Journal article
Comparison of baroreceptive to other afferent synaptic transmission to the medial solitary tract nucleus
American journal of physiology. Heart and circulatory physiology, Vol.295(5), pp.H2032-2042
11/2008
Handle:
https://hdl.handle.net/2376/112550
PMCID: PMC2614577
PMID: 18790834
Abstract
Cranial nerve visceral afferents enter the brain stem to synapse on neurons within the solitary tract nucleus (NTS). The broad heterogeneity of both visceral afferents and NTS neurons makes understanding afferent synaptic transmission particularly challenging. To study a specific subgroup of second-order neurons in medial NTS, we anterogradely labeled arterial baroreceptor afferents of the aortic depressor nerve (ADN) with lipophilic fluorescent tracer (i.e., ADN+) and measured synaptic responses to solitary tract (ST) activation recorded from dye-identified neurons in medial NTS in horizontal brain stem slices. Every ADN+ NTS neuron received constant-latency ST-evoked excitatory postsynaptic currents (EPSCs) (jitter < 192 micros, SD of latency). Stimulus-recruitment profiles showed single thresholds and no suprathreshold recruitment, findings consistent with EPSCs arising from a single, branched afferent axon. Frequency-dependent depression of ADN+ EPSCs averaged approximately 70% for five shocks at 50 Hz, but single-shock failure rates did not exceed 4%. Whether adjacent ADN- or those from unlabeled animals, other second-order NTS neurons (jitters < 200 micros) had ST transmission properties indistinguishable from ADN+. Capsaicin (CAP; 100 nM) blocked ST transmission in some neurons. CAP-sensitive ST-EPSCs were smaller and failed over five times more frequently than CAP-resistant responses, whether ADN+ or from unlabeled animals. Variance-mean analysis of ST-EPSCs suggested uniformly high probabilities for quantal glutamate release across second-order neurons. While amplitude differences may reflect different numbers of contacts, higher frequency-dependent failure rates in CAP-sensitive ST-EPSCs may arise from subtype-specific differences in afferent axon properties. Thus afferent transmission within medial NTS differed by axon class (e.g., CAP sensitive) but was indistinguishable by source of axon (e.g., baroreceptor vs. nonbaroreceptor).
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Details
- Title
- Comparison of baroreceptive to other afferent synaptic transmission to the medial solitary tract nucleus
- Creators
- Michael C Andresen - Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, Oregon 97239-3098, USA. andresen.ohsu@gmail.comJames H Peters
- Publication Details
- American journal of physiology. Heart and circulatory physiology, Vol.295(5), pp.H2032-2042
- Academic Unit
- Integrative Physiology and Neuroscience, Department of
- Publisher
- United States
- Grant note
- R01 HL041119 / NHLBI NIH HHS R01 HL083115 / NHLBI NIH HHS HL-41119 / NHLBI NIH HHS HL-56460 / NHLBI NIH HHS F32 HL088894 / NHLBI NIH HHS
- Identifiers
- 99900547412701842
- Language
- English
- Resource Type
- Journal article