Transsynaptic Long-Term Potentiation in the Hippocampus of Behaving Mice

Abstract

Long-term potentiation (LTP) is an experimental procedure that shares certain mechanisms with neuronal learning and memory processes and represents a well-known example of synaptic plasticity. LTP consists of an increase of the synaptic response to a control stimulus following the presentation of a high-frequency stimulation (HFS) train to an afferent pathway. This technique is studied mostly in the hippocampus due to the latter’s high susceptibility and its laminar nature which facilitates the location of defined synapses. Although most preceding studies have been performed in vitro, we have developed an experimental approach to carry out these experiments in alert behaving animals. The main goal of this study was to confirm the existence of synaptic changes in strength in synapses that are post-synaptic to the one presented with the HFS. We recorded field excitatory post-synaptic potentials (fEPSPs) evoked in five hippocampal synapses, from both hemispheres, of adult male mice. HFS was presented to the perforant pathway (PP). We characterized input/output curves, paired-pulse stimulation, and LTP of these synapses. We also performed depth-profile recordings to determine differences in fEPSP latencies. Collected data indicate that the five selected synapses have similar basic electrophysiological properties, a fact that enables an easier comparison of LTP characteristics. Importantly, we observed the presence of significant LTP in the contralateral CA1 (cCA1) area following the control stimulation of non-HFS-activated pathways. These results indicate that LTP appears as a physiological process present in synapses located far away from the HFS-stimulated afferent pathway.

Cognitive performance in aged rats is associated with differences in distinctive neuronal populations in the ventral tegmental area and altered synaptic plasticity in the hippocampus

“…The herein-described differences in functional responses observed between experimental groups may thus be due not only to the basal state of the nervous system per se but also to how those nervous systems responded to the methodological procedures and pharmacological treatments used, in our case, used anaesthetics. Compounds like choral hydrate ( Adrien et al, 1989 ; LacKamp et al, 2009 ; Guo et al, 2017 ; Tamano et al, 2017 ), isoflurane ( Romero-Barragan et al, 2021 ) or ketamine xylazine cocktails ( Alkire et al, 2008 ; Laverne et al, 2022 ) are commonly used anaesthetics in electrophysiological studies of brain neuronal circuits. Like several other general anaesthetics, chloral hydrate and its active metabolite trichloroethanol augments GABAergic inhibitory neurotransmission ( Peoples and Weight, 1994 ).…”