We have investigated the effects of ascending inhibitory pathways on two centrally generated rhythmic motor patterns in a simple vertebrate model, the young Xenopus tadpole. Tadpoles swim when touched, but when grasped respond with slower, stronger struggling movements during which the longitudinal pattern of motor activity is reversed. Surgical spinal cord transection to remove all ascending c...

Autoradiographic analysis of the primary retinal projections in the thornback guitarfish reveals both contralateral and ipsilateral projections to diencephalic, pretectal, and tegmental nuclei and the optic tectum. A total of 12 retino-recipient cell groups receive ipsilateral as well as contralateral inputs. To date, all studies using Fink-Heimer or autoradiographic methods in elasmobranch fis...

Rhythmic locomotion in Xenopus laevis embryos is controlled by a central pattern generator in the spinal cord. This was demonstrated in experiments in which movements were blocked by tubocurarine or o--bungarotoxin (Kahn and Roberts, 1982a; Boothby and Roberts, 1988) and activity was recorded either extracellularly with suction electrodes on the ventral roots or intracellularly with microelectr...

The extremely high concentration of urea found in elasmobranch blood (approx. 400 mmol I") is secondary to nearly complete reabsorption (90—95 %) of this solute in the renal tubules (Forster, 1967), and a branchial urea permeability which is approximately 1 % that of the toad bladder (<10 X 10~cm s", Payan, Goldstein & Forster, 1973). Evans, Oikari, Kormanik & Mansberger (1982) have recently sh...

The trigeminal complex of lampreys, like that of anamniotic gnathostomes, consists of profundus and 'mandibulo 'mandibulomaxillary' branchesa, s. The pro-fundus branch possesses a distinct ganglion (supraorbital ganglion) separate from the ganglion (suboptical ganglion) of the 'mandibulomaxillary' brancheslL However, both ganglia send their processes into the medulla as a single trigeminal sens...