The growth and maintenance of dendritic form is dependent on normally functioning excitatory afferents. We have now examined the development of dendritic arbors in the gerbil lateral superior olive (LSO), following contralateral cochlear removal at postnatal day 7, a manipulation that substantially eliminates driven inhibitory transmission. Previous studies have demonstrated that the morphology of LSO dendritic arbors varies with tonotopic position and becomes more restricted with age. The presumed decrease of inhibitory transmission in the contralateral LSO resulted in a hypertrophic response. Quantification of Golgi-impregnated neurons revealed that dendrites had a significantly greater number of branch points, and their arbors were more spread out along the frequency axis compared to normal. This was especially apparent in the high frequency projection region where the glycine receptor density is known to be 4-fold higher than in the low frequency projection region. A measure of LSO nucleus size, cross-sectional area, was identical to control values, indicating no overt signs of degenerative phenomena. Cochlear ablation resulted in a significant atrophy of the ipsilateral LSO, with significant effects on dendritic structure. We conclude that decreased inhibitory transmission during development does not lead to a net degenerative response. Rather, the postsynaptic neurons exhibit a hypertrophic phenotype that may be due to the persistence of an immature state. These results indicate that activity-dependent morphogenetic events are a consequence of both excitatory and inhibitory synaptic transmission.

No abstract

The effect of fever on the development of teeth is a highly controversial question. The difficulties in obtaining accurate clinical evidence, and in following case histories for several years are undoubtedly the factors which are largely responsible for the lack of precise information on this subject. Stein (1) observed the teeth of several children who were known to have had fever during infancy and early childhood. He maintains that when he examined these teeth he observed enamel hypoplasia in several instances.Recently, three preliminary reports which deal with the effect of artificially induced fever on the structure of the developing tooth appeared simultaneously. Berman (2), working with rats and rabbits, exposed the animals to intense conditions of fever and reported changes in the structure of the dentin as a result of this treatment. Bevelander and Bernstein (3) subjected a number of rats to an increase in body temperature by means of exposure to short-wave emanations and reported certain changes in the pulpal tissues of the treated specimens. Garrison (4) subjected a number of rats to fever and also reported abnormal calcification of dentin and certain changes in the pulpal tissues. This paper deals with the observations made on a much more extended series of experiments than those previously reported. The problem with which we are concerned is this: Does fever produce deleterious effects on the developing tooth? By subjecting test animals under carefully controlled conditions to an increase in body temperature which may be induced either by short-wave emana-

No abstract

No abstract