Abstract
Background: Diverse forms of long-term potentiation (LTP) have been described, but one of the most investigated is encountered in the glutamatergic synapses of the hippocampal cornu Ammonis (CA1) subfield. However, little is known about synaptic plasticity in wildlife populations. Laboratory animals are extremely inbred populations that have been disconnected from their natural environment and so their essential ecological aspects are entirely absent. Proechimys are small rodents from Brazil’s Amazon rainforest and their nervous systems have evolved to carry out specific tasks of their unique ecological environment. It has also been shown that long-term memory duration did not persist for 24-h in Proechimys, in contrast to Wistar rats, when both animal species were assessed by the plus-maze discrimination avoidance task and object recognition test.Methods: In this work, different protocols, such as theta burst, single tetanic burst or multiple trains of high frequency stimulation (HFS), were used to induce LTP in hippocampal brain slices of Proechimys and Wistar rats.Results: A protocol-independent fast decay of early-phase LTP at glutamatergic synapses of the CA1 subfield was encountered in Proechimys. Long-term depression (LTD) and baseline paired-pulse facilitation (PPF) were investigated but no differences were found between animal species. Input/output (I/O) relationships suggested lower excitability in Proechimys in comparison to Wistar rats. Bath application of d-(-)-2-amino-5-phosphonopentanoicacid (D-AP5) and CNQX prevented the induction of LTP in both Proechimys and Wistar. However, in marked contrast to Wistar rats, LTP induction was not facilitated by the GABAA antagonist in the Amazon rodents, even higher concentrations failed to facilitate LTP in Proechimys. Next, the effects of GABAA inhibition on spontaneous activity as well as evoked field potentials (FPs) were evaluated in CA1 pyramidal cells. Likewise, much lower activity was detected in Proechimys brain slices in comparison to those of the Wistar rats.Conclusions: These findings suggest a possible high inhibitory tone in the CA1 network mediated by GABAA receptors in the Amazon rodents. Currently, neuroscience research still seeks to reveal molecular pathways that control learning and memory processes, Proechimys may prove useful in identifying such mechanisms in complement to traditional animal models.
Highlights
Synaptic transmission is the hub of neural communication
The ratio of fEPSP slope to fiber volley (FV) amplitude at each input stimulation level enables to quantify the synaptic strength connection. When comparing this synaptic strength connection before and 80-min after 4HFS, Wistar rats (Figure 1B) presented potentiation starting at 20% of the maximal stimulus contrasting to Proechimys rodents (Figure 1A) that showed increased synaptic transmission only after 40% of the maximal stimulus, suggesting that stronger stimulation is required for synaptic excitatory transmission efficacy in the Neotropical rodents
The only difference between Proechimys and Wistar rats was observed at maximum stimulus intensity after HFS, suggesting an augmentation of synaptic transmission in Wistar rats (Figure 1H)
Summary
Synaptic transmission is the hub of neural communication. Essential for several brain functions, synaptic plasticity, a key attribute of synaptic transmission, is a dynamic modification in the efficacy of synaptic strength, converting information processing into neural circuits (Vitureira and Goda, 2013). By controlling the synaptic strength, glutamatergic and GABAergic neurotransmission systems are very plastic and ensure brain homeostatic regulation. In this context, it has remained an open question how one does conciliate the properties of a particular and accurately wired brain with the competence to acquire knowledge, learning and memory. Laboratory animals are extremely inbred populations that have been disconnected from their natural environment and so their essential ecological aspects are entirely absent (Klaus and Amrein, 2012; Keifer and Summers, 2016). Diverse forms of long-term potentiation (LTP) have been described, but one of the most investigated is encountered in the glutamatergic synapses of the hippocampal cornu Ammonis (CA1) subfield. It has been shown that long-term memory duration did not persist for 24-h in Proechimys, in contrast to Wistar rats, when both animal species were assessed by the plus-maze discrimination avoidance task and object recognition test
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