Direct and indirect enkephalinergic synaptic inputs to the rat arcuate nucleus studied by combination of retrograde tracing and immunocytochemistry

The origin of both direct and indirect enkephalinergic innervation potentially able to influence neurons of the rat arcuate nucleus has been investigated by combining enkephalin immunocytochemistry and retrograde axonal transport of a wheatgerm agglutinin-Apo horseradish peroxidase-gold complex. Twe...

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Published in:	Neuroscience 1993-08, Vol.55 (4), p.1055-1066
Main Authors:	Magoul, R., Dubourg, P., Benjelloun, W., Tramu, G.
Format:	Article
Language:	eng
Subjects:	Afferent Pathways - anatomy & histology Amino Acid Sequence Anatomy Animals Arcuate Nucleus of Hypothalamus - anatomy & histology Arcuate Nucleus of Hypothalamus - physiology Axonal Transport Biological and medical sciences Brain Mapping Brain Stem - anatomy & histology Brain Stem - physiology Central nervous system Diencephalon - anatomy & histology Diencephalon - physiology Enkephalin, Methionine - analogs & derivatives Enkephalin, Methionine - analysis Enkephalins - analysis Enkephalins - physiology Fundamental and applied biological sciences. Psychology Gold Horseradish Peroxidase Hypothalamus - anatomy & histology Hypothalamus - physiology Male Microscopy, Immunoelectron Molecular Sequence Data Rats Rats, Wistar Synapses - ultrastructure Telencephalon - anatomy & histology Telencephalon - physiology Vertebrates: nervous system and sense organs Wheat Germ Agglutinins
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Summary:	The origin of both direct and indirect enkephalinergic innervation potentially able to influence neurons of the rat arcuate nucleus has been investigated by combining enkephalin immunocytochemistry and retrograde axonal transport of a wheatgerm agglutinin-Apo horseradish peroxidase-gold complex. Twenty four hours after tissue injections of small volumes (20 nl) of the tracer into the arcuate nucleus, rats were treated with colchicine and killed. In order to localize the enkephalinergic cells which directly innervate the arcuate nucleus, Vibratome sections were first silver-stained for detection of the wheatgerm agglutinin-Apohorseradish peroxidase gold complex and then processed for enkephalin immunohistochemistry. To study the indirect enkephalinergic input to the arcuate nucleus, an electron microscope detection of immunorcactivc synapses was carried out in areas rich in retrogradely labeled perikarya. Perikarya both immunoreactive and retrogradely labeled were observed ipsilaterally to the injection site in telencephalic structures such as the bed nucleus of the stria terminals is, medial preoptic and adjacent periventricular areas. Hypothalamic ipsilateral doubly labeled cells were localized principally in the dorsomedial nucleus and rostral arcuate nucleus. The major direct inputs arising from brainstem structures concerns the dorsal and ventral parabrachial nuclei. Moreover, at the ultrastructural level, numerous enkephalinergic terminals were demonstrated to synapse with retrogradely labeled perikarya and dendrites localized in the medial preoptic area, the hypothalamic paraventricular nucleus and the parabrachial nuclei providing evidence for an important enkephalinergic input on neurons projecting to the arcuate nucleus. Taken together, our light and electron microscope studies strongly suggest that the arcuate nucleus is the target of an enkephalinergic control originating from several regions and acting either directly or indirectly on neurons projecting to the arcuate nucleus.
ISSN:	0306-4522 1873-7544