Direct fiber connections between the frontal cortex and the hypothalamus in the rat: an electron microscope study

The direct fiber connections between the frontal cortex and the hypothalamus, especially the ventromedial nucleus and the lateral hypothalamus have been studied by electron microscopy using the orthograde terminal degeneration technique. The results obtained are as follows: Typical electron dense degeneration of the axon terminals is constantly recognized in the neuropil of the lateral hypothalamus on the same side following a lesion of the frontal cortex. On the other hand, the degenerating terminals are found in the field of the neuropil of the frontal cortex following the lesions of either the VMH or the LH, exclusively ipsilaterally. The present study demonstrates the existence of direct fiber connections from the frontal cortex to the LH and from the LH to the frontal cortex in the rat, and suggests the possible existence of a direct projection from the VMH to the frontal cortex.