Pharmacological identification of delta and mu opiate receptors on bulbar respiratory neurons.

The opiate receptors of central neurons related to the generation of the respiratory rhythm were identified using microiontophoresis of the synthetic opioid peptides DSLET (Tyr-D-Ser-Gly-Phe-Leu-Thr) and TRIMU-4 (Tyr-D-Ala-Gly-NH-CH (CH3)-CH2-CH(CH3)2), exhibiting a high selectivity for delta and mu receptors respectively. Both agonists induced depressions of spontaneous and L-glutamate-induced discharges; the effects were antagonized by naloxone and not mimicked by a related almost inactive peptide DSLLET (Tyr-D-Ser-Gly-Leu-Leu-Thr). The effect of DSLET had a faster time course than that of TRIMU-4 and persisted after prolonged applications of TRIMU-4. It is concluded that delta and mu receptors subtypes are distinct and are both present on central respiratory-related neurons.