AMP Accumulation In Brain Slices Research Articles

Regional Difference in Responsiveness of Adenosine‐Sensitive Cyclic AMP‐Generating Systems in Chronic Epileptic Cerebral Cortex of the Rat

Cyclic AMP accumulation in brain slices incubated with adenosine or the adenosine analogue 2-chloroadenosine was examined in different areas of rat cerebral cortex following a unilateral injection of FeCl2 solution into the sensorimotor cortex to induce chronic epileptic activity. In the epileptic cortex, cyclic AMP accumulation in cortical slices was elicited three- to 11-fold by adenosine. The elicitation by adenosine of cyclic AMP accumulation was markedly inhibited by the adenosine antagonist 8-phenyltheophylline. In anterior cortical areas of rats in which the appearance of electrographic isolated spikes was dominant either ipsilateral or contralateral to the injection site 8 days or more after the injection, the adenosine-elicited accumulation of cyclic AMP was greater on the side of dominant spike activity than on the other. In anterior cortical areas of rats showing nearly equal spike activity on the two sides 19 days or more after the injection, the cyclic AMP accumulation was greater on the side ipsilateral to the injection site than on the other. In anterior and posterior cortical areas of rats showing spike-and-wave complexes and isolated spikes 1 month or more after the injection, the cyclic AMP accumulation was greater on the ipsilateral side than on the other. Similar regional differences in the adenosine-elicited accumulation of cyclic AMP were detected in the presence of the adenosine uptake inhibitor dipyridamole or the phosphodiesterase inhibitor DL-4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (Ro 20-1724). The cyclic AMP accumulation was elicited five- to 17-fold by 2-chloroadenosine, in which case the elicitation was markedly inhibited by 8-phenyltheophylline. Regional differences in the 2-chloroadenosine-elicited accumulation of cyclic AMP were similar to those with adenosine and were detected in the presence of Ro 20-1724 or adenosine deaminase. The regional differences which correlated with the electrographic discharge patterns were due mainly to persistent changes in cyclic AMP accumulation on the primary epileptic side. These results suggest that alterations in adenosine-sensitive cyclic AMP generation in the cortex are associated with the neurochemical process leading to chronic iron-induced epilepsy.

Calmodulin Involvement in Stress‐ and Corticosterone‐Induced Down‐Regulation of Cyclic AMP‐Generating Systems in Brain

Manipulation of the hypothalamic-pituitary-adrenal axis selectively alters alpha-adrenergic potentiation of the cyclic AMP response to beta-adrenergic receptor stimulation in rat cerebral cortex. Calcium has been implicated in this alpha-receptor-mediated response, which may involve activation of phospholipases A2 and C and/or calmodulin-dependent adenylate cyclase. We therefore investigated the effects of stress and corticosterone (CORT) on membrane calmodulin-dependent adenylate cyclase and noradrenaline-stimulated cyclic AMP accumulation in brain slices. Repeated stress for 21 days selectively attenuated the adenylate cyclase response to calcium/calmodulin in cerebral cortex membranes, without affecting basal or forskolin-stimulated enzyme activity. There was no such effect in hippocampal membranes. The same pattern of response was elicited by daily CORT injection (50 mg/kg s.c.) for 21 days, while vehicle injection had no effect. CORT in the drinking water (400 micrograms/ml) elicited the same reduction of body weight as CORT injections, but had no effect on calmodulin adenylate cyclase. In parallel with calmodulin adenylate cyclase, cyclic AMP accumulation elicited by noradrenaline in slices of cerebral cortex was suppressed by both stress and daily CORT injections, with smaller effects observed with CORT in the drinking water. Unlike calmodulin adenylate cyclase, noradrenaline-stimulated cyclic AMP accumulation in hippocampus showed the same suppression as that in cerebral cortex. These results are discussed in relation to the differential mode of coupling of alpha-adrenergic receptors to cyclic AMP-generating systems between brain regions.(ABSTRACT TRUNCATED AT 250 WORDS)

γ‐Aminobutyric AcidB Receptor Activation Modifies Agonist Binding to β‐Adrenergic Receptors in Rat Brain Cerebral Cortex

The interaction of isoproterenol with beta-adrenergic receptor (beta AR) binding sites was measured in membranes prepared from rat brain cerebral cortical slices previously incubated in the presence or absence of gamma-aminobutyric acid (GABA) receptor agonists. Both GABA and baclofen, but not isoguvacine, altered beta AR agonist binding by increasing the affinity of both the low- and high-affinity binding sites and by increasing the proportion of low-affinity receptors. The response to baclofen was stereoselective, and the effect of GABA was not inhibited by bicuculline. The results suggest that GABAB, but not GABAA, receptor activation modifies the coupling between beta AR and stimulatory guanine nucleotide-binding protein, which may in part explain the ability of baclofen to augment isoproterenol-stimulated cyclic AMP accumulation in brain slices.

