Transient cAMP production drives rapid and sustained spiking in brainstem parabrachial neurons to suppress feeding

Abstract

Brief stimuli can trigger longer lasting brain states. G protein-coupled receptors (GPCRs) could help sustain such states by coupling slow-timescale molecular signals to neuronal excitability. Brainstem parabrachial nucleus glutamatergic neurons (PBNGlut) regulate sustained brain states such as pain, and express Gs-coupled GPCRs that increase cAMP signaling. We asked whether cAMP directly influences PBNGlut excitability and behavior. Both brief tail shocks and brief optogenetic stimulation of cAMP production in PBNGlut neurons drove minutes-long suppression of feeding. This suppression matched the duration of prolonged elevations in cAMP, Protein Kinase A (PKA), and calcium activity in vivo and in vitro. Shortening this elevation in cAMP reduced the duration of feeding suppression following tail shocks. cAMP elevations in PBNGlut neurons rapidly lead to sustained increases in action potential firing via PKA-dependent mechanisms. Thus, molecular signaling in PBNGlut neurons helps prolong neural activity and behavioral states evoked by brief, salient bodily stimuli.

Competition between stochastic neuropeptide signals calibrates the rate of satiation

“…These feeding-related calcium responses during biPACstimulation sessions continued to grow across trials, ultimately exceeding the amplitude of control traces (Figures 7A topmiddle and 7B). In the absence of feeding, biPAC stimulation did not excite PVH MC4R neurons in vivo 98,113 (Figures 7A and S7C-S7F). The accelerated emergence of excitation is likely caused by cAMP-mediated synaptic plasticity that strengthens excitatory inputs [114][115][116] , as whole-cell recordings in brain slices show that cAMP production by biPAC activation triggers a small but consistent potentiation of spontaneous EPSC (sEPSC) amplitudes (Figures 7C-7E; see Figures S7G-S7I for additional slice data).…”

“…Photometry measurements of Axon-GCaMP6s 97 in vivo showed that our stimulation protocol triggers short-lived calcium transients with similar amplitudes and decay kinetics in fasted and fed mice (Figures S5A-S5B), ruling out the axonexcitability hypothesis. To test the second hypothesis, we compared the clearance kinetics of cAMP produced by the bluelight-activated adenylyl cyclase, biPAC 55,98,99 . In brain slices from fasted and fed mice, cAMP clearance in PVH MC4R neurons occurred within several minutes and did not differ between fasted and fed states (Figure S5C), ruling out the cAMPclearance hypothesis.…”

“…Therefore, we used a classifier to apply to determine hit trials (increments or decrements) or miss trials (no change in cAMP). Previous studies showed slow cAMP dynamics across many different brain areas 55,95,98,99 , so we assumed that cAMP also operates on a slow timescale in the PVH and pre-smoothed the single-trial cADDis trials before classification. The classifier is based on the area under receiver operating characteristic curve (auROC) applied to ΔF/F0 data from the pre-stimulation baseline and the post-stimulation period.…”