The Journal of Comparative Neurology

نویسنده

  • WALTER WILCZYNSKI
چکیده

Horseradish peroxidase (HRP) histochemistry was used to visualize cells afferent to the bullfrog torus semicircularis. These afferent cells are located in several sensory and nonsensory nuclei. The sensory structures which project to the torus are mainly auditory nuclei, with the major input coming from the ipsilateral superior olive. A very small contralateral projection is also present. In addition, afferents arise from the contralateral, and to a lesser extent ipsilateral, dorsal acoustic nucleus and nucleus caudalis, both primary eighth nerve nuclei. A vestibular input is also apparent in that HRP-positive cells were seen in the magnocellular vestibular nucleus and among elongated bipolar cells a t the ventral border of the eighth nerve nuclei. In addition, the torus receives somatosensory input from the contralateral perisolitary band. Afferents from spinal cord cells proved difficult to visualize. Nonsensory areas throughout the brain innervate the torus as well. In the medulla, HRP-positive cells were present bilaterally in both medial and lateral reticular areas. The tegmentum contributes a major input from the superficial isthmal reticular nucleus and a minor input from the tegmental fields. Commissural toral projections are also present. Descending forebrain input arises from the pretectal gray bilaterally, the ventral half of the ipsilateral lateral pretectal nucleus, and, possibly, from the ipsilateral posterior thalamic nucleus. HRP-positive cells were also occasionally seen in the posterior tuberculum, ventral hypothalamus, and caudal suprachiasmatic preoptic area. Finally, a telencephalic projection from the ipsilateral anterior entopeduncular nucleus is present. Acoustic signaling plays a significant, even dominant, role in the social behavior of anuran amphibians. It is important to individuals for mate selection and the maintainance of breeding aggregations, and is crucial to the species as a whole in insuring reproductive isolation (Blair, '58). To date, physiological studies have shown several areas of the anuran central nervous system to be involved in auditory processing (for review, see Capranica, '76). The largest of these areas lies in the mesencephalon, and, as in other nonmammals, is termed the torus semicircularis. The anuran torus semicircularis is a large, well-developed portion of the midbrain roof homologous to the mammalian inferior colliculus and similar midbrain roof areas in other vertebrates (Ariens-Kappers et al., '60). Toral association with the auditory system is well-established physiologically (Potter, '65; LoftusHills, '71; Capranica, '76) and experimental anatomical studies have shown a heavy input from the medullary auditory areas (Fuller and Ebbesson, '73; Rubinson and Skiles, '75). However, the torus also receives somatosensory (Ebbesson, '76) and hypothalamic (Neary and Wilczynski, '77b) inputs. These additional afferents suggest that, like the mesencephalic portion of the visual system, the optic tectum, the torus is not a simple relay nucleus but rather an important sensory integration center. As such, the torus might have a range of afferents similar to the optic tectum, which receives several sensory and nonsensory inputs presumed to modulate its sensorimotor functions (Trachtenberg and Ingle, '74; Wilczynski and Northcutt, '77). Information about toral connections is too sparse to determine if this hypothesis is correct. There is as yet no full appreciation of the total pattern of toral connections. Auditory and some nonauditory inputs have been described, but in no case have the cells of origin been precisely identified. Walter Wilczynski's present address is Cornell University, Section of Neurobiology and Behavior, Ithaca, New York 14853. 0021-996718111983-0421$04.00

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تاریخ انتشار 2004