Objectives To investigate whether measles, mumps, and rubella (MMR) vaccination is associated with bowel problems and developmental regression in children with autism, looking for evidence of a "new variant" form of autism.

During metamorphosis, ranid frogs shift from a purely aquatic to a partly terrestrial lifestyle. The central auditory system undergoes functional and neuroanatomical reorganization in parallel with the development of new sound conduction pathways adapted for the detection of airborne sounds. Neural responses to sounds can be recorded from the auditory midbrain of tadpoles shortly after hatching, with higher rates of synchronous neural activity and lower sharpness of tuning than observed in postmetamorphic animals. Shortly before the onset of metamorphic climax, there is a brief ''deaf'' period during which no auditory activity can be evoked from the midbrain, and a loss of connectivity is observed between medullary and midbrain auditory nuclei. During the final stages of metamorphic development, auditory function and neural connectivity are restored. The acoustic communication system of the adult frog emerges from these periods of anatomical and physiological plasticity during metamorphosis.Many species of anuran amphibians undergo a developmental process called metamorphosis, during which the aquatic larval tadpole transforms into a partly terrestrial frog. Metamorphosis involves considerable alterations in body morphology, peripheral and central nervous system structures, and behaviors (1, 2). This process has been studied extensively in several neural systems, particularly visual, motor, and lateral line systems (3-7). Little is known about the development of central auditory system function across metamorphosis (6-8) even though acoustic cues play a paramount role in regulating social behaviors in adult frogs (9). We report here physiological work characterizing neural responses to sounds in a central auditory nucleus during the period of neuroanatomical rearrangement across the transition from tadpole to frog.Stages of metamorphosis are classified according to changes in body morphology in the posthatching period (10). Premetamorphic animals (stages 25-30) have no or rudimentary external hind limb buds. Early prometamorphic animals (stages 31-37) show emerging hind limb buds at different degrees of differentiation. Tadpoles in these early stages have neither an external tympanum nor an extratympanic opercularis system for sound conduction to the inner ear organs, and there are several hypotheses regarding the identity of a potential acoustic pathway in these animals (11-13). Late prometamorphic animals (stages 38-41) show final stages of external hind limb differentiation and internal development of forelimbs. By stage 41, the extratympanic sound conduction pathway operating in adults (which includes the opercularis muscle and the operculum cartilage, connecting the shoulder girdle to the oval window in the inner ear) has developed (11). Animals in metamorphic climax (stages 42-45) show emergence of forelimbs, degeneration of the tail, and remodeling of the head, including loss of the oral disk, broadening of the mouth, and change in eye position. The lateral line system has degenerated by climax. I...

No abstract

Tadpoles (Xenopus laevis) have a lateral line system whose anatomical structure has been described, but whose functional significance has not been closely examined. These experiments tested the hypothesis that the lateral line system is involved in rheotaxis. Tadpoles in developmental stages 47-56 oriented toward the source of a water current. Orientation was less precise after treatment with cobalt chloride or streptomycin, but was similar to that of untreated animals after exposure to gentamicin. In no current conditions, tadpoles exhibited a characteristic head-down posture by which they held themselves in the water column at an angle around 45°. This body posture became significantly less tilted in the presence of water current. Treatment with cobalt chloride or streptomycin increased the angle of tilt close to that seen in no current conditions, while gentamicin treatment tended to decrease tilt angle. The data are consistent with anatomical and physiological findings that tadpole neuromasts are similar to superficial, but not canal, neuromasts in fishes, and they suggest that the lateral line system is involved in both directional current detection and currentrelated postural adjustments in Xenopus.