A result in one experimental background may not recur in another. Reporting that difference is more informative than describing a compound as uniformly active. Primary study
What was reported
Researchers compared BALB/c and C57Bl/6 mice with different emotional and stress-response phenotypes. In BALB/c mice, Selank produced an anxiety-related behavioral effect and increased the measured persistence of plasma leu-enkephalin. Comparable behavioral and enkephalinase effects were not observed in C57Bl/6 mice. The measured half-life concerned leu-enkephalin, not Selank. Primary report
Our appraisal: do not turn a response difference into a human prediction rule
The comparison suggests that baseline biological context matters. It does not identify a clinically usable responder category. A laboratory strain combines many inherited and physiological characteristics, whereas a human anxiety diagnosis does not map neatly onto a single mouse strain.
The biochemical observation and the behavior should also remain distinguishable. Their occurring together is compatible with a mechanistic explanation, but it does not alone prove that one caused the other. Stronger attribution would require interventions that selectively test the proposed connection.
There is a specific measurement trap here: the persistence of an endogenous peptide protected from degradation is not the persistence of the administered compound. Assigning the reported leu-enkephalin half-life to Selank would describe the wrong molecule.
Finally, a significant result in one strain and a nonsignificant result in another is not, by itself, a formal statistical test of a strain-by-treatment interaction. The direct comparison of effects is the relevant test when making that stronger claim.
The study therefore supports careful attention to experimental background and molecular identity. It does not show that all anxious people will respond, establish human efficacy, or provide a pharmacokinetic schedule for Selank.
Frequently asked questions
Were two mouse strains compared?
Yes.
Was the reported response uniform across strains?
No.
Which strain showed the highlighted effect?
BALB/c.
Did the half-life result describe Selank itself?
No, it described leu-enkephalin.
Does parallel behavior and chemistry prove mediation?
No.
Is a mouse strain a human diagnostic category?
No.
Does this establish a human responder test?
No.