ACTIVITY CHANGES OF THE CAT PARAVENTRICULAR HYPOTHALAMUS DURING PHASIC RESPIRATORY EVENTS

We monitored the spatiotemporal organization of cellular activity in t he medial paraventricular hypothalamus during spontaneously-occurring periods of increased inspiratory effort followed by prolonged respirat ory pauses (sigh/apnea) in the freely-behaving cat. Paraventricular hy pothalamic activity was assayed by video images of light captured with a stereotaxically-placed fibre optic probe. Respiratory activity was measured through electromyographic wire electrodes placed in the diaph ragm. Sigh/apnea events appeared in all behavioural stales, and especi ally during quiet sleep. Overall paraventricular hypothalamic activity declined transiently, with the onset of decline coinciding with the b eginning of the sigh inspiratory effort, reached a nadir at apnea onse t 4.4+0.5 s from the beginning of the sigh, increased during the cours e of the apnea, and subsequently rebounded above baseline to peak at 1 0.9+2.5 s after sigh onset. Scattered, small areas of the imaged regio n were activated or depressed independently of the overall image value s. The data suggest that paraventricular hypothalamic activity changes dynamically during phasic respiratory events, and may contribute to t he progression of the sigh/apnea. We speculate that the medial paraven tricular hypothalamus influences breathing patterns through projection s to parabrachial respiratory phase-shift regions, and that longer-lat ency influences may also be exerted indirectly through blood pressure effects from paraventricular hypothalamic projections to medullary car diovascular nuclei. Additionally, the paraventricular hypothalamus may convey respiratory influences from other rostral structures, such as the hippocampus. (C) 1997 IBRO. Published by Elsevier Science Ltd.