Two short peptides developed in Russian neuropharmacology research labs in the 1980s and 1990s have, over the past two decades, accumulated a body of literature that puts them firmly in the cognitive peptide category. Selank and Semax are structurally simple, mechanistically distinct from most Western-developed research peptides, and largely unfamiliar to researchers outside the regions where they were first characterised. Here is an overview of what published work actually reports about them.

Origins and structure

Both peptides emerged from work at the V.V. Zakusov Institute of Pharmacology in Moscow. Semax is a heptapeptide derived from a fragment of adrenocorticotropic hormone (ACTH) — specifically the 4-10 region — modified at the C-terminus to extend its biological half-life and remove the endocrine activity of the parent ACTH molecule. The result is a peptide with central nervous system effects but without the hypothalamic-pituitary-adrenal axis activation that characterises ACTH itself.

Selank is a heptapeptide derived from tuftsin, an immunomodulatory fragment of immunoglobulin G. Like Semax, the natural sequence was modified at the C-terminus to extend stability. Both peptides share a similar engineering philosophy: take a short bioactive fragment with known central effects, stabilise it for in-vivo work, and characterise its behaviour as an isolated research compound.

The BDNF connection

One of the most replicated findings in Semax research is upregulation of brain-derived neurotrophic factor (BDNF) expression in specific brain regions following peptide administration in rodent models. BDNF is a central player in synaptic plasticity, neuronal survival, and learning-related circuit remodeling. The Semax effect on BDNF appears to be rapid, regionally specific (particularly in hippocampal and cortical tissue in published studies), and reproducible across multiple laboratories.

The mechanism by which Semax produces this effect is not fully resolved. Proposed pathways include modulation of melanocortin receptor signaling, direct effects on neurotrophin gene transcription, and indirect effects through neurotransmitter systems. The downstream consequences observed in animal models — effects on memory performance in standard learning paradigms, attentional measures, and recovery markers in injury models — appear to depend on this BDNF response.

Selank and the anxiolytic literature

Selank’s most studied behavioural effect in animal models is anxiolytic-like activity in standard tests (elevated plus maze, open field, light-dark box). Unlike benzodiazepines, Selank does not appear to act primarily through GABA-A receptor potentiation in published mechanistic studies. The proposed pathway involves modulation of serotonergic and possibly enkephalinergic systems, alongside effects on cytokine profiles that link back to the peptide’s tuftsin origin.

This mechanistic distinction is what makes Selank interesting as a research tool: it produces anxiolytic-like behavioural readouts without the sedation, motor impairment, or tolerance development typically associated with GABAergic compounds in the same animal assays.

Intranasal administration as a research route

Both peptides have been extensively studied via intranasal administration in animal models. The route bypasses first-pass metabolism and provides a more direct path to central nervous system compartments through olfactory and trigeminal pathways. Intranasal pharmacokinetic studies in rodents have measured peptide entry into cerebrospinal fluid within minutes of administration, supporting the use of this route in mechanistic research.

For research design purposes, intranasal administration introduces its own variables: solution volume, concentration, the specific delivery device, and animal positioning all affect bioavailability and need to be standardised across experimental groups.

Half-life and structural stability

Native ACTH(4-10) and native tuftsin both have very short biological half-lives — on the order of minutes in plasma. The C-terminal modifications introduced in Semax (Pro-Gly-Pro) and Selank (Pro-Gly-Pro) extend functional half-life substantially by resisting carboxypeptidase cleavage. This is a deliberate piece of medicinal chemistry, not an accident: the parent fragments would not be useful research compounds without this stabilisation.

Open mechanistic questions

Despite the accumulated literature, several mechanistic questions remain active in the research field:

• Whether Semax’s central effects depend primarily on melanocortin receptor signaling or on other receptor systems.
• The molecular target responsible for Selank’s anxiolytic-like profile in animal models.
• The relationship between immune modulation effects (clearer for Selank, due to its tuftsin origin) and the central nervous system observations.
• The translation of rodent BDNF effects to other species in well-controlled studies.

These open questions are what make the compounds active research subjects rather than closed chapters.

Research handling notes

Both peptides are typically supplied lyophilized and dissolve readily in sterile water or bacteriostatic water. Standard aliquoting and -20°C storage practices apply. HPLC purity verification is essential because the modified terminal residues are sensitive to incomplete coupling during synthesis, which can produce sequence-related impurities that complicate mechanistic interpretation.

Related reading: Peptides Explained: The Ultimate Guide