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Amygdala efferents form inhibitory-type synapses with a subpopulation of catecholaminergic neurons in the rat Nucleus tractus solitarius
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Amygdala efferents form inhibitory-type synapses with a subpopulation of catecholaminergic neurons in the rat Nucleus tractus solitarius

V M Pickel, E J van Bockstaele, J Chan and D M Cestari
Journal of comparative neurology (1911), v 362(4), pp 510-523
27 Nov 1995
PMID: 8636464

Abstract

Afferent Pathways Amygdala - cytology Animals Catecholamines - physiology Dendrites - physiology Immunohistochemistry Male Microinjections Microscopy, Electron Myelin Sheath - physiology Neural Inhibition - physiology Neural Pathways Neurons - cytology Neurons - enzymology Neurons - ultrastructure Neurons, Efferent - cytology Neurons, Efferent - enzymology Neurons, Efferent - ultrastructure Phytohemagglutinins Presynaptic Terminals - physiology Rats Rats, Sprague-Dawley - anatomy & histology Solitary Nucleus - cytology Synapses - physiology Tyrosine 3-Monooxygenase - metabolism
The central nucleus of the amygdala (CNA) integrates visceral responses to stress partially through efferent projections to portions of the medial nuclei of the solitary tracts (mNTS) containing catecholaminergic neurons. To determine anatomical sites for CNA modulation of these neurons, immunoperoxidase detection of anterogradely transported Phaseolus vulgaris-leucoagglutinin (PHA-L) or biotinylated dextran amine (BDA) was combined with immunogold-silver labeling of the catecholamine-synthesizing enzyme, tyrosine hydroxylase, in adult rat mNTS. From 350 anterogradely labeled terminals identified within the intermediate mNTS, 30% formed symmetric, inhibitory-type synapses and the remainder lacked recognized junctions as seen within a single plane of section. Of the terminals forming symmetric synapses, 16% were presynaptic to tyrosine hydroxylase immunoreactive dendrites and the remainder to unlabeled dendrites. The level of tyrosine hydroxylase immunoreactivity as assessed by density of gold-silver particles was significantly lower in dendrites receiving synaptic input from CNA efferents as compared with dendrites of the same sizes (2.0 microns 2 in mean area) which received synapses from unlabeled terminals or lacked recognizable synaptic inputs. When separately examined without regard to afferent input, the medium- and larger-sized dendrites having mean cross-sectional areas of 1-3 microns 2 also contained significantly less tyrosine hydroxylase immunoreactivity than small (< 1 micron 2) dendrites. These results suggest that CNA efferents to the mNTS inhibit non-catecholamine-containing neurons and a subpopulation of catecholaminergic neurons distinguished by their low levels of tyrosine hydroxylase. The findings also indicate that small, presumably more distal, dendrites in the intermediate mNTS may synthesize and/or release catecholamines.

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