Bradycardia elicited by microinjections of nociceptin/orphanin FQ into the intermediolateral cell column at T1–T2 in the rat

Microinjections (30 nl) of nociceptin/orphanin FQ (N/OFQ) into the intermediolateral cell column (IML) at T1 and T2 levels of the spinal cord elicited bradycardia. The decreases in HR were 12.3 ± 2.9, 17.3 ± 2.7, 26.7 ± 3.1, and 18.6 ± 3.4 beats/min in response to 0.075, 0.15, 0.62, and 1.25 mM concentrations, respectively. Maximally effective concentration of N/OFQ was 0.62 mM. No changes in BP were elicited by microinjections of N/OFQ into the IML at T1–T2. The bradycardic responses were completely blocked by prior microinjections of a N/OFQ receptor (NOP receptor) antagonist ([N-phe1]-nociceptin-(1-13)-NH2, 9 mM) into the IML at T1–T2. Blockade of myocardial β-1 adrenergic receptors also abolished the bradycardic responses elicited by microinjections of N/OFQ into the IML. It was concluded that activation of NOP receptors in right IML at T1–T2 by N/OFQ elicited bradycardic responses which were mediated via the sympathetic nervous system.