An autoradiographic study of the efferent connections of the preoptic region in the rat.

The normal morphology of the rat preoptic region has been briefly described on the basis of Nissl- and silver-stained preparations and its efferent connections have been studied autoradiographically in over 50 rat brains with single small injections of 3H-proline, or various mixtures of 3H-proline, 3H-leucine, and 3H-lysine. Injections in the anteroventral part of the lateral preoptic area labeled fibers projecting through, and perhaps to, the anterior and lateral hypothalamic areas and ending in the supramammillary region, and ventral fiber lamina of the mammillary complex; other labeled fibers ended in the periventricular hypothalamic gray and the internal lamina of the median eminence. The posteromedial lateral preoptic area projects to the same regions, as well as to the medial septal-diagonal band complex, and to the lateral habenula through the stria medullaris. Injections of the posterolateral lateral preoptic area labeled each of the above fiber systems as well as fibers to the main olfactory bulb, anterior olfactory nucleus and taenia tecta. Other fibers coursed over the genu of the corpus callosum, through the stria terminalis and ansa peduncularis to the medial, cortical and basal amygdaloid nuclei and the anterior amygdaloid area, and through the medial forebrain bundle to the substantia nigra. The transition region between the lateral preoptic and lateral hypothalamic areas at the level of the supraoptic nucleus has widespread connections as a whole (a) with the medial septal-diagonal band complex, lateral septum and bed nucleus of the stria terminalis, (b) through or to most of the hypothalamus, the substantia nigra, central tegmental field, central gray, superior central nucleus, and the locus coeruleus, (c) through the stria medullaris to the lateral habenula (bilaterally), parataenial, paraventricular, and mediodorsal nuclei of the thalamus, (d) through the stria terminalis and ansa peduncularis to the central, medial and cortical nuclei of the amygdala, and (e) to the main olfactory bulb, anterior olfactory nucleus, cingulate bundle, olfactory tubercle, medial septal-diagonal band complex and the lateral septum.