no-bridgeKS49 (nob) has been shown to have a disturbed protocerebral bridge (pb). Using monoclonal antibodies that stain selectively some central complex regions we found that the protocerebral pridge defect is accompanied by a loss of certain inputs and outputs of the central complex. Mutant nob flies have a reduced climbing activity due to a reduced average walking speed and to a spastic state. Their mean longevity is drastically reduced, suggesting that nob is a pleiotropic gene. The nob mutant is impaired in habituation and in Pavlovian conditioning of the proboscis extension reflex (PER), although its initial reactivity to the sucrose stimulus is normal. Tested in habituation of the PER by ipsi- and contralateral stimulations, the nob mutant shows some difficulties in the "data exchange" between the two brain hemispheres, suggesting that the central complex may coordinate information processing in the two hemispheres.

Resume Nous avons entrepris dans le cadre de cet article une approche de psychologie experimentale sur les processus d'apprentissage chez la drosophile. Cette etude vise a confirmer l'importance de l'occurrence d'une stimulation aversive (chlorhydrate de quinine) sur la probability d'extrusion proboscidienne consecutive a la presentation d'une solution sucree. En reprenant les procedures classiques d'habituation comportementale et de conditionnement associatif de Medioni et Vaysse (1975), nous avons etabli que le role de la quinine n'etait pas simplement et universellement aversif comme postule jusqu'alors, mais que seule sa presentation en consecutivite immediate avec la presentation sucree etait de nature a hater la disparition du reflexe proboscidien. En revanche, sa presentation avant ou en association, voire a intervalle d'une ou de deux minutes apres la stimulation sucree est plut6t de nature a retarder la disparition du reflexe proboscidien. Parmi les diverses hypotheses emises, seule une interpretation en termes de «punition conditionnee» est susceptible d'expliquer l'ensemble des resultats.

The conditioned inhibition of courtship in male was quantitatively and sequentially studied in the Drosophila melanogaster neurological mutant no-bridgeKS49 (nob). After being paired first with a previously fertilized (unreceptive) female, wild-type Berlin males court virgin, receptive females less vigorously (if not at all) then naive wild-type males do. This conditioned inhibition is characterized by the latency of the first contact, the frequency and duration of the courtship acts, and the sequential organization of the kinetograph. In contrast, when presented with the same sequence, the nob males were not inhibited, as reflected in all courtship parameters; their courtship performance with virgin females was similar to that of naive nob males. This behavior pattern could be due to the disorganization of their protocerebral bridge interrupting inhibitory interactions between the two brain hemispheres, thereby causing uncoordinated descending inhibition of the motor behavior. The results suggest that the central complex could be the high brain center controlling this kind of learning.

Male courtship events of two neurological mutants (nobridgeKS49 (nob) and minibrain3 (mnb)) of Drosophila melanogaster were recorded and subjected to quantitative and sequential analysis. The nob mutation, which disorganizes the protocerebral bridge, causes specific defects in courtship: a low frequency of the copulation attempt and the disappearance of the licking – copulation attempt sequence. Thus, the nob males were unable to copulate with receptive females within the 30-min observation. We think that this may be due to an abnormality in their wing vibrations. The mnb mutant, characterized by a reduction of the brain (by more than 50%), exhibited difficulties in initiating courtship and in maintaining contact with the female during courtship. These courtship defects may be due to visual and locomotor anomalies.