Reproducible increases in intramammary pressure after spinal cord stimulation in lactating rats.

Intramammary pressure was recorded in anaesthetized lactating rats during electrical stimulation of the anterolateral pathways in the T12/L1 region of the spinal cord. In 18 rats, electrical stimulation at 10 Hz or more for 10-30 s caused a reproducible increase in intramammary pressure. The mammary gland responses were similar to those resulting from stimulation of the neurohypophysis with the same parameters, and were eliminated after complete destruction of the neural stalk; they were not associated with any consistent change in blood pressure. In 3 rats, a mammary gland response to spinal cord stimulation was obtained only after administration of the beta-adrenergic blocker, propranolol, which facilitates suckling-induced reflex milk-ejections. These results suggest that spinal cord stimulation can cause the release of oxytocin; the functional significance of such a release is discussed in relation to the milk-ejection reflex.