Spinogenesis

Spinogenesis is the process by which a neuron grows new dendritic spines — the small protrusions that stud the branches of nerve cells and form the receiving end of most excitatory synapses. It is a form of structural plasticity: rather than strengthening an existing connection, it creates a new physical contact point between neurons.

The term is sometimes used interchangeably with neuroplasticity, but it is more specific. A finding that a substance drives spinogenesis means the tissue, examined under a microscope, contains more spines than before — a concrete anatomical change. Whether that change accounts for any lasting subjective or therapeutic effect in a person is a separate question, and one the field has not fully answered.

How it works · its role

New spines emerge from the actin cytoskeleton, the internal scaffold that gives a neuron its shape. NMDA receptors, which detect concurrent activity on both sides of a synapse, admit calcium into the cell when activated; this triggers a signalling cascade that reorganises actin and pushes a protrusion outward. Growth factors — particularly BDNF acting through its TrkB receptor — also drive spine formation via the mTOR pathway.

A new spine begins as a thin, unstable filopodium. Over hours or days, if it contacts an axon terminal and receives reinforcing activity, it can mature into a stable, mushroom-shaped spine with a full postsynaptic density. Many candidate spines retract before reaching that stage; those that stabilise represent genuinely new synaptic contacts.

Relevance to substances & effects

Spinogenesis comes up most often in discussions of rapidly acting antidepressants. Ketamine's fast mood effect has been linked to a rapid increase in prefrontal cortex spine density — one proposed mechanism for why improvement can follow a single dose and persist after the drug has cleared.

Research in rodents and cell cultures indicates that serotonergic psychedelics — psilocybin, DMT, LSD — can also drive rapid spinogenesis in prefrontal cortical neurons. This structural change is offered as part of the mechanistic story for their enduring antidepressant and anxiolytic effects, though the weight of evidence currently rests on animal and ex vivo work rather than direct human imaging.

SSRIs appear to promote spine density more gradually, likely through sustained BDNF upregulation. In contrast, chronic heavy use of alcohol, stimulants, and opioids has been associated with reduced spine density in some cortical regions. Spinogenesis, in this sense, sits at both ends of the spectrum: something certain substances build, and something others erode.