Abstract
Rat brain slices comprising the perirhinal cortex (PC) and a portion of the lateral nucleus of the amygdala (LA), in standard medium, can generate synchronous oscillatory activity that is associated with action potential discharge and reflects the activation of glutamatergic and GABAergic receptors. We report here that similar synchronous oscillatory events are recorded in the PC in response to single-shock, electrical stimuli delivered in LA. In addition, we found that the latency of these responses progressively increased when the stimulus interval was varied from 10 to 1 s; for example, the response latency during stimuli delivered at 1 Hz was more than twofold longer than that seen during stimulation at 0.1 Hz. This prolongation in latency occurred after approximately 5 stimuli, attained a steady value after 24-35 stimuli, and recovered to control values 30 s after stimulation arrest. These frequency-dependent changes in latency continued to occur during NMDA receptor antagonism but weakened following application of GABAA and/or GABAB receptor blockers. Our findings identify a new type of short-term plasticity that is mediated by GABA receptor function and may play a role in decreasing neuronal network synchronization during repeated activation. We propose that this frequency-dependent adaptive mechanism influences the excitability of limbic networks, thus potentially controlling epileptiform synchronization.
Highlights
It is well established that amygdala and perirhinal cortex (PC) neuronal networks are interconnected both anatomically and functionally [23]
We have previously reported that spontaneous, network-driven events associated with action potential discharge can be recorded in rat brain slices comprising the PC along with a portion of the lateral nucleus of the amygdala (LA) during incubation with standard medium [32]
In the remaining six neurons, low strength LA stimuli induced a postsynaptic response that could contain both excitatory postsynaptic potential (EPSP) and inhibitory postsynaptic potential (IPSP) components depending on the neuron resting membrane potential; in these experiments, only stronger electrical stimulation of the LA produced action potential discharges associated with rhythmic membrane oscillations (Fig. 1C, inset b)
Summary
It is well established that amygdala and perirhinal cortex (PC) neuronal networks are interconnected both anatomically and functionally [23]. We have previously reported that spontaneous, network-driven events associated with action potential discharge can be recorded in rat brain slices comprising the PC along with a portion of the lateral nucleus of the amygdala (LA) during incubation with standard medium [32]. These network oscillations reflect the activation of ionotropic glutamatergic and GABAergic receptors and are influenced by gap junction conductance. Similar in vitro spontaneous activity occurs in brain slices obtained from amygdala-kindled rats [39, 40] as well as in isolated rodent hippocampal slices obtained from “control” animals [37, 46, 47]
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