The gamma-hydroxybutyrate signalling system in brain: organization and functional implications.

Focussed microwave radiation: a technique to minimize post mortem changes of cyclic nucleotides, dopa and choline and to preserve brain morphology

The Serotonin-Producing Neurons of the Midbrain Median and Dorsal Raphe Nuclei

Pharmacological profile of apigenin, a flavonoid isolated from Matricaria chamomilla

Less than two decades ago Sutherland and Rall (1958; Rall et al., 1957) discovered a heat stable factor now known as adenosine 3′,5′-monophosphate, which accumulated in particulate fractions of liver homogenates exposed to epinephrine. This factor activated the breakdown of glycogen by soluble cytoplasmic enzymes. Although epinephrine activates glycogenolysis in intact hepatocytes, the hormone has no such effect on the soluble enzymes. Sutherland and Rall (1960; Rall and Sutherland, 1958, 1961, 1962) proposed that epinephrine might trigger the glycogenolytic response of hepatocytes by activating the synthesis of this nucleotide (cyclic AMP) whose structure (Fig. 1) by then had been shown to contain a unique cyclic phosphate bond (Lipkin et al., 1959). The polypeptide hormone glucagon also triggers the glycogenolytic response of liver, and activates the synthesis of cyclic AMP. From these and related observations on the actions of other hormones, the concept arose that cyclic AMP functioned as an intracellular “second messenger”, synthesized in response to certain hormones and which, by activating the appropriate sequence of enzymes, produced the specific biologic response of the target cell to the hormone (Sutherland et al., 1965).

The role of cyclic nucleotides in central synaptic function.

Subcutaneous injections of isoniazid or picrotoxin increase the cerebellar content of 3′,5′-cyclic guanosine monophosphate (cGMP) without changing the 3′,5′-cyclic adenosine monophosphate cAMP. This increase was dose dependent and the threshold for the cGMP increase was lower than that for convulsions. In cerebellum the increase of cGMP content elicited by isoniazid but not that caused by picrotoxin was paralleled by a decrease of GABA content. Diazepam doses starting from 1.74 μmol/kg intraperitoneally produced a dose dependent decrease of cerebellar cGMP concentration without changing cAMP or GABA content. Smaller doses of diazepam (0.5 μmol/kg i.p.) failed to decrease the basal cerebellar content of cGMP. However, this dose of diazepam antagonized the increase of cGMP produced by isoniazid but not that produced by picrotoxin. Higher doses of diazepam were necessary to block the increase of cerebellar cGMP elicited by picrotoxin. Low doses of diazepam (0.14 μmol/kg) antagonized the convulsions in 50% of the rats injected with 3.3 mmol/kg of isoniazid. The doses of diazepam required to block picrotoxin, pentylenetetrazol or strychnine convulsions were 7, 25 and 40 times higher than those required to block isoniazid convulsions, respectively. Desmethyldiazepam, chloridiazepoxide, oxazepam were also several times more potent in antagonizing isoniazid than picrotoxin, pentylenetetrazol, or strychnine convulsions. In contrast, barbiturates were equipotent against all the convulsants studied. These experiments suggest that diazepam may act in the CNS either by altering the disposition of endogenous GABA or by mimicking the action of GABA at specific synaptic receptors.

Evidence for an involvement of GABA in the mediation of the cerebellar cGMP decrease and the anticonvulsant action of diazepam

A "recptor unit" for gamma-aminobutyric acid (GABA), which includes brainlike receptor binding sites for tritium-labeled GABA and benzodiazepines (diazepam, clonazepam, and flunitrazepam) and a thermostable endogenous protein (GABA modulin) that inhibits both GABA and benzodiazepine binding, has been demonstrated in membranes prepared from NB2a neuroblastoma and C6 glioma clonal cell lines. In these cells, as in brain, diazepam (1 micromolar) prevents the effect of GABA modulin, and in turn GABA (0.oma and, to a lesser extent, the glioma cells represent a suitable model to study the interactions and the sequence of membrane and intracellular events triggered by the stimulation of benzodiazepine and GABA receptors.

GABA receptors in clonal cell lines: a model for study of benzodiazepine action at molecular level.

We studied the relationship between changes of 3′,5′-cyclic adenosine monophosphate (cAMP) and tyrosine hydroxylase (TH) activity in adrenal medulla of rats exposed to cold stress Exposure of rats to 4° C produced a ten-fold increase of the cAMP content of adrenal medulla in about 30 min This increase persisted for about one hour; the levels of cAMP returned to control value within 120 min in spite of the continued exposure to 4° C In rats with monolaterally denervated (splanchnicotomized) adrenal, the exposure to 4° C produced only insignificant changes of cAMP concentration During the exposure to 4° C we also observed an increase (about two times) of catecholamine turnover rate as measured by 3H-dopamine efflux from adrenal glands This increased efflux persisted for 6 h of exposure to cold suggesting that the efflux of 3H-dopamine can increase without a simultaneous increase of cAMP concentrations Exposure of rats to 4° C for two hour also increases (about two times) the TH activity as measured 24 h later Exposure of the animals to 4° C for a time period longer than two hour (4 or 24 h) failed to produce further increases of TH activity These results support the concept that the increase of cAMP concentrations in adrenal medulla may play a central role in initiating the chain of biochemical events modulating the synthesis of TH

Involvement of 3′,5′-cyclic adenosine monophosphate in the increase of tyrosine hydroxylase activity elicited by cold exposure

Gamma-hydroxybutyric acid (GHBA) in doses that increased the striatal dopamine (DA) content of rat brain failed to increase the affinity of striatal tyrosine hydroxylase (TH) for its pterdine cofactor or to change the sensitivity of the enzyme to the inhibition by DA. Haloperidol (1 mg/kg) decreased the apparent Km of striatal TH for the pteridine cofactor. However, when GHBA was injected before haloperidol it prevented the decrease in the apparent Kn of TH, in a dose related manner. In vitro GHBA (10(-4) M) neither changed the stimulation of the striatal adenylyl cyclase by DA nor its inhibition by haloperidol. These results suggest that in striatal dopaminergic terminals the Kn of TH for the pteridine cofactor is regulated by an molecuular mechanism which requires that the impulse flow in the DA neurons is unimpaired.

The regulation of striatal tyrosine hydroxylase. Effects of gamma hydroxybutric acid and haloperidol

The transsynaptic induction of tyrosine 3-monooxygenase (TH) in rat adrenal medulla is preceded by an early increase in the ratio of cyclic adenosine monophosphate (AMP) to cyclic guanosine monophosphate, an activation of cytosol cyclic AMP-dependent protein kinase, and a subsequent translocation of protein kinase catalytic subunits from cytosol to subcellular particles. As a result of this translocation, nuclear protein kinase activity increases during the induction of TH. Transection of splanchnic nerve reverts these events and prevents the induction of TH. Thus, adrenal medulla activation and translocation of cyclic AMP-dependent protein kinase may act as a long-range messenger for the genetic regulation of TH synthesis.

https://science.sciencemag.org/content/sci/193/4254/691.full.pdf

Alessandro Guidotti

Papers

Evidence for an involvement of GABA in the mediation of the cerebellar cGMP decrease and the anticonvulsant action of diazepam

GABA receptors in clonal cell lines: a model for study of benzodiazepine action at molecular level.

Involvement of 3′,5′-cyclic adenosine monophosphate in the increase of tyrosine hydroxylase activity elicited by cold exposure

The regulation of striatal tyrosine hydroxylase. Effects of gamma hydroxybutric acid and haloperidol

Induction of tyrosine 3-monooxygenase in adrenal medulla: role of protein kinase activation and translocation