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We described the NADPH-diaphorase-containing neurons and fibres in the brain of the frog Rana esculenta. In the telencephalon stained cells occurred in the olfactory bulb, all subdivisions of the pallium, the diagonal band, the medial septum and the striatum. The olfactory glomeruli showed the most intense enzyme reaction. The neuropil of the accessory olfactory bulb was also heavily stained and this staining extended to the rostral diencephalon through the ventral lateral pallium. Fibre staining was less intense in the medial pallium and the medial septum. In the diencephalon, NADPH-diaphorase staining was concentrated in the middle third of this part of the brain. The stained cells were embedded in a dense network of thin, stained fibres and terminals in the lateral anterior and central thalamic nuclei. Faintly stained cells were present also in the posterior preoptic nucleus, anterior thalamic nucleus, nucleus of Bellonci, corpus geniculatum thalamicum and the suprachismatic nucleus. In the mesencephalon, heavily stained cells occurred in the nucleus profundus mesencephali, anterodorsal, anteroventral and especially in the posterodorsal tegmental nuclei. Neuronal staining was less intense in the optic tectum and the torus semicircularis. Thick, intensely stained fibres occupied the lateral part of the tegmentum and the 7th layer of the tectum. A loose network of thin fibres occupied the periventricular area and all tegmental nuclei. In the rhombencephalon, the reticular nuclei and the inferior raphe nucleus showed the most intense staining, while some cells in the nucleus of the solitary tract and the dorsal column nuclei were less intensely stained. Heavy staining of fibres was characteristic of the spinal trigeminal tract, the solitary tract and the reticulospinal pathway.

The distribution of cocaine- and amphetamine-regulated transcript peptide (CARTp)- like immunoreactivity was studied only in the rat central nervous system (CNS). In mammals, CART peptides occur among others in brain areas that control feeding behavior. We mapped CARTp-immunoreactive structures in the CNS of the frog Rana esculenta and assumed that differences may exist in the CARTp-containing neuronal populations between the frog, which does not feed in winter, and the rat. In the forebrain, immunoreactive cells and fibers were found in the olfactory bulb, nucleus accumbens, amygdala, medial pallium, septum, striatum, the preoptic nuclei, ventromedial nucleus, central thalamic nucleus, and the hypothalamus. The optic pathway was free of immunoreactivity. The neurohypophysis showed intense immunostaining. In the mesencephalon, many cells were stained in the Edinger-Westphal nucleus, and a few in the optic tectum, where fibers were stained in all plexiform layers. In the retina, some cells in the inner nuclear layer contained CARTp. In the rhombencephalon, cells were stained in the raphe nuclei, central gray, nucleus of the solitary tract, and the vicinity of motor nuclei. Neurons of the motor cranial nerves were densely innervated by CARTp-positive fibers originating from the spinal cord. In the spinal cord, preganglionic cells were stained, and motoneurons were surrounded by immunoreactive varicose axon terminals. Major differences were found between the frog and the rat brains in the distribution of CARTp in the visual system, olfactory bulb, preoptic area, and the motor nuclei. Some of these differences may be related to feeding behavior of these animals.

The immunocytochemical distribution of authentic proenkephalin-containing perikarya and nerve fibers in the brain of Rana esculenta was determined with antisera directed toward different epitopes of preproenkephalin. The pattern of proenkephalinlike immunoreactivity was similar with antisera directed toward [Met5]-enkephalin, [Met5]-enkephalin-Arg6, [Met5]-enkephalin-Arg6-Phe7, [Leu5]-enkephalin, and metorphamide; however, the intensity of the labelling varied depending on the target antigen. Proenkephalin-containing perikarya were located in all major subdivisions of the brain except the metencephalon. In the telencephalon, immunoreactive perikarya were detected in the dorsal, medial, and lateral pallium; the medial septal nucleus; the dorsal and ventral striatum; and the amygdala. In the diencephalon, immunoreactive perikarya were detected in the preoptic nucleus, in the dorsal and ventral caudal hypothalamus, and in an area that appeared to be homologous to the paraventricular nucleus. In the mesencephalon, numerous immunoreactive perikarya were detected in layer 6 of the optic tectum and a few scattered perikarya were detected in layer 4 of the optic tectum. Immunoreactive perikarya also occurred in the laminar nucleus of the torus semicircularis. In the rhombencephalon, immunoreactive perikarya were detected in the obex region and the nucleus of the solitary tract. Immunoreactive fibers of varying density were observed in all major subdivisions of the brain with the densest accumulations of fibers occurring in the dorsal pallium, the lateral and medial forebrain bundles, the amygdala, the periventricular hypothalamus, the superficial region of the caudolateral brainstem, and in a tract that appeared to be homologous to the tractus solitarius. The extensive system of proenkephalin-containing perikarya and nerve fibers in the brain of an amphibian showed many similarities to the distribution of proenkephalin-containing perikarya and nerve fibers previously described for the amniote brain.

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