LLuïsa Camón

Working memory deficits in transgenic rats overexpressing human adenosine A2A receptors in the brain

Adenosine receptors in the central nervous system have been implicated in the modulation of different behavioural patterns and cognitive functions although the specific role of A(2A) receptor (A(2A)R) subtype in learning and memory is still unclear. In the present work we establish a novel transgenic rat strain, TGR(NSEhA2A), overexpressing adenosine A(2A)Rs mainly in the cerebral cortex, the hippocampal formation, and the cerebellum. Thereafter, we explore the relevance of this A(2A)Rs overexpression for learning and memory function. Animals were behaviourally assessed in several learning and memory tasks (6-arms radial tunnel maze, T-maze, object recognition, and several Morris water maze paradigms) and other tests for spontaneous motor activity (open field, hexagonal tunnel maze) and anxiety (plus maze) as modification of these behaviours may interfere with the assessment of cognitive function. Neither motor performance and emotional/anxious-like behaviours were altered by overexpression of A(2A)Rs. TGR(NSEhA2A) showed normal hippocampal-dependent learning of spatial reference memory. However, they presented working memory deficits as detected by performance of constant errors in the blind arms of the 6 arm radial tunnel maze, reduced recognition of a novel object and a lack of learning improvement over four trials on the same day which was not observed over consecutive days in a repeated acquisition paradigm in the Morris water maze. Given the interdependence between adenosinic and dopaminergic function, the present results render the novel TGR(NSEhA2A) as a putative animal model for the working memory deficits and cognitive disruptions related to overstimulation of cortical A(2A)Rs or to dopaminergic prefrontal dysfunction as seen in schizophrenic or Parkinsons disease patients.

Seizures and neuronal damage induced in the rat by activation of group I metabotropic glutamate receptors with their selective agonist 3,5-dihydroxyphenylglycine.

While it is well documented that the overactivation of ionotropic glutamate receptors leads to seizures and excitotoxic injury, little is known about the role of metabotropic glutamate receptors (mGluRs) in epileptogenesis and neuronal injury. Intracerebroventricular (i.c.v.) infusion of the group I mGluR specific agonist (R,S)‐3,5‐dihydroxyphenylglycine (3,5‐DHPG) (1.5 μmol) to conscious rats produced severe and delayed seizures (onset at 4 hr) in 70% of the animals. The i.c.v. infusion of the group I mGluR non‐selective agonist 1S,3R‐1‐aminocyclopentane‐1,3‐dicarboxylic acid (1S,3R‐ACPD) (2 μmol) produced a similar rate of severe seizures, but with an early onset (0.6 hr). The analysis of motor activity showed that 3,5‐DHPG elicited higher central stimulatory action than did 1S,3R‐ACPD. Histopathological analysis of the hippocampus showed that 3,5‐DHPG produced severe neuronal damage mainly in the CA1 pyramidal neurons and, to a lesser extent, in the CA3. Although 1S,3R‐ACPD infusion also induced a slight injury of the CA1 and CA3 pyramidal neurons, damage was greater in the CA4 and dentate gyrus cells. In conclusion, the in vivo activation of group I mGluRs with the selective agonist 3,5‐DHPG produces hyperexcitatory effects that lead to seizures and neuronal damage, these effects being more severe than those observed after infusion of the non‐selective agonist 1S,3R‐ACPD. J. Neurosci. Res. 51:339–348, 1998. © 1998 Wiley‐Liss, Inc.

Lindane Administration to the Rat Induces Modifications in the Regional Cerebral Binding of [3H]Muscimol, [3H]‐Flunitrazepam, and t‐[35S]Butylbicyclophosphorothionate: An Autoradiographic Study

Abstract: The effect of lindane administration on the specific binding of ligands to different sites on the GABAA receptor‐ionophore complex was studied in the rat brain by receptor mapping autoradiography. [3H]Muscimol (Mus), [3H]flunitrazepam (Flu), and t‐[35S]butylbicyclophosphorothionate (TBPS) were used as specific ligands of GABA, benzodiazepine, and picrotoxinin binding sites, respectively. Rats received a single oral dose of 30 mg/kg lindane and they were classified into two groups according to the absence or presence of convulsions. Vehicle‐treated groups acted as controls. The effect of the xenobiotic on ligand binding was measured in different brain areas and nuclei 12 min or 5 h after its administration. Lindane induced a generalized decrease in [35S]TBPS binding, which was present shortly after dosing. In addition, [3H]Flu binding was increased in lindane‐treated animals, this modification also appearing shortly after administration but diminishing during the studied time. Finally, lindane induced a decrease in [3H]Mus binding, which became more evident over time. These modifications were observed both in the presence and in the absence of convulsions. However, an increase in [3H]‐Mus binding was detected shortly after lindane‐induced convulsions. The observed decrease in [35S]TBPS binding is in agreement with the postulated action of lindane at the picrotoxinin binding site of the GABAA receptor chloride channel. The effects observed on the binding of [3H]Flu and [3H]Mus may be secondary to the action of lindane as an allosteric antagonist of the GABAA receptor.

Brain metabolites of lindane and related isomers: Identification by negative ion mass spectrometry

The application of a new method of gas chromatography-mass spectrometry (GC-MS) to the study of some aspects of the metabolism of hexachlorocyclohexanes is presented. Instead of the classical mode of ionization (Electron Impact, EI), this method uses chemical ionization, recording only the negative ions produced. This enables a tremendous enhancement of the signal when chlorinated compounds elute from the chromatographic column. The mass spectra obtained consist generally in the ions corresponding to the molecular weight of the compound analyzed. The sensitivity of the method is higher than any other GC method described: the limit of detection of several organochlorine compounds can be as low as 60 femtograms. Using this method we have been able to identify several Lindane metabolites (tetra-, penta- and hexachlorocyclohexenes, tetra- and pentachlorobenzene) in rat brain homogenates without any purification step. Using this method, a quantitative study of the main metabolites found in brain after treatment with 4 different HCH isomers has been performed. This study reveals that the HCH isomers are cleared from the brain via different metabolic pathways, with a rate of production of metabolites which is inversely correlated to their half lives in brain.