Dorsal respiratory group

Opioids are potent respiratory depressants, causing a dose-dependent decrease in respiratory frequency, tidal volume and minute ventilation and increased arterial partial pressure of carbon dioxide (PaC02) (Carvey 1998). Opioids depress chemosensors in the brainstem, decreasing the ventilatory response to carbon dioxide. Opioids also depress rhythmicity in the dorsal respiratory group in the nucleus tractus solitarius, attenuating the respiratory cycle. Opioids, however, do not diminish hypoxic ventilatory drive. Significant elevations in Paco2 can result in increased ICP after opioid administration. 

Neurophysiological and neuroanatomical studies have selectively labeled the central projections of chemosensitive libers caudally to the obex within the NTS in cats and rats, whereas barosensory libers project rostral to the obex (57-59). The NTS, which contains the premotor neurons of the dorsal respiratory group (60), is now recognized as the major projection site of chemosensory libers. Neurons of caudal NTS with carotid chemoreceptor inputs project onto the ventrolateral medulla (61) that contains the premotor neurons of the ventral respiratory group (60). 

Compare and contrast functions of the dorsal and ventral respiratory groups in the medullary respiratory center... 

Takeda M, Matsumoto S. Discharge patterns of dorsal and ventral respiratory group neurons during spontaneous augmented breaths observed in pentobarbital anesthetized rats. Brain Res 1997 749 95-100. 

The respiratory centers arc neuronal groups found primarily in the medulla and pons of the brain stem. The medullary respiratory center comprises a dorsal and ventral group, located in the reticular formation of the medulla below the fourth ventricle. They are believed to be central targets for OP toxicity through an unknown mechanism. Damage to these neuronal control centers will affect inspiration and expiration. 

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