TRP channel activation and cholinergic signaling in insect thermoregulation: evidence from the American cockroach.

Transient receptor potential (TRP) channels mediate insect thermosensation, yet the downstream neurotransmitter pathways linking TRP activation to behavioral output remain unclear. We investigated the role of nicotinic acetylcholine receptors (nAChRs) in thermoregulatory and neural responses induced by TRP ligands in the American cockroach, Periplaneta americana. Extracellular recordings from the ventral nerve cord showed that capsaicin reduced spontaneous neuronal firing, whereas the selective α7-containing nAChR antagonist MG 624 increased baseline activity. Notably, nicotinic receptor blockade prevented the capsaicin-induced suppression of neuronal activity, suggesting an interaction between cholinergic signaling and capsaicin-induced neuronal modulation. Behaviorally, capsaicin shifted thermal preference toward cooler temperatures, consistent with TRP-mediated heat avoidance. This response, as well as the effect of the TRPV1 antagonist capsazepine, was markedly attenuated by MG 624 pretreatment. Grooming assays revealed differential modulation of antennal and leg grooming, suggesting distinct neural mechanisms and partial interaction between cholinergic and monoaminergic pathways. Despite pronounced neural and behavioral effects, neither TRP ligands nor nicotinic receptor blockade significantly altered whole-animal metabolic rate, as assessed by CO₂ production. Together, these findings indicate that cholinergic signaling contributes to behavioral responses induced by TRP ligands and interacts with capsaicin-induced neuronal modulation in P. americana. The results provide new insight into the neurochemical integration of thermosensory signaling and highlight cholinergic pathways as important contributors to insect thermoregulatory responses.