Psilocybin and ketamine affect novel neuropeptides gene expression in the rat hypothalamus

Psychedelics are able to trigger highly intense and profound alterations in self-consciousness, perception, affective, and cognitive processes. Indeed, recent studies show that ketamine and psilocybin could be used as fast-acting antidepressants. However, the molecular and neurochemical mechanisms of these psychedelics and their actions at the level of diverse brain structures remains so far unclear. Hypothalamic neuropeptides are involved in a wide spectrum of neuronal activities being responsible for the central control of all fundamental autonomic functions.

The purpose of this exploratory pilot study was to assess the gene expression of both classical and novel neuropeptides, including nesfatin-1, phoenixin (PNX), spexin (SPX), neuromedin U (NMU), neuropeptide S (NPS), and their known receptors in the hypothalamus of male Wistar-Han rats subjected to single injections of psilocybin (dose 2 or 10 mg/kg) and ketamine (dose10 mg/kg). Total mRNA was isolated from homogenized tissue and real-time PCR was used for estimation of related gene expression.

It was found that a single administration of the higher dose of psilocybin increased the mRNA expression of most noncanonical neuropeptides examined in the study, with only the case of NMU there with a decrease in gene expression. Interestingly, psilocybin administration also increased mRNA expression of the serotonin receptors: 5-HT1A, 5-HT2A, and 5-HT2B, but not 5HT-2C. In contrast, the effect of ketamine on the expression of neuropeptides was much more limited compared to psilocybin, only increasing transcripts of NUCB2, GPR173, and POMC were demonstrated.

These results suggest for the first time that selected psychedelics may enhance the signaling of 5-HT2A receptors or inhibit NMDA receptor activity, affecting neuropeptide signaling and serotonin transmission in the rat hypothalamus, which may contribute to a better understanding of psychedelic action in the brain.