An attempt to correlate brain areas containing melatonin-binding sites with rhythmic functions: a study in five hibernator species.

High affinity melatonin-binding sites have been described, by means of autoradiography with 2-125I-melatonin as the ligand, in more than 60 brain areas of about 20 mammalian species, with dramatic variations in the nature and number of labelled structures among the different species studied. As melatonin is involved in the synchronization of biological rhythms, we have tried to correlate the brain areas containing melatonin-binding sites with some rhythmic functions typical of given species. Therefore, we have studied the location of melatonin-binding sites in the complete brain of five long-day breeders with hibernation cycles, viz. one insectivore and four rodents. With the exception of the suprachiasmatic nuclei and the pars tuberalis of the pituitary, both of which contain binding sites in all five species, few reactive structures are common, even among species from the same family, e.g. the edible dormouse and the garden dormouse.

Topographical mapping of the thalamocortical projections in rodents and comparison with that in primates.

The general topographical organization of the thalamo-cortical projection of two rodents, the Siberian hamster (Phodopus sungorus) and the Guinea pig (Cavia aperta) was investigated with the HRP-method and compared with that of the new world primate marmoset (Cal-lithrix jacchus) as shown in a companion study by Brysch et al. (1990). HRP was injected into various regions of the cortex in different animals and hemispheres, and plots were made of the retrogradely stained thalamic projection neurons. The thalamocortical projection is virtually identical in both rodent species. It is topological throughout in that nearby cortical injections label nearby, though overlapping cell groups in the thalamus. Cortical injections in a rostro-caudal progression labelled thalamic projection zones on top of each other, layered like tiles on a roof or fish scales, beginning in the rostromedial and ending in the caudo-dorsal thalamus. The progression vector of thalamic zones projecting successively from more rostral to more caudal cortical zones is twisted and turns from a predominantly mediolateral direction in the anterior thalamus to an essentially ventro-dorsal direction in the posterior thalamus In the marmoset, the thalamo-cortical topography follows the same topological rule, with the exception of the lateral geniculate body which is translocated latero-ventrally and separated from the rest of the thalamus as in all primates. This suggests a general thalamo-cortical mapping rule common to all mammals which can be related to gradients and timing of cell birth in the thalamus. It is proposed that this mapping rule is the consequence of successive appositions of neurons in the medio-ventral thalamus during ontogenetic development.

The accessory optic fiber system of the golden hamster with special reference to retinohypothalamic projection.

The hamster accessory optic fiber system has been investigated with the use of de Olmos-Ingram and Fink-Heimer silver methods following the production of unilateral ocular enucleation. It was found that this fiber system consists of both crossed and uncrossed inferior and superior fasciculi. The fibers of the inferior fasciculus (anterior accessory optic tract) run along the medial edge of the cerebral peduncle and terminate within the medial terminal nucleus of the accessory optic system. The fibers of the superior fasciculus (posterior accessory optic tract) leave the main optic tract, pass superficially over the medial geniculate nucleus and the cerebral peduncle; they synapse within the dorsal, the lateral and the medial terminal accessory optic nuclei. The presence of a retinohypothalamic tract could not be confirmed.