Effects of maternal and sibling deprivation on basal and stress induced hypothalamic-pituitary-adrenal components in the infant rat

Prolonged maternal deprivation during early infancy increases basal- and stress-induced corticosterone (CORT) levels, but the underlying mechanism is not clear. In general, stressors activate the hypothalamic-pituitary-adrenal (HPA) axis, with secretion and compensatory synthesis of hypothalamic cortcotropin-releasing hormone (CRH). In the infant rat, we have demonstrated that maximally tolerated acute cold stress induced a robust elevation of plasma CORT throughout the first 2 postnatal weeks. However CRH messenger RNA (CRH-mRNA) abundance 4 h subsequent to cold stress was enhanced only in rats aged 9 days or older. This suggests a developmental regulation of the CRH component of the HPA-response to this stressor. The present study examined whether increased basal and cold stress-induced CORT levels after 24 h of maternal deprivation were due to enhanced CRH-mRNA abundance in the hypothalamic paraventricular nucleus (PVN). CRH-mRNA abundance, and basal- and cold-induced plasma CORT levels were measured in maternally deprived 6 and 9-day-old pups compared to non-deprived controls. Maternal deprivation increased basal and cold-induced CORT levels on both 6 and 9-day-old rats. CRH-mRNA abundance in the PVN of deprived rats did not differ from that in non-deprived rats. Our results indicate that the enhanced basal and stress-induced plasma CORT observed after 24 h maternal deprivation is not due to increased CRH-mRNA abundance in the PVN.

Corticotropin-releasing hormone mediates the response to cold stress in the neonatal rat without compensatory enhancement of the peptide's gene expression

A variety of stressors activate the hypothalamic-pituitary-adrenal axis, with secretion and compensatory enhanced synthesis of hypothalamic corticotropin-releasing hormone (CRH). Whether CRH is a major effector in the stress response of the neonatal rat and whether the peptide's gene expression is subsequently up-regulated are not fully understood. We studied the effect of cold-separation stress on plasma corticosterone (CORT) levels and CRH messenger RNA (CRH-mRNA) abundance in the paraventricular nucleus. Rats (4-16 days old) were subjected to maximal tolerated cold-separation. CORT and CRH-mRNA abundance were measured before and at several time points after stress. Cold-separation stress resulted in a significant plasma CORT increase in all age groups studied. This was abolished by the administration of an antiserum to CRH on both postnatal days 6 and 9. CRH-mRNA increased in rats aged 9 days or older, but not in 6-day-old rats, by 4 h after stress. These results suggest the presence of robust CRH-mediated adrenal responses to cold-separation stress in neonatal rats. Before postnatal day 9, however, the compensatory increase in CRH-mRNA abundance is minimal.

Glucocorticoid receptor mRNA ontogeny in the fetal and postnatal rat forebrain

Glucocorticoid receptor (GR) ontogeny and distribution in postnatal rat brain have been demonstrated, but onset and distribution of GR gene expression during fetal life has not been reported. This study focuses on the distribution of GR-mRNA in the fetal and postnatal rat forebrain, with emphasis on hypothalamic and limbic structures. Time pregnant rats were decapitated at 8:30-9:30 AM on Gestational Days 14 (F14), F16, F17, F18, and F19. Postnatally, rats were sacrificed on Days 1, 4, 6, 10, and 16. Cryostat sections were subjected to in situ hybridization, using a cRNA probe directed to the GR-mRNA. GR-mRNA was detectible in the hippocamposeptal formation as early as F14. By F16, GR gene expression was evident in the hypothalamic paraventricular nucleus (PVN) as well. During late gestation (F17-F19), GR-mRNA was localized also in the thalamus, hippocampus, amygdala, and discrete cortical regions. Postnatally, GR-mRNA abundance was high in the PVN, CA1/CA2 hippocampal field, piriform cortex and dorsal endopiriform nucleus, specific amygdaloid nuclei, and the suprachiasmatic nucleus. In PVN, GR-mRNA was present prior to the onset of CRH gene expression (F17), which may suggest a role for GR in neuronal differentiation.

Duplication of 10 nucleotides in the erythroid band 3 (AE1) gene in a kindred with hereditary spherocytosis and band 3 protein deficiency (band 3PRAGUE)

We describe a duplication of 10 nucleotides (2,455-2,464) in the band 3 gene in a kindred with autosomal dominant hereditary spherocytosis and a partial deficiency of the band 3 protein that is reflected by decreased rate of transmembrane sulfate flux and decreased density of intramembrane particles. The mutant allele potentially encodes an abnormal band 3 protein with a 3.5-kD COOH-terminal truncation; however, we did not detect the mutant protein in the membrane of mature red blood cells. Since the mRNA levels for the mutant and normal alleles are similar and since the band 3 content is the same in the light and dense red cell fractions, we conclude that the mutant band 3 is either not inserted into the plasma membrane or lost from the membrane prior to the release of red blood cells into circulation. We further show that the decrease in band 3 content principally involves the dimeric laterally and rotationally mobile fraction of the band 3 protein, while the laterally immobile and rotationally restricted band 3 fraction is left essentially intact. We propose that the decreased density of intramembrane particles decreases the stability of the membrane lipid bilayer and causes release of lipid microvesicles that leads to surface area deficiency and spherocytosis.

