Chiara Perra

Functional correlation between allopregnanolone and [35S]‐TBPS binding in the brain of rats exposed to isoniazid, pentylenetetrazol or stress

1 The relation between changes in the cerebral cortical concentration of allopregnanolone and γ‐aminobutyric acid (GABA) type A receptor function after intracerebroventricular injection of this neurosteroid was investigated in male rats. 2 Intracerebroventricular administration of allopregnanolone (1.25 to 15 μg) produced a maximal increase (100 fold at the highest dose) in cortical allopregnanolone concentration within 5 min; the concentration remained significantly increased at 15 and 30 min, before returning to control values by 60 min. 3 The same treatment induced a rapid and dose‐dependent decrease in the binding of t‐[35S]‐butylbicyclophosphorothionate ([35S]‐TBPS) to cerebral cortical membranes measured ex vivo, an effect mimicked by the benzodiazepine midazolam but not by the 3β‐hydroxyepimer of allopregnanolone. The time course of changes in [35S]‐TBPS binding paralleled that of brain allopregnanolone concentration. 4 In a dose‐dependent manner, allopregnanolone both delayed the onset of convulsions and inhibited the increase in [35S]‐TBPS binding to cortical membranes induced by isoniazid. The potency of allopregnanolone in inhibiting [35S]‐TBPS binding in isoniazid‐treated rats was approximately four times that in control animals. 5 The ability of allopregnanolone to decrease [35S]‐TBPS binding in isoniazid‐treated rats also correlated with its anticonvulsant activity against pentylenetetrazol‐induced seizures as well as its inhibitory effect on the increase in [35S]‐TBPS binding induced by foot shock. 6 The results indicate that the in vivo administration of allopregnanolone enhances the function of GABAA receptors in rat cerebral cortex and antagonizes the inhibitory action of stress and drugs that reduce GABAergic transmission.

Isoniazid-induced inhibition of GABAergic transmission enhances neurosteroid content in the rat brain

Isoniazid (375 mg/kg, s.c.), a drug that decreases GABAA receptor-mediated transmission, elicited a time-dependent increase of neuroactive steroid (pregnenolone, progesterone and allotetrahydrodeoxycorticosterone) concentrations in rat brain and plasma. This treatment also time-dependently increased the plasma concentration of corticosterone. Brain and plasma neuroactive steroid levels peaked between 40 and 120 min after isoniazid administration, respectively, and returned to control values by 5 hr. Acute foot shock stress mimicked the effect of isoniazid by increasing in a time-dependent manner the same neuroactive steroids both in brain and plasma. Abecarnil (0.3 mg/kg, i.p.), a beta-carboline derivative with anxiolytic properties, antagonized the effect of both isoniazid and foot shock on brain and plasma neuroactive steroids and on plasma corticosterone level. These data indicate that an inhibition of central GABAergic transmission enhances the concentrations of THDOC and its precursors pregnenolone and progesterone in the rat brain and plasma as well as the plasma levels of corticosterone. This finding suggests that GABA exerts a tonic inhibitory action on the mechanisms involved in the regulation of the synthesis and release of these neuroactive steroids in the central nervous system and plasma.

α-Thalassemia carrier identification by DNA analysis in the screening for thalassemia

Differentiation between heterozygous α‐thalassemia and several phenotypically resembling alleles at the β‐globin gene cluster such as coinherited δ‐ and β‐thalassemia or γδβ‐thalassemia is a critical step in genetic counseling. In this paper we report our experience in the identification of the α‐thalassemia carrier state using polymerase chain reaction (PCR)‐based methods, and the feasibility and simplification of screening for thalassemia using this approach. α‐Globin genotype was determined by PCR‐based method in 526 adult subjects with reduced mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH), normal hemoglobin A2 and F, and normal serum iron. To verify the reliability of the protocol used, in 68 of these subjects we performed globin chain synthesis analysis and in 101 we determined α‐globin genotype by Southern blot analysis. Five hundred twenty‐one (99%) of 526 subjects examined were identified as carriers of one or two α‐thalassemia alleles. The identification of the α‐thalassemia carrier state may be fast and accurate by PCR‐based method, avoiding other cumbersome and expensive methods such as globin chain synthesis and Southern blot analysis. Am. J. Hematol. 59:273–278, 1998.

Chronic ethanol intoxication enhances [3H]CCPA binding and does not reduce A1 adenosine receptor function in rat cerebellum

The effects of acute and chronic treatment with ethanol on the function of A1 adenosine receptor in the rat cerebellar cortex were investigated. Acute administration of ethanol (0.5-5 g/kg) had no effect on the binding of the A1-receptor agonist [3H]2-chloro-N6-cyclopentyladenosine ([3H]CCPA) or that the antagonist [3H]8-cyclopentyl-1-3-dipropylxanthine ([3H]DPCPX) in rat cerebellar cortical membranes. Rats were rendered ethanol dependent by repeated forced oral administration of ethanol (12-18 g/kg per day) for 6 days. [3H]CCPA binding was increased by 23% in cerebellar cortical membranes prepared from rats killed 3 h after ethanol withdrawal compared with saline-treated animals. The increase in [3H]CCPA binding was still apparent 12-24 h after the last ethanol administration, but was no longer detectable 3-6 days after ethanol withdrawal. In contrast, the binding of [3H]DPCPX was not modified in the cerebellar cortex of rats killed at various times after ethanol withdrawal. The acute administration of CCPA [0.25-1 mg/kg, intraperitoneally (IP)] suppressed the tremors and audiogenic seizures apparent 24 h after ethanol withdrawal. Moreover, repeated coadministration of CCPA (0.5 mg/kg, IP, four times daily) and ethanol did not prevent the generation of audiogenic seizures during withdrawal but completely prevented mortality. Finally, CCPA antagonized with similar potencies and efficacies the isoniazid-induced convulsions observed in control and ethanol-withdrawn rats. These results indicate that long-term treatment with intoxicating doses of ethanol enhances [3H]CCPA binding but does not reduce the anticonvulsant efficacy of CCPA or the function of A1 adenosine receptors.

Somatic deletion of the normal beta-globin gene leading to thalassaemia intermedia in heterozygous beta-thalassaemic patients.

Two β‐thalassaemia patients, whose constitutive genotype was β39C/β39C→T, had the clinical phenotype β‐thalassaemia intermedia. Analysis of leucocyte DNA showed the presence of the mutated β39C→T‐gene exclusively, while the normal β39C‐gene was also present in reticulocyte RNA. Deletional analysis of chromosome 11p15.5 on leucocyte DNA showed large deletions including the β‐globin gene. Two populations of erythroid progenitors, one heterozygous and the other hemizygous for the β39C→T mutation, were demonstrated in one case. This confirms that, in heterozygous individuals, β‐thalassaemia intermedia may be caused by inactivation of the β‐locus in trans as a result of chromosome 11p15.5 deletions in a subpopulation of haematopoietic cells.