Subcellular localization of neurotransmitters and releasing factors in the rat median eminence.

The neurohaemal part of the median eminence of the rat hypothalamus is characterized by numerous nerve terminals which end near a rich network of fenestrated capillaries. An attempt was made to isolate different types of nerve terminals by means of sucrose density-gradient centrifugation. The subcellular fractions obtained were assayed for dopamine, noradrenaline and 5-hydroxytryptamine. In addition FSHand GH-releasing activities were determined. A sample of each fraction obtained was taken for electron microscopical observations. Dopamine, noradrenaline, 5-hydroxytryptamine, GHand FSH-releasing factors were present in higher concentration in the nerve endings. A further fractionation showed that noradrenaline was present in the lightest synaptosomal band, dopamine in the middle one, and 5-hydroxytryptamine in the heaviest. GH-RF and FSH-RF were recovered mainly from the band containing dopamine. The relevance of this localization to the physiological role of the median eminence is discussed.

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