The scientific interest in this combination comes from the different research pathways represented by the two components, with dedicated functional-connectomic work examining both peptides’ effects side by side (Learn more). Semax literature frequently examines BDNF, neuronal plasticity, learning and oxidative-stress responses; Selank literature includes GABAergic signalling, stress-related models and neuroimmune regulation, alongside related nootropic-research peptides such as Semax and Selank individually.
Semax: four residues borrowed from ACTH
Semax begins as a piece of adrenocorticotropic hormone. Its opening residues, Met-Glu-His-Phe, match positions 4 to 7 of ACTH, part of a region that animal studies linked to attention and learning decades ago, separate from the hormone's job of signalling to the adrenal glands. Chemists at the Institute of Molecular Genetics of the Russian Academy of Sciences added Pro-Gly-Pro to that fragment, giving the heptapeptide Met-Glu-His-Phe-Pro-Gly-Pro (C37H51N9O10S, about 813.9). Papers usually describe it as a non-hormonal analogue of ACTH(4-10).
Its best-known mechanistic result comes from the rat hippocampus. After a single application, Semax raised BDNF protein by up to 1.4-fold and phosphorylation of the BDNF receptor TrkB by 1.6-fold, while messenger RNA for BDNF exon III rose threefold (Learn more). The same rats produced more conditioned avoidance responses in a learning task, tying the molecular change to behaviour in that model. BDNF (brain-derived neurotrophic factor) is a key growth signal for synaptic plasticity, so this result anchors much Semax work.
Selank: tuftsin rebuilt for neuroscience research
Tuftsin is a natural four-residue fragment, Thr-Lys-Pro-Arg, released from the heavy chain of immunoglobulin G and first characterised as a stimulant of phagocytic immune cells. On its own it is short-lived, so the Institute of Molecular Genetics, working with the V.V. Zakusov Research Institute of Pharmacology, lengthened it with Pro-Gly-Pro to improve its metabolic stability. The result, Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro, C33H57N11O9, about 751.9), keeps a foot in immunology while being studied mainly in the brain.
Its link with GABA, the brain's main inhibitory transmitter, is the area most researchers come to it for. In rats, Selank shifted the expression of 45 out of 84 neurotransmission genes in the frontal cortex one hour after administration and 22 after three hours, and those changes correlated with the pattern produced by GABA itself (Learn more). A follow-up in IMR-32 human neuroblastoma cells found no direct effect on the same genes, leading the authors to favour an indirect, allosteric influence on GABA-A receptor signalling rather than straightforward gene switching.
Pro-Gly-Pro: the tail both peptides share
Set the two sequences next to each other and the common ending jumps out. Pro-Gly-Pro belongs to a family of short proline- and glycine-rich fragments known as glyprolines, which the Moscow group also studies as regulatory peptides in their own right. Proline-rich sequences resist many of the peptidases that rapidly trim short peptides in blood and tissue, so capping each core sequence with this tripeptide was a deliberate design decision to keep both molecules intact long enough to study.
The shared tail also explains why the two are so often discussed as a pair. They come from the same institute and the same design approach, yet their front halves trace back to entirely different parents: one to a pituitary hormone, the other to an antibody fragment. A combined vial therefore gives researchers a neat way to compare a melanocortin-derived and an immune-derived peptide built on an identical chemical chassis, within one experiment.
Stroke, stress and the transcriptome studies
Both peptides have been examined with genome-wide expression tools. In rats that underwent temporary blockage of the middle cerebral artery, RNA sequencing of the frontal cortex 24 hours later found ischaemia altering 3,774 genes; Semax and a sister peptide, ACTH(6-9)PGP, reduced those disturbances for 1,171 genes associated with immune and nerve-signalling pathways (Learn more). In an acute restraint-stress model, Semax changed the activity of more than 1,500 genes in the rat hippocampus, many of them in the opposite direction to the stress.
Selank's stress research has been mainly behavioural. In rats kept under unpredictable chronic mild stress, the elevated plus maze was used to compare Selank, the benzodiazepine diazepam and the two given together; anxiety measures in the combination group did not differ from pre-stress values. The contrast is instructive: Semax data lean towards injury and plasticity readouts, Selank data towards stress behaviour and inhibitory signalling.
Russian medicines and research material: the distinction
Semax and Selank are unusual among research peptides in holding medicine status in one country. In Russia, Semax is registered as a prescription nasal-drop nootropic and has been included on the national List of Vital and Essential Drugs, while Selank is registered as a 0.15% nasal-drop anxiolytic, with its original registration dating from 2009. Both registrations are held by the Russian company Peptogen.
Neither peptide is authorised as a medicine by the UK's MHRA, the European Medicines Agency or the US FDA, and most of the clinical literature is Russian-language. The Crown Peptides blend is research material produced by peptide synthesis; it is not the registered Russian product and is not formulated as nasal drops.
