Effect Of Orexin-1Receptor Antagonist On The Ability Of Learning And Memory And The Hippocampal Neuronal Cell Proliferation In Chronic Pentylenetetrazol-kindled Rats

ObjectiveTo investigate the effects of Orexin-1receptor （OX1R） on spatial learning andmemory as well as the hippocampal neuronal cell proliferation in the pentylenetetrazol（PTZ）-kindled rats.MethodsSixty male wistar rats weighing180～220g were randomly divided into two groups：PTZ-kindled group（n=48） and non-kindled group （n=12）. The PTZ-kindled group wasrandomly divided into four subgroups （n=12）. Control group （NS+NS）：intraperitonealinjection of saline and intraventricular injection of saline； PTZ+NS group：intraperitoneal injection of pentylenetetrazol and intraventricular injection of saline；PTZ+OXA group：intraperitoneal injection of pentylenetetrazol and intraventricular injectionOrexin-A； PTZ+SB group： intraperitoneal injection of pentylenetetrazol andintraventricular injection of SB334867；PTZ+SB+OXA group：intraperitoneal injectionof pentylenetetrazol and intraventricular injection of SB334867and Orexin-A. Everyday at8：00, The PTZ-kindled rats were intraperitoneally injected into subthreshold doses of thePTZ （35mg/kg），30consecutive days until reached kindling standard. Non-kindled ratswere intraperitoneally injected into equal saline. After kinding，the rats were fixed on thestereotaxic instrument，Stainless steel micro-catheter of3.5mm length were verticalimplanted.Following seven days recovery from surgery，the rats were applied to theexperiment in the following days. According to the different groups，before training，8μlsaline8μl of Orexin-A (14μg·8μl^-1) or8μl SB (6μg·8μl^-1)，was intracerebroventricularinjection respectively， Morris water maze， intraperitoneal injection of BrdU and immunofluorescence techniques were used to investigate the spatial learning and memoryand expressions of Bromodeoxyuridine （BrdU），Doublecortin（DCX）and Neuronal Nuclei（NeuN） in the hippocampal dentate gyrus.Results1.When30days，90%of the rats reach the kinding criterion.2. Place navigation test： Compared with the non-kinding epilepsy group （NS+NS），all induced epileptic rats escape latency was significantly prolonged （p<0.01）. Furtherobserve the induced epileptic rats，the PTZ+OXA group rats the escape latency issignificantly shorter than the PTZ+NS group （p<0.01），while the PTZ+SB+OXAgroup rats the escape latency was significantly prolonged compared with the PTZ+OXAgroup（p<0.01）.Spatial probe test：Compared with the PTZ+NS group，PTZ+OXA group rats thenumber of through the platform quadrant the increased （p<0.01），at the same time theplatform quadrant swimming time prolonged （p<0.01）.Compared with the PTZ+OXAgroup，intracerebroventricular injection of SB following the injection of Orexin-A，thenumber of rats through the platform quadrant reduced （p<0.05），the platform quadrantswimming time shorten （p<0.01）.3.Further studies using the immuno-fluorescene of BrdU have revealed more BrdUand BrdU/DCX positive cells in the Subgranular zone （SGZ） of the dentate gyrus in thePTZ+OXA rats（p<0.01），compared with those in PTZ+SB+OXA rats.And more BrdU andBrdU/NeuN positive cells in the hippocampal dentate gyrus in the PTZ+OXA rats，compared with those in PTZ+SB+OXA rats.Moreover，compared with PTZ+NS rats，more positive cells in the SGZ of the hippocampal dentate gyrus in PTZ+OXA rats.ConclusionThe learning and memory ability of chronic PTZ-kindled rats can be improved byOrexin-A via OX1R.This could be due to the OX1R-mediated cell proliferation inhippocampal dentate gyrus and the regulation of the integration of newborn neurons intoneuronal circuits to receive input of normal signal.