The Section on Molecular Neuroscience studies the molecular components of chemically-coded neurotransmission. The laboratory is known for molecular biological characterization and functional analysis of neuropeptide and neurotransmitter vesicular transporter genes and proteins; characterizing signaling pathways for stimulus-secretion-synthesis coupling in neuroendocrine cells; and identifying PACAP as a master regulator of stress responding centrally and peripherally. The lab has recently identified NCS-Rapgef2 as a novel cAMP effector linking Gs-coupled GPCR activation to activation of the MAP kinase ERK in neurons and endocrine cells.
Cyclic AMP is perhaps the best-known second messenger controlling synaptic plasticity underlying experience-driven behavior. We have previously demonstrated that cAMP signaling is parcellated via multiple effectors in neuroendocrine cells. Thus, PKA signals through CREB to affect neuron-specific gene regulation; Epac signals through p38 to affect growth arrest; and NCS-Rapgef2 signals through ERK to affect neuritogenesis (see e.g. Emery et al., J. Biol. Chem. 292: 12220-12231, 2017). In fact, the activation of ERK by cyclic AMP, via NCS-Rapgef2, appears to be a unique feature of neurons and neuroendocrine cells in adult mammals.
Our long-term goal is to examine the parcellation of cAMP signaling during neurotransmission in the brain, at the genetic, cellular, morphological, and biochemical levels, and their penetrance to experience-driven behavior in the mouse. We do not yet know the discrete targets, in brain, of the NCS-Rapgef2/ERK-, PKA/CREB- and Epac/p38-specific cAMP signaling pathways elucidated in cellula. However, progress is being made. We now know that NCS-Rapgef2 is required for activation of ERK, and transcription of the downstream immediate early gene Egr-1/Zif268 by Gs-coupled GPCR activation in ventral striatum (nucleus accumbens, NAc) and hippocampus (see Jiang et al., eNeuro 4(5): e0248 1-17, 2017). NCS-Rapgef2 expression in ventral striatum (nucleus accumbens) is also required for cocaine-dependent activation of ERK (but not of CREB), and for cocaine-induced locomotor sensitization and conditioned place preference (see Jiang et al. bioRxiv: https://doi.org/10.1101/2020.07.02.184754). Requirements for NCS-Rapgef2 signaling in hippocampal long-term potentiation underlying contextual and cued fear memory are being studied in collaboration with the laboratories of Uri Ashery at Tel Aviv University and Hugo Tejeda in the NIMH-IRP.
Parcellated cyclic AMP signaling is likely to be functionally critical at neuropeptidergic, and catecholamine-modulated as well as glutamate-driven synapses in the brain. The Gs-coupled GPCR PAC1, the receptor for the neuropeptide PACAP, in the retinohypothalamic projection to the suprachiasmatic nucleus required for environmental re-setting of circadian rhythm through photosensitive retinal ganglion cell activation (see e.g. Lindberg et al. Frontiers in Neuroscience 13, Article 1281, 2019). A recently constructed conditional PACAP knock-out mouse, in conjunction with Rapgef2- and CREB-conditional knockout mice, are being deployed to determine the cAMP effectors required in vivo for PACAP-dependent activation of the HPA axis, PACAP-dependent stress-induced hypophagia, and PACAP-dependent aversive responding. PACAPergic synapses mediating stress-dependent relapse to cocaine preference in rodents are also being investigated, in the context of parcellated cAMP signaling in both the PACAP- and dopamine-dependent components of this translationally important behavior.
The SMN is also engaged in a long-term collaborative effort with the National Center for Advancing Translational Science (NCATS) to develop assays for high-throughput screening for PACAP antagonists. Full functioning of the PAC1 receptor, including high-affinity recognition of peptide antagonists, requires components found only in neuroendocrine cells. ‘Reverse translation’ of this finding, in conjunction with recent cryo-EM data obtained by Sexton and colleagues, and others, for the structure of the PACAP-liganded PAC1 receptor, to better understand PACAP signaling during the stress response and to develop more efficacious PAC1 antagonists, is underway.
Zheng Li, Mario Penzo, Hugo Tejeda (Dendritic Dynamics Hub, IRP)
Advice and consultation, optical imaging experimentation
Chip Gerfen (IRP)
Generation of genetically altered mice for study of NCS-Rapgef2 signaling in ventral striatum
Limei Zhang (UNAM)
Identifying role of PACAP co-transmission in excitatory and inhibitory neurons via in situ hybridization mapping studies.
Marc Ferrer, Xin Hu, and Mark Henderson (NCATS)
Assay design for high-throughput screening for PAC1 antagonists; Structural analysis of PAC1 receptor and design of peptide-based PAC1 antagonists
Eberhard Weihe (Univ. Marburg)
Chemical neuroanatomy of PACAPergic innervation and extra-neuronal expression in atherosclerosis
Uri Ashery (TAU)
Cyclic AMP and synaptic potentiation in Schaeffer collateral and perforant pathways of hippocampus
Sushil Mahata (UC San Diego)
PACAP actions at the adrenomedullary synapse-effects on exocytosis