Axonal Projections from the Pontine Parabrachial-Kölliker-Fuse Nuclei to the Bötzinger Complex as Revealed by Antidromic Stimulation in Cats
The pontine parabrachial and Kölliker-Fuse nuclear complex (NPB-KF) has been assumed to be the anatomical location of the pneumotaxic center (11). It contains high density of respiratory neurons with various discharge patterns (3, 6). Destruction or electrical stimulation of this area is known to produce profound changes in the respiratory rhythm (5, 24, 25). It is suggested that the NPB-KF exerts its effects by specifically modulating the activity of the medullary inspiratory ‘off-switch’ mechanism, which terminates inspiration and ensures the phase transition from inspiration to expiration (8, 9). However, axonal projections from the NPB-KF to the medullary structures specifically involved in the inspiratory ‘off-switch’ effects have not been well delineated. Previous studies by us demonstrated that the nucleus raphe magnus, a structure involved in the inspiratory ‘off-switch’, received strong axonal projections from the NPB-KF area (1, 21, 22). Another possible neuron group which may transmit the function of the NPB-KF is the Bötzinger complex (Böte). The Böt. c. is known as a group of expiratory neurons in the vicinity of the retrofacial nucleus (14, 19). Most of those neurons have an augmenting firing pattern and widespread inhibitory connections to the medullary inspiratory premotor neurons (10, 12, 18). Recent studies by Smith et al. (20) and us (23) with the retrograde WGA-HRP tracing method revealed that the Böt. c. received strong projections from the lateral NPB and the KF. These studies suggest that these projections are composed of axons from the pontine respiratory and/or non-respiratory neurons which would modulate the activities of expiratory neurons in the Böt. c.
KeywordsAxonal Projection Nucleus Parabrachialis Respiratory Neuron Axonal Arborization Ventral Respiratory Group
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