GALR1

GALR1 is the primary inhibitory galanin receptor - a class A GPCR that couples to Gi/o to suppress adenylyl cyclase, reduce cAMP, and activate GIRK channels in hippocampal, hypothalamic, amygdala, spinal cord, and dorsal root ganglion neurons. It mediates galanin's anticonvulsant, antinociceptive (in neuropathic states), and memory-modulating effects. GALR1 is the most tractable galanin receptor subtype for epilepsy and pain scaffolds, distinct from GALR2 (Gq/11, pronociceptive, proliferative) and GALR3 (Gi/o, mainly peripheral/metabolic). Every scaffold targeting neuropathic pain, epilepsy, or hippocampal circuit modulation via the galanin system routes through this card.

GALR1 (chromosome 18q23, 349 aa) adopts the canonical rhodopsin-like 7-TM GPCR fold. Galanin is a 29-aa neuropeptide (human: 30 aa) with a C-terminally amidated pharmacophore in the N-terminal 1–15 residues; residues 1–15 define the receptor-binding helix that inserts into the extracellular vestibule, while the C-terminal portion modulates subtype selectivity. GALR1 binds full-length galanin with Ki ~0.1–1 nM. Cryo-EM structures of the GALR1–Gₒ complex (2022) reveal galanin adopting an α-helical conformation parallel to the membrane in the orthosteric pocket, with inward displacement of TM2/TM6 extracellularly and outward TM6 shift intracellularly opening the Gi docking cavity. Activated Gαi inhibits adenylyl cyclase → ↓cAMP; Gβγ opens GIRK channels → membrane hyperpolarization → reduced excitability and neurotransmitter release (ACh, glutamate, substance P). GALR2 activates Gq/11 → PLC/Ca²⁺/MAPK and is pronociceptive at low doses; GALR3 is Gi-coupled but peripherally dominant. Galanin expression is upregulated after nerve injury and estrogen exposure.

No galanin receptor-targeting drug is approved. NAX 5055 (GALR1-preferring galanin analog) reduces seizure severity in rodent epilepsy models with potency superior to standard anticonvulsants - the most advanced GALR1-targeted peptide. Galantide (M15) and M35 are canonical non-selective research antagonists (galanin(1-13)/substance P or bradykinin chimeras, sub-nM affinity). SNAP 37889 is the selective GALR3 antagonist (Ki 17 nM vs. >10,000 nM at GALR1/2). For peptide research, the tractable recipes are: NAX 5055 analogs with D-amino acid stabilization for improved CNS half-life in epilepsy models; galanin(1-15) N-terminal fragments with lactam bridge cyclization for GALR1 selectivity over GALR2; chimeric galanin(1-13)/substance P variants at the GALR1/GALR2 boundary to probe subtype-specific pain pharmacology; and spexin (14-aa endogenous GALR2/3 ligand) as a scaffold for GALR2-biased probes targeting obesity and metabolic endpoints.