Neu-P11Improves Cognitive Impairment In A Rat Model Of Alzheimer Disease

Objective:The neuroendocrine substance melatonin derived from serotonin is a hormonesynthesized and secreted rhythmically by the pineal gland under the influence of thecircadian system and alternating light/dark cycles. In recent years, the results of thestudy show that, exogenous melatonin can regulate the cognitive function and reducethe pathological changes of the AD through many kinds of ways. Neu-P11, a newtype of melatonin receptor agonists, has high affinity for melatonin receptors and canenhance the neurotransmission of gamma-aminobutyric acid neurons. In this study, wefirstly examined whether Neu-P11could enhance memory performance in the objectrecognition task, and then detected if Neu-P11could improve cognitive impairment intwo AD model rats, finally, the underlying mechanisms by which Neu-P11exerts itseffects in PC12cell were also discussed.Methods:1. The effects of Neu-P11on memory performance in the objective recognitiontask in rats: The behavioral procedure involved two phases: a4-min training trial anda3-min retention test trial. vehicle, melatonin and Neu-P11were injected2h beforetraining phase in the morning or in the afternoon. The retention test was run4h or24h after training phase to assess the short-term and long-term memory performance,respectively. The total time spent exploring on the training phase and thediscrimination index on the test phase was recorded.2. The effects of Neu-P11on cognitive impairment induced byintrahippocampal microinjection of Aβ1-42in AD model rats: The rat ADmodel was established by stereotactically injecting Aβ(1–42)into the right hippocampus.After establishment of AD model, the Y-maze task and the object recognition task wastested21and30days after drug administration, respectively. After behavioral procedures, the rats were decapitated, and their brains were removed for histology.3. The effects of Neu-P11on cognitive impairment induced by PCCmicroinjection of NaN3in AD model rats: The step-down inhibitory avoidancetask involved a training session and a test session with a24h interval. Rats wereunder anesthesia1h after training session and then received a microinjection ofsodium azide (NaN3) into the posterior cingulate cortex. Rats received two injectionsof Neu-P11or vehicle (i.p.)2h and6h after microinjection. The open field andelevated plus maze tests were run2and4h after test session of inhibitory avoidancetask, respectively, to evaluate the rats’ locomotor activity and anxiety state. Afterbehavioral procedures, the rats were decapitated, and their brains were removed forhistology.4. The effects of Neu-P11on glutamate-induced injury in PC12cells:24h afterthe PC12cell was seeded, the cells were preincubated with Neu-P11or melatonin0hbefore treatment with4mM glutamate;24h after co-incubation, the cell viability wasevaluated by MTT assay, the MMP was assessed by flow cytometry.5. The effects of Luzindole, a melatonin receptor antagonist, and WAY-100635,a selective5-HT1A receptor antagonist, on the protective effects of Neu-P11against glutamate-induced injury in PC12cells:24h after the PC12cell was seeded,the cells were preincubated with Neu-P110h before treatment with4mM glutamate;Luzindole and WAY-100635were added to the culture medium30min and10minrespectively before exposure to Neu-P11. After24h incubation, cellular viability andmitochondrial membrane potential（MMP）were evaluated by MTT assay and flowcytometry respectively.Results:1. The effects of Neu-P11on memory performance in the objective recognitiontask in rats: In the short-term and long-term memory task, compared with the vehiclegroup, rats with Neu-P11administrated both in the morning and in the afternoonshowed more levels of the discrimination scores, whereas rats with melatoninadministrated only in the afternoon showed more levels of the discrimination scores. In a variety of processing conditions, there was no significant difference in the totaltime spent exploring between groups.2. The effects of Neu-P11on cognitive impairment induced byintrahippocampal microinjection of Aβ1-42in AD model rats: In the Y-mazetask, there was no significant difference in the number of total entries in the fourgroups. Compared with the control group, the AD group showed less levels of thealternation ratio; The Neu-P11group showed more levels of the alternation ratio thanthe AD group; There was no significant difference in the alternation ratio between theAD group and the melatonin group. In the objective recognition task, there was nosignificant difference in the total time spent exploring both objects in the four groupsduring the training phase. During the retention test phase, compared with the controlgroup, the AD group showed less levels of the discrimination scores; The Neu-P11group showed more levels of the discrimination scores than the AD group; There wasno significant difference in the discrimination scores between the AD group and themelatonin group.3. The effects of Neu-P11on cognitive impairment induced by PCCmicroinjection of NaN3in AD model rats: In the Step-down inhibitory avoidancetask, there was no significant difference in the latency in the four groups during thetraining session; The Neu-P11group and the vehicle group showed more levels in thelatency than the AD group during the test session; There was no a significantdifference in the latency in the only NaN3-treated rats during the test sessioncompared with the training session; The Neu-P11-treated NaN3rats presented asignificant increase of latency during the test session compared with the trainingsession. There was no a significant difference in the distance and the parametersobserved in the elevated plus maze activities(the percentage of the time spent in theopen arms、percentage of entries in the open arms、the number of entries in the closedarms) between groups.4. The effects of Neu-P11on glutamate-induced injury in PC12cells:glutamate(4mM) decreased significantly the cell viability and produced a significant dissipation of MMP in PC12cells; Neu-P11and melatonin significantly attenuatedglutamate-induced injury.5. The effects of Luzindole, a melatonin receptor antagonist, and WAY-100635,a selective5-HT1A receptor antagonist, on the protective effects of Neu-P11against glutamate-induced injury in PC12cells: glutamate(4mM) decreasedsignificantly the cell viability and produced a significant dissipation of MMP in PC12cells; Neu-P11attenuated glutamate-induced loss of cell viability and MMP, whichwas abolished by luzindole and WAY-100635when administrated alone or together.Conclusion：Neu-P11enhances memory performance in the object recognition task andimproves cognitive impairment in a rat model of Alzheimer disease, and it’simproving effects for AD may involve activating of melatonin and5-HT1A receptorand then antagonizing glutamate-induced neurotoxicity.