Amygdala neurones: converging synaptic inputs produced by median eminence and medial preoptic area stimulations in rats

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Abstract
Amygdaloid afferent inputs from the median eminence and the medial preoptic area were studied electrophysiologically in urethane-anesthetized female rats. Stimulation of the surface of the median eminence produced orthodromic responses in about 80% of the 47 amygdala units and about 65% of the responsive cells showed an excitation. Stimulation of the ipsilateral medial preoptic area orthodromically excited 17 and inhibited 20 of the 49 units. Stimulation of the contralateral medial preoptic area evoked orthodromic excitation in 9 and inhibition in 3 of the 22 units. These stimuli were ineffective for producing antidromically conducted impulses. Of the 30 amygdala units, 16 tested for responses to median eminence and ipsilateral medial preoptic area stimulation responded orthodromically with excitation or inhibition. The latency of the response to median eminence stimulation was approximately equal to the response to ipsilateral preoptic area stimulation in 4 of these 16 units. A characteristic bursting discharge was observed in 11 amygdala units during and after ipsilateral preoptic area stimulation. A transitory inhibition was evoked simultaneously with the bursting discharge in some units. Of the 11 units, 7 were tested for median eminence stimulation; a transitory excitation occurred in each of these units. Converging synaptic inputs apparently exist from tuberoinfundibular neurons and the ipsilateral medial preoptic area to certain amygdala neurons. A specific neural pathway exists mediating a characteristic self-sustained bursting discharge in some amygdala neurons after such stimulation.

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