Immunohistochemical localization of enkephalin in the central nervous system and pituitary of the lizard, Anolis carolinensis.

The topographical distribution of enkephalin in the central nervous system of the lizard, Anolis carolinensis, has been studied by the immunoperoxidase technique with antiserum to leucine-enkephalin. Immunoreactive enkephalin perikarya, fibers and probably terminals are widely distributed throughout the central nervous system, which agrees well with the distribution of enkephalins in the mammalian brain. Enkephalin-containing perikarya are found in the subpallium (septum, nucleus accumbens, striatum, amydgala), preoptic and hypothalamic region, ventromedial nucleus and ventromedial area of thalamus, pretectal geniculate nucleus and posterodorsal nucleus of pretectum, nucleus of the lateral lemniscus, locus ceruleus, spinal trigeminal nucleus, nucleus of the solitary tract, medial parvocellular nucleus, and dorsal horn of the spinal cord. Enkephalinergic fibers and terminals are found in the above-mentioned areas as well as in the pallium (medial and dorsal cortex, dorsal ventricular ridge), dorsomedial and anterior dorsolateral nucleus of the thalamus, habenula, nucleus of the stria medullaris, torus semicircularis, mesencephalic tegmental area, interpeduncular nucleus, mesencephalic trigeminal nucleus, central gray, reticular formation, raphe nucleus, substantia nigra, isthmus region, and nucleus of the trapezoid body. Enkephalinergic pathways appear to exist between the septum and the medial cortex, nucleus accumbens and nucleus of the lateral olfactory tract, striatum and certain mesencephalic structures, hypothalamus and tegmentum, and between nucleus of the lateral lemniscus and torus semicircularis. In the pituitary, cells of the pars intermedia, and certain cells of the rostral pars distalis also show immunoreactivity to enkephalin antiserum. The distribution of enkephalin immunoreactivity throughout the hypothalamus and in the median eminence suggests involvement in neuroendocrine regulation. Presence of enkephalin in many extrahypothalamic brain areas indicates its important role in various sensory functions and in behavioral and autonomic integration.