Collateral projection from the amygdalo--hippocampal transition area and CA1 to the hypothalamus and medial prefrontal cortex in the rat.

Amygdaloid and hippocampal neurons projecting to both the medial prefrontal cortex and hypothalamus by way of axon collaterals were examined in the rat by double labeling method using fluorescence retrograde tracers. Fluoro-gold was injected in the medial prefrontal cortex, while Fluoro-red was injected into the ventromedial and ventral premammillary nuclei of the hypothalamus. The results indicated that neurons which sent axon collaterals to both the medial prefrontal cortex and hypothalamus constituted 50 or 30% of populations of medial prefrontal cortex-projecting neurons in the amygdalo-hippocampal transition area or in CA1, respectively. Possible roles of the neurons with axon collaterals in sexually related aggressive and/or defensive behavior were discussed.