A Neurophysiological Approach to the Identification, Connections and Pharmacology of the Hypothalamic Tuberoinfundibular System

Abstract

Hypothalamic hypophysiotropic or ‘tuberoinfundibular’ neurons can be identified by antidromic activation following electrical stimulation on the surface of the median eminence. These neurons appear to be localized within the medial hypothalamic and preoptic areas. Both the source and the nature (i.e. excitatory or inhibitory) of connections of these identified neurons can be examined with electrophysiological methods. Afferent pathways appear to originate in the medial preoptic area, amygdala, hippocampus, lateral septum and retina. Axon collaterals of some tuberoinfundibular neurons engage recurrent excitatory and inhibitory pathways and/or project to the anterior hypothalamic area, medial preoptic area, paraventricular nucleus, amygdala, lateral septum and midline thalamus. Neuropharmacological studies indicate that gamma-aminobutyric acid, catecholamines and possibly some hypothalamic peptides may participate in synaptic transmission in afferent or efferent connections in the tuberoinfundibular system.

In vitro Neurophysiology of Identified Rat Hypothalamic ‘Neuroendocrine’ Neurons

“…2) served to identify 14 tuberoinfundibular neurons. Antidromic activation laten cies ranged from 3 to 8 ms. Spontaneous activity patterns resembled those seen in in vivo recordings [9], Following antidromic activation, two spontaneously active tuberoin fundibular cells displayed a silent period of 100-140 ms which could be observed at current intensities below the threshold for antidromic activation, and suggested activation of a recurrent inhibitory pathway. Twelve of the non-antidromically activated mediobasal hypothalamic cells dis played orthodromic activation to the same stimulus, sug gesting that they were interneurons activated through axon collaterals of tuberoinfundibular neurons.…”

“…5, 8-10 for re view] have defined at least two general populations of mam malian hypothalamic 'neuroendocrine' neurons: tuberoin fundibular cells, projecting to the median eminence and secreting releasing or release-inhibiting factors into the pi tuitary portal circulation; neurohypophyseal cells, project ing to the neural lobe of the pituitary and secreting peptide hormones into the systemic circulation. During in vivo neu rophysiological experiments, antidromic activation from axon terminals in the median eminence [9] or the neural lobe/pituitary stalk [8] serves to identify tuberoinfundibular or neurohypophyseal neurons, respectively. However, lack of recording stability has generally restricted these in vivo electrophysiological investigations to extracellular observa tions.…”

Association of Cocaine- and Amphetamine-Regulated Transcript-Immunoreactive Elements with Thyrotropin-Releasing Hormone-Synthesizing Neurons in the Hypothalamic Paraventricular Nucleus and Its Role in the Regulation of the Hypothalamic–Pituitary–Thyroid Axis during Fasting

“…Several possibilities should be considered. Because the PVN contains a large number of CART-IR neurons and immunohistochemical and electrophysiological studies have provided evidence for the existence of synaptic connections between neurons within the parvocellular PVN itself (Renaud, 1981;Swanson and Sawchenko, 1983), these CART-IR axon varicosities may originate locally within the PVN. Alternatively, TRH neurons in the PVN may be innervated by CART-containing axons originating from neuronal groups outside the PVN.…”

A synaptocentric view of the neuroendocrine response to stress

“…, 2002). Parvocellular and magnocellular neuroendocrine cells have been identified through the use of electrophysiological manipulations [antidromic activation of their efferent targets (Renaud, 1981)] or dye uptake [retrograde labels such as DiI or fluorogold, taken up at terminals in the pituitary (Dyball et al. , 1991; Yang et al.…”