Distinct frequency preferences of different types of rat hippocampal neurones in response to oscillatory input currents.

1. Coherent network oscillations in several distinct frequency bands are seen in the hippocampus of behaving animals. To investigate how different neuronal types within this network respond to oscillatory inputs we made whole-cell current clamp recordings from three different types of neurones in the CA1 region of rat hippocampal slices: pyramidal cells, fast-spiking interneurones and horizontal interneurones, and recorded their response to sinusoidal inputs at physiologically relevant frequencies (1-100 Hz). 2. Pyramidal neurones showed firing preference to inputs at theta frequencies (range 2-7 Hz; n = 30). They showed subthreshold resonance in the same frequency range (2-7 Hz; mean 4.1 +/- 0.4 Hz; n = 19). 3. Interneurones differed in their firing properties. Horizontal interneurones in the stratum oriens showed firing preference to inputs at theta frequencies (range 1.5-10 Hz; n = 10). These interneurones also showed resonance at low frequencies (range 1-5 Hz; mean 2.4 +/- 0.5 Hz; n = 7). In contrast, fast-spiking interneurones with cell bodies in the pyramidal cell layer fired preferentially at input frequencies in the gamma band (range 30-50 Hz; n = 10/12). These interneurones showed resonance at beta-gamma frequencies (10-50 Hz; mean 26 +/- 5 Hz; n = 7/8). 4. Thus, in the hippocampus, different types of neurones have distinct frequency preferences. Therefore, in the CA1 layer of the hippocampal network, a compound oscillatory input may be segregated into distinct frequency components which are processed locally by distinct types of neurones.