We investigated the influence of 2-APB (2-aminoethoxy-diphenylborate) acute exposure on hippocampal oscillations using time–frequency analysis methods including continuous wavelet transform and short-time Fourier transform. We hypothesized that acute exposure to 2-APB drastically reduced the hippocampal γ oscillations. We estimated the hippocampal oscillations' time–frequency representations from 24 hippocampal slices in five rats. Our results indicated that it took at least 100 ms to see any hippocampal activities in response to the 100 Hz stimulus. The hippocampal oscillations' spectral energies dominated in the 31–60 Hz and 61–90 Hz frequency bands in the early time (100–200 ms) segment post-stimulus and in the 31–60 Hz and 61–90 Hz frequency bands after 200 ms until 400 ms post-stimulus. They were noticeably reduced in the late time segment (above 400 ms). The hippocampal oscillations' spectral energies in the 31–60 and 61–90 Hz frequency bands still dominated the early time segment after the acute 2-APB exposure. The 2-APB exposure never changed the energy content in all three frequency bands in the early time segment (p > 0.01). The exposure significantly reduced the energy content in both the mid-time segment and in the 31–60 Hz frequency band (p < 0.001) and in both the second time segment and in the 61–90 Hz frequency band (p < 0.01). Additionally, in the late time segment, the energy content in all three frequency bands was notably reduced post-drug exposure (p < 0.001).