Age-Dependent Vasopressinergic Modulation of NOC/oFQ-Induced Impairment of NMDA Cerebrovasodilation After Brain Injury

Abstract

This study was designed to characterize the role of vasopressin in nociceptin/orphanin FQ (NOC/oFQ)-induced impairment of NMDA cerebrovasodilation after fluid percussion brain injury (FPI) as a function of age in newborn (1-5 days old) and juvenile (3-4 weeks old) pigs equipped with a closed cranial window. Previous studies have observed that NOC/oFQ is released into CSF and contributes to impaired NMDA induced pial artery dilation following FPI to a greater extent in newborn versus juvenile pigs. Topical vasopressin (40 pg/mL), a concentration approximating that observed in CSF following FPI in the newborn, increased CSF NOC/oFQ from 69 ± 3 to 102 ± 8 pg/mol under non-FPI conditions. CSF NOC/oFQ was elevated within 60 min of FPI (70 ± 3 to 444 ± 51 pg/mL), but release was attenuated by MEAVP, a vasopressin antagonist, in the newborn (71 ± 3 to 146 ± 11 pg/mL). CSF vasopressin and NOC/oFQ were not elevated as greatly in the juvenile following FPI and MEAVP correspondingly did not attenuate CSF NOC/oFQ release as much as in the newborn. Under noninjury conditions, vasopressin (40 pg/mL) coadministered with NMDA (10^-8, 10^-6 M) attenuated pial dilation to this excitatory amino acid (9 ± 1% and 16 ± 1% vs. 3 ± 1% and 5 ± 2%). Following FPI in the newborn, NMDA-induced pial artery dilation was reversed to vasoconstriction, and both NOC/oFQ and vasopressin receptor antagonists partially prevented these alterations (9 ± 1%) and 16 ± 1%, sham control; -7 ± 1% and -12 ± 1%, FPI; -2 ± 1% and -3 ± 1%, FPI-NOC/oFQ antagonist; and 1 ± 1% and 4 ± 1%, FPI-vasopressin antagonist). NMDA-induced pial dilation was only attenuated following FPI in the juvenile and modestly restored by NOC/oFQ and vasopressin receptor antagonists. These data show that vasopressin, in concentrations present in CSF following FPI, contributes to the release of CSF NOC/oFQ following such an insult. The greater release of vasopressin following FPI in the newborn contributes to the corresponding greater release of NOC/oFQ in the newborn versus the juvenile. Moreover, vasopressin also contributes to the impairment of NMDA cerebrovasodilation after brain injury to a greater extent in newborn versus juveniles. These data suggest that vasopressin modulates NOC/oFQ-induced impairment of NMDA cerebrovasodilation after brain injury in an age-dependent manner.