Ventral Fibers Research Articles

Hyperdipsia produced by severing ventral septal fiber systems

The septum of male hooded rats (N = 59) was completely isolated from the rest of the brain (ISS) or was partially isolated by severing dorsal (DP), ventral (VP), anterior (AP), or posterior (PP) fiber tracts using a knife-cut technique. Daily water intakes and intakes following hypertonic NaCl and polyethylene glycol (PG) injections were measured. The septum totally degenerated for the ISS group and these rats had normal or hypodipsic daily intakes, likewise for intakes following NaCl and PG. Rats of the VP group sustained little septal damage, yet these cuts yielded the highest percentage (55 percent) of hyperdipsic daily drinkers of any group. The daily hyperdipsic rats drank normally in response to NaCl and PG, demonstrating a dissociation between daily drinking and drinking in response to specific thirst stimuli. The results indicate the importance of ventral fiber systems in the production of Septal Hyperdipsia, and support the notion that the septum has multiple effects upon water regulation.

Effects of septal-fiber knife cuts on rat open-field social behavior

Rats that received various septal fiber tract knife cuts were observed in an open-field to assess preoperative and postoperative social behaviors. Ventral septal fiber knife cuts, isolated septum knife cuts, and anterior-lateral knife cuts result in increases in contact time; in decreases in aggressive behaviors/100 sec contact time; and in no change in the number of contacts. Anterior, posterior, or dorsal fiber knife cuts failed to produce significant changes in contact time, aggressive or submissive behavior, number of contacts, and activity. A postoperative decrease in initiating aggressive behaviors may explain increases in contact time following ventral septal fiber, isolated septum, and anterior-lateral knife cuts. The ventral-septal fiber tracts were critical in mediating social behavior, implying that — in relation to social behavior — there is a functional connection through the ventral fibers between structures beneath the septum (hypothalamus) and the septal nuclei.

Some behavioral effects of transecting ventral or dorsal fiber connections of the septum in the rat.

The behavioral effects of large electrolytic lesions in the septal area were compared with those of knife cuts that severed the ventral or dorsal connections of this structure. Rats with septal lesions lost weight and were transiently hyperdipsic. Ventral cuts produced similar effects, but dorsal cuts did not. All three operations decreased the latency to eat in a novel environment, increased the intake of sweetened milk, enhanced acquisition of a food-rewarded running response, and facilitated acquisition of a shuttle box avoidance response, The lesion, but neither of the knife cuts, reduced the effects of punishment and impaired the acquisition of a one-way avoidance response.

Vestibulocerebellar Input in the Frog: Anatomy

Publisher Summary The central projection of the VIII nerve in amphibians is described by Ariens Kappers, Huber, and Crosby as consisting of two roots that arise from separate anterior and posterior ganglia on the VIII nerve. In the frog, the posterior root enters the medulla dorsally and the anterior root ventrally, after which they divide to ascend rostrally and descend caudally in the medulla. The dorsal portion is believed to go primarily to the nucleus dorsomagnocellularis while the ventral fiber bundles enter the ventral nucleus of the VIII nerve, which has been suggested to be homologous to Deiters' nucleus. The projection of the primary fibers in the VIII nerve has been studied in the frog with the Fink and Heimer technique. It was found that the primary fibers project to three main regions of the brain: (1) the auditory-vestibular complex; (2) the deep cerebellar nuclei; and (3) the cerebellum. The cyto- and myeloarchitectonics of the auditory-vestibular complex and the deep cerebellar nuclei shows distinct cell groupings within these projection sites.

Preferential selection of central pathways by regenerating optic fibers

The time-course and general features of optic nerve regeneration in goldfish were followed in sections prepared at spaced intervals between 3 and 67 days after nerve section. Differential route and destination preferences of fibers from different parts of the retina were then tested by removing specific portions of the retina in combination with complete section of the optic nerve. With the dorsal half of the retina destroyed, surviving ventral fibers became segregated beyond the nerve scar and selectively entered the medial tract to connect with dorsal tectum. Conversely, when dorsal retina remained intact, the regenerating fibers filled selectively the lateral tract and the ventral tectum. Fibers from the posterior (temporal) hemiretina invaded the anterior portion of the tectum and did not extend into the posterior regions. Conversely, those from the anterior hemiretina bypassed the anterior zones to innervate the posterior tectum. Fibers from the center of the retina, after reaching the parallel layer within the tectum, bypassed the plexiform layer in the margin to connect only in the central zone. The plexiform layer in the marginal zones was innervated only when fibers were available from the peripheral retina. The results furnish direct microscopical evidence for the orderly selective termination of optic fibers in the brain centers. They also demonstrate a remarkable and unexpected (presumably chemotactic) selectivity in the tendency of different retinal fiber groups to choose and to follow specific central pathways en route to their synaptic destinations. The thesis that specific chemical affinities govern the formation and maintenance of neuronal associations is extended on the basis of the present results to include the patterning of central fiber pathways.

Clinical and experimental observations with methiodal, an absorbable myelographic contrast agent.

The intrathecal iniectuni of methiodal in myelography is associated with spinal anesthesia, pain, and autonomic dysfunction. Experiments carried out in cats revealed that methiodal blocked conduction in the ventral and dorsal route fibers, an action which did not develop in peripheral nerves. Other experiments in cats indicated that the duration of the effects on conduction is a consequence of slow removal of the drug rather than of delayed recovery. The results of these experiments are taken to indicate that the effects of methiodal may be ascribed to an action on the spinal cord or nerve roots.

Analysis of the rapid responses of Nereis and Harmothoë (Annelida).

The giant-fibre responses of Harmothoë and Nereis have been studied with emphasis on the afferent and efferent path ways and the sites of the rapid accommodation of the fast response. When the bundle of sensory neurones of the anal cirrus is stimulated the giant-fibres respond at the first shock. This terminal junction then rapidly accommodates to further afferent excitation. In Harmothoë the muscles which effect the rapid movements of the giant-fibre response are directly innervated by large axons of unipolar cell bodies in the central nervous system. In each segment one neurone of this type supplies both dorsal and ventral longitudinal muscle fibres. By use of a bridge technique this neurone has been isolated. At the first stimulus above a single sharp threshold the resulting nerve muscle preparation gives a maximum electrical response, which is independent of the stimulus strength. A reduced response persists for many repetitions at low frequency. In addition to this fast motor neurone a slower system in the same muscles is indicated by the muscle-action potentials and by observation of the movements. An axon-axon synapse seen histologically between the lateral giant fibres and the large motor neurone to the longitudinal muscle has been identified with the rapidly accommodating physiological junction between these elements. At this level of analysis the afferent and efferent relations of the giant fibres, and in particular the fast motor innervation, are broadly comparable with those of some arthropods.