The role of pallidal substance P and neurokinin receptors in the consolidation of spatial memory of rats

Background: The tachykinin substance P (SP) facilitates learning and memory processes after its central administration. Activation of its different receptive sites, neurokinin-1 receptors (NK1Rs), as well as NK2Rs and NK3Rs was shown to influence learning and memory. The basal ganglia have been confirmed to play an important role in the control of memory processes and spatial learning mechanisms, and as part of the basal ganglia, the globus pallidus (GP) may also be involved in this regulation. SP-immunoreactive fibers and terminals, as well as NK1Rs and NK3Rs, were shown to be present in the GP.

Methods: The present study aimed to examine whether the SP administered into the GP can influence spatial memory consolidation in the Morris water maze (MWM). Therefore, male Wistar rats received a post-trial microinjection of 0.4 microliters of 10 ng SP, 100 ng SP, or vehicle solution. The possible involvement of pallidal NK1Rs and NK3Rs in the SP effects was also studied by applying WIN51708 for NK1R antagonism and SR142801 as a selective NK3R antagonist.

Results: Our results showed that the lower dose of SP significantly decreased escape latency on the second day compared to control animals, while the higher dose was ineffective. Prior treatment with the NK1R antagonist WIN51708 could not block, while the NK3R antagonist SR142801 inhibited the effects of SP on memory consolidation in the MWM.

Conclusion: Our results are the first to demonstrate that SP improves consolidation of spatial memory in the GP, and this effect is mediated through NK3Rs but not NK1Rs.