Mendez-Couz, M. | bioRxiv Science

bioRxiv2021

Hippocampal Neuropeptide Y2 receptor blockade improves spatial memory retrieval and modulates limbic brain metabolism

IntroductionThe neuropeptide Y (NPY) is broadly distributed in the central nervous system (CNS), and it has been related to neuroprotective functions. NPY seems to be an important component to counteract brain damage and cognitive impairment mediated by drugs of abuse and neurodegenerative diseases, and both NPY and its Y2 receptor (Y2R) are highly expressed in the hippocampus, critical for learning and memory. We have recently demonstrated its influence on cognitive functions; however, the specific mechanism and involved brain regions where NPY modulates spatial memory by acting on Y2R remain unclear. MethodsHere, we examined the involvement of the hippocampal NPY Y2R in spatial memory and associated changes in brain metabolism by bilateral administration of the selective antagonist BIIE0246 into the rat dorsal hippocampus. To further evaluate the relationship between memory functions and neuronal activity, we analysed the regional expression of the mitochondrial enzyme cytochrome c oxidase (CCO) as an index of oxidative metabolic capacity in limbic and non-limbic brain regions. ResultsThe acute blockade of NPY Y2R significantly improved spatial memory recall in rats trained in the Morris water maze that matched metabolic activity changes in spatial memory processing regions. Specifically, CCO activity changes were found in the dentate gyrus of the dorsal hippocampus and CA1 subfield of the ventral hippocampus, the infralimbic region of the PFC and the mammillary bodies. ConclusionsThese findings suggest that the NPY hippocampal system, through its Y2R receptor, influences spatial memory recall (retrieval) and exerts control over patterns of brain activation that are relevant for associative learning, probably mediated by Y2R modulation of long-term potentiation and long-term depression. HighlightsO_LIUnder hippocampal Y2R antagonism, place preference memory retrieval is enhanced C_LIO_LISpatial retrieval enhancement under Y2R blockade is correlated with changes in regional brain energy metabolism C_LIO_LIEnhanced retrieval associated CCO activity increases in the dorsal DG, while decreasing in the ventral CA1, IL cortex and mammillary bodies C_LIO_LIY2R exert control over patterns of brain activation that are relevant for spatial memory expression C_LI

animal behavior and cognition↗

bioRxiv2021

Genetic depletion of BDNF impairs both context-dependent and context-independent extinction learning of a spatial appetitive task

Brain derived neurotropic factor (BDNF) supports neuronal survival, growth, and differentiation and is involved in forms of hippocampus-dependent learning, as well as hippocampus-dependent learning. Extinction learning (EL) comprises active inhibition of no-longer relevant learned information, in conjunction with a decreased response of a previously learned behavior. It is highly dependent on context, and evidence exists that it requires hippocampal activation. Concordantly, the participation of BDNF in hippocampus-dependent memory is experience-dependent. BDNF has been associated with synaptic plasticity needed for acquisition and extinction learning of fear conditioning. However, little is known about its influence on the extinction and renewal of spatial appetitive extinction learning (EL). In this study, in BDNF+/--mice we evaluated to what extent BDNF contributes to spatial appetitive EL in the presence (ABA) or absence (AAA) of a context change. Daily training, to reach acquisition criterion in a T-maze, resulted in a similar outcome in BDNF+/--mice or their wildtype (wt) littermates. EL was delayed in the AAA, and significantly impaired in the ABA-context compared to EL in wt littermates. When renewal was tested in the ABA paradigm we detected a significant response in wt controls, but not in BDNF+/--mice. Taken together, these results support an important role for BDNF in EL in AAA and ABA context, as well as renewal of a spatial appetitive task, processes that relate to information updating and retrieval.

neuroscience↗