Responses of hypothalamic neurons to repetitive amygdaloid stimulation

Abstract

The effects of various frequencies of basal and lateral amygdaloid stimulation upon the firing of extracellularly recorded single neurons, DC potentials, and slow potentials recorded within the tuberal hypothalamus were studied in unanaesthetized cats with midbrain lesions: (a) Negative DC shifts, closely time-locked to the stimulus, were observed with repetitive stimulation in either the lateral or basal amygdala, the largest shift being produced by the latter region. (b) Posttetanic potentiation of the evoked potential was much greater with lateral than with basal amygdaloid stimulation. Analysis of the excitability cycles revealed secondary depression of evoked potential amplitude only with basal amygdaloid stimulation. (c) Increasing the stimulation frequencies in either the lateral or basal amygdala reversed the responses of certain single neurons from activation to complete inhibition. The frequency of stimulation required for this effect was predictable from the single shock responses of these neurons. The results indicate that the frequency of electrical stimulation within the amygdala is an important determinant of the hypothalamic response, and confirm observations by other workers of functional differences between basal and lateral amygdala in the responses produced by high frequency stimulation. The findings further suggest, however, that a compartmentalization of the amygdala into functional regions based solely on responses to high frequency amygdaloid stimulation should be viewed with caution.