Neonatal Period In Rat Research Articles

Axon ramification following unilateral cortical ablation in neonatal rats

We confirmed the formation of an aberrant ipsilateral corticospinal tract after unilateral cerebral cortical ablation during the neonatal period in rat. This tract was studied using anterograde horseradish peroxidase (HRP) tracing. Ramifications of the axons in the pyramidal tract were found to contribute to the ipsilateral tract at the level of the pyramidal decussation, suggesting that ramification of immature axons plays an important role in the formation of the ipsilateral corticospinal tract.

Development of sensitivity to cAMP-inducing hormones in the rat stomach.

Development of cAMP responses to secretin, pancreatic glucagon, and histamine was measured in gastric glands of fetal (day 20), postnatal (days 1-30), and adult rats (day 65). cAMP stimulation by these hormones was already detected on day 20 of gestation. cAMP generation showed biphasic variations during the 1st days of life and at the onset of weaning (day 20). Anticipated weaning at day 14 triggered precocious maturation (efficacies) of the cAMP-generating systems sensitive to secretin, glucagon, and histamine without changing the potencies of the hormones. During development, the general characteristics (potency and pharmacological or regulatory properties) of the receptor-cAMP systems studied were comparable with those evidenced in adult rats. At days 5, 20, and 65, vasoactive intestinal peptide and the peptide having N-terminal histidine and C-terminal isoleucine amide (PHI) were about 100 times less potent than secretin (EC50 = 1.5 X 10(-9) M secretin). The histamine action could be blocked by the competitive H2-receptor antagonist cimetidine (70-100% inhibition) as well as by the noncompetitive inhibitor somatostatin (37-62% inhibition). The data indicate that these regulatory hormones (secretin, glucagon(s), histamine, and somatostatin) might have a direct effect on gastric glands and may modulate their biological activities (metabolism, differentiation, proliferation, and exocrine and endocrine secretions) from the neonatal period in rats. The important physiological role of weaning on the final maturation of the cAMP-generating systems in rat gastric glands is underlined.

Monosodium glutamate exposure in the neonate alters hypothalamic and pituitary neuropeptide levels in the adult

Administration of monosodium glutamate (MSG) during the neonatal period in rats produced differential effects on the contents of various neuropeptides in the hypothalamus: β-endorphin (β-E) level was reduced by 70% while substance P (SP), neurotensin (NT) and Met 5-enkephalin (ME) levels were not significantly changed (ME content of male rats was slightly reduced). The contents of ME, SP, and NT in striatum and hippocampus were also unaffected by the same treatment. Male rats contain higher pituitary content of β-endorphin-like immunoreactivity (β-ELI) than female rats. MSG treatment reduced the pituitary content of β-ELI and abolished the sex difference in β-ELI level seen in the control rats. MSG treatment in the neonates by eliminating β-E neurons while sparing ME neurons in the brain may be a useful tool for studying the different functions of these two separate opioid peptides.

Sex differences in serum testosterone and in exchangeable brain cell nuclear estradiol during the neonatal period in rats

Sex differences in serum testosterone and in exchangeable brain cell nuclear estradiol during the neonatal period in rats