The morphology and connections of neurons in the gasping centre of adult rats

Abstract

Neuronal activities in the intermediate reticular nucleus and adjacent lateral tegmental field are critical for the neurogenesis of the ventilatory pattern of gasping. We report herein the anatomical features of these neurons, their axonal projections and the location of neurons providing afferent inputs. These neuroanatomical evaluations were performed by iontophoretic injection of the tracer Neurobiotin® into the region of the intermediate reticular nucleus of the rat. At the site of injection, neurons having soma of 30-50 μm were filled. Labelled axons and terminals were observed in ipsilateral regions which contain neurons having established functions in the control of ventilatory activity. These regions include the nucleus ambiguus and motor nuclei of the hypoglossal and facial nerves. In addition, axonal projections extended to the contralateral region of the intermediate reticular nucleus. From this contralateral region, retrograde tracing revealed projections to the site of injection. Similarly, many ipsilateral regions which received axonal terminals from the region of the intermediate reticular nucleus had reciprocal projections to this region. These anatomical results support the physiological observation that the neurogenesis of gasping involves a synchronized activation of diverse components of the brainstem ventilatory control system.