The supramammillary region of the cat sends substance P-like immunoreactive axons to the hippocampal formation and the entorhinal cortex.

A combined method of the tracing of WGA-HRP (wheat germ agglutinin-conjugated horseradish peroxidase) and the immunohistochemistry of substance P (SP) showed that many SP-like immunoreactive neurons in the supramammillary nucleus of cat hypothalamus sent their axons to the hippocampal formation. SP-like immunoreactive axons in the hippocampal formation and entorhinal cortex were markedly reduced in number ipsilaterally after placing an electrothermic lesion in the supramammillary region of the hypothalamus.