Methods for implanting steroid-containing cannulae into the paraventricular nucleus of neonatal rats

Implantation of cannulae into brains of neonatal rats presents methodological difficulties. We discuss such issues as avoiding tissue injury, and describe successful techniques. Cannulae size, methods of preparation, insertion, and securing are evaluated. We present a modified cannula holder applicable to the soft neonatal brain. Application of these methods to the study of glucocorticoid receptors in the neonatal rat hypothalamus is illustrated.

Effects of a specific glucocorticoid receptor antagonist on corticotropin releasing hormone gene expression in the paraventricular nucleus of the neonatal rat

Mechanisms controlling the synthesis of corticotropin releasing hormone (CRH) in neonatal rats, and the ontogeny of glucocorticoid (GC) feedback control of hypothalamic CRH remain unknown. Specific issues are whether stress induces up-regulation of CRH gene expression during the first postnatal week, and the role of GC feedback, at the hypothalamic level, in the stress-hyporesponsive period. We studied the ontogeny of the negative feedback regulation of CRH gene expression by GC in the paraventricular nucleus (PVN). We implanted chronic cannulae containing a GC-receptor antagonist, RU 38486, in rats on postnatal days 3 to 13. Three days later, animals were sacrificed, and brains were analyzed for CRH-messenger RNA (CRH-mRNA), using semi-quantitative in situ hybridization. Animals implanted with cholesterol-containing cannulae served to evaluate the stressful effect of implantation on CRH-mRNA abundance. The presence of GC receptor messenger RNA (GR-mRNA) in the PVN of neonatal rats was also determined. RU 38486 did not increase CRH-mRNA abundance during the first postnatal week, despite the presence of GR-mRNA in the PVN. Chronic-implantation stress also failed to increase CRH synthesis. CRH gene expression in the PVN was enhanced in infant rats implanted with RU-38486 on postnatal day 9 or later. Cholesterol implantation on days 9, 10 (but not later), resulted in increased PVN-CRH-mRNA. Thus, CRH-mRNA is up-regulated by chronic blockade of GC receptors only subsequent to the eighth postnatal day. Furthermore, such blockade does not affect the response of CRH-mRNA to chronic stress in the neonatal rat.

Effect of cocaine and 5-HT3 receptor antagonists on 5-HT-induced [3H]dopamine release from rat striatal synaptosomes

The effect of serotonin (5-HT) on the release of tritium from striatal synaptosomes previously loaded with [3H]dopamine ([3H]DA) was studied. 5-HT stimulated both the spontaneous and Ca(2+)-evoked efflux of tritium in a concentration-dependent manner. This effect was not mimicked by the non-selective 5-HT agonist, d-lysergic acid diethylamide. Further, the stimulatory effects of 5 muM 5-HT were unaffected by the selective 5-HT3 receptor antagonists, MDL-72222 and GR-38032F. On the other hand, cocaine and the selective DA uptake inhibitor, nomifensine completely antagonized the effect of 5 muM 5-HT on spontaneous tritium efflux with IC50 values of 0.2 and 0.09 muM, respectively. The effect of 5-HT on Ca(2+)-evoked tritium efflux was also blocked by these DA uptake inhibitors, albeit at somewhat higher concentrations. These data support the hypothesis that 5-HT induces the release of DA from striatal nerve terminals via a mechanism involving the transport of 5-HT into the dopaminergic terminal, rather than by activating 5-HT3 receptors as has been proposed to account for the effect of 5-HT observed in striatal slices.

Chronic cocaine treatment impairs the regulation of synaptosomal 3H-DA release by D2 autoreceptors

The effect of repeated administration of cocaine on presynaptic D2 autoreceptor sensitivity in synaptosomes was studied. In rats treated chronically with saline, the dopamine D2 agonist 2-(N-propyl-N-2-thienylethylamino)-5-hydroxytetralin (N-0437) caused a significant inhibition of the Ca2(+)-evoked 3H-DA release from synaptosomes prepared from the nucleus accumbens and from the striatum; this effect was blocked by the D2 antagonist sulpiride. However, chronic cocaine pretreatment abolished the effect of N-0437 in both areas, suggesting a subsensitivity of release-modulating terminal DA autoreceptors. Subsensitive DA autoreceptors would enhance stimulated DA release from mesolimbic and nigrostriatal terminals and may play a role in the behavioral sensitization observed in this paradigm.

