Neuropeptides in Cognitive Research: Selank, Semax, and DSIP

Three small synthetic peptides developed in Russia between the 1970s and 1990s — selank, semax, and delta sleep-inducing peptide (DSIP) — occupy a distinct corner of the neuropeptide literature. All three are short, proteolytically stabilized regulatory peptides; all three are delivered intranasally in their characteristic research protocols; and all three have substantial clinical-research records published primarily in Russian-language journals with growing English-language reviews.

This brief reviews each compound, the proposed mechanisms, and the position the published record occupies relative to the broader neuropeptide literature.

Selank is a synthetic heptapeptide developed at the Institute of Molecular Genetics of the Russian Academy of Sciences. The sequence (Thr-Lys-Pro-Arg-Pro-Gly-Pro) extends the natural immunomodulatory tetrapeptide tuftsin with a Pro-Gly-Pro tripeptide that confers stability against aminopeptidase cleavage and enables intranasal CNS delivery.

The proposed mechanism is multimodal. The most-cited activity is anxiolytic effect without sedation, dependence, muscle relaxation, or cognitive impairment — a profile distinct from benzodiazepines and most other anxiolytic compounds. Mechanistically the compound modulates GABAergic tone without binding the GABA-A receptor directly; engages enkephalinase inhibition, raising endogenous enkephalin tone; and increases hippocampal brain-derived neurotrophic factor (BDNF) and TrkB expression.

The clinical-research record includes trials in generalized anxiety disorder and adjustment disorders, primarily conducted in Russian institutions. The Western-language clinical record is essentially absent. For research applications, selank is studied in models where anxiolytic mechanism characterization is the experimental question.

Semax is a synthetic heptapeptide (Met-Glu-His-Phe-Pro-Gly-Pro) developed at the same Russian institute, derived from a fragment of adrenocorticotropic hormone (ACTH 4-7) with a Pro-Gly-Pro stabilizing tail. The compound is registered as a medication in Russia for cerebrovascular and cognitive indications.

The mechanism includes modulation of dopaminergic and serotonergic systems, increased hippocampal BDNF expression, and effects on neuroplasticity-related gene expression. Distinct from selank, semax has nootropic and neuroprotective activity in stroke and ischemic injury models — the rodent literature is substantial in this area and supports the clinical registration in cerebrovascular indications.

The Russian clinical-research record on semax in stroke recovery is the largest body of human data on any compound in this brief. Reproducibility outside Russia has not been systematically tested.

DSIP is a 9-amino-acid peptide (Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu) originally isolated from rabbit cerebral venous blood during electrical stimulation of the thalamic sleep-induction region. The discovery dates to the 1970s and the compound has been characterized in sleep, stress-response, and analgesic contexts.

The mechanism remains incompletely characterized. Reported activities include modulation of slow-wave sleep architecture, normalization of stress-axis activity, modulation of endorphin and enkephalin tone, and effects on circadian and ultradian rhythms. The receptor target has not been definitively identified — DSIP is one of the few well-characterized neuropeptides without a confirmed receptor, which is a notable limitation of the mechanism literature.

The clinical-research record is older than the other two compounds and concentrated in the 1980s and 1990s. Modern reviews exist but the body of contemporary clinical work is limited.

All three compounds share intranasal administration as the characteristic route in their research protocols. The pharmacokinetic rationale is twofold: short systemic half-life makes parenteral administration impractical for sustained CNS effect, and intranasal delivery achieves CNS exposure via the olfactory and trigeminal pathways while minimizing peripheral exposure.

All three are proteolytically stabilized by sequence design — Pro-Gly-Pro tails in selank and semax, natural resistance to proteolysis in DSIP — which is essential for intranasal delivery to produce measurable CNS effects.

The most important contextual note for these three compounds is the language and geography of the published record. The Russian neuropeptide research tradition is substantial and methodologically reasonable, but it is largely separate from the Western neuroscience literature and reproducibility has not been systematically established in Western laboratories.

For a clinician reading the evidence, this means: the rodent mechanism work is reasonably well-characterized; the Russian clinical-research record is real but not independently reproduced at scale; and any extrapolation to Western clinical contexts rests on that gap. The compounds are best characterized as research tools with substantial preclinical signal and limited independent clinical confirmation outside Russia.

Selank, semax, and DSIP occupy a distinct corner of the neuropeptide literature defined by intranasal delivery, proteolytic stabilization through sequence design, and a research record concentrated in Russian institutions. For a practitioner discussing the compounds, the cleanest framing is to characterize the mechanism work as substantial and the independent clinical replication as limited, and to read the literature on those terms.