Control of breathing by endogenous opioid peptides: possible involvement in sudden infant death syndrome

Experiments have been performed in order to evaluate the respiratory consequences of a suppression or accumulation of endogenous opioid peptides, in the neuronal network which generates the motor respiratory activity. Iontophoretic application of naloxone onto respiratory neurons increases their firing activity and increases their respiratory modulation. On the other hand the local injection of kelatorphan (an enkephalinase inhibitor) decreases the firing of respiratory neurons and thus reduces the respiratory modulation. This effect of kelatorphan mimics the effect on respiratory neuron of an iontophoretic application of met-enkephalin. Furthermore the local injection of kelatorphan reduces the frequency of the respiratory output recorded from the phrenic nerve. This effect is reversed by systemic administration of naloxone. The results demonstrate the involvement of endogenous opioid peptides in the control of breathing suggesting that in Sudden Infant Death Syndrome a possible dysregulation in opioidergic system could occur.