Dissection of the chemical cues underlying courtship learning

The conditioned stimulus (CS) for courtship conditioning has been assumed for many years to be a component of the female's cuticular hydrocarbon. To determine what chemicals constitute the CS, we trained males to discriminate between mature and immature females and suppress courtship specifically to the type of female that was associated with unsuccessful courtship (Ejima et al., 2005). This "trainer-specific" learning is mediated by hydrocarbon olfactory cues because it can be reconstituted with an extract of pheromone and a generic courtship object. GC-MS analysis of the immature and mature virgin hydrocarbon profiles revealed a limited number of compounds that were specific to each type of female. These compounds are candidates to be CSs. The nature of the unconditioned stimulus (US) for trainer-specific learning is not clear, but appears to be the failure of the male to copulate. In cases where the male was allowed to copulate during training, no learning occurred and subsequent courtship was not suppressed. In many other paradigms, failure to obtain an expected reward has been shown to be aversive.

Training with a mated female produces a qualitatively different outcome compared to training with virgins: males show a generalized suppression of courtship towards all types of females. This generalization of learning can be reproduced by presentation of mated female pheromonal extracts during training with a virgin. To determine what the chemical US for mated female conditioning was, we compared mature virgin and mated female pheromonal profiles by GC-MS. Mated females differ from age-matched virgins in only one compound, cis-vaccenyl acetate (cVA). This hydrocarbon is produced only by males, and is transferred to females during copulation in the ejaculate. The presence of cVA during training with a virgin female can produce generalized suppression of courtship, indicating that it is sufficient to act as a US.

The effects of cVA on behavior, however, appear to be context-dependent. We have found that the ability to produce generalized courtship suppression varies with the nature of the stimulatory pheromones that cVA is paired with. In addition, other researchers have found that, at feeding sites, cVA can act as a aggregation pheromone (Bartelt et al., 1985; Xu et al., 2005). Thus the context and probably the processing of this olfactory cue can influence its behavioral meaning to the animal.

Additional behavior topics:

• Courtship conditioning
• Anatomical mapping of behavioral circuits
• Bidirectional modulation of behavior with CaMKII
• Dissection of the chemical cues underlying courtship learning
• Motor Behaviors

 

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