Alpha-adrenoceptor stimulation, but not muscarinic stimulation, increases cyclic AMP accumulation in brain slices due to protein kinase C mediated enhancement of adenosine receptor effects.

In the present study, using rat hippocampal slices, we have further examined the stimulatory effect of alpha 1-adrenoceptors on the accumulation of cyclic AMP, which is known to depend on calcium and adenosine. The addition of noradrenaline (NA) stimulated the accumulation of [3H]inositol phosphates in [3H]inositol-treated slices. This effect was shared by carbachol (10-100 mumol l-1) but not by the adenosine receptor agonist 2-chloroadenosine (100 mumol l-1). The stimulatory effect of the alpha-agonists (phenylephrine or NA + propranolol) on cyclic AMP was shared by a diacylglycerol derivative, sn-1-oleyl-2-acetyl glycerol (OAG), and by the tumour-promoting phorbol esters phorboldibutyrate (PDiBu) and tetradecanoyl phorbol acetate (TPA). PDiBu caused a translocation of protein kinase C from soluble to particulate fractions. The effects of PDiBu and alpha-adrenoceptor stimulation on cyclic AMP were not additive. Surprisingly, carbachol (1-1000 mumol l-1) did not stimulate cyclic AMP accumulation in rat hippocampal slices either in the presence or in the absence of an adenosine receptor agonist. The results are compatible with the opinion that alpha-adrenoceptor stimulating drugs enhance the formation of inositol phosphates and diacylglycerol, which synergistically activate protein kinase C, which in turn augments the stimulation of cyclic AMP formation. Thus, a neurotransmitter whose principal biological effect is to stimulate inositol phosphate formation can influence cyclic AMP formation by virtue of an interaction with the actions of the ubiquitous neuromodulator adenosine. The fact that the effect of the alpha-receptor stimulation was not mimicked by a muscarinic agonist could indicate that other factors besides activation of inositol phospholipid hydrolys are important for this receptor-receptor interaction.

Adrenocortical steroids modify neurotransmitter-stimulated cyclic AMP accumulation in the hippocampus and limbic brain of the rat.

Glucocorticoid hormones are known to affect limbic system structures that have high levels of specific receptors for glucocorticoids, especially the hippocampus (HIPP). To understand how glucocorticoids may affect synaptic transmission, we have tested the effects of adrenal removal and glucocorticoid replacement on neurotransmitter-stimulated cyclic AMP accumulation in brain slices from the rat limbic system. Adrenalectomy (ADX) caused an enhancement of vasoactive intestinal peptide (VIP)-stimulated cyclic AMP accumulation in HIPP, amygdala (AMYG), and septum (SEP). In HIPP, ADX increased the cyclic AMP response to isoproterenol (ISOP) and decreased the response to histamine (HIST). In the AMYG and SEP, ADX did not affect significantly the action of ISOP, but ADX did decrease the response to HIST in AMYG. Administration of dexamethasone or corticosterone reversed the effects of ADX on cyclic AMP accumulation in the HIPP. The dexamethasone action on VIP-stimulated cyclic AMP accumulation takes place within 48 h and is most apparent in the mid-range of the VIP dose-response curve. These results demonstrate that glucocorticoids regulate neurotransmitter-stimulated cyclic AMP generation in a fashion that is specific, both for the neurotransmitter involved and for the brain regions affected.

Phorbol esters enhance neurotransmitter-stimulated cyclic AMP production in rat brain slices.

The effect of phorbol esters on cyclic AMP production in rat CNS tissue was examined. Using a prelabeling technique for measuring cyclic AMP accumulation in brain slices, it was found that phorbol 12-myristate, 13-acetate (PMA) enhanced the cyclic AMP response to forskolin and a variety of neurotransmitter receptor stimulants while having no effect on second messenger accumulation itself. A short (15-min) preincubation period with PMA was required to obtain maximal enhancement, whereas the augmentation was lessened by prolonged exposure (3 h) to the phorbol. The response to PMA was concentration dependent (EC50 = 1 microM) and regionally selective, being most apparent in forebrain, and was not influenced by removal of extracellular calcium or by inhibition of phosphodiesterase or phospholipase A2. Only those phorbols known to stimulate protein kinase C augmented the accumulation of cyclic AMP. Moreover, the membrane substrates phosphorylated by endogenous C kinase and by a partially purified preparation of this enzyme were similar. The results suggest that phorbol esters, by activating protein kinase C, modify the cyclic AMP response to brain neurotransmitter receptor stimulation in brain by influencing a component of the adenylate cyclase system beyond the transmitter recognition site.

