Hypothalamic Leu-enkephalin-immunoreactive fibers terminate on calbindin-containing somatospiny cells in the lateral septal area of the rat.
Correlated light and electron microscopic double-immunostaining experiments for Leu-enkephalin and calbindin were employed to determine the postsynaptic targets in the septal complex of Leu-enkephalin fibers. Chronic surgical isolation of the septal complex from its hypothalamic afferents and retrograde tracer studies using wheat germ agglutinin-conjugated horseradish peroxidase, both followed by an immunostaining for Leu-enkephalin, were performed to elucidate the location of the origin of these axon terminals. Furthermore, a colocalization study for glutamic acid decarboxylase and Leu-enkephalin was carried out on hypothalamic sections to determine their possible coexistence in cells projecting to the lateral septum. These studies revealed that 1) Leu-enkephalin-immunoreactive axons form pericellular baskets around a population of lateral septal area neurons; 2) they establish exclusively asymmetric synaptic contacts on their soma and initial dendritic segments; 3) 10% of the lateral septal area calbindin-containing cells, which are all of the gamma-aminobutyric acid (GABA)-ergic somatospiny type, are innervated by Leu-enkephalin-immunoreactive baskets; 4) only 40% of the Leu-enkephalin target neurons are calbindin immunopositive; 5) the septopetal Leu-enkephalin fibers derive from neurons located in the ipsilateral perifornical area and anterior hypothalamus; and 6) none of their cells of origin cocontains the inhibitory transmitter GABA. These observations indicate that hypothalamic Leu-enkephalin-containing neurons are non-GABAergic excitatory cells. Hence, they can effectively stimulate a population of lateral septal area neurons, including the somatospiny cells, which are all GABAergic. Therefore, after stimulatory Leu-enkephalin action, these neurons can inhibit their postsynaptic targets, including other projective lateral septal neurons.
Szeidemann
Z
Z
Department of Obstetrics and Gynecology, Yale University School of Medicine, New Haven, Connecticut 06520-8063, USA.
Shanabrough
M
M
Leranth
C
C
D000818:Animals; D064026:Calbindins; D004743:Enkephalin, Leucine / Q000032:analysis*; D007031:Hypothalamus / Q000737:chemistry*; D007150:Immunohistochemistry; D009411:Nerve Endings / Q000737:chemistry*; D009412:Nerve Fibers / Q000737:chemistry*; D009419:Nerve Tissue Proteins / Q000032:analysis; D009474:Neurons / Q000737:chemistry*; D051381:Rats; D017207:Rats, Sprague-Dawley; D064030:S100 Calcium Binding Protein G / Q000032:analysis; D012688:Septum Pellucidum / Q000737:chemistry*; D005680:gamma-Aminobutyric Acid / Q000032:analysis
D064026:Calbindins; D009419:Nerve Tissue Proteins; D064030:S100 Calcium Binding Protein G; D005680:gamma-Aminobutyric Acid; D004743:Enkephalin, Leucine