antagonist, cause respiratory arrest, and raised the baseline blood pressure. Bilateral block abolished the baro-pressure reflex. Because of the respiratory arrest, the baro-ventilatory reflex could not be determined. Further experiments indicated that ventilation is sustained by both NMDA and non-NMDA receptor activation, while the increase in baseline arterial pressure is only mediated via NMDA receptors. The results confirmed that the CVLM forms an obligatory synapse for mediating the baro-pressure reflex via both NMDA and non-NMDA receptors.;The effects of neural blockade on ventilation were examined with a hypothetical neural network model. This model was then used to suggest experiments to further elucidate the role of ventrolateral medullary structures in cardio-respiratory control.