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 n ucleus of the hypothalamus (PVN) in modulating respiratory output. Exp eriments were performed in urethane anesthetized, vagotomized and mech anically ventilated Wistar rats. Electromyographic activity of the dia phragm (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 addit ion of 7% CO2 in O-2. Microinjection of L-glutamate (4 nmol, 100 nl) i nto the PVN produced an increase in peak D-EMG, and an increase in fre quency of D-EMG discharge. Changes in respiratory timing were mainly d ue 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-EM G increased by 101 +/- 28% from the baseline (P < 0.05). In addition, neuroanatomical tracing studies suggest the presence of direct connect ion between PVN and phrenic motoneurons. The results indicate that PVN neurons participate in regulation of breathing activity and in coordi nation of cardiovascular and respiratory functions. (C) 1997 Elsevier Science Ireland Ltd.