Exploring the potential role of sonic hedgehog cell signalling pathway in antidepressant effects of nicotine in chronic unpredictable mild stress rat model

Abstract

Nicotine is the most common and highly addictive drug of abuse, associated with several life-threatening diseases and high mortality. Nicotine abuse is the concerted effort to feel reward and fight depression in depressed individuals. The underlying mechanism of nicotine is to activate the brain reward system in the central nervous system and provide an antidepressant effect. Antidepressants provide their therapeutic effect by stimulating hippocampal neurogenesis, which can be correlated with brain derived neurotrophic factor (BDNF) expression in the hippocampus. BDNF interacts with Wnt/β-catenin and sonic hedgehog (Shh) signalling cascade to stimulate hippocampal neurogenesis. Shh is the marker of hippocampal neurogenesis and also involved in the neuropathology of depression. But knowledge in this area to identify the potential therapeutic target is limited. In our study, we explored the role of BDNF, Wnt/β-catenin and Shh signalling in depression and the involvement of these signalling pathways in providing an antidepressant effect by nicotine. Our investigations showed that chronic unpredictable mild stress induced depression results declined expression of BDNF, Wnt/β-catenin, Shh and its downstream transcription factors GLI1/2/3 and NKX2.2 in the hippocampus of male Wistar rat. Moreover, we also observed that nicotine administration increased the expression of these signalling molecules in providing the antidepressant effects.

Keywords: Neuroscience.

Fig. 1

Schematic representation of experimental design. After 28 days of CUMS procedure FST, OFT and MWM were carried and thereafter, rat brain hippocampus samples were collected by animals sacrifice.

Fig. 2

Total time immobile in forced swim test (FST) monitored for 5 min, results are expressed as Mean ± SE (n = 6). Significant difference between CON and CUMS is indicated by *p < 0.05 and by #p < 0.05 between CUMS vs CUMS + NIC group.

Fig. 3

Open field test (OFT) monitored for 5 min. Time spent in the central zone (3A) and total distance travelled in the central zone (3B), results are expressed as Mean ± SE (n = 6). Significant difference between CON and CUMS is indicated by ***p < 0.001 and by #p < 0.05 between CUMS vs CUMS + NIC group. total distance traveled (3C), number of line crossing (3D), total freezing time (3E) and number of freezing episodes (3F) are not significant. (3G) ANY-maze images of open field test.

Fig. 4

(4A) Escape latency in Morris water maze (MWM), results are expressed as Mean ± SE (n = 6). Significant difference between CON vs CUMS is marked as *p < 0.05 and CUMS vs CUMS + NIC group is indicated by ##p < 0.01, (4B) Time spent in the target quadrant, results are expressed as Mean ± SE (n = 6), Significant difference was not observed. (4C) ANY-maze images of open field test.

Fig. 5

mRNA expression of genes by RT-PCR, β-Actin, BDNF, Shh, GLI1, GLI2, GLI3, NKX2.2, PAX6 and β-catenin in rat hippocampus, all the gels were run separately and grouped as Fig. 5A, M- Marker/DNA ladder of 1000 bp, N-Negative control. The qRT-PCR mRNA expression showed as (5B) BDNF mRNA expression, Shh (5C), GLI2 (5D), GLI3 (5E), NKX2.2 (5F), PAX6 (5G) and β-catenin (5H). Results are expressed as Mean ± SE (n = 3). Significant differences between CON vs NIC is expressed as •; CON vs CUMS is expressed as *; NIC vs CUMS is expressed as ⊕ and CUMS vs CUMS + NIC is expressed by #. p value <0.05 considered as significant.