BILATERAL PROJECTIONS OF THE PONTINE MICTURITION CENTER TO THE SACRALPARASYMPATHETIC NUCLEUS IN THE RAT

Previous work has revealed that pontine micturition center (PMC) neuro ns send projections to the sacral parasympathetic nucleus (SPN) of the intermediolateral (IML) regions of L6-S1 spinal cord segments in rats . Although unilateral SPN injections will retrogradely label PMC neuro ns bilaterally, it is not known whether single PMC neurons project bil aterally to the SPN. There may be two different populations of PMC neu rons on each side of the brainstem, with both groups independently con necting to the SPNs on opposite sides of the spinal cord. To verify on e of these alternatives, a small injection of either rhodamine-labeled latex microspheres or a red fluorescent emulsion was made into the SP N on one side of the cord; a similar injection of either fluorescein-t agged microspheres or a green fluorescent emulsion was made into the E ther. After at least seven days, the rats were perfused. Inspection of 40 mu m cord sections confirmed the similar placement of these inject ions along the rostrocaudal axis of the cord and that no tracer had sp read across midline. Thirty-micron brain sections were examined for fi lled neurons. Red, green and double labeled neurons were found bilater ally in the PMC, subcoeruleus, and A5 regions. Although some red nucle us cells a ere also filled, they were only singly labeled and always l ocated contralateral to the injection. Finally, immunohistochemical st aining of dopamine-P-hydroxylase (DBH) containing cells confirmed that some labeled cells were also noradrenergic. We therefore conclude tha t some PMC, subcoeruleus, and A5 neurons send axons to the SPN on both sides of the lumbosacral cord. (C) 1998 Elsevier Science B.V.