Top down signaling from the cortex to the hypothalamus is critical to link cognitive and emotional processing to homeostasis and motivation. Acute activation of the circuit from the medial prefrontal cortex (mPFC) to the posterior hypothalamus (PH), a region that modulates stress responding and cardiovascular function, produces sexually divergent physiological stress responses. We hypothesized that this divergence could be explained by PH neuronal excitability and differential postsynaptic targeting of the excitatory mPFC inputs within the PH. The function and anatomy of this circuit was tested with patch clamp electrophysiology and tracing studies in male and female Sprague Dawley and Long Evans rats (PND 72-141). A triple transgenic approach, using transgenic GAD-Cre rats, Cre-dependent Colorswitch virus, and channelrhodopsin (ChR2), was used to investigate circuit-specific inputs onto postsynaptically defined neurons within the PH. Both anterograde and retrograde tracing was conducted to gain a comprehensive understanding of circuit organization and stress reactivity. Within the PH, spontaneous firing properties were similar between males and females, with increased excitability in female neurons compared to males and spontaneous action potential frequency dependent not on sex, but on estrous phase. Spontaneous excitatory postsynaptic current (sEPSCs) and inhibitory postsynaptic current (sIPSC) analysis revealed inhibitory tone in both male and female PH, consistent with previously reported in vivo evidence. This inhibitory tone was significantly elevated in males compared to females. Interestingly, spontaneous firing properties were indistinguishable between glutamatergic and GABAergic neurons within the PH. At the mPFC-PH circuit level, the majority of PH neurons received mPFC inputs. In males, mPFC inputs preferentially synapsed onto GFP-expressing glutamatergic PH neurons over mCherry-expressing GABAergic PH neurons. This preference was not observed in females. Retrograde tracing indicated significantly greater PH projection density in females than males within the tenia tecta (TT) and infralimbic (IL) regions of the ventral mPFC. However, an equal proportion of PH-projecting mPFC neurons was activated by acute restraint stress in males and females. Anterograde tracing revealed, surprisingly, a comparable density of mPFC terminals within the PH, indicating that male and female rats have a similar density of presynaptic input despite the significantly greater number of PH-projecting neurons within the mPFC of female rats. Together, these results elucidate anatomical and neurophysiological mechanisms of circuit connectivity that help to explain sexual divergence in stress responding between males and females. Data from this project identify mechanisms for the sexual divergence in the function of cortical-hypothalamic signaling and how cognitive and emotional signaling from the prefrontal cortex differentially regulates homeostasis and motivation between sexes. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Bouchet et al. (Fri,) studied this question.