Shawn Schapiro

Early Experience Effects upon Cortical Dendrites: A Proposed Model for Development

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.

Harderian Gland: Development and Influence of Early Hormonal Treatment on Porphyrin Content

The porphyrin content of the rat Harderian gland remains low until 12 days of age at which time both porphyrin content and concentration rapidly increase. Intraperitoneal administration of tetraiodothyronine (thyroxine) into newborn animals advances the appearance of porphyrin in the gland. Conversely, a single injection of cortisol acetate into newborns retards the appearance of porphyrin. The time of porphyrin appearance in the gland parallels the time for maturation of the evoked cortical response to visual stimulation in normal and hormone-treated animals.

Hormonal influences upon the maturation of the rat brain's responsiveness to sensory stimuli

Abstract The effects of the neonatal administration of cortisol or thyroxine upon the maturation of electrocortical responses to sensory stimuli were studied in the rat. Evoked potentials were recorded from control and hormone treated animals. Records were obtained from immature animals at least 6 days old and from adults. Thyroxine injection on postnatal Days 2, 3 and 4 accelerated by approximately 2–3 days the maturation of evoked cortical responses to visual, auditory and sciatic nerve stimulation. Cortisol administration on postnatal Day 1 retarded development of the evoked response to these same sensory stimuli. These effects were more marked in the visual cortex than other areas. Our results agree with previous reports that these hormones cause a chronological displacement of various biochemical, behavioral and neurophysiological parameters of development and suggest that the hormonal climate bathing the growing neuron may be one factor in the internal environment which plays a role in determining the rate of development of the CNS.

Effects of neonatal thyroxine and hydrocortisone administration on the development of dendritic spines in the visual cortex of rats.

Abstract Hydrocortisone and thyroxine were administered to neonatal rats in order to study the effects of these hormones on the morphology of cortical neurons and the formation of dendritic spines. Animals were killed at various times within 1 month and the rapid Golgi techniques performed. Counts of spines were calculated at stations on the apical, oblique, terminal, and basal dendrites. The lateral width of the basal dendrites, length of the apical dendrites, and the length and width of the cell bodies were also recorded. The spines first appeared at day 4 and at 12–14 days their density was roughly one-half of the density of maturity. The most rapid growth of spines occurred between 8 and 14 days of life. The administration of thyroxine accelerated the development of spines, whereas hydrocortisone slowed their development. The growth of basal dendrites was unaffected by thyroxine and perhaps slightly slowed by hydrocortisone. The shift in time of development produced by the administration of hydrocortisone and thyroxine corresponds to the shift in development of the evoked potential. The findings suggest that the development of spines is more relevant to the maturation of the evoked potential than the growth of dendrites.

Neonatal Cortisol Administration Effect on Growth, the Adrenal Gland and Pituitary-Adrenal Response to Stress.

Summary 1. The effect of graded multiple doses of Cortisol (0.1-2.5 mg/100 g) on adrenal weight of 2-5-day-old and 30–33-day-old rats was compared. At all but the highest dose levels greater adrenal atrophy occurred in the infants. This suggests a greater sensitivity of the steroid feedback mechanism to cortical hormones during the early postnatal period. 2. The effect upon growth and development of a single massive injection of Cortisol (1 mg) on postnatal day 2 was studied. Severe effects on growth and physical appearance were observed and a characteristic “corticoid stigmata”and “corticoid runt”are described. The secretion of ACTH in response to stress was normal in the “runted”animals and ovarian cycles were maintained. Thymus weight was not disproportionately affected although the adrenal glands were somewhat enlarged. Brain cholesterol was decreased.

Corticoid response to stress in the steroid-inhibited rat.

Summary A method is described which permits both the ascorbic acid and corticosteroid content of the same adrenal gland to be determined. Adrenal response to the stress of unilateral adrenalectomy was investigated in normal and hydrocortisone-inhibited rats. Hydrocortisone administration prevented the ascorbic acid depletion which occurred in untreated animals in response to stress. The steroid-inhibited animals, however, exhibited an increase in adrenal corticosterone concentrations equal to that of the saline treated controls, although the basal level from which this increase occurred was markedly lower. It is suggested that pre-treatment with hydrocortisone may alter the physiological “set” at which the corticoid component of the stress response is operating, but does not inhibit the response itself.

Neonatal cortisol administration and immunological impairment in the adult rat.

Summary Newly born rats, on the first postnatal day of life, received a single, intra-peritoneal injection of 1 mg cortisol and 60 to 70 days later their immunological response to 2 different antigens, sheep red blood cells and S. typhosa H, was assessed. The hormone treated rat produced less antibodies in response to both these antigenic challenges than did control animals.