Electroconvulsive shock does not induce c-fos and junB, but TIS1 and TIS8/zif-268, in neonatal rat hippocampus

Serial electroconvulsive Seizure alters dendritic complexity and promotes cellular proliferation in the mouse dentate gyrus; a role for Egr3

BACKGROUND

Despite being one of the safest, most effective treatments for severe mood disorders, the therapeutic mechanisms of electroconvulsive therapy remain unknown. Electroconvulsive seizure (ECS) induces rapid, high-level expression of immediate early genes (IEGs) and brain-derived neurotrophic factor (BDNF), in addition to stimulation of neurogenesis and dendritic remodeling of dentate gyrus (DG) neurons. We have previously shown that this upregulation of BDNF fails to occur in the hippocampus of mice lacking the IEG Egr3. Since BDNF influences neurogenesis and dendritic remodeling, we hypothesized that Egr3-/- mice will exhibit deficits in neurogenesis and dendritic remodeling in response to ECS.

OBJECTIVE

To test this hypothesis, we examined dendritic remodeling and cellular proliferation in the DG of Egr3-/- and wild-type mice following repeated ECS.

METHODS

Mice received 10 daily ECSs. Dendritic morphology was examined in Golgi-Cox-stained tissue and cellular proliferation was analyzed through bromodeoxyuridine (BrdU) immunohistochemistry and confocal imaging.

RESULTS

Serial ECS in mice results in dendritic remodeling, increased spine density, and cellular proliferation in the DG. Loss of Egr3 alters the dendritic remodeling induced by serial ECS but does not change the number of dendritic spines or cellular proliferation consequences of ECS.

CONCLUSION

Egr3 influences the dendritic remodeling induced by ECS but is not required for ECS-induced proliferation of hippocampal DG cells.

Egr-1-d2EGFP transgenic rats identify transient populations of neurons and glial cells during postnatal brain development

The inducible transcription factor Egr-1 has been extensively studied in the adult brain but potential roles during development are largely unexplored. Here we describe the analysis of a new transgenic rat model (egr-1 promoter driving a destabilized GFP molecule) that has provided novel information about the postnatal roles of Egr-1. We show that Egr-1 is more widely expressed in the neonatal brain than was previously appreciated, and is not restricted to neurons; it is expressed in glial cells in the postnatal neocortex and hippocampus. This pattern of expression has been revealed due to cellular filling by GFP, permitting co-localization with glial markers. The transgene/Egr-1 is also expressed in a novel population of cells associated with Cajal-Retzius-like neurons within the marginal zone of the postnatal neocortex. Both of these cellular populations are transient, being limited to the neonatal period, before Egr-1 expression becomes established in an adult-like pattern within neocortical neurons, CA1 hippocampus, and striatum. Another transient population of transgene/Egr-1 cells in the bed nucleus of the stria terminalis is maintained until pre-adolescence. The transient phenotype of these cells involves a low relative expression of the neuronal marker NeuN, perhaps indicating a failure to achieve full neuronal differentiation. Egr-1 is therefore present in a diverse range of cell-types during postnatal development. Transgenic expression of a destabilized fluorescent marker has permitted identification of these novel cell populations and will facilitate further analysis of the transcriptional mechanisms that underlie the specific functions and fate of these cells during postnatal brain development.

Impact of room air resuscitation on early growth response gene-1 in a neonatal piglet model of cerebral hypoxic ischemia

