Regulation of the efficacy of adrenergic synaptic transmission by adrenergic autoreceptors in rat brain slices

A mathematical model was developed based on the putative functional role of adrenergic autoreceptors for quantifying processes of synaptic depression, facilitation, stabilization of PSP amplitude, and rise in this amplitude produced by increased stimulation rate. Synaptic depression and facilitation are brought about by activation of - and -adrenergic autoreceptors respectively. A "steady release zone" is found between curves of adrenergic autoreceptor activity and this is responsible for stabilizing noradrenaline release during a series of presynaptic impulses. Experimental findings on labeled noradrenaline (³H-NA) release from rat brain slices showed that adrenergic autoreceptors do in fact form a stable release zone responsible for autofacilitation and stabilization of³H-NA release produced by 5-fold consecutive K⁺ depolarizations of slices spaced 30 min apart. Lack of a stable release zone in curves showing adrenergic autoreceptor activity produces destabilization of³H-NA release. These curves (together with the stable release zone) shift in the direction of high noradrenaline concentrations when stimulus intensity is increased.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 390–399, May–June, 1987.