The Afferent Path of the Milk-Ejection Reflex in the Brain of the Guinea-Pig

Abstract

The afferent path of the milk-ejection reflex has been studied in the brain of the lactating guinea-pig in light pentobarbitone anaesthesia. Square\x=req-\ wave pulses were applied between an indifferent electrode in the scalp and a monopolar electrode inserted stereotaxically in the brain. The brain was transected at the mid-cerebellar level to eliminate activation of the sympathetico-adrenal system, and milk-ejection pressure was monitored to detect release of neurohypophysial hormone(s).The afferent path of the reflex in the caudal midbrain was very compact and lay in the lateral tegmentum. More rostrally, milk-ejection responses were obtained from the tectum and mesencephalic central grey, but the major pathway remained in the lateral tegmentum and passed forward to lie ventromedial to the medial geniculate body, after which it divided into two components which we have termed the dorsal and ventral paths.The dorsal path traversed dorsomedially across the brainstem to reach the parafascicular thalamic nucleus, the extreme rostral central grey and the periventricular region at the meso-diencephalic boundary, and then continued forward to reach the pituitary stalk and the medial and dorsal hypothalamus. The ventral path traversed ventromedially to enter the subthalamus and then the lateral hypothalamus, in which it passed both to the rostral basal diencephalon and to the pituitary stalk.In the diencephalon, milk-ejection responses were obtained after stimulation of part of the ventral thalamus, the lateral, dorsal and anterior hypothalamic areas, the dorsomedial, ventromedial, arcuate, supraoptic and paraventricular nuclei, and the pituitary stalk.It is suggested from these findings that in the guinea-pig the suckling stimulus ascends by the spinothalamic system, and continues rostrally to relay with the medial and ventral thalamus, the dorsal longitudinal fasciculus and the medial forebrain bundle. Other ascending pathways in the medial lemniscus and mammillary peduncle may also be involved, but appear to be of only minor significance.

The hypothalamic neurosecretory pathways for the release of oxytocin and vasopressin in the cat

“…This work establishes that there are afferent pathways from the mammary gland and the uterus to the PVN. In the guinea-pig and rabbit the afferent pathway of the milkejection reflex has also been traced to the paraventricular nucleus (Tindal et al 1967(Tindal et al , 1969.…”

The winged helix gene,Foxb1, controls development of mammary glands and regions of the CNS that regulate the milk-ejection reflex

“…Lesions in the mammillothalamic tract have been linked to the prevention of seizures but have not been correlated to the milk ejection reflex (Mirski and Ferrendelli, 1984). Other work has implicated the tegmentum, which lies just ventral to the tectum, in this reflex by demonstrating that the milk ejection reflex pathway passes in close association with the posterior thalamic complex near the medial geniculate body (Tindal et al, 1967(Tindal et al, , 1969, which in turn receives projections from the inferior and superior colliculi (Powell and Hatton, 1969) (see Fig. 6).…”

The Afferent Pathway of the Milk-Ejection Reflex in the Mid-Brain of the Goat

“…More recently, the afferent pathway of the milk-ejection reflex has been located in the mid-brain of the guinea-pig and rabbit (Tindal, Knaggs & Turvey, 1967, 1969 and its forward projection to the hypothalamus has been described in detail in the guinea-pig (Tindal & Knaggs, 1971). From these studies it was concluded that the pathway in the mid-brain was compact and lay bilaterally in the lateral tegmentum in association with the spinothalamic tract.…”