The maturation of swimming behavior and the evoked cortical response to sciatic stimulation were studied in newborn rats receiving thyroxine or cortisol. Compared to that of controls the maturation of swimming is accelerated or delayed 2 to 3 days by thyroxine or cortisol treatment, respectively, and this corresponds to ontogenetic shifts in the characteristics of the evoked potential. Front leg movement during swimming normally diminishes at about 16 days of age and is inhibited by day 22. Thyroxine also advances and cortisol delays the age at which this inhibitory mechanism becomes evident, and compresses (thyroxine) or expands (cortisol) the time interval over which it becomes functional. During early postnatal life certain circuilating hormones can affect the rate and chronology of central nervous system maturation. Swimming behavior may be a simple model to use in studies concerned with factors affecting the functional and behavioral development of the central nervouts system.
We studied the effects of environmental stimulation on the development of rat cortical pyramidal cell synaptic loci (dendritic spines) and the number of such cells staining by the rapid Golgi technique. Stimulation three to five times a day from the day of birth increased the number of spines per micrometer in 8-day-old animals and increased the number of neurons stanining at 8 to 16 days of age. This effect of afferent input upon development of the dendritic spine may represent the neuroanatomical basis for the influence of early experience on subsequent behavior. The number of neurons staining by the rapid Golgi technique appears to be related to those that are functionally involved at the time of tissue preparation.
MATERLALS AND METHODSAntigen preparations. Coccidioidin was prepared by the toluene lysis method published previously (13, 25) but with the following modification. After lysis of the fungus mat with toluene-saturated distilled water, the filter-sterilized lysate was lyophilized, removing the toluene, and then dissolved with the original broth 541 on August 8, 2020 by guest http://iai.asm.org/ Downloaded from
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