Direct and indirect connections between cochlear root neurons and facial motor neurons: pathways underlying the acoustic pinna reflex in the albino rat.

Cochlear root neurons (CRNs) are involved in the acoustic startle reflex, which is widely used in behavioral models of sensorimotor integration. A short-latency component of this reflex, the auricular reflex, promotes pinna movements in response to unexpected loud sounds. However, the pathway involved in the auricular component of the startle reflex is not well understood. We hypothesized that the auricular reflex is mediated by direct and indirect inputs from CRNs to the motoneurons responsible for pinna movement, which are located in the medial subnucleus of the facial motor nucleus (Mot7). To assess whether there is a direct connection between CRNs and auricular motoneurons in the rat, two neuronal tracers were used in conjunction: biotinylated dextran amine, which was injected into the cochlear nerve root, and Fluoro-Gold, which was injected into the levator auris longus muscle. Under light microscopy, close appositions were observed between axon terminals of CRNs and auricular motoneurons. The presence of direct synaptic contact was confirmed at the ultrastructural level. To confirm the indirect connection, biotinylated dextran amine was injected into the auditory-responsive portion of the caudal pontine reticular nucleus, which receives direct input from CRNs. The results confirm that the caudal pontine reticular nucleus also targets the Mot7 and that its terminals are concentrated in the medial subnucleus. Therefore, it is likely that CRNs innervate auricular motoneurons both directly and indirectly, suggesting that these connections participate in the rapid auricular reflex that accompanies the acoustic startle reflex.

Neonatal food restriction and binaural ear occlusion interfere with the maturation of cortical motor pyramids in the rat.

Golgi-Cox-impregnated pyramidal neurons of layer five motor cortical area were investigated in control, binaural ear-occluded control, undernourished and binaural ear-occluded undernourished Wistar rats of 12, 20 and 30 days of age. In neonatally undernourished, binaural ear-occluded-undernourished and partly in ear-occluded-control subjects, there were significant reductions in both the number and extent of the distal part of the dendritic branches of motor pyramids compared to their controls. Moreover, minimal effects on perikarya measurements were observed. These findings suggest that neonatal undernutrition and the concurrent reduction of auditory cues affect dendritic arbor development and possibly the convergence of the auditory experience upon motor pyramids and may interfere with the neocortical modulation of postural and movements activities.

Effects of preweaning sensorimotor stimulation on behavioral and neuronal development in motor and visual cortex of the rat.

The present study investigates the effects of early sensorimotor stimulation on behavioral and neuronal cytodifferentiation in motor and visual cortex of lactating rats. Seventy-two male and female Sprague-Dawley albino rats were systematically submitted to environmental stimulation during the early postnatal period (postnatal days 5-21). On postnatal day 22, four behavioral tests were performed (open field, narrow path crossing, hind limb support and ascending on a rope). In order to evaluate dynamic neuronal changes induced by sensorimotor enrichment, brains were stained through the Golgi-Cox-Sholl method. Morphometric studies were carried out in pyramidal neurons located in motor and visual cortical layers II and III, by measuring their basal dendritic length and branching. Further, wide cortical field studies were performed with the aim of evaluating the degree of development reached by clusters of pyramidal cells. The results indicate that sensorimotor stimulation carried out during the suckling period produced a significant increase in neuronal cytodifferentiation as observed in single cell studies. However, collective neuronal evaluations yielded less significant results. Consistently, rats exposed to enriched environments showed a better performance in behavioral adaptive responses.

Alumina cream-induced focal motor epilepsy in cats. Part 3. Ultrastructure of the epileptogenic focus.

In this study the ultrastructure of motor cortex adjacent to alumina cream (AC) deposits was studied during the latent, convulsive and remission stages of an experimental model of epilepsy in cats. Findings were compared with those observed in sham-operated animals. Where AC was injected, amorphous material surrounded by macrophages containing phagocytic vacuoles was observed. At the edge of these areas, neither fibrous capsule, nor other inflammatory elements were seen. Changes in size and number of fibrous astrocytic processes and morphological signs of progressive degeneration of neuronal elements at the perilesional cortex were found through the latent, convulsive and remission stages. These findings support the idea that presence of clinical and EEG seizures in AC lesioned animals is independent of scar formation and other inflammatory elements. On the other hand, the significance of increased astrocytic processes and progressive degeneration signs of the perilesional cortex in the physiopathogenesis of convulsive activity requires further investigation. (Arch. Invest. Méd. (Méx) 7:157, 1976).