Sex-specific organization and synaptic signaling in prefrontal-hypothalamic circuitry.

Top down signaling from the cortex to the hypothalamus is critical to link cognitive and emotional processing to homeostasis and motivation. This study investigates signaling from the medial prefrontal cortex (mPFC) to the posterior hypothalamus (PH), a region that modulates endocrine and autonomic stress responses and motivated behaviors. The function and anatomy of this circuit was examined with patch clamp electrophysiology and mapping studies in male and female rats. Spontaneous firing properties of PH neurons were determined in a cell-type specific manner by combining a transgenic glutamic acid decarboxylase-Cre rat with Cre-dependent colorswitch virus to determine postsynaptic cell-type identity. Overall, PH neurons were more excitable in females compared to males and, in both sexes, data indicated tonic inhibition within the PH, with significantly greater inhibition in males. Using Channelrhodopsin-assisted circuit mapping to query the mPFC-PH circuit, we found that a majority of PH neurons received input from the mPFC and mPFC synapses targeted glutamatergic cells over GABAergic PH cells. Retrograde tracing revealed more PH-projecting neurons in females, specifically within the tenia tecta and infralimbic regions of the mPFC, with significantly more stress-activated PH-projecting cells in the female prelimbic cortex. Anterograde tracing revealed, surprisingly, no sex differences in mPFC presynaptic terminal density in the PH, despite more PH-projecting cell bodies in the female mPFC. These data help to elucidate the sexual divergence in cortical-hypothalamic signaling and how cognitive and emotional information from the prefrontal cortex may differentially regulate homeostasis and motivation between sexes. Significance Statement: Neural signaling between the prefrontal cortex and the hypothalamus is important for maintaining homeostasis, particularly during contextual challenges such as stressors. Here we find multiple aspects of sex-specific organization and neurophysiology in this circuitry. Excitatory inputs from the medial prefrontal cortex target both excitatory and inhibitory neurons within the posterior hypothalamic nucleus in both sexes. However, there are sex differences in the number of stress-activated neurons in the prefrontal cortex that innervate the posterior hypothalamus, as well as differences in hypothalamic inhibitory signaling and estrous cycle-dependent effects on neuronal excitability. Altogether, these data suggest that organizational, synaptic, and hormonal factors may contribute to sex-specific behavioral and physiological integration.