Protein kinase C inhibition rescues manic-like behaviors and hippocampal cell proliferation deficits in the sleep deprivation model of mania

Abstract

Background: Recent studies revealed that bipolar disorder may be associated with deficits of neuroplasticity. Additionally, accumulating evidence has implicated alterations of the intracellular signaling molecule protein kinase C (PKC) in mania.

Methods: Using sleep deprivation (SD) as an animal model of mania, this study aimed to examine the possible relationship between PKC and neuroplasticity in mania. Rats were subjected to SD for 72 h and tested behaviorally. In parallel, SD-induced changes in hippocampal cell proliferation were evaluated with bromodeoxyuridine (BrdU) labeling. We then examined the effects of the mood stabilizer lithium, the antipsychotic agent aripiprazole, and the PKC inhibitors chelerythrine and tamoxifen on both behavioral and cell proliferation impairments induced by SD. The antidepressant fluoxetine was used as a negative control.

Results: We found that SD triggered the manic-like behaviors such as hyperlocomotion and increased sleep latency, and reduced hippocampal cell proliferation. These alterations were counteracted by an acute administration of lithium and aripiprazole but not of fluoxetine, and only a single administration of aripiprazole increased cell proliferation on its own. Importantly, SD rats exhibited increased levels of phosphorylated synaptosomal-associated protein 25 (SNAP-25) in the hippocampus and prefrontal cortex, suggesting PKC overactivity. Moreover, PKC inhibitors attenuated manic-like behaviors and rescued cell proliferation deficits induced by SD.

Conclusions: Our findings confirm the relevance of SD as a model of mania, and provide evidence that antimanic agents are also able to prevent SD-induced decrease of hippocampal cell proliferation. Furthermore, they emphasize the therapeutic potential of PKC inhibitors, as revealed by their antimanic-like and pro-proliferative properties.

Keywords: bipolar disorder; hippocampal cell proliferation; manic-like behaviors; protein kinase C; sleep deprivation.

Figure. 1.

Behavioral phenotype of rats submitted to a sleep deprivation (SD). (A) 72h of SD increased locomotor activity, sleep latency, and penile erections. (B) SD had no effect on behaviors in the forced swim test or on spontaneous alternation in a Y-maze. (C) SD increased adrenal glands and decreased body weights. Data represent the mean ± S.E.M. of 7–8 rats/group. *p < 0.05, **p < 0.01, ***p < 0.001 vs control (CC) group.

Figure. 2.

Hyperlocomotion and insomnia induced by sleep deprivation (SD) are attenuated by antimanic agents (lithium and aripiprazole), but not by the antidepressant fluoxetine. Locomotor activity and sleep latency were assessed in control (CC) and SD rats after (A and B) an acute injection of lithium (100mg/kg, i.p.), aripiprazole (1mg/kg, i.p.), fluoxetine (10mg/kg, i.p.), or (C and D) a chronic treatment with fluoxetine (10mg/kg/day i.p., for 21 days). Data represent the mean ± S.E.M. of 7–8 rats/group. *p < 0.05, **p < 0.01, ***p < 0.001 vs respective CC group. #p < 0.05, ##p < 0.01, ###p < 0.001 vs SD-vehicle.

Figure. 3.

Sleep deprivation (SD) decreases hippocampal cell proliferation, which is rescued by antimanic but not antidepressant treatments. (A) Representative photomicrographs of dorsal and ventral hippocampi (bottom: enlarged view of boxed area in top) of control (CC) and SD rats. Arrows indicate examples of clusters of BrdU positive cells (scale bar = 20 μm). The majority of the BrdU-labeled cells are located in the subgranular zone (SGZ) of the dentate gyrus at the border between the granule cell layer (GCL) and hilus (H), and appeared in irregular shapes as clusters of 3–4 cells. (B) 72h of SD decreased cell proliferation in dorsal and ventral hippocampi. Acutely injected lithium (100mg/kg, i.p.) and aripiprazole (1mg/kg, i.p.), but not fluoxetine (10mg/kg, i.p.), counteracted the SD-induced hippocampal cell proliferation decrease. Values plotted are mean ± S.E.M. of 5–6 rats/group. *p < 0.05, ***p < 0.001 vs respective CC group; ¤¤p < 0.01, ¤¤¤p < 0.001 vs CC-vehicle; ##p < 0.001 vs SD-vehicle.

Figure. 4.

PKC inhibition prevents manic-like behaviors and rescues hippocampal cell proliferation in the sleep deprivation (SD) model. (A) Western blot, showing representative results of protein levels of phosphorylated and non-phosphorylated forms of SNAP-25 in the prefrontal cortex and hippocampus of control (CC) and SD rats. Densitometric analysis performed on 8 rats/group showed an increase of phospho-SNAP-25/SNAP-25 ratio in SD rats. Results are expressed as a percentage of increase relative to the response of CC, which was set at 100%. (B) The PKC inhibitors chelerythrine (3mg/kg, s.c.) and tamoxifen (80mg/kg, i.p.) reduced manic-like behavioral alterations (hyperlocomotion, insomnia, and increased penile erections) in SD rats. Data represent the mean ± S.E.M. of 7–8 rats/group. (C) An acute injection of chelerythrine (3mg/kg, s.c.) or tamoxifen (80mg/kg, i.p.) rescued hippocampal cell proliferation in SD rats. Values plotted are mean ± S.E.M. of 5–6 rats/group. *p < 0.05, **p < 0.01, ***p < 0.001 vs respective CC group; #p < 0.05, ##p < 0.01, ###p < 0.001 vs SD-vehicle.