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The Neural Input of the Milk Ejection Reflex in the Hypothalamus

Institute de Neurobiologia Obligado 2490, Buenos Aires, Argentina

Abstract

This paper describes an attempt to trace the afferent neural pathways to the hypothalamus involved in the milk ejection reflex and to determine the role played by the afferents to the Paraventricular nuclei in this reflex. Conscious lactating rats that were subjected to natural suckling stimuli after performing stereotaxically controlled discrete transections in the diencephalon were employed in this study.

A conical incision around the hypothalamus interrupting all nervous afferents and at the same time avoiding damage to the connections between the neurosecretory nuclei and the neurohypophysis caused blockage of the milk ejection reflex.

Simple cuts disrupting rostral, dorsal, lateral or caudal hypothalamic afferents showed that only the caudal fibers caused blockage of the milk ejection reflex.

When making multiple cuts simultaneously interrupting afferents to two or three aspects of the hypothalamus in different combinations, the milk ejection reflex was blocked only when these cuts had involved caudal fibers.

The fact that only the interruption of caudal afferents caused blockage of the milk ejection reflex demonstrates that they contain the major bundles of the milk ejection afferent pathway.

Discrete transections of different afferents to the Paraventricular nuclei showed that milk ejection reflex action persisted after interrupting rostral, caudal, lateral, dorsal or ventral fibers. A spherical transection cutting off all afferents simultaneously, and at the same time causing necrosis of the nuclei also failed to block the milk ejection reflex.

These findings demonstrate that the triggering of the milk ejection reflex does not require the integrity of the Paraventricular nuclei afferents. (Endocrinology 92: 973, 1973)

Footnotes

¹ Instituto Asociado del Consejo Nacional de Investigaciones Cientificas y Técnicas de la República Argentina.

Received September 17, 1971.