Monosynaptic facilitatory pathway from the hypothalamic ventromedial nucleus to the frontal cortex in the rat.

Stimulation of the ventromedial nucleus (VMH) evoked a short latency negative wave with two peaks (cN1 and cN2) followed by a small positive wave (cP) at the ipsilateral dorsal frontal cortex (area 10) in the rat. The maximum response was observed from the lateral edge of the frontal pole. From the depth profiles of recordings, cN1 changed polarity at a depth of about 4 mm and the cN1-cN2 changed into a large compound action potential at the medioventral part of the frontal pole at a depth of about 6 mm. Since the surface evoked potential and the compound action potential followed high frequency stimulation, these respective potentials are concluded to be due to antidromic and monosynaptic activation of the cortical neurons. This was verified by unit recording experiments. The cP was concluded to be produced by the initial rise of the monosynaptic EPSP.