Cyclic adenosine monophosphate: selective increase in caudate nucleus after administration of L-dopa

A method for stimulation of cyclic AMP levels in vivo by intracerebral injection in the rat olfactory tubercle

A method is described for stimulation of cAMP levels in brain by direct injection of dopamine (DA) and other neuroactive substances. Intracerebral microinjection was preceded by intraperitoneal injection of 3-isobutyl-1-methylxanthine (IBMX) to inhibit cyclic nucleotide phosphodiesterase. In vivo adenylate cyclase and phosphodiesterase activities were terminated by focused microwave radiation and the injected tissue assayed for protein and cAMP content. Increases in cAMP levels in response to injections of DA were both time- and dose-dependent. Animals receiving only vehicle or sham injections into the olfactory tubercle had basal cAMP levels of 5 pmol/mg protein. Up to five-fold increases above basal (25 pmol cAMP/mg protein) were observed for DA. With the injection of other neuroactive substances, values ranging from 160 pmol cAMP/mg protein for norepinephrine (NE), to 15 pmol cAMP/mg protein for gamma-amino butyric acid (GABA) were observed. The present study demonstrates that neuroactive substances can stimulate cAMP production in vivo when injected directly into brain tissue.

The effects of probenecid on cyclic adenosine 3',5'-monophosphate levels in cerebrospinal fluid and on brain phosphodiesterase activity in the rat

In rats, probenecid exhibits a dose-dependent increase in the concentration of cyclic adenosine 3',5'-monophosphate (cAMP) in cisternal cerebrospinal fluid (CSF). Maximal accumulation is reached 2 h after IP administration at a dosage of 150 mg/kg body weight. Serum levels of cAMP are unchanged after 200 mg/kg probenecid. In vitro investigations show an inhibitory effect of probenecid on the uptake of cAMP into the isolated choroid plexus of the rabbit. A non-competitive inhibition of probenecid on a high affinity fraction of cyclic nucleotide phosphodiesterase from rat brain homogenates is demonstrated with an inhibitor constant of 3.4 X 10(-3M. The results appear to validate the "probenecid test" for cAMP in clinical diagnostics.

L-dopa mediated accumulation of cyclic AMP in isolated rabbit retinae in vitro. Effects of light and/or pharmacological factors

The ability of L-dopa to stimulate the formation of cyclic AMP in pieces of intact rabbit retina in vitro has been studied and compared with that of dopamine and of other dopamine-mimetic drugs. Dose-dependent effects were measured in response to 5 microM up to 100 microM L-dopa with a maximal stimulation after 20 min of incubation at 35 degrees C. The L-dopa precursor, tyrosine, was totally ineffective. The L-dopa mediated response was detectable only in pieces of intact tissues (and not in homogenates) and is presumably due to the formation of newly formed dopamine, since it was completely inhibited by a decarboxylase inhibitor (benserazide). The biochemical response (cyclic AMP increase) was facilitated by ambient light, this effect being potentiated by 56 mM K+ or fully inhibited by 1 mM gamma-butyrolactone (GBL). The data suggest that the measurement of cyclic AMP levels in pieces of rabbit retina may provide a useful neurochemical model for the study of physiological and/or pharmacological agents able to interact at pre- and/or post-synaptic dopaminergic sites.

Adenosine 3':5'-monophosphate-dependent in vitro phosphorylation of synaptosomal membrane proteins from rat corpus striatum following systemic administration of L-DOPA and bromocriptine

In vitro phosphorylation of synaptosomal membrane preparation from rat striata was stimulated by addition of 5 microM cAMP, Administration of L-DOPA to rats treated previously with an L-amino acid decarboxylase inhibitor, or administration of bromocriptine resulted in a marked decrease in the in vitro phosphorylation presumably by increasing endogenous cAMP levels and thereby stimulating endogenous protein phosphorylation.

