The 2-deoxyglucose uptake method as a first screen for neurotoxic compounds

Role of the dorso-caudal neostriatum in filial imprinting of the domestic chick: a pharmacological and autoradiographical approach focused on the involvement of NMDA-receptors

Newly hatched domestic chicks were either acoustically imprinted on 400 Hz tone pulses or visually imprinted on a rotating red light. Compared to naive control animals, both groups of imprinted chicks expressed significantly enhanced stimulus evoked 2-fluoro-2-deoxyglucose (2-FDG) uptake in circumscribed areas of the dorso-caudal neostriatum (Ndc). This enhanced excitability after imprinting seems not to be related to changes of NMDA-receptor densities as measured by quantitative receptor autoradiography. However, pharmacological blockade of NMDA-receptors in the dorso-caudal neostriatum leads to a marked suppression of stimulus-evoked 2-FDG uptake in the dorso-caudal neostriatum and also in the interconnected imprinting relevant forebrain area, medio-rostral neostriatum/hyperstriatum ventrale (MNH). Furthermore, chicks which received bilateral Ndc injections of the competitive NMDA antagonist DL-2-amino-5-phosphono valeric acid (APV) during the imprinting experiments showed a dose-dependent decrease of imprinting success compared to vehicle-injected controls. These results indicate that the dorso-caudal neostriatum may represent a polysensory associative brain region in which visual and acoustic features of imprinting objects may be integrated. The activation in this area evoked by the imprinting stimulus during and after imprinting is critically dependent on NMDA-receptor activation, which appears to be required for this learning process.

Sequelae of parenteral domoic acid administration in rats: comparison of effects on different metabolic markers in brain

Parenterally administered domoic acid, a structural analog of the excitatory amino acids glutamic acid and kainic acid, has specific effects on brain histology in rats, as measured using different anatomic markers. Domoic acid-induced convulsions affects limbic structures such as hippocampus and entorhinal cortex, and different anatomic markers can detect these neurotoxic effects to varying degrees. Here we report effects of domoic acid administration on quantitative indicators of brain metabolism and gliosis. Domoic acid, 2.25 mg/kg i.p., caused stereotyped behavior and convulsions in approximately 60% of rats which received it. Six to eight days after domoic acid or vehicle administration, the animals were processed to measure regional brain incorporation of the long-chain fatty acids [1-(14)C]arachidonic acid ([14C]AA) and [9,10-(3)H]palmitic acid ([3H]PA), or regional cerebral glucose utilization (rCMRglc) using 2-[1-(14)C]deoxy-D-glucose, by quantitative autoradiography. Others rats were processed to measure brain glial fibrillary acidic protein (GFAP) by enzyme-linked immunosorbent assay. Domoic acid increased GFAP in the anterior portion of cerebral cortex, the caudate putamen and thalamus compared with vehicle. However, in rats that convulsed after domoic acid GFAP was significantly increased throughout the cerebral cortex, as well as in the hippocampus, septum, caudate putamen, and thalamus. Domoic acid, in the absence of convulsions, decreased relative [14C]AA incorporation in the claustrum and pyramidal cell layer of the hippocampus compared with vehicle-injected controls. In the presence of convulsions, relative [14C]AA incorporation was decreased in hippocampus regions CA1 and CA2. Uptake of [3H]PA into brain was unaffected. Relative rCMRglc decreased in entorhinal cortex following domoic acid administration with or without convulsions. These results suggest that acute domoic acid exposure affects discrete brain circuits by inducing convulsions, and that domoic acid-induced convulsions cause chronic effects on brain function that are reflected in altered fatty acid metabolism and gliosis.

Blood-brain barrier dysfunctions following systemic injection of kainic acid in the rat

Changes in blood-brain barrier (BBB) permeability and cerebral metabolic activity following intravenous injection of kainic acid (KA; 6, 12 mg/Kg) in rats were assessed by calculating respectively a blood-to-brain transfer constant (Ki) for [14C]alpha-aminoisobutyric acid and local cerebral glucose utilization (LCGU) values, at different times (1 h, or acute seizures phase, and 48 h, or chronic pathology phase) after the induction of seizures. A significant increase in the local permeability of the BBB was observed 1 h after the injection of KA 6 mg/Kg (eliciting no significant changes in cerebral metabolic activity, except within the frontal cortex and the hippocampus) and 12 mg/Kg (which induced a marked and widespread enhancement of LCGU). On the contrary, during the pathology phase, persistent regional increases in Ki values were evidenced in rats treated with the lowest dose of the convulsant, but not in rats injected with KA 12 mg/Kg (a dose able to cause extensive neuronal damage). Thus one can speculate that: 1) KA-induced regional changes in the permeability of the BBB are not correlated with changes in neuronal activity; 2) opening of the BBB is not reliably associated with neuronal injury.

Cerebral glucose uptake in lindane-treated rats

The pesticide and ectoparasiticide lindane, gamma-isomer of hexachlorocyclohexane, is a powerful CNS-stimulant inducing convulsions and other signs of hyperexcitability in mammals. The present work was carried out to investigate the effect of lindane on brain regional glucose uptake at convulsant and non-convulsant doses. Local glucose uptake was measured in male Wistar rats using a modification of the 2-deoxyglucose (2-DG) method. Animals received i.p. [3H]2-DG and the amount of label in different brain structures of control and lindane-treated animals was assayed by a liquid scintillation counting of 18 dissected regions. Lindane at single convulsant dose (150 mg/kg, p.o.) increased 2-DG uptake in olfactory tubercules, hypothalamus, hippocampus, parafloculi and hypophysis. The uptake was decreased in parietal cortex, thalamus and pons-medulla. The pattern of 2-DG uptake after a single non-convulsant dose of 30 mg/kg p.o. was not so modified. After 1 week of treatment with 10 mg/kg per day p.o., increased 2-DG uptake was observed in superior colliculi while it was decreased in parietal cortex. The increase of 2-DG uptake in limbic regions observed at the convulsive dose agrees with the experimental association between poisoning signs induced by lindane and damage in the limbic system.