Pancreatic autoantibodies, HLA DR and PTPN22 polymorphisms in first degree relatives of patients with type 1 diabetes and multiethnic background.

AIM: To evaluate the prevalence of pancreatic auto-antibodies (PAb) as well as its relationship with HLA DR B1 and PTPN22 polymorphisms in first degree relatives (FDR) of Brazilian patients with Type 1 diabetes (T1D) and multiethnic background. METHODS: FDR of patients with T1D were interviewed and blood was sampled for PAb measurement, HLA DRB1 and PTPN22 genotyping. Genotyping was also performed in index cases. RESULTS: In FDR (n=78), 16.7% presented at least one PAb. These individuals had a higher prevalence of HLA DRB1* 03 than others (p=0.03), without differences in PTPN22 genotyping. While the genetic profile was similar in FDR with PAb and their index cases, those without PAb had a lower frequency of HLA DR B1 * 03 than their correspondent patients (p=0.009). CONCLUSION: In this multiethnic population, a significant proportion of FDR of T1D patients had PAb, which was associated with HLA DR B1 * 03 but not with the PTPN22 polymorphism.

Distribution of Fos immunoreactivity in the rat brain after freezing or escape elicited by inhibition of glutamic acid decarboxylase or antagonism of GABA-A receptors in the inferior colliculus.

It has been shown that electrical stimulation of the central nucleus of the inferior colliculus (IC) at freezing or escape thresholds activates different neural circuits in the brain. Since electrical stimulation activates cell bodies and fibers of passage it is necessary to use chemical stimulation that activates only post-synaptic receptors. To examine this issue in more detail, we took advantage of the fact that GABAergic neurons exert tonic control over the neural substrates of aversion in the IC. Reduction of GABA transmission in this structure was performed with the use of semicarbazide - an inhibitor of the GABA synthesizing enzyme glutamic acid decarboxylase (GAD) - and the GABA-A receptor antagonist bicuculline. Depending on the dose employed local infusions of semicarbazide (6.0 microg/0.2 microl) or bicuculline (40 ng/0.2 microl) into this region caused freezing and escape, respectively. The results obtained showed that freezing behavior induced by semicarbazide was associated with an increase in Fos expression in the dorsomedial column of the PAG (dmPAG) only, while bicuculline-induced escape was related to widespread increase in Fos labeling, notably in the periaqueductal gray, hypothalamus nuclei, amygdaloid nuclei, the laterodorsal nucleus of thalamus (LD), the cuneiform nucleus (CnF) and the locus coeruleus (LC). Thus, the present data support the notion that freezing and escape behaviors induced by GABA blockade in the IC are neurally segregated: acquisition of aversive information of acoustic nature from the IC probably uses the dmPAG column as a relay station to higher brain centers whereas bicuculline-induced escape activates structures involved in both sensory processing and motor output of defensive behavior. These results support the existence of distinct neural circuits mediating the sensory and motor responses of the defense reaction. The extent of the brain activation during freezing appears to be limited to the anatomical connections of the dmPAG, whereas an overall activation of the limbic system predominates during escape behavior induced by IC stimulation.

Diurnal variation in the proconvulsant effect of 3-mercaptopropionic acid and the anticonvulsant effect of androsterone in the Syrian hamster.

GABA is the principal neurotransmitter of the mammalian circadian system, and its activity is subject to diurnal and circadian variations, with maximal values in hypothalamic turnover, content and binding during the night. In this study we have examined rhythms in the proconvulsant effect of inhibition of glutamate decarboxylase (GAD) in hamsters (Mesocricetus auratus) as well as the anticonvulsant effect of androsterone, a neurosteroid that positively modulates the GABA(A) receptor. Administration of 10-60 mg/Kg of 3-mercaptopropionic acid (3-MPA, a GAD inhibitor) induced convulsions that were analyzed by an ad-hoc severity scale, with a lower sensitivity threshold at 24:00 h. Moreover, the latency for first and maximal convulsive response times was significantly lower at night. A similar temporal profile (maximal effect at midnight) was found for picrotoxin-induced seizures. Androsterone (40 mg/Kg) completely inhibited 3-MPA-induced tonic/clonic seizures at 12:00 h, while it had a partial inhibitory effect at 24:00 h. These results support the importance of temporal regulation of GABAergic modulation in the central nervous system.

Inhibition of synaptosomal [3H]glutamate uptake and [3H]glutamate binding to plasma membranes from brain of young rats by glutaric acid in vitro.

Synaptosomes and plasma membrane preparations from brain of 30-day-old rats were incubated with glutaric acid at final concentrations ranging from 10 nM to 1 mM for the determination of glutamate uptake and binding, respectively. [3H]Glutamate uptake into synaptosomes was inhibited by approximately 50% by 1 mM glutaric acid, corresponding to the concentration found in brain of glutaric acidemic children. In addition, in the presence of extracellular Na+ concentrations, the same dose of glutaric acid decreased by about 30% [3H]glutamate binding to brain plasma membranes. The results indicate that the inhibition of both glutamate uptake into synaptosomes and glutamate binding to plasma synaptic membranes by the metabolite could result in elevated concentrations of the excitatory neurotransmitter in the synaptic cleft, potentially causing excitotoxicity to neural cells, a fact that may be related to the brain damage characteristic of glutaric acidemia type I.

Valproic acid differs in its in vitro effect on glutamic acid decarboxylase activity in neonatal and adult rat brain.

1. The in vitro effect of valproic acid (VA) (10(-6) to 10(-3) M) on glutamic acid decarboxylase (GAD) activity in whole brain and cerebral cortex (CC) of neonates and of adult rats was examined. 2. VA did not induce changes on GAD activity either in CC or in the rest of the brain (RB) of adult animals. 3. But at 10(-3) M, VA induced an increase in GAD activity in homogenates of noncortical brain areas of neonates; no increments were found in CC of these animals. This latter increase was detected in the membrane-bound fraction of the enzyme and was not due to physicochemical nonspecific changes related to the potential solvent activity of VA at this high concentration. 4. We may conclude that VA induces changes on GAD activity in neonatal stages of development but not in adult brain. Therefore, although a direct enhancement of GAD activity may play a role in the mechanism of action of VA in pediatric patients, this cannot be verified in the adult population.

A possible inhibitory action of baclofen on hippocampus GABAergic neurones.

1. The function of the gamma-aminobutyric acid (GABA)ergic system in certain areas of the rat brain was investigated after baclofen treatment (30 mg/kg for 4 days). 2. Two h after the last dose of baclofen GAD activity was reduced in the hippocampus without changes in GABA levels. 24 h after baclofen, GAD activity was increased and the GABA content was decreased. 3. 48 h after the last dose both parameters returned to control values. 4. These results were not observed in any of the other areas investigated: frontal cerebral cortex, corpus striatum, olfactory bulbs, and medio basal hypothalamus. 5. In conclusion, the present study shows that baclofen 30 mg/kg for 4 days, induces an inhibitory action on hippocampus GABAergic neurones, which begins to disappear after 24 h free of drug.