mTOR

mTOR (mechanistic target of rapamycin) is a protein kinase — an enzyme that activates other proteins by adding phosphate groups — sitting at the centre of a signalling network that governs cell growth, protein synthesis, and the recycling of cellular material.

In neurons it takes on a more specific role: when activated by upstream signals, it enables the rapid production of structural proteins at synapses, supporting the formation of new dendritic spines — the small protrusions on nerve cells where incoming signals are received.

It appears across this encyclopedia primarily in discussions of psychedelics, where it features in a proposed neuroplasticity pathway alongside BDNF and the receptor TrkB. That evidence base is real but largely preclinical; much of it rests on cell culture and animal models.

How it works · its role

mTOR exists inside the cell as part of two distinct complexes, mTORC1 and mTORC2. In the context of neuroplasticity, mTORC1 is the relevant one. It integrates signals from upstream sensors — among them the growth-factor receptor TrkB and the kinase Akt — and, when active, phosphorylates proteins that govern translation: the cellular process of building new proteins from genetic instructions.

At synapses, this means an activated mTOR cascade can rapidly supply the structural proteins a neuron needs to grow or stabilise new dendritic spines. This local, demand-driven synthesis is thought to be one mechanism underlying synaptic strengthening during learning and memory consolidation.

mTORC1 also acts as a brake on autophagy — the process by which cells break down and recycle their own components. The balance between building and clearing is considered important for long-term synaptic maintenance.

Relevance to substances & effects

The mTOR pathway enters this encyclopedia most directly through serotonergic psychedelics. Psilocin, LSD, and related compounds appear to act as agonists at TrkB — the receptor for brain-derived neurotrophic factor (BDNF) — at concentrations lower than those required to activate serotonin receptors. TrkB activation feeds into the PI3K–Akt–mTOR cascade, and the result in cell and animal studies is measurable growth of dendritic spines.

This is the cellular basis for the term psychoplastogen: a compound proposed to promote structural synaptic plasticity. Ketamine's rapid antidepressant effects are thought to involve a related but distinct route — AMPA receptor potentiation leading to BDNF release, then TrkB activation, then mTOR signalling downstream.

The clinical significance of these findings is actively debated. Human neuroimaging broadly supports increased neural connectivity following psychedelic use, but direct mechanistic confirmation of the mTOR pathway in living human brains remains limited.