The paraventricular nucleus of the hypothalamus influences respiratory timing and activity in the rat

In this study we sought to determine the role of the paraventricular nucleus of the hypothalamus (PVN) in modulating respiratory output. Experiments were performed in urethane anesthetized, vagotomized and mechanically ventilated Wistar rats. Electromyographic activity of the diaphragm (DEMG) was recorded and used to define the respiratory effects of PVN stimulation. The ventilation rate and volume were pre-adjusted so that baseline activity was 30% of the activity observed upon addition of 7% CO2 in O2. Microinjection of l-glutamate (4 nmol, 100 nl) into the PVN produced an increase in peak DEMG, and an increase in frequency of DEMG discharge. Changes in respiratory timing were mainly due to shortening of expiratory time (0.66±0.06 s vs. 0.90±0.10 s; mean±SEM; P005). The rate of rise of DEMG increased by 101±28% from the baseline (P