Convergence of thermal signals on the reticulospinal neurons in the midbrain, pons and medulla oblongata

Abstract

A total of 670 reticulo spinal (RfS) and non-RfS neurons in the mesencephalic, pontile and medullary reticular formation (mRf, pRf and mdRf) were studied for the responsiveness to changes in temperatures of local brain sites, preoptic and anterior hypothalamus (PO/AH) and skin in the urethane anesthetized rat. Local thermoresponsiveness was found in 49.6% of 139 mRf neurons, 61.9% of 160 pRf neurons and 75.4% of 126 mdRf neurons. While the ventromedial region of pRf and mdRf contained predominantly warm-responsive neurons (54.8% and 62.5%), cold-responsive neurons were much more frequently found in the mRf (33.8%) and the dorsolateral region of pRf (41.9%) and mdRf (50.0%). Responsiveness to hypothalamic temperature and/or skin temperature was observed in about 40–74% of Rf neurons. Higher incidence of responsiveness to remote temperatures was found among locally thermoresponsive neurons than among locally thermounresponsive neurons in all three areas. Particularly, there was a high degree of convergence of ‘cold’ signals from local and remote sites on the RfS neurons in the mRf and the dorsolateral pRf and mdRf. Microinjections of procaine and glutamate into these regions decreased and increased the cold-induced increase in EMG activity and shivering without any correlated changes in cardiovascular and respiratory parameters and pilomotor activity. The results suggest that RfS and non-RfS neurons in the mRf and the dorsolateral pRf and mdRf are involved in the control of thermoregulatory muscle tone and shivering.