CONNECTIONS BETWEEN THE PONTINE RETICULAR-FORMATION AND ROSTRAL VENTROLATERAL MEDULLA

Pontine reticular formation (PRF) neurons provide tonic excitatory dri ve to sympathetic nerves and are involved in cardiovascular control [K . Hayes and L. C. Weaver. Am. J. Physiol. 263 (Heart Circ. Physiol, 32 ): H1567-H1575, 1992]. However, connections between the PRF and the we ll-known vasomotor region in the rostral ventrolateral medulla (RVLM) are unknown. In propofol (Diprivan)- anesthetized rats we investigated arterial pressure, heart rate, and renal nerve responses to microinje ction of glycine (1.0 M, 60 nl) into the PRF before and after injectio n of the synaptic blocking agent cobalt chloride (4.0 mM, 200 nl) into the RVLM. Glycine injections into the PRF caused decreases in arteria l pressure, heart rate, and discharge of renal sympathetic nerves. Syn aptic blockade of the RVLM almost eliminated cardiovascular and sympat hetic responses to glycine injections into the PRF and blocked somatos ympathetic reflexes in the renal nerve. Cobalt injections into the RVL M had very small effects on basal renal nerve firing, arterial pressur e, or heart rate. These results suggest that the neurons within the RV LM relay influences from the PRF to sympathetic preganglionic neurons. Because injections of the excitatory amino acid antagonist, kynurenat e, into the RVLM also interrupted responses to blockade of the PRF and blocked somatosympathetic reflexes, glutamate is a likely neurotransm itter from the PRF to the RVLM and for somato-sympathetic reflexes.