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 (D[EMG]) 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 D(EMG), and an increase in frequency of D(EMG) 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; P < 0.05), while inspiratory time was less affected (0.48 +/- 0.04 vs. 0.51 +/- 0.04 s; P > 005). The rate of rise of D(EMG) increased by 101 +/- 28% from the baseline (P < 0.05). In addition, neuroanatomical tracing studies suggest the presence of direct connection between PVN and phrenic motoneurons. The results indicate that PVN neurons participate in regulation of breathing activity and in coordination of cardiovascular and respiratory functions.