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PVN‐projecting NTS neurons receive both direct and indirect inputs from solitary tract afferents
Author(s) -
Fawley Jessica,
Hegarty Deborah,
Aicher Sue,
Doyle Mark,
Beaumont Eric,
Andresen Michael
Publication year - 2020
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.2020.34.s1.05696
Subject(s) - solitary tract , trpv1 , neuroscience , resiniferatoxin , brainstem , solitary nucleus , neuron , neurotransmission , chemistry , sensory system , nucleus , receptor , biology , transient receptor potential channel , biochemistry
Cranial vagal afferents first synapse on second‐order neurons in the brainstem nucleus of the solitary tract (NTS). Synaptic transmission in the NTS regulates a wide diversity of homeostatic functions and NTS neurons project widely to other brain regions, including the paraventricular nucleus of the hypothalamus (PVN). The PVN itself is also highly heterogeneous and its neurons both receive and send projections to many other brain areas. Expression of the Transient Receptor Potential Vanilloid receptor (TRPV1) distinguishes solitary tract (ST) afferents as either C‐fibers (TRPV1+) or A‐fibers (TRPV1‐). Sensitivity to resiniferatoxin (RTX), an agonist to the non‐selective cation channel TRPV1, differentiates the two. It is unknown if TRPV1+ or TRPV1− afferents selectively innervate PVN‐projecting neurons or whether every contact on a single PVN neuron is from a segregated pathway to the PVN (i.e., information from A‐ and C‐fibers remains on a labelled line). To identify NTS neurons that specifically project to the PVN, we injected the fluorescent retrograde tracer rhodamine into the PVN. In rhodamine‐positive NTS neurons, responses to ST‐shocks elicited EPSCs with latencies that had either low jitters (<200 μM) that identified direct afferent connections, or high jitter (>200 μs) that identified indirect, higher order inputs. Extensive recruitment curves identified the number and synaptic order of each input. Most neurons received a mix of 2 nd and higher order inputs. A minority of cells received only higher‐order contacts or only direct inputs. The amplitude variance of evoked EPSCs for higher order inputs was significantly greater and had more failures than that of second order inputs. Asynchronous release from indirect inputs was often absent. A majority of afferents were TRPV1+ and all neurons had an all‐or‐none response to RTX. These preliminary results suggest that all inputs on PVN‐projecting NTS neurons, including neurons that receive both second and higher inputs, are either all TRPV1+ or all TRPV1−. Support or Funding Information HL133505 and HL141560