Effects of acute and chronic administration of cocaine on striatal uptake, compartmentalization and release of [3H]dopamine

The effects of acute and repetitive administration of cocaine were studied on several parameters associated with the uptake and release of [3H]dopamine ([3H]DA) in the striatum. It was found that repetitive administration of cocaine followed 7 days later by acute challenge with cocaine, produced an increase in the Vmax with no change in the affinity of the uptake carrier for either dopamine (DA) or cocaine. The intracellular compartmentalization of [3H]DA in synaptosomes was not altered by either acute or repeated treatment with cocaine. However, chronic administration of cocaine abolished the stimulatory effect that 1 microM amphetamine normally has on the efflux of [3H]DA from the fast pool in untreated synaptosomes. The K(+)-stimulated release of [3H]DA from slices of striatum was not affected by acute or chronically administered cocaine; however, chronically administered cocaine, plus acute challenge with cocaine potentiated the effect of amphetamine on the K(+)-induced release of [3H]DA. This was accompanied by a reduction of the effect of amphetamine on the spontaneous release of DA. In addition, chronically administered cocaine plus acute challenge with cocaine increased K(+)-stimulated release of [14C]acetylcholine [( 14C]ACh). These data suggest that repetitive administration of cocaine, in a regimen that elicits behavioral sensitization, alters the substrates through which amphetamine exerts its effects on the subcellular distribution and release of [3H]DA, and further, that challenge with cocaine of sensitized rats produces a compensatory increase in the uptake of [3H]DA that is correlated with increased depolarization-induced release of [14C]ACh.

Inhibition by phenytoin of in vitro secretion of calcitonin from rat thyroid glands and cultured rat C cells

Baby rat thyroid glands and cultured rat medullary carcinoma C cells were incubated acutely with phenytoin (38-100 microM), and the calcitonin (CT) secreted into the serum-free medium was measured by radioimmunoassay (RIA). Phenytoin did not alter CT release from glands or C cells incubated in 1 mM Ca, but, when Ca was raised to 1.75 or 2.5 mM, a marked inhibitory effect of phenytoin was apparent. The inhibitory effect could be negated by including 10 microM BAY-K-8644 in the medium. Inhibitory effects on CT release also were obtained with 100 microM trifluoperazine or 100 microM nitrendipine, and these inhibitory effects also were counteracted by 10 microM BAY-K-8644. The results show that clinically relevant amounts of phenytoin can inhibit CT release, perhaps by interfering with C-cell Ca channels or by inhibiting calmodulin-dependent processes.

Linkage between phencyclidine (PCP) and N-methyl-D-aspartate (NMDA) receptors in the cerebellum

It has been suggested that phencyclidine (PCP) receptors may not be linked with N-methyl-D-aspartate (NMDA) receptors in all brain areas. We found that NMDA enhanced [3H]TCP (a PCP analog) binding in extensively washed cortical, but not cerebellar membranes. However, PCP potently inhibited NMDA-induced [3H]norepinephrine release from cerebellar slices in a concentration-dependent manner, suggesting that a subtype of cerebellar PCP receptors is functionally linked with NMDA receptors. It is suggested that this subtype cannot be demonstrated by [3H]TCP binding because of the predominance of low affinity PCP receptors in the cerebellum.

Comparison of the effects of MK-801 and phencyclidine on catecholamine uptake and NMDA-induced norepinephrine release

MK-801 was found to be more potent than phencyclidine (PCP) as an inhibitor of N-methyl-D-aspartate-induced [3H]norepinephrine (NE) release and [3H]TCP binding in the hippocampus. On the other hand, MK-801 was slightly less potent than PCP to enhance kainate-stimulated [3H]NE release and to inhibit hippocampal [3H]NE uptake. Further, MK-801 was strikingly less potent than PCP as an inhibitor of striatal synaptosomal [3H]dopamine uptake. These data are discussed with reference to the therapeutic potential of MK-801.

Phencyclidine (PCP)-like inhibition of N-methyl-D-aspartate-evoked striatal acetylcholine release, H-TCP binding and synaptosomal dopamine uptake by metaphit, a proposed PCP receptor acylator

The phencyclidine (PCP) receptor acylator, metaphit, has been reported to act as a PCP antagonist. Recent electrophysiological and behavioral assessments of metaphit action have revealed, however, that this compound can also act as a PCP-like agonist. The present study examined the effects of metaphit on the inhibition of N-methyl-D-aspartate (NMDA)-induced 3H-acetylcholine (ACh) release, 3H-TCP binding and synaptosomal 3H-dopamine (DA) uptake in the rat striatum. Preincubation of striatal slices for 10 min in the presence of metaphit, followed by a prolonged washout, produced a concentration-dependent inhibition of the ACh release evoked by 300 microM NMDA. At high concentrations, preincubation with PCP also resulted in inhibition of this measure. However, this could be reduced by extending the washout period, a procedure which had no effect on the inhibition produced by metaphit. At 10 microM, metaphit resulted in a 53% reduction in NMDA-evoked ACh release while PCP had no effect under identical conditions. Preincubation of slices in 10 microM PCP and metaphit reduced the metaphit inhibition by 62%. The effects of PCP and metaphit, alone or in combination, on NMDA-induced ACh release were paralleled by a loss of 3H-TCP binding sites in striatal tissue incubated under identical conditions suggesting that metaphit exerts long-lasting agonist-like actions on PCP receptors coupled to NMDA receptors. Although these results do not explain the ability of metaphit to antagonize PCP effects in other assays, we did observe that preincubation of striatal synaptosomes with metaphit also resulted in an irreversible inhibition of 3H-DA uptake. These data are discussed in relation to the interaction of metaphit with PCP receptors in various systems.