| This project investigated the influence of the dorsal periaqueductal gray (dPAG), a central neural integration structure of defense behaviors and emotional reactions, on respiratory activities and reflexes. Electrical stimulation and chemical microinjection were used to activate the dPAG. Chemical microinjection was performed with glutamate receptor angonist D,L-homocysteic acid (DLH), or GABAA (gamma-aminobutyric acid) receptor antagonist bicuculline (Bic) into the dPAG. Cardio-respiratory parameters were assessed in spontaneously breathing, vagal intact, anesthetized Sprague-Dawley rats.;Electrical stimulation of the dPAG decreased inspiratory time (Ti) and expiratory time (Te) resulting in an increased respiratory frequency (f R). Stimulation of the dPAG also increased respiratory muscle activities of both diaphragm and external abdominal oblique muscle, especially the baseline activities of muscle electromyography (EMG). There was a dose-dependent increase in the respiratory response following increased electrical stimulus frequency and intensity. Activation of the dPAG elicited hypertension and tachycardia. There is regional difference in the dPAG elicited respiratory responses, but not the cardiovascular responses. Activation of the caudal dPAG elicited a greater increase in fR than the rostral region, due to a greater decrease in Ti and Te, and a greater increase in diaphragm EMG activity.;Cardio-respiratory responses from the dPAG activation are similar to those elicited by peripheral chemoreceptor stimulation with intravenous potassium cyanide (KCN). When KCN was delivered after dPAG activation with Bic microinjection, or simultaneously with DLH microinjection in the dPAG, the peak respiratory response and latency-to-peak were similar to the response to KCN alone. This suggests that peripheral chemoreceptor stimulation blocked descending excitatory inputs from the dPAG to the brainstem respiratory network. Inspiratory or expiratory occlusion significantly increased Ti or Te during occlusion respectively. Activation of the dPAG significantly enhanced this prolongation effect. Inspiratory occlusion significantly increased diaphragm EMG activity during occlusion, which was further enhanced with dPAG activation.;In conclusion, activation of the dPAG stimulates the brainstem respiratory network. These descending excitatory inputs further interact with brainstem neural respiratory reflexes. These studies demonstrated the influence of the central affective system in the neural control of breathing, and enhanced our understandings of the neural mechanism of the respiratory behaviors in patients with emotional changes. |
