Abstract
The tree shrew, as a primate-like animal model, has been used for studying high brain functions such as social emotion and spatial learning memory. However, little is known about the excitatory synaptic transmission in cortical brain areas of the tree shrew. In the present study, we have characterized the excitatory synaptic transmission and intrinsic properties of pyramidal neurons in the anterior cingulate cortex (ACC) of the adult tree shrew, a key cortical region for pain perception and emotion. We found that glutamate is the major excitatory transmitter for fast synaptic transmission. Excitatory synaptic responses induced by local stimulation were mediated by AMPA and kainate (KA) receptors. As compared with mice, AMPA and KA receptor mediated responses were significantly greater. Interestingly, the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) and miniature excitatory postsynaptic currents (mEPSCs) in tree shrews was significantly less than that of mice. Moreover, both the ratio of paired-pulse facilitation (PPF) and the time of 50% decay for fast blockade of NMDA receptor mediated EPSCs were greater in the tree shrew. Finally, tree shrew neurons showed higher initial firing frequency and neuronal excitability with a cell type-specific manner in the ACC. Our studies provide the first report of the basal synaptic transmission in the ACC of adult tree shrew.
Highlights
The tree shrew has a well-developed brain and central nervous system
Glutamate mediated excitatory synaptic transmission in the tree shrew To explore the excitatory synaptic transmission in the anterior cingulate cortex (ACC) of the tree shrew, whole cell patch-clamp recordings were performed on pyramidal neurons in layer II/III of the ACC
Small residual excitatory postsynaptic currents (EPSCs) persisted in the presence of CNQX 10 min after perfusion. These EPSCs were blocked by following application of NMDA receptor antagonist D-2-amino-5-phosphonopentanoic acid (AP5, 50 μM) (Baseline: −138.4 ± 8.5 pA; CNQX: -11.2 ± 2.0 pA, 8.1 ± 1.5% of baseline; D-2amino-5-phosphonopentanoic acid (AP5): −6.8 ± 1.4 pA, 4.9 ± 1.0% of baseline; n = 8 neurons/4 tree shrews; Fig. 2e and f ). These results indicate that, as with the rodents, glutamate is the major excitatory synaptic transmitter in the ACC pyramidal neurons of the tree shrew and the post-synaptic responses are mainly mediated by amino-3hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA)/KA receptors, but less mediated by NMDA receptor
Summary
The tree shrew has a well-developed brain and central nervous system. Cumulative evidence has shown that the tree shrew is an ideal animal model for brain diseases of humans. Some information involved in cognitive impairment during aging, such as the amyloid accumulation and somatostatin degeneration, is missing in the mice and rats but can be found in monkeys and tree shrews [6, 7]. Both animal and human studies have consistently demonstrated that the anterior cingulate cortex (ACC) plays important roles in many major brain functions such as awareness, emotion, memory, and pain [8,9,10,11,12,13,14,15]. The tree shrew will be a valuable primate-like animal for the mechanism of cortical synaptic transmission and plasticity, especially in the ACC
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