Involvement of Hippocampal Inputs and Intrinsic Circuit in the Acquisition of Context and Cues During Classical Conditioning in Behaving Rabbits

Abstract

Learning-related changes in strength in selected hippocampal synapses have been described recently. However, information is scarce regarding the spatial-temporal sequence of changes in synaptic weights taking place during the acquisition of a classical conditioning task and the contribution of both context (environmental details) and cues (conditioned and unconditioned stimuli: CS, US) to those activity-dependent changes. We recorded in rabbits the monosynaptic field excitatory postsynaptic potentials (fEPSPs) evoked at 6 different hippocampal synapses during the acquisition and extinction of a classical eyeblink conditioning using trace or delay paradigms, as well as during pseudoconditioning and in the absence of CS and US presentations (context). Context and pseudoconditioning training evoked early, lasting changes in synaptic strength in perforant pathway synapses in dentate gyrus (PP-DG), and hippocampal CA3 (PP-CA3) and CA1 (PP-CA1) areas. Pseudoconditioning also evoked early, nonlasting changes in strength within the intrinsic hippocampal circuit (CA3-CA1 and CA3-cCA1 synapses). In contrast, during both trace and delay training sessions, synaptic changes in strength were mostly noticed within the intrinsic hippocampal circuit (DG-CA3, CA3-CA1, CA3-cCA1). The response of hippocampal synapses to afferent impulses seems to be modulated by both context and cues during associative learning in behaving rabbits.

Implicit Memory in Monkeys: Development of a Delay Eyeblink Conditioning System with Parallel Electromyographic and High-Speed Video Measurements

“…Even though the attained level of CR% (approximately 60%) in the present study is lower than that observed in cats and rabbits [13, 30, 31], it is comparable to or higher than the level reported in some human or mouse conditioning experiments [5, 12, 14, 24]. The present study is the first attempt to evaluate eyeblink conditioning in monkeys and is significant in three ways: as the first report of monkey eyeblink conditioning by EMG, as the first by video processing, and as the first report of the delayed version of eyeblink conditioning in monkeys.…”

Elemental or contextual? It depends: individual difference in the hippocampal dependence of associative learning for a simple sensory stimulus

“…However, the hippocampus may well be involved in processing both contextual and non-contextual stimuli. For example, in a trace eyeblink conditioning task, changes in synaptic strength were noticed among the hippocampal subfields when an elemental stimulus (CS) was associated with an air puff (US), whereas synaptic connections were strengthened between the entorhinal cortex and the hippocampus when only a context (the environment in which the CS-US associations were taking place) was associated with the US in the absence of the CS (Carretero-Guillén et al, 2013). Furthermore, some prior studies report effects of dorsal hippocampal manipulations on fear conditioning to a tone stimulus (Maren et al, 1997; Bast et al, 2003).…”

Glutamatergic Projections from the Entorhinal Cortex to Dorsal Dentate Gyrus Mediate Context-Induced Reinstatement of Heroin Seeking

“…The dDG receives glutamatergic input from the EC through the perforant pathway (PP) (Deng et al , 2010), and the EC plays a role in both spatial and nonspatial memory processes (Van Cauter et al , 2013). In addition, conditioned context learning can evoke lasting changes to the synaptic strength in PP–dDG (Carretero-Guillen et al , 2013) and there is evidence that neuronal activity in the DG is mainly dependent on GluN2B-mediated neurotransmission (Ge et al , 2007). …”