Disinhibition of the dorsomedial hypothalamus increases the frequency of augmented breaths in the anesthetized rat

The present study was undertaken to identify if activation of the dorsomedial hypothalamus (DMH) elicits augmented breaths (ABs). DMH disinhibition in urethane anesthetized rats produced both an increase in baseline respiratory rate (RR) and an increase in the number of ABs. The increase in RR was associated with a decrease in both the time of inspiration (T_i) and expiration (T_e) and the peak change in RR was observed 5 min post DMH activation. In contrast, the increase in ABs was greatest during the first 1.25 min, and both T_is of the ABs did not change significantly from pre-injection values. The T_e of the ABs did decrease but remained significantly greater than the T_e of the normal breath during DMH disinhibition. Our results support the hypothesis that the central neural pathway involved in the maintenance of normal respiratory pattern may be distinct from pathways involved in the generation of ABs.