Frequency-dependent plasticity of potentials evoked by repetitive stimulation of the lateral olfactory tract in rat olfactory cortex slices.

Habituation and sensitization were demonstrated in slices of olfactory cortex. One of the habituation properties, its dependence on the frequency of the lateral olfactory tract (LOT) stimulation, was tested. It was used in the frequency ranges (1, 10, 20, 30, 40, 50 and 100 impulses/s) which imitated the spontaneous activity of pyriform cortex (PC). Monosynaptic field potentials (FPs) were recorded in PC. Repeated stimulation with one of the frequencies of this range evoked different types of reactions in the PC populations of neurons. Three groups of neuronal reactions were distinguished. The first group of neurons manifested habituation (H-group), while the second one demonstrated sensitization (S-group). In the third group primary sensitization was observed, which then transformed into a short-term phase, when the amplitude of FPs did not change. After that the habituation was found to develop (S-H-group). In the H-group, it was more difficult to evoke habituation at the frequencies of 20-40/s and the number of stimuli in a trial of repeated stimuli (n) being equal to 10 and 150. In the S-group, it was more difficult to induce sensitization at the frequencies of 30-40/s and n equal to 10 and 150. This data proves that the development of habituation and sensitization depends on two factors at least: on the frequency of stimulation and on the type of excited synapse/cell population. Thus, in the PC neuronal populations, a property of habituation suggested by Thompson and Spencer [Psychol. Rev., 73 (1966) 16-43] (higher stimulation frequency causes more rapid and/or pronounced habituation) is not true for all ranges of frequencies.