Effects of stress on rat brain adenosine 3',5'-monophosphate in vivo

Analysis of cyclic adenosine-3',5'-monophosphate levels in structures of the "informational" and "motivational" systems of the rat brain during acquisition of a conditioned active avoidance reaction

Cyclic adenosine-3'5'-monophosphate (cAMP) levels in structures of the "informational" and "motivational" systems of the brain were measured during acquisition of a conditioned two-sided active avoidance reflex in rats. cAMP levels were measured in three groups of animals--intact animals, trained animals, and an active control group (given uncombined presentations of the conditioned (light) and unconditioned (electric shock) stimuli)--immediately after reproduction of the acquired reflex. Significant accumulation of cAMP levels in brain structures was seen in animals of the active control group in the hypothalamus and in trained animals in the left and right hippocampus and the right frontal cortex. Positive correlations were found between cAMP levels in symmetrical parts of the frontal cortex, amygdala, and hypothalamus in animals of all study groups. In addition, active control rats and trained rats showed interhemisphere and intrahemisphere correlations between cAMP levels in brain macrostructure, whose patterns were specific for each group. The pattern of correlations observed here is assessed from the point of view of the role of the "informational" and "motivational" structures in the organization of adaptive behavior.

Short-term effects of postnatal manipulation on central beta-adrenoceptor transmission

Neonatal handling is known to induce long-lasting changes in behavioral and neuroendocrine responses to stress. Since the central noradrenergic system participates in the adaptive responses to stressful conditions we have analyzed the effects of postnatal handling on beta-adrenoceptor binding sites and isoprenaline- and forskolin-stimulated cyclic AMP accumulation in cerebral cortex, hippocampus and cerebellum of rats at 1 and 3 months of age. Handled animals showed reduced emotional reactivity and lower ACTH and corticosterone secretion after stress. Binding studies using [(3) H]CGP12-177 revealed increased beta-adrenoceptor binding sites in handled rats in cerebellum and cerebral cortex with no changes in hippocampus, and decreased affinity in all cerebral regions. Handling reduced basal levels of cyclic AMP in hippocampus and cerebellum but not in cerebral cortex. The concentration-response curves of cyclic AMP to isoprenaline were displaced to the right in cerebellum of handled rats without differences in Emax; however, Emax was significantly reduced in cerebral cortex and hippocampus. Direct stimulation of the catalytic subunit of adenylyl cyclase by forskolin reduced the efficiency in hippocampus and cerebellum, but not in cerebral cortex of handled animals. It is concluded that neonatal handling reduces the binding properties of beta-adrenoceptor and its primary biochemical responses in the young rat brain, which may account for the reduced responsiveness to stress attained in the handled rats, and may explain the persistence of the effect. The present study emphasizes the role of the central noradrenergic system in modulating the behavioral and neurendocrine responses to neonatal handling.

Stress-induced increase of extracellular levels of cyclic AMP in rat cortex

Previous studies have suggested that stress may increase levels of cyclic AMP (cAMP) in the brain but these findings have been controversial due to the use of stressful procedures to inactivate brain enzymes. The present experiment therefore used a non-stressful technique, microdialysis, to assay extracellular levels of cAMP in the rat cortex after stress. Experiments were conducted 2 days after implantation of probes in the frontal cortex. Significant increases were found after the mild stressors of restraint or intraperitoneal injection of saline suggesting that increased tissue levels of cAMP had occurred. These responses were potentiated by local infusion of the phosphodiesterase (PDE) inhibitor, rolipram. It is concluded that one or more adenylate cyclase-coupled receptors in the cortex is activated by mild stress and that this activation can be detected in vivo by microdialysis.

Changes in the levels of cyclic nucleotides in rat brain during the sleep-wakefulness cycle

Changes in the levels of adenosine 3',5'-monophosphate (cAMP) and guanosine 3',5'-monophosphate (cGMP) in the discrete regions of rat brain during the sleep-wakefulness cycle were studied using a microwave fixation method. Rats were restrained in a specially designed frame in which they could move their heads and extremities freely and take food and water ad libitum. The rats were acclimatized to the microwave applicator for 1 h a day for 5-7 days, and then they were sacrificed by microwave irradiation of the heads under polygraphic monitoring. This procedure made it possible to obtain tissue for the analysis of cyclic nucleotides at different times during the sleep-wakefulness cycle. The content of cAMP in the various regions of the brain except the cerebellum decreased during sleep. In the hippocampus, midbrain, pons-medulla and cerebellum, the level of cGMP was highest during wakefulness, whereas in the striatum it was highest during paradoxical sleep. In the midbrain and pons-medulla, the level of cGMP was higher during paradoxical sleep than during slow-wave sleep. These changes of cyclic nucleotide contents may reflect the changes in the release of putative neurotransmitters during the sleep-wakefulness cycle. Our findings suggest that cyclic nucleotides may play some roles in the regulation of the sleep-wakefulness cycle.