Behavioural sensitivity to pia in selectively bred mice is related to a number of A 1 adenosine receptors but not to cyclic AMP accumulation in brain slices

In a dose of 0.1 mg/kg, PIA had marked behavioural effects in long-sleep mice (which show a high sensitivity to ethanol, while no significant effect was observed in short sleep mice (low sensitivity to ethanol). The number of [ 3H]PIA binding sites in cortex and subcortical brain regions was significantly higher in long-sleep than in short-sleep mice. The K D value was higher in cortex and cerebellum in the short-sleep mice, but there were no differences in the number of hippocampal β-adrenoceptors or in the adenosine analogue-induced increase in cyclic AMP accumulation in slices of mouse hippocampus.

Characteristics of chick cerebral beta-adrenoceptors assessed by cyclic adenosine 3',5' monophosphate formation and [3H]-propranolol binding.

Chick cerebral beta-adrenoceptors have been characterised by measurement of cyclic AMP accumulation in brain slices and assessment of the specific binding of [3H]-propranolol to cerebral membranes. The binding of [3H]-propranolol was inhibited by beta-adrenoceptor agonists and antagonists with affinities that correlated well with their ability to stimulate cyclic AMP formation or to antagonise the cyclic nucleotide accumulation induced by isoprenaline. The relative potencies of a number of drugs in several cerebral regions suggests that the receptors may be of the beta2 subtype. Regional distribution studies revealed the highest density of binding sites in the cerebellum and lowest in the optic lobes. However, the concentration of [3H]-propranolol that produced half-maximal specific binding was similar in all regions. Subcellular fractionation of cerebral hemisphere tissue demonstrated an enrichment of [3H]-propranolol binding sites in the synaptosomal and microsomal fractions. There are discrepancies between the topographical distribution of beta-adrenoceptor binding sites and the endogenous noradrenaline level in chick brain and between the number of binding sites and the intrinsic activity of beta-adrenoceptor mediated cyclic AMP formation.

REGULATION OF CYCLIC ADENOSINE 3′, 5′‐MONOPHOSPHATE CONCENTRATION IN CHICK CEREBRAL HEMISPHERES DURING DEVELOPMENT

Abstract— Investigations have been carried out into developmental aspects of cyclic AMP metabolism and responsiveness to neurohormones in chick cerebral hemispheres. The in vivo cyclic AMP concentration, measured after freeze‐blowing, was found to be highest in the embryonic brain, and changes in the cyclic nucleotide content produced by ischaemia increased with age. The magnitude of the in vivo increases in cyclic AMP produced by isoprenaline and by histamine decreased throughout the first postnatal month. The onset of isoprenaline‐ and histamine‐induced cyclic AMP accumulation in brain slices occurred around 17 days embryonic age, reached a maximum at about 3 days post‐hatch and fell to approx 50% of this response at 28 days of age. Adenosine stimulated cyclic AMP formation to a similar extent at all ages studied.The activities of adenylate cyclase and cyclic AMP phosphodiesterase of hemisphere homogenates were found to reach maximum near the time of hatching. Since the overall pattern of responsiveness of the cerebral cyclic AMP system to neurohormones does not correlate with these variations in enzyme activities, it is suggested that changes occurring at the synaptic receptor level may explain the developmental variations observed.

Subsensitivity of noradrenaline-stimulated cyclic AMP accumulation in brain slices of d-amphetamine-treated mice

Subsensitivity of noradrenaline-stimulated cyclic AMP accumulation in brain slices of d-amphetamine-treated mice

Depolarization-evoked accumulation of cyclic AMP in brain slices: inhibition by exogenous adenosine deaminase

In guinea pig cerebral cortical slices labeled during a prior incubation with radioactive adenine, electrical stimulation or the presence of depolarizing agents such as veratridine, ouabain, and high concentrations of K + elicit a marked accumulation of radioactive cyclic AMP. This accumulation is reduced in all cases by the presence of theophylline, a compound that antagonizes the stimulatory effects of adenosine on cyclic AMP accumulation in brain slices. Exogenous adenosine deaminase also reduced the accumulation of cyclic AMP elicited by electrical stimulation, veratridine, and high concentrations of K +. Thus, adenosine formed in neuronal compartments under depolarizing conditions appears to be released into the extracellular medium as a prerequisite to stimulation of the cyclic AMP-generating system. Adenosine deaminase does not prevent the reduction in levels of ATP under depolarizing conditions, nor does it antagonize the accumulation of cyclic AMP elicited by a combination and norepinephrine. Adenosine deaminase does not, however, prevent the accumulations of cyclic AMP elicited by the depolarizing agent, ouabain.