CRH gene expression in the fetal rat is not increased after pharmacological adrenalectomy.

A regimen of twice daily metyrapone injections (100 mg/kg), resulted in pharmacological adrenalectomy of pregnant rats and fetuses in utero, i.e. depression of plasma corticosterone and elevation of plasma adrenocorticotropic hormone (ACTH). Toxicity was minimal on days 14-17 of pregnancy, and increased with higher maternal weight and pregnancy progression. Corticotropin releasing hormone (CRH) messenger RNA abundance in the pregnant adults increased significantly within 48 h of metyrapone initiation. No change in CRH gene expression in the paraventricular nucleus of fetuses (days 17-18) was seen, even after 72 h of the regimen. This is compatible with the independence of CRH gene expression of glucocorticoid feedback in the fetal rat

Ontogeny of somatostatin gene expression in rat diencephalon.

Somatostatin gene expression is first detectable, using in situ hybridization, on the 14th fetal day in rat diencephalon. Other structures expressing somatostatin messenger RNA include the anterior basal periventricular nucleus, amygdalo-hippocampal complex, dorsolateral thalamus and distinct areas in the parieto-frontal cortex. Semiquantitative analysis reveals that somatostatin synthesis increases progressively throughout the last third of fetal life and onto postnatal life

Corticotropin-releasing hormone is a rapid and potent convulsant in the infant rat.

Corticotropin-releasing hormone (CRH) administered into the cerebral ventricles of rats during the first postnatal week caused a specific and stereotyped behavior sequence: rhythmic chewing and licking (jaw myoclonus) were followed by 'limbic'-type seizures. The onset of the seizures was much more rapid (2-45 min vs 3-7 h) than in adult rats, and the convulsant doses were much lower (50 x 10(-12) mol per gram brain weight vs 750 x 10(-12) mol per gram brain weight in adults). CRH potency in inducing seizures varied inversely with age. CRH-induced seizures occurred prior to any changes in serum corticosterone, and were eliminated by the administration of a CRH antagonist, as well as of phenytoin. Electrocorticographic correlates of CRH-induced behaviors in the infant rat were inconsistent, suggesting a subcortical origin of CRH-induced paroxysmal events in the immature brain

Fetal and maternal levels of corticosterone and ACTH after pharmacological adrenalectomy.

A paradigm of pharmacological adrenalectomy of pregnant rats and fetuses in utero is described. A regimen of twice daily metyrapone injections (10 mg/100 gm body weight), results in marked depression of serum corticosterone in pregnant and in fetal rats without surgical trauma and stress. The technique should be useful in a wide variety of studies involving the developing brain-adrenal axis

The in vivo proconvulsant effects of corticotropin releasing hormone in the developing rat are independent of ionotropic glutamate receptor activation.

Corticotropin releasing hormone (CRH) produces age-dependent limbic seizures in the infant rat. Both the phenotype and the neuroanatomic matrix of CRH-induced seizures resemble the seizures induced by the rigid glutamate analogue, kainic acid (KA), and by rapid amygdala kindling. The experiments described in this study tested the hypothesis that the in vivo proconvulsant effects of CRH require activation of ionotropic glutamate receptors. Non-competitive (+MK-801) or competitive (CGP-39551) antagonists of N-methyl-d-aspartate (NMDA) receptors decreased or eliminated the motor effects of CRH, but electrographic CRH-induced seizures were unaffected. Administration of CRH antagonists did not affect the acquisition or the maintenance of rapid kindling, which are mediated by NMDA and alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) receptor activation, respectively. CRH receptor blockers failed to alter the latency or duration of seizures induced by activation of KA receptors, and threshold doses of CRH and KA had additive effects. CRH given repeatedly decreased the convulsant threshold dose of KA, probably via injury to hippocampal neurons. These results suggest that CRH and glutamate increase neuronal excitability via independent mechanisms. Because the proconvulsant effects of CRH are highly specific to the developmental period, glutamate-receptor-independent, CRH-receptor mediated excitation may account for some of the enhanced susceptibility to seizures during this period

Febrile seizures: an appropriate-aged model suitable for long-term studies.

Seizures induced by fever are the most prevalent age-specific seizures in infants and young children. Whether they result in long-term sequelae such as neuronal loss and temporal lobe epilepsy is controversial. Prospective studies of human febrile seizures have found no adverse effects on the developing brain. However, adults with temporal lobe epilepsy and associated limbic cell loss frequently have a history of prolonged febrile seizures in early life. These critical issues may be resolved using appropriate animal models. Published models of hyperthermic seizures have used 'adolescent' and older rats, have yielded a low percentage of animals with actual seizures, or have suffered from a high mortality, rendering them unsuitable for long-term studies. This article describes the establishment of a model of febrile seizures using the infant rat. Hyperthermia was induced by a regulated stream of mildly heated air, and the seizures were determined by both behavioral and electroencephalographic (EEG) criteria. Stereotyped seizures were generated in 93.6% of 10-11-day-old rats. EEG correlates of these seizures were not evident in cortical recordings, but were clearly present in depth recordings from the amygdala and hippocampus. Prolonged febrile seizures could be induced without burns, yielding a low mortality (11%) and long-term survival. In summary, in infant rat paradigm of EEG-confirmed, hyperthermia-induced seizures which is suitable for long-term studies is described. This model should be highly valuable for studying the mechanisms and sequelae of febrile seizures

Abnormal corticosterone regulation in an immature rat model of continuous chronic stress.

Neuroendocrine correlates of chronic stress in human infants have not been established. The goal of the present study was to create an animal model of continuous chronic stress using the immature rat to measure basal plasma corticosterone, and secretion of plasma corticosterone in response to an acute stress. This was achieved by modulation of the cage environment for rat pups and their mothers. During postnatal days 2-9, pups were maintained in three groups: (1) handled, (2) not handled and with ample bedding; and (3) not handled with limited bedding. On postnatal day 9, some pups from each group were subjected to acute cold-separation stress and were killed 90, 240, or 360 min later along with unstressed controls. The group not handled and with limited bedding manifested increased plasma corticosterone output even without cold exposure and a sustained increase of plasma corticosterone after cold-separation stress. Plasma corticosterone interanimal variability was increased and body weight was decreased in these pups, typical of a state of chronic stress. The first model of continuous stress in infant rats in which upregulation of hypothalamic-pituitary-adrenal axis is achieved without maternal separation is presented. This paradigm may more closely approximate the human situation of chronically stressed, neglected infants