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Spontaneous unit discharges (SUD) were recorded simultaneously from the VMH and lateral area (LH) of the hypothalamus in cats by glass capillary electrodes. Effects of ether anesthesia and electrical stimulation of the LH and VMH structures on the activity of the VMH and LH alone and the reciprocal relation between them were determined. Distributions of SUD frequencies and interspike intervals were determined, and after the stationarity of the time series had been established, auto and cross-correlation functions were calculated. Results on the intimate reciprocal relation between the VMH and LH fit the predictions of a stochastic model quite well and were also confirmed by changes in the EEG recorded from both hypothalamic regions in chronic twelve-hour food deprived animals.

A transistorized high input impedance and low noise preamplifier which can be mounted on the electrode positioner in a chronic preparation for the recording of unit discharges is described.

A transistorized high input impedance, low noise and high stability preamplifier is described. The circuit has a wide linear dynamic input range. The circuit can be miniaturized for chronic preparations and the recording of unit discharges by placing the two relatively large potentiometers in a remote location.

A single and double microelectrode positioner for use in chronic preparations to record unit activity is described. A jig for the accurate positioning of the electrode and a push-pull hydraulic driving mechanism are also described.