Abstract
This study investigated the expression pattern, regulation of expression, and the role of hippocampal small-conductance Ca2+-activated K+ (SK) channels in memory deficits after cerebral hypoperfusion (CHP) with or without melatonin treatment, in rats. Adults male Wistar rats (n=20/group) were divided into (1) a sham (2) a sham+melatonin (3) a two-vessel occlusion (2-VO) model, and (4) a 2-VO+melatonin. Melatonin was administered (i.p.)to all rats at a daily dose of 10mgkg(-1) for 7days starting at the time of 2-VO-induction. In contrast to 2-VO rats, melatoninincreasedthe latencyofthe passive avoidance learning test and decreased time to find the hidden platform in Water Morris Test inall tested rats. In addition, it concomitantly downregulated SK1, SK2, and SK3 channels,downregulated mRNA levels of TNF alpha and IL-1 beta, enhanced BDNF levels and activity of PKA levels, and restored the levels ofcholinergicmarkersin the hippocampi of the treated-rats. Mechanistically, melatonin significantly prevented CHP-induced activation of ERK1/2, JNK, and P38 MAPKat least by inhibiting ROS generation and enhancing the total antioxidant potential. In cultured hypoxic hippocampal neurons, individual blockage of MAPK signaling by the MEK1/2 inhibitor (U0126), but not by the P38 inhibitor (SB203580) or JNK inhibitor (SP600125), completely prevented the upregulation of all three kinds of SK channels. These data clearly confirm that upregulation of SK channels plays a role in CHP-induced memory loss and indicate that melatonin reverses memory deficits after CHPin rats, at least by,downregulation of SK1, SK2, and SK3 channels in theirhippocampi.