Low-Molecular Neurotrophin-3 Mimetics with Different Patterns of Postreceptor Signaling Activation Attenuate Differentially Morphine Withdrawal in Rats.

The accumulated evidence suggests that varying levels of tyrosine kinase receptor signaling pathway activity may regulate opiate-associated neuroadaptation of noradrenergic system. Neurotrophin-3 (NT-3) interacts with tropomyosin receptor kinases (TRKs), binding mainly to TRKC receptors, which are expressed within noradrenergic neurons in the blue spot (locus coeruleus, LC). Considering the difficulties in delivering full-length neurotrophins to the CNS after systemic administration, low-molecular mimetics of loop 4 in NT-3, hexamethylenediamide bis-(N-monosuccinyl-L-asparaginyl-L-asparagine) (GTS-301), and hexamethylenediamide bis-(N-γ-oxybutyryl-L-glutamyl-L-asparagine) (GTS-302), activating TRKC and TRKB receptors, were synthesized. The aim of the study is comparative examination of the effects of NT-3 dipeptide mimetics on the signs of morphine withdrawal in outbred white rats with opiate dependence, as well as investigation of activation of postreceptor signaling pathways by the mimetics. Dipeptides GTS-301 and GTS-302 after acute administration at doses of 0.1, 1.0, and 10.0 mg/kg (i.p., intraperitoneal) had a dose-dependent effect on the specific morphine withdrawal symptoms with the most effective dose being 1.0 mg/kg. Maximum decrease in the total index of morphine withdrawal syndrome for GTS-301 was 31.3% and for GTS-302 - 41.4%. Unlike GTS-301, GTS-302 weakened mechanical allodynia induced by morphine withdrawal, reducing tactile sensitivity. When studying activation of the postreceptor signaling pathways by the NT-3 mimetics in the HT-22 hippocampal cell culture, a different pattern of postreceptor signaling was shown: GTS-302 (10^-6 M), similar to NT-3, activates all three MAPK/ERK, PI3K/AKT/mTOR, and PLCγ1 pathways, while GTS-301 (10^-6 M) triggers only MAPK/ERK and PLCγ1 pathways. Thus, the identified features of attenuation of the morphine withdrawal syndrome in the rats under GTS-301 and GTS-302 effects could be associated with different activation pattern of the postreceptor pathways.