Specific binding sites for arginine-vasopressin (AVP) were detected in rat brain after incubation of tissue sections with [3H]AVP. AVP and two selective AVP antagonists are capable of displacing [3H]AVP with an ICso in the 10-s-10 -7 molar range, while oxytocin and ACTH4-l0 were much less effective. The neuroanatomical distribution of [3H]AVP-labeled sites was studied with autoradiography utilizing tritium-sensitive LKB film and computerized densitometry for quantitative analyses of the film images. The highest density of [3H]AVP binding sites was observed in hippocampal regions, the lateral septum, olfactory and amygdaloid nuclei, and the nucleus tractus solitarii (NTS) of the brainstem.Arginine-vasopressin (AVP) influences memory processes [4,6]. This action of AVP takes place in certain discrete limbic-midbrain regions [7]. AVP also acts on biochemical and electrophysiological processes in these areas. It was found that the peptide affects indices for catecholamine turnover in the hippocampal dentate gyrus, dorso-lateral septum and nucleus tractus solitarii (NTS) [7,12], and alters the firing pattern of neurons in the lateral septum [5]. Immunocytochemical studies have demonstrated that these limbic-midbrain regions are innervated by AVPcontaining neurons [3]. Recent advances in autoradiographic methods introduced by Kuhar and coworkers [8] have made it possible to study receptor distribution in vitro in brain sections. A modification using tritium-sensitive sheet film has been introduced [9]. Based on this method preliminary reports have appeared showing that autoradiography of [3H]AVP binding sites is feasable [2,10,13]. In the present *On leave of absence from the
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