Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, C5
Synaptic profile of Nucleus Tractus Solitarius neurons involved with the peripheral chemoreflex pathways in rats.
D. Accorsi-Mendonca1, J. A. Castania1, L. G. Bonagamba1, B. H. Machado1, R. M. Leao1
1. Physiology, University of Sao Paulo, Ribeirao Preto, SP, Brazil.
The glomus cells in the carotid bodies (CB) detect low pO2 level in arterial blood and the carotid sinus nerve conveys this information to 2nd-order neurons in the nucleus tractus solitarius (NTS) via tractus solitarius (TS), which is part of the chemoreflex pathways. It has been demonstrated that in 2nd-order NTS neurons receiving inputs from the aortic depressor nerve (ADN), the TS stimulation presents high temporal fidelity. However, the temporal properties of synaptic activity in NTS neurons receiving inputs from CB are not well known. Herein using patch-clamp recordings combined with fluorescence labeling of chemosensitive afferents in NTS we studied TS evoked excitatory post-synaptic currents (TS-eEPSCs) on identified NTS 2nd-order neurons that receive afferent inputs from the CB in brainstem slices from Wistar rats (~300g). The experiments were performed in CB-NTS 2nd-order neurons and compared with ADN-NTS 2nd-order NTS neurons recorded in the same experimental conditions. The amplitudes of TS-eEPSCs were similar in both groups but the latencies and standard deviation (SD) of latency (jitter) were significantly higher in the CB-NTS neurons (latency: 4.3 ± 0.2 ms; SD: 0.5 ± 0.04 ms, n=21) than in ADN-NTS neurons (latency: 3.4 ± 0.3 ms; SD: 0.2 ± 0.05 ms, n=13). The CB-NTS neurons also presented higher failure rate during high frequency trains of stimulus and in a complex series of double-labeling experiments we documented that some CB-NTS 2nd-order neurons send direct projections to the rostral-ventrolateral medulla (RVLM). We conclude that: a) CB-NTS 2nd-order neurons present temporally-distinct post-synaptic currents when compared with ADN-NTS 2nd-order neurons; b) low SD of latency of TS-eEPSCs is not necessarily a characteristic of all 2nd-order neurons in the NTS and c) the presence of direct connections between these 2nd-order neurons in the NTS and RVLM is indicative that these synaptic properties of CB-NTS neurons are relevant for the processing of respiratory and autonomic responses to chemoreflex activation.
Where applicable, experiments conform with Society ethical requirements