ACTH-like neurotropic peptides: possible regulators of rat brain cyclic AMP

The influence of behaviorally active, N-terminal fragments of ACTH on the accumulation of cAMP in rat brain investigated in broken cell preparations of subcortical tissue, in slices of neostriatum and in vivo. ACTH1--24 has a biphasic effect on the activity of adenylate cyclase in broken cell preparations of rat brain subcortical tissue: concentrations below 25 micrometer stimulated, whereas concentrations of 0.1 mM and higher inhibited adenylate cyclase activity. The magnitude of the stimulation was dependent on the concentrations of ATP and Mg2+ in the incubation medium. Structure activity studies revealed that at a concentration of 10(-4) M ACTH1--16-NH2 and ACTH4--7 also inhibited the activity of adenylate cyclase, whereas ACTH11--24, ACTH1--10, ACTH4--10, [D-Phe7]ACTH1--10 and [D-Phe7]ACTH4--10 were inactive in this respect. Addition of 0.8 mM EGTA but not of 0.25 mM Ca2+ prevented the inhibition by 10(-4) M ACTH1--24. GMP-N-P (10(-5) M), naltrexone (10(-3) M) and ergometrine (10(-3) M) did not influence the inhibitory effect. ACTH1--24 enhanced the accumulation of cAMP in slices from rat brain neostriatum in a dose-dependent manner. This effect was already maximal 7.5 min after the addition of the peptide and was potentiated by isobutylmethylxanthine, a potent inhibitor or phosphodiesterase. Intraventricular injection of 1 microgram ACTH1--16-NH2 in rats significantly elevated (+ 27%) the concentration of cAMP in the septal region 60 min after the injection of the peptide. The results are discussed in terms of a possible involvement of cAMP as a second messenger in the central nervous system for N-terminal fragments of ACTH.

Stress-induced alterations of cyclic nucleotide levels in brain: effects of centrally acting drugs

Acute stressing procedures cause a shortlasting increase in the levels of guanosie 3',5'-monophosphate (cGMP) in mouse brain without significantly influencing the concentrations of adenosine 3'-5'-monophosphate (cAMP). Animals were pretreated with various centrally acting drugs before being stressed in order to study the involvement of specific neurotransmitters in the stress-induced rise of cGMP levels. Centrally depressant drugs affecting different synaptic mechanisms, such as chlorpromazine, reserpine, haloperidol, diazepam, and pentobarbital, inhibited the cCMP increase elicited by stress. Pretreatment with atropine, diphenhydramine, antazoline, cyproheptadine, phentolamine, bunitrolol, and indomethacin had no significant effect. Clonidine and both the (-)- and (+)-isomers of propranolol inhibited the stress-induced cGMP increase in a dose-related manner. Our results suggest that norepinephrine, serotonin, acetylcholine, or prostaglandins are not involved in the elevation of cGMP levels elicited by acute stress. Participation of other neurotransmitter(s), such as dopamine or GABA, cannot be excluded.

Preliminary study of the use of dansyl chloride to determine cyclic-3',5'-AMP in tissues

A highly sensitive method for the determination of cyclic-3',5'-AMP has been developed which involves the reaction of the substance with dansyl chloride and the subsequent separation of the dansyl-cyclic-3',5'-AMP derivative by thin-layer chromatography. Experiments with standard solutions of 3H-cyclic-3',5'-AMP have shown that there is a direct relationship between the amount of dansyl-3H-cyclic-3',5'-AMP recovered and that dansylated. The procedure is exceedingly sensitive, allowing milligram quantities of material to be analysed for its endogeneous cyclic-3',5'-AMP content. With the use of 14C-adenine as substrate, this method permits the separation of 14C-cyclic-3',5'-AMP formed from the substrate and other 14C-containing compounds, thus allowing the turn-over of cyclic-3'-5'-AMP to be studied. The usefullness of the method is demonstrated by analysing the turn-over and endogenous content of cyclic-3'-5'-AMP in rat nervous tissue.

Effects of electroshock and drugs administered in vivo on protein kinase activity in rat brain

The effect of electroshock and treatment with reserpine, amphetamine or lithium chloride on protein kinase activity in synaptic membrane fragments prepared from rat brain was investigated. Naive rats subjected to electroshock procedures showed significant increases in both basal and cyclic AMP-stimulated activity irrespective of whether the treatment was sham, acute or chronic. These increases did not occur in animals which had been tamed by daily handling for 15 days prior to treatment, suggesting that the response was induced by the stress of an unfamiliar situation. Administration of lithium chloride and reserpine caused a small but significant increase in the stimulated activity. Doses of d-amphetamine of 5 mg/kg had no effect on either basal or stimulated activity, but higher doses (up to 15 mg/kg) resulted in a pronounced increase in both activities, which may have been related to drug-induced stress.