Amygdala, the center of emotion, is involved in several psychiatric disorders and is sensitive to chronic stress. Basolateral amygdaloid complex (BLA) is composed of three nuclei; lateral nucleus (LA), basolateral nucleus (BL) and basomadial nucleus (BM). In the BLA, sensory information from the cortex and the thalamus are evaluated in terms of emotional valence and these signals are transmitted to central nucleus of amygdala. Previously, we showed that the projection neuron in BLA receives rhythmic inhibitory inputs which are evoked by synchronous firings of interneurons. Such neurons were mostly distributed in BL. In addition, this inhibitory oscillation requires the glutamatergic transmission within BLA, suggesting that local network activities are essential for the oscillation. The frequency of this network oscillation (0.1-3 Hz) is similar to that of delta wave (1-4 Hz) observed in LA of cats during slow wave sleep, but the physiological role of the slow oscillation remains unknown.
In the present study, acute sleep deprivation (morning, 3 hours) was performed on juvenile Wistar rats (P14-24) by housing an animal in the cage in which 1.5-2 cm height of water was filled. Thereafter, coronal slices were prepared for electrophysiological recording. We observed reduced input resistance and neuronal excitability of projection neurons in BL in sleep-deprived rats, while the spike threshold and resting membrane potential were not altered. Moreover, power spectrum analysis revealed that low-frequency (0.1-3 Hz) power of the slow oscillation (rhythmic inhibitory inputs) was decreased. The decline was caused by the reduction of synaptic current amplitude, because the main peak frequency of the oscillation was not significantly different between naive and stressed rats. Acute sleep deprivation failed to affect the input resistance and power of inhibitory oscillation in P15-17 rats, suggesting that younger animals might be less vulnerable to stress. It is concluded that acute stress such as sleep deprivation affects neuronal and network properties in BL.