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We previously reported that the pharmacological properties of the hippocampal GABA A receptor and the expression of several subunits are modified during normal ageing. However, correlation between these post-synaptic modifications and pre-synaptic deficits were not determined. To address this issue, we have analysed the mRNA levels of several GABAergic molecular markers in young and old rat hippocampus, including glutamic acid decarboxylase enzymes, parvalbumin, calretinin, somatostatin, neuropeptide Y and vasoactive intestinal peptide (VIP). There was a differential age-related decrease in these interneuronal mRNAs that was inversely correlated with up-regulation of the a1 GABA receptor subunit. Somatostatin and neuropeptide Y mRNAs were most frequently affected (75% of the animals), then calretinin and VIP mRNAs (50% of the animals), and parvalbumin mRNA (25% of the animals) in the aged hippocampus. This selective vulnerability was well correlated at the protein/cellular level as analysed by immunocytochemistry. Somatostatin interneurones, which mostly innervate principal cell distal dendrites, were more vulnerable than calretinin interneurones, which target other interneurones. Parvalbumin interneurones, which mostly innervate perisomatic domains of principal cells, were preserved. This age-dependent differential reduction of specific hippocampal inteneuronal subpopulations might produce functional alterations in the GABAergic tone which might be compensated, at the post-synaptic level, by up-regulation of the expression of the a1 GABA A receptor subunit.

We have investigated the age-dependent modifications in the expression of eight different subunits of the ␥-aminobutyric acid, type A (GABA A ) receptor (␣1, ␣2, ␣3, ␣5, ␤2, ␤3, ␥2S, and ␥2L) and all four subunits of the ␣-amino-3-hydroxy-5-methylsoxazole-4-propionate (AMPA) receptor (GluR1-4) in the hippocampus of 24-month-old rats. All aged hippocampi displayed a remarkable increase (aged/adult ratio, 3.53 ؎ 0.54) in the mRNA levels of the short version of the ␥2 subunit in parallel with a similar increase in the ␥2 subunit protein (aged/adult ratio, 2.90 ؎ 0.62). However, this increase was not observed in the mature receptor. On the other hand, the expression of the different ␣ subunit mRNAs increased moderately with aging, displaying a heterogeneous pattern. The most frequent modification consisted in an increase in the expression of the ␣1 subunit mRNA (aged/adult ratio, 1.26 ؎ 0.18), in parallel with a similar increase on the ␣1 protein (aged/adult ratio, 1.27 ؎ 0.12) and in the ␣1 incorporated to the assembled GABA A receptor (tested by immunoprecipitation; aged/ adult ratio, ‫؍‬ 1.20 ؎ 0.10). However, in the same hippocampal samples, no major modifications were observed on the expression of the AMPA receptor subunits. As a whole, these results indicated the existence of an increased expression of the GABA A receptor subunits and a preservation of the AMPA receptor at the hippocampal formation. These modifications could reflect the existence of specific deficiencies (neuronal loss and/or deafferentiation) on the GABAergic system in the aged rats.Normal aging is associated with memory and/or learning impairments that could reflect modifications at the hippocampal formation (1). The GABA A 1 and AMPA receptors (major fast inhibitory and excitatory receptor complexes, respectively) could be implicated in these alterations (2, 3).Both neurotransmitter receptors are composed of a high number of subunits in a, probably, pentameric or tetrameric conformation. The GABA A receptors are formed by the combination of a total of 19 subunits grouped in eight families: ␣1-6, ␤1-3, ␥1-3, ␦, 1-3, ⑀, , and (Ref.5; for a review, see Ref. 4).The AMPA-preferring ionotropic glutamate receptor is composed by four subunits (GluR1-4) displaying different splicing isoforms (for a review, see Ref. 6). This high molecular heterogeneity can generate multiple receptor isotypes, displaying particular physiological and pharmacological properties. It is known that the sensitivity for benzodiazepines (anxiolytic/hypnotic drugs that interact to the GABA A receptor) increase during aging in humans and in rodents (7). Previous work from our group has demonstrated the existence of agingassociated modifications in both the pharmacological properties and the molecular composition of the GABA A receptors in rat hippocampus (8 -10). These changes could reflect a sensitization process of the GABA A receptor (see also Ref. 11). However, the age-dependent modifications on the expression of the different subunits of the GABA A receptor are currently ...

Ecological communities used in biological pest control are usually represented as three-trophic level food chains with top-down control. However, at least two factors complicate this simple way of characterizing agricultural communities. First, agro-ecosystems are composed of several interacting species forming complicated food webs. Second, the structure of agricultural communities may vary in time. Efficient pest management approaches need to integrate these two factors to generate better predictions for pest control. In this work, we identified the food web components of an avocado agro-ecosystem, and unravelled patterns of co-occurrence and interactions between these components through field and laboratory experiments. This allowed us to predict community changes that would improve the performance of the naturally occurring predators and to test these predictions in field population experiments. Field surveys revealed that the food-web structure and species composition of the avocado community changed in time. In spring, the community was characterized by a linear food chain of Euseius stipulatus, an omnivorous mite, feeding on pollen. In the summer, E. stipulatus and a predatory mite, Neoseiulus californicus, shared a herbivorous mite prey. Laboratory experiments confirmed these trophic interactions and revealed that N. californicus can feed inside the prey nests, whereas E. stipulatus cannot, which may further reduce competition among predators. Finally, we artificially increased the coexistence of the two communities via addition of the non-herbivore food source (pollen) for the omnivore. This led to an increase in predator numbers and reduced populations of the herbivore. Therefore, the presence of pollen is expected to improve pest control in this system.

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