GABA-ergic innervation of thyrotropin-releasing hormone-synthesizing neurons in the hypothalamic paraventricular nucleus of the rat.
To determine whether GABA-ergic axons are anatomically situated to directly influence TRH neurons in the PVN, double-labeling light- and electronmicroscopic immunocytochemistry was performed using antisera against glutamic acid decarboxylase (GAD) and prothyrotropin-releasing hormone (proTRH). In the anterior, periventricular and medial parvocellular subdivisions of the PVN, GAD-immunoreactive (IR) axon varicosities were closely apposed to all proTRH containing cell bodies and proximal dendrites. Ultrastucturally, GAD-IR nerve terminals established symmetric type synapses with both perikarya and dendrites of proTRH-IR neurons, indicating the inhibitory nature of the contacts. Since a subpopulation of neuropeptide Y (NPY) neurons in the hypothalamic arcuate nucleus co-synthesize GABA, and NPY-containing neurons of arcuate nucleus origin densely innervate TRH neurons in the PVN, we performed triple labeling immunocytochemistry to elucidate the origin of the GAD-IR innervation of hypophysiotropic TRH neurons. While axons co-containing GAD and NPY were observed throughout the PVN, only approximately 10% of GAD-IR terminals in contact with TRH neurons were found to contain NPY-immunoreactivity. We conclude that GABA-ergic neurons are in position to act directly on hypophysiotropic TRH neurons and while this innervation arises partly from neurons in the arcuate nucleus that co-synthesize NPY, the majority of the GABA-ergic input arises from other neuronal groups.
Fekete
Csaba
C
Department of Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary.
Wittmann
Gábor
G
Liposits
Zsolt
Z
Lechan
Ronald M
RM
D000344:Afferent Pathways / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000378:metabolism / Q000648:ultrastructure; D003712:Dendrites / Q000378:metabolism* / Q000648:ultrastructure; D004734:Energy Metabolism / Q000502:physiology; D005508:Food Deprivation / Q000502:physiology; D005968:Glutamate Decarboxylase / Q000378:metabolism; D007030:Hypothalamo-Hypophyseal System / Q000378:metabolism / Q000648:ultrastructure; D007150:Immunohistochemistry; D008297:Male; D008854:Microscopy, Electron; D009433:Neural Inhibition / Q000502:physiology; D009478:Neuropeptide Y / Q000378:metabolism; D010286:Paraventricular Hypothalamic Nucleus / Q000378:metabolism* / Q000648:ultrastructure; D017729:Presynaptic Terminals / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D009435:Synaptic Transmission / Q000502:physiology; D013963:Thyroid Hormones / Q000378:metabolism; D013973:Thyrotropin-Releasing Hormone / Q000096:biosynthesis* / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D009478:Neuropeptide Y; D013963:Thyroid Hormones; D005680:gamma-Aminobutyric Acid; D013973:Thyrotropin-Releasing Hormone; D005968:Glutamate Decarboxylase