Tardive dyskinesia: a clinical test of the supersensitivity hypothesis

Patients with tardive dyskinesia showed no significant difference in CSF HVA when compared with groups of schizophrenic or depressives. CSF cAMP in the tardive dyskinesia group was significantly lower when compared to schizophrenics but not depressives. These results do not support a dopamine-receptor supersensitivity hypothesis in permanent tardive dyskinesia.

Neuroleptic drugs block both the hyperactivity and the increase in caudate nucleus cyclic AMP concentration produced by the administration of tranylcypromine and L-dopa to rats

Injection of rats with tranylcypromine and L-dopa increased brain dopamine concentrations and produced a behavioural syndrome that includes hyperactivity. It also elevated caudate nucleus cyclic AMP concentrations by approximately 50% in vivo, probably by stimulating dopamine receptors. Pretreatment with chlorpromazine inhibited both the tranylcypromine/L-dopa-induced behaviour and elevated cyclic AMP concentrations in a dose-dependent manner. Haloperidol and alpha-flupenthixol also inhibited both effects, while beta-flupenthixol and pimozide were without effect. Since none of these drugs altered the tranylcypromine/L-dopa-induced rise of brain dopamine, it is likely that they produced their effect by inhibiting dopamine-sensitive adenylate cyclase. A good correlation was found to exist between the neuroleptic inhibition of both the increased behavioural activity and the increased caudate nucleus cyclic AMP concentrations produced by tranylcypromine and L-dopa.

Rapid microwave fixation of rat brain

A new microwave device which inactivates brain enzymes rapidly and uniformly is described. From the results obtained with microwave irradiation at two power levels (0.8 kW and 4.5 kW), it has been demonstrated that the high power microwave irradiation has several advantages over the low power irradiation. In its application to neurochemical studies, significant increase in the DOPAC level was found in the irradiated brain, while there were no statistical differences in the levels of NE, DA, 5-HT and 5-HIAA between microwave irradiation and decapitation. Significant increase in the Ach level and marked reduction of the choline level were observed after microwave irradiation. There were no significant differences in the level of cyclic GMP in the brain between the two methods of sacrifice, while significant reduction of the cyclic AMP level was observed in the irradiated brain.

Parkinsonism and levodopa: a five-year experience

Seventy parkinsonian patients were treated continuously with levodopa for five years. During the first year, sixty-three patients (90 per cent) improved. After five years, however, only thirty-seven patients remained improved while thirty-three patients (48 per cent) experienced progressive disease. Complications of treatment, albeit nonfatal, increased in frequency during the five-year interval. The reason for early improvement and subsequent deterioration of parkinsonian symptoms and signs in spite of levodopa therapy remains unexplained. It suggests that Parkinson's disease may not be simply a striatal dopamine deficiency syndrome and that treatment with levodopa is more than replacement therapy.

Adenosine 3',5'-cyclic monophosphate as a possible mediator of rotational behaviour induced by dopaminergic receptor stimulation in rats lesioned unilaterally in the substantia nigra

A possible involvement of c-AMP in the rotational behaviour induced by a stimulation of dopamine receptors in corpus striatum of rats was investigated. Rats were lesioned unilaterally in the substantia nigra with 6-hydroxydopamine. Intraventricular injection of dopamine, norepinephrine and apomorphine induced rotational behaviour towards the intact side as did dibutyryl c-AMP (dB-c-AMP). Dopamine, norepinephrine and apomorphine could activate adenylate cyclase in homogenates of caudate nucleus. The activation by dopamine was blocked by haloperidol. I.p. injected apomorphine increased c-AMP content bilaterally in caudate nucleus and caused turning towards the intact side; theophylline potentiated and haloperidol blocked the effect. In non-lesioned rats, dopamine and norepinephrine, when injected unilaterally into the caudate nucleus, elicited truning twoards the non-injected side if the rats were pretreated with reserpine and tranylcypromine. c-AMP and dB-c-AMP given similarly to rats pretreated with theophylline also produced turning towards the non-injected side regardless the pretreatment with reserpine and tranylcypromine. All these results emphasize the possibility that c-AMP acts as a second messenger in the central dopaminergic pathway in rats. The supersensitivity of the dopaminergic system which developed after denervation is also discussed.

