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The Pontine A 5 Noradrenergic Cells which Project to the Spinal Cord Dorsal Horn are Reciprocally Connected with the Caudal Ventrolateral Medulla in the Rat
Author(s) -
Tavares Lsaura,
Lima Deolinda,
Coimbra Antonio
Publication year - 1997
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1111/j.1460-9568.1997.tb01662.x
Subject(s) - spinal cord , anatomy , medulla , retrograde tracing , biology , pons , tyrosine hydroxylase , neuroscience , dorsum , dopamine
A disynaptic pathway linking the caudal ventrolateral medulla (VLM) to the spinal cord via the A 5 noradrenergic cell group of the pons has recently been described in the rat. In the present work, the projections of the A 5 to the VLM and to the spinal dorsal horn were studied with double‐tracing techniques combined with immunostaining of the noradrenaline‐synthesizing enzyme dopamine‐β‐hydroxylase. Cholera toxin subunit B (CTb) injected into the VLM and fluoro‐gold injected into the spinal dorsal horn produced double retrograde labelling of A 5 neurons immunoreactive for dopamine‐β‐hydroxylase, which received appositions of fibre varicosities labelled anterogradely with CTb injected into the VLM. After injecting CTb into the A 5 , retrogradely labelled neurons occurred in the VLM. These neurons were contacted by anterogradely labelled fibres from the A 5 group. These observations indicate that the VLM cells acting upon the A 5 spinally projecting neurons, which are likely to exert an α 2 ‐adrenoreceptor‐mediated inhibition on the spinal cord, are targeted by collaterals of the A 5 spinal cord‐bound axons. The A 5 ‐VLM pathway may be the anatomical substrate of a negative feedback circuit whereby the modulatory action of the VLM on the spinal cord is self‐inhibited through activation of the A 5 .