Early growth response gene-1 (Egr-1) is up-regulated by hypoxia-ischemia (HI) and reactive oxygen species (ROS) in adult animals, functioning as a master switch in inflammation and thrombogenesis. We hypothesized that resuscitation from HI with 100% O2 would result in greater Egr-1 expression, ROS, and cell death (CD) in the brains of newborn piglets than 21% O2. Two control groups breathed 21% O2 for 1 h followed by 21% or 100% O2 for 1 h. Two HI groups underwent carotid artery occlusion and breathed 8-12% O2 for 1 h followed by occlusion release and 21% or 100% O2 for 1 h. Brain Egr-1 mRNA and protein were analyzed via quantitative PCR and Western blot. CD and ROS were measured by fluorescence microscopy. Egr-1 mRNA expression increased throughout the brain in response to HI with regional heterogeneity, but protein levels did not. Resuscitation with 100% oxygen did not cause any additional Egr-1 mRNA, Egr-1 protein, CD, or ROS production as compared with 21% oxygen. There was no difference in physiologic recovery after HI with room air compared with 100% O2 resuscitation. However, 100% O2 administration was associated with increased CD in the brainstem independent of HI. Therefore, 100% O2 may have been toxic to some brainstem cells and potentially have significance in long-term neurologic sequelae seen after neonatal HI/resuscitation. Egr-1 protein levels may be tightly regulated in an attempt to diminish neurotoxicity or to enhance plasticity at this stage of development.

Altered GABAergic neurotransmission in mice lacking dopamine D2 receptors

The levels of glutamic acid decarboxylase (GAD) were strongly increased in the cortex and the striatum in dopamine D2 receptors null (D2R-/-) mice, which show a significant locomotor impairment. In this study, the effects of different GABAergic drugs on locomotor activity were analyzed in D2R-/- mice. After administering muscimol (1 mg/kg), a GABA(A) receptor agonist, the D2R-/- mice showed increased locomotor activity up to 200%. When the muscimol dose was increased (4-6 mg/kg), the D2R-/- mice exhibited seizure-like behavior, and the electroencephalographic (EEG) recordings during these behaviors showed a high amplitude rhythmic epileptiform activity in these mice. In situ hybridization showed that after injecting muscimol in the D2R-/- mice, the expression of enkephalin and immediate early gene, NGFI-A, was closely regulated with the locomotor activity regulated by GABAergic stimulation. These results suggest that the absence of D2R alters the GABAergic neurotransmission, specifically on GABA(A)-receptor mediated signaling, and stimulating the GABA(A) receptor can reverse the dysfunction of GABAergic inhibition in the motor circuits in the basal ganglia.

Postnatal handling increases the expression of cAMP-inducible transcription factors in the rat hippocampus: the effects of thyroid hormones and serotonin

Postnatal handling increases glucocorticoid receptor expression in the rat hippocampus, thus altering the regulation of hypothalamic synthesis of corticotropin-releasing hormone and the hypothalamic-pituitary-adrenal response to stress. The effect on glucocorticoid receptor gene expression represents one mechanism by which the early environment can exert a long-term effect on neural development. The handling effect on hippocampal glucocorticoid receptor expression is dependent on peripheral thyroid hormone release and the activation of ascending serotonergic pathways. In primary hippocampal cell cultures, serotonin (5-HT) increases glucocorticoid receptor expression, and this effect appears to be mediated by increased cAMP levels. In the current studies we examined the in vivo effects of handling on hippocampal cAMP-protein kinase A (PKA) activity. In 7-d-old rat pups, we found that (1) postnatal handling increased adenylyl cyclase activity and hippocampal cAMP levels, (2) the effect of handling on cAMP levels was completely blocked by treatment with either propylthiouracil (PTU), a thyroid hormone synthesis inhibitor, or the 5-HT receptor antagonist, ketanserin, and (3) handling also increased hippocampal PKA activity. We then examined the effects of handling on cAMP-inducible transcription factors. Handling rapidly increased levels of the mRNAs for nerve growth factor-inducible factor A (NGFI-A) (zif268, krox24) and activator protein-2 (AP-2) as well as for NGFI-A and AP-2 immunoreactivity throughout the hippocampus. Finally, we found that the effects of handling on NGFI-A and AP-2 expression were significantly reduced by concurrent treatment with either PTU or ketanserin, effects that paralleled those on cAMP formation. NGFI-A and AP-2 have been implicated in the regulation of glucocorticoid receptor expression during development. Thus, these findings suggest that postnatal handling might alter glucocorticoid receptor gene expression via cAMP-PKA pathways involving the activation of NGFI-A and AP-2.