Opposite regulation by glucocorticoids of the alpha 1B- and alpha 2A-adrenoreceptor mRNA levels in rat cultured anterior hypothalamic slices

Cyclic adenosine 3',5'-monophosphate responsive element binding protein phosphorylation is required but not sufficient for activation of corticotropin-releasing hormone transcription

cAMP is a major regulator of CRH transcription. However, receptors activating CRH neurons (alpha-adrenergic and glutamatergic) do not signal through cAMP, suggesting that calcium phospholipid-dependent signaling synergizes with small elevations of intracellular cAMP. To test this hypothesis, we examined the relationship between activation of CRH transcription, cAMP production, and cAMP response element binding protein (CREB) phosphorylation in neuronal cultures treated with the adenylyl cyclase stimulator, forskolin, the phorbol ester, phorbol-12-myristate-13-acetate (PMA), or their combination. Forskolin, at threshold concentrations for cAMP production and CREB phosphorylation, induced CRH promoter-driven luciferase activity in 4B cells (EC(50) = 0.7 microm) and CRH primary transcript in hypothalamic neurons (EC(50) = 0.6 microm). PMA alone failed to activate CRH transcription despite being as effective as forskolin in phosphorylating CREB (Ser133 and Ser121). Although PMA potentiated the effect of low forskolin concentrations on CRH transcription and CREB phosphorylation, there was no correlation between phosphorylated CREB levels and activation of CRH transcription. Similarly, the calcium/calmodulin-dependent kinase inhibitor, KN-93, enhanced PMA plus forskolin-stimulated CREB phosphorylation and inhibited CRH transcription. Suppression of CREB phosphorylation by the protein kinase A inhibitor, H89, or the CREB dominant negative, A-CREB, did not affect basal but blocked forskolin-stimulated transcription. This study shows that calcium phospholipid-dependent pathways potentiate the ability of small elevations of intracellular cAMP to activate CRH transcription, providing a mechanism by which non-cAMP-dependent regulators induce CRH gene expression. In addition, the data indicate that phosphorylated CREB is essential but not sufficient for activation of CRH transcription, suggesting that full promoter stimulation requires the interaction of phosphorylated CREB with a coactivator.

Adrenalectomy potentiates noradrenergic suppression of GABAergic transmission in parvocellular neurosecretory neurons of hypothalamic paraventricular nucleus

Glucocorticoids are known to regulate both the noradrenergic and GABAergic inputs to the paraventricular nucleus (PVN). However, little is known about the effects of glucocorticoids on the interaction of these two input systems. Here we examined the effects of bilateral adrenalectomy (ADX) on the noradrenergic modulation of GABAergic transmission in the type II PVN neurons labeled with a retrograde dye injected into the pituitary stalk. Noradrenaline either reduced or augmented the frequency of spontaneous inhibitory postsynaptic current (sIPSC) without changing the amplitude and decay time constant. These effects were blocked by alpha2A- and alpha(1A/1L)-adrenoceptor antagonists, respectively. ADX increased the proportion of the neurons showing the noradrenergic reduction and the extent of reduction in the IPSC frequency. The ADX-induced changes were reversed by supplementation of ADX rats with corticosterone (10-mg pellet). ADX also potentiated the noradrenergic reduction in the frequency of miniature IPSC and paired-pulse facilitation of evoked IPSC. BRL 44408 (3 microM), a alpha2A-adrenoceptor antagonist, blocked the noradrenergic reduction in ADX rats. Corticotropin-releasing hormone and/or vasopressin transcripts were detected in neurons displaying noradrenergic augmentation or reduction of IPSC frequency. ADX enhanced the proportion of neurons expressing corticotropin-releasing hormone. Collectively, the results suggest that depletion of corticosterone by ADX markedly potentiates the noradrenergic suppression of GABAergic transmission mediated by the alpha2A-adrenoceptors on the GABAergic terminals in the parvocellular neurosecretory PVN neurons. These results may provide a novel synaptic mechanism for the glucocorticoid-induced plasticity in the noradrenergic modulation of neuroendocrine function of the PVN.

Effects of norepinephrine on rat cultured microglial cells that express alpha1, alpha2, beta1 and beta2 adrenergic receptors

Microglial cells rapidly become activated in response to even minor damage of neurons, suggestive of the intimate interactions between neurons and microglial cells. Although mediators for microglia-neuron interactions have not been well identified, neurotransmitters are possible candidates transmitting signals from neurons to microglial cells. Among the neurotransmitters, we focused on the effects of norepinephrine and other adrenergic agonists on the functions of rat cultured microglial cells. Reverse transcriptase polymerase chain reaction studies revealed that microglial cells expressed mRNAs encoding alpha1A, alpha2A, beta1 and beta2 receptors. Norepinephrine and a beta2 adrenergic agonist terbutaline elevated intracellular cAMP level of microglial cells. Norepinephrine, an alpha1 agonist phenylephrine, a beta1 agonist dobutamine and terbutaline suppressed the expressions of mRNAs encoding pro-inflammatory cytokines, interleukin-6 and tumor necrosis factor alpha. Release of tumor necrosis factor alpha and nitric oxide was suppressed by norepinephrine, phenylephrine, dobutamine and terbutaline. An alpha2 agonist clonidine and dobutamine upregulated the expression of mRNA encoding catechol-O-methyl transferase, an important enzyme to degrade norepinephrine. Norepinephrine, dobutamine and terbutaline upregulated the expressions of mRNA encoding 3-phospshoglycerate dehydrogenase, an essential enzyme for synthesis of L-serine and glycine, which are amino acids necessary for neuronal survival. Clonidine upregulated the expression of mRNA encoding an anti-apoptotic factor Bcl-xL. These results suggest that norepinephrine participates in the regulation of brain function at least partly by modulating the functions of microglia.

Ketanserin attenuates the behavioural effects of corticosterone: implications for 5-HT(2A) receptor regulation

The effects of chronic corticosterone treatment on sexual behaviour and wet-dog shakes were investigated in both female and male rats. The serotonergic type 2A (5-HT(2A)) receptor antagonist ketanserin was administered to test the hypothesis that the behavioural effects of corticosterone were mediated by increased 5-HT(2A) receptor activity. Rats were randomly assigned to one of four chronic treatment groups: control, ketanserin alone, corticosterone alone, or ketanserin and corticosterone. Ketanserin attenuated the corticosterone-induced changes in both sexual behaviour and wet-dog shakes. Ketanserin alone had no effect on these behaviours. Results suggest that increased 5-HT(2A) receptor activity mediates the effects of corticosterone on sexual behaviour and wet-dog shakes.