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

AIMS: We 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 METHODS: Preparations 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 degrees 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 microM) 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 FINDINGS: PMS 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. SIGNIFICANCE: Results 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.

Effect of 2,4-dinitrophenol under non-oxygenated condition in pons-medulla-spinal cord preparations in newborn rats: comparison with medulla-spinal cord preparations.

We tested whether depression of respiratory frequency (fR) under non-oxygenated artificial cerebrospinal fluid (aCSF) in pons-medulla-spinal cord (PMS) and medulla-spinal cord (MS) preparations is significantly influenced by the mitochondrial uncoupler 2,4-dinitrophenol (2,4-DNP) in newborn rats. Preparations were obtained from 0- to 4-day-old rats, and fR was monitored at the C4 ventral root in environmental temperature (24 degrees C). 2,4-DNP was dissolved in aCSF (1, 10 or 30 microM; pH 7.4), and we measured fR in PMS (n=19) and MS (n=16), both of which were superfused with aCSF equilibrated with oxygenated (95% O2-5% CO2) or non-oxygenated (10% O2-5% CO2, balanced with pure N2) gas. Our results showed that: (1) fR was significantly lower in PMS than MS, (2) fR was significantly decreased under non-oxygenated aCSF in both PMS and MS and (3) fR under non-oxygenated aCSF was significantly increased by 2,4-DNP applications at 10 and 30 microM in PMS but not in MS. Our results suggest that depression in fR under non-oxygenated aCSF in PMS and MS may not be due simply to O2 limitation, and 2,4-DNP has a stimulant effect on the medullary respiratory rhythm generator (RRG) through pontine RRG regulatory mechanisms under non-oxygenated aCSF.

Effect of alpha1-adrenergic receptor antagonist on the noradrenaline-induced facilitation in respiratory rhythm in newborn rat pons-medulla-spinal cord preparations.

We hypothesized that facilitation of respiratory rhythm by noradrenaline (NA) in rat pons-medulla-spinal cord preparations is mediated through alpha1-adrenergic receptors. In 0- to 4-day-old rats, the respiratory frequency (fR) was monitored at the C4 ventral root and trigeminal motor (VMO) outputs. fR at temperature (Te)=23 degrees C was lower than that at a higher Te (27 degrees C) and was increased by NA. At 23 degrees C, lower concentrations of NA were needed to produce the same increases in fR seen at 27 degrees C. With highest NA concentration we tested (50 microM), activity at C4 was maintained in all preparations at both Te, whereas that at VMO was maintained in 50% (27 degrees C) or 88% (23 degrees C) of the preparations. Particularly, tonic activity at C4 appeared in all preparations at both Te, but that at the VMO occurred in 0% (27 degrees C) or 18% (23 degrees C) of the preparations. Based on these results, we used the lower Te (23 degrees C) and applied a low concentration of NA (3 microM) to the preparations. We found that: (1) with the addition of NA, fR was increased without the occurrence of tonic activity and (2) NA-related fR facilitation was inhibited by pre-treatment with the alpha1-adrenergic receptor antagonist prazosin (2 microM). fR was increased by application of the alpha1-adrenergic receptor agonist phenylephrine (4 microM), and this response was inhibited by prazosin (4 microM). At Te=23 degrees C, fR facilitation by NA in newborn rat pons-medulla-spinal cord preparations was obtained by activation of alpha1-adrenergic receptors.