CYCLIC AMP/*SECRETl cyclic AMP into push-pull perfusates in freely moving rats

Cyclic AMP was found in perfusates of push-pull cannula's, chronically placed in the lateral ventricle of freely moving rats. After addition of norepinephrine, dopamine or adenosine to the perfusates the output of cyclic AMP was enhanced, whilst serotonin and histamine were found to be ineffective. The effects of noradrenaline and dopamine on cyclic AMP were found to be mediated by different receptors: haloperidol antagonized only the dopamine response. The effect of norepinephrine was mimicked by isoprenaline, a beta-adrenergic agonist, but was not blocked by propranolol. L-DOPA, given intraperitoneally, increased cyclic AMP levels in the perfusate. We conclude that the release of cyclic AMP into the extracellular medium is a normally occurring phenomenon in brain tissue.

Cyclic adenosinemonophosphate in cerebrospinal fluid. Effects of theophylline, L-dopa and a dopamine receptor stimulant in rats

The effects of L-Dopa and the dopamine receptor stimulant ET-495 on cisternal cAMP levels were studied in rats. L-dopa (100-200 mg/kg) increased cisternal cAMP levels by 60 to 80% of controls. When peripheral Dopa-decarboxylase was inhibited, smaller doses of L-Dopa were effective. Fla-63, an inhibitor of dopamine-beta-hydroxylase lowered the increase induced by L-Dopa which was completely suppressed by propranolol, not by phentolamine, suggesting that the cAMP increase is mediated through a central beta-adrenoceptor stimulation. ET-495 failed to influence cAMP levels which argues against a dopamine-sensitive adenylate cyclase involved in the L-Dopa effect. Moreover, large increases of cisternal cAMP were observed after treatment with theophylline , not papaverine which suggests different effects of these "phosphodiesterase inhibitors" on the cyclic AMP systems in the central nervous system or on transport mechanisms.

Effects of narcotic analgesic drugs on the cyclic adenosine 3',5'-monophosphate-adenylate cyclase system in rat brain

1. The concentrations of cyclic adenosine 3',5'-monophosphate (cyclic AMP), measured in discrete brain areas removed from rats killed by microwave irradiation, rose transiently in most areas after the administration of morphine. The most pronounced changes, however, were found 2 h after doses of either 10 or 60 mg/kg morphine when cyclic AMP levels declined significantly in the hypothalamus, medulla and cerebellum. In morphine-tolerant rat brains there were no decreases in cyclic AMP levels. 2. Basal adenylate cyclase activity in crude nerve-ending fractions from discrete areas of rat brain was unaffected by the addition of active analgesic agonists, antagonists or inactive isomers to the assay medium in vitro, except for a nonspecific inhibition at drug concentrations of 1 mM. 3. The acute administration of morphine or levorphanol, but not dextrorphan produced transient increases in basal cyclase activity of crude nerve-ending preparations from midbrain and striatum. In morphine-tolerant rats, these changes in basal adenylate cyclase activity were no longer seen.

Adenosine 3',5'-monophosphate content in rat caudate nucleus: demonstration of dopaminergic and adrenergic receptors

Dopamine, apomorphine, isoproterenol, and norepinephrine each increased the concentration of adenosine 3',5'-monophosphate in slice of rat caudate nucleus. The concentrations of dopamine, apomorphine isoproterenol, and norepinephrine causing half-maximal increases were 60, 150, 0.03 and 30 micromoles per liter, respectively. The effect of dopamine was blocked by fluphenazine, a dopamine receptor antagonist, but not by propranolol, a beta-andrenergic receptor antagonist. Conversely, the effect of isoproterenol was blocked by propranolol but not by fluphenazine. The results suggest that in rat caudate nucleus there are two distinct catecholamine receptors capable of causing increased concentrations of adenosine 3',5'-monophosphate, one having the characteristic of dopamine receptor, and the other having the characteristics of beta-adrenergic receptor.