Research ReportDevelopment of theta rhythm in hippocampal formation slices perfused with 5-HT1A antagonist, (S)WAY 100135

- The application of 3 and 10 µM of (S) WAY 100135 induced hippocampal theta.
- 10 µM (S) WAY 100135-induced theta oscillations resembled cholinergic theta.
- Serotonergic projection is involved in the depression of HPC theta oscillations in vitro.

Numerous studies have revealed that median raphe nuclei stimulation induces desynchronization of hippocampal field activity in vivo. Some findings provide evidence for tonic regulation of the theta oscillation of the septo-hippocampal system via the serotonergic system. To date the involvement of serotonergic transmission in theta rhythm generation in hippocampal slices has never been investigated. Thus the aim of the present study was to test whether HPC in vitro preparation is capable of producing theta in the presence of compounds modulating the activity of 5-HT1A receptors. To achieve this a series of experiments designed to determine the effect of different concentrations of the 5-HT1A receptor antagonist (S)WAY 100135 on HPC field activity was carried out. The dominant field potential pattern recorded within HPC slices was epileptiform activity, with a maximum frequency ranging from 0.19±0.06 Hz to 0.69±0.10 Hz. In addition, after the bath application of (S)WAY 100135 in concentrations 3 and 10 µM rhythmic epochs in the theta frequency range were also noted. The highest probability of theta rhythm production was observed after the bath perfusion with a solution of (S) WAY 100135 at a concentration of 10 μM. These theta rhythm epochs were characterized by a higher-than-average amplitude compared to carbachol-induced theta epochs and shorter time duration, with no apparent differences in the average frequency and duration of intervals between theta epochs. These results obtained herein of in vitro studies provide direct evidence for the involvement of serotonergic receptors in the depression of oscillatory activity in the HPC theta band.