Ventrolateral lesions at the ponto-medullary junction and the effects of noradrenaline on respiratory rhythm in rat brainstem–spinal cord preparations

AimsWe examined whether responses of respiratory frequency (fR) to noradrenaline (NA) were eliminated by mechanical lesions in the ventrolateral area at the ponto-medullary junction in preparations of newborn rat pons–medulla–spinal cord (PMS).Main methodsPreparations obtained from 2- to 4-day-old rats were superfused with artificial cerebrospinal fluid that was equilibrated with oxygenated (95% O2 plus 5% CO2) gas, and fR was monitored at the C4 ventral root at 24 °C. Bilateral lesions were made in the ventrolateral area between the VIth cranial nerve root and the anterior inferior cerebellar artery in PMS (n = 11). The resting fR and response to exogenous NA (7 μM) were compared with those of medulla–spinal cord (MS) preparations (n = 6). Immunohistochemistry of PMS preparations was performed to detect tyrosine hydroxylase (TH)-positive neurons at the ponto-medullary junction.Key findingsPMS preparations with the lesions had (1) a significantly higher resting fR but (2) significantly less fR facilitation after NA application than those of intact PMS preparations, and (3) significantly lower resting fR and (4) significantly less fR reduction after NA application than those of MS preparations. TH-positive neurons were detected in the region from the rostral dorsolateral to the caudal ventrolateral pons (the A5 area), as well as in the ventral area near the facial nucleus.SignificanceResults suggest that ventrolateral area at ponto-medullary junction plays a significant role in exogenous NA-induced fR changes under the influence of pons-induced tonic fR inhibition in newborn rat brainstem–spinal cord preparations.