Role Of GABA_B Receptors In Hippocampal-dependent Cognitive Deficits And Affective Disorder And Pharmacological Intervention In Chronically Hypoperfused Rats

Part Ⅰ The dynamic alteration of GABAB receptors in hippocampal CA1 mediate the affective disorder induced by chronic cerebral hypoperfusionObjection:Chronic cerebral hypoperfusion (CCH) causes affective disorders, yet the mechanisms underlying the disease process remained unclear. Methods:The permanent occlusion of the bilateral common carotid arteries (two-vessel occlusion,2VO) was performed to induce CCH. Rats were randomly distributed into sham-operated 4,8 and 12 weeks group,2VO 4,8 and 12 weeks group. The depressive-like behaviors were evaluated by sucrose preference, novelty suppress feeding and forced swim test; The anxiety-like behaviors were evaluated by open field test, elevated plus maze and social behaviors test. The total, surface and intracelluar expressions of GABAB1 and GABAB2 subunit in hippocampal CA1 were quantified by western blot. Results:Our data showed that the depressive- and anxiety-like behaviors could be observed in rats of 2VO 4,8, and 12 weeks group in behavioural tests. In addition, a significant reduction of GABAB1 surface expression and total expression in CA1 was observed in the group that suffered 4 weeks ischemia but neither 8 nor 12 weeks. While GABAB2 surface expression and total expression in CA1 was decreased throughout the ischemia time-scales (4,8 and 12 weeks). Conclusions:Our findings indicated the GABAB receptors are associated with chronic cerebral ischemia induced affective disorders. In the early phase of cerebral ischemia (4 week), the affective disorder was accompanied by the alteration of both GABAB1 and GABAB2 subunits which may be involved in the occurrence process of depressive- and anxiety-like behaviors induced by 2VO; In the delayed phase of cerebral ischemia (8,12 week), the affective disorder was accompanied by the alteration of GABAB2 subunits which may play a dominate role in the developmental process of depressive- and anxiety-like behaviors induced by 2VO.PartⅡ Clonidine ameliorates cognitive impairment induced by chronic cerebral hypoperfusion via up-regulation of the GABAB1 and GAD67 in hippocampal CA1 in ratsObjection:Chronic cerebral hypoperfusion may cause cognitive impairment, but the underlying neurobiological mechanism is poorly understood. In this study, we investigated whether Clonidine, a2-adrenergic receptor agonist, could play neuroprotective effects against chronic ischemic brain injury and the related mechanism. Methods:Rats were subjected to permanent bilateral occlusion of the common carotid arteries (two-vessel occlusion,2VO). Three weeks later, administrated with 0.05mg/kg Clonidine (intraperitoneal injection, i.p.) for 7 days. Cognitive function was evaluated by Morris water maze (MWM). Immunofluorescence and western blot were used to detect the protein levels. Results:The cognitive function was impaired, the expression of neuronal nuclei (NeuN), Glutamic acid decarboxylase 67 (GAD67) and y-aminobutyric acid-B receptor 1 (GABAB1) in hippocampal CA1 area were decreased after 2VO, which were not observed in CA3 and dentate gyrus (DG). Administration of 0.05mg/kg Clonidine (i.p.) for 7 days could improve cognitive function and the expression of NeuN, GAD67 and GABAB1 in hippocampal CA1, but without affecting the protein levels in CA3 and DG. Conclusions:Clonidine could ameliorate cognitive deficits and neuronal impairments induced by chronic cerebral hypoperfusion via up-regulation of GABAB1 and GAD67 in hippocampal CA1.PartⅢ Activation of GABAB2 subunits alleviates the anxiety-like behaviours by improving Kir3 surface expression via BDNF/TrkB/NCAM signalling in rats with chronic cerebral hypoperfusionObjection:Anxiety is a common affective disorder that torments a large number of people and may occur after an ischemia event to delay the physical and cognitive recovery. However, anxiety after ischemia has received fewer attentions, and mechanisms underlying anxiety-like behaviours induced by chronic cerebral ischemia are poorly reported. Methods:In the present study, the chronic cerebral hypoperfusion model was established by the permanent occlusion of the bilateral common carotid arteries (two-vessel occlusion,2VO) in rats, and anxiety-related behaviours were evaluated. Results:The results indicated that 2VO induced obvious anxiety-like behaviours; the surface expressions of GABAB2 were down-regulated; Brain derived neurotrophic factor (BDNF), tyrosine kinase B (TrkB) and neural cell adhesion molecule (NCAM) were reduced; Meanwhile, the surface expressions of the G protein-activated inwardly rectifying potassium (GIRK, Kir3) channels were up-regulated in hippocampal CA1 in 2VO rats. Baclofen, a GABAB receptor agonist, significantly ameliorated the anxiety-like behaviours. It also improved the down-regulation of GABAB2 surface expression, restored the levels of BDNF, TrkB and NCAM, and reversed the increased surface expression of Kir3 in hippocampal CA1 in 2VO rats. However, the effects of baclofen were absent in shRNA-GABAB2 infected 2VO rats. Conclusions:These results suggested that activation of GABAB2 subunits could improve Kir3 channel surface expressions via plausible BDNF/TrkB/NCAM signalling in hippocampal CA1, which may alleviate the anxiety-like behaviours in rats with chronic cerebral hypoperfusion.