Odour maps in the brain of butterflies with divergent host-plant preferences.

Butterflies are believed to use mainly visual cues when searching for food and oviposition sites despite that their olfactory system is morphologically similar to their nocturnal relatives, the moths. The olfactory ability in butterflies has, however, not been thoroughly investigated. Therefore, we performed the first study of odour representation in the primary olfactory centre, the antennal lobes, of butterflies. Host plant range is highly variable within the butterfly family Nymphalidae, with extreme specialists and wide generalists found even among closely related species. Here we measured odour evoked Ca(2+) activity in the antennal lobes of two nymphalid species with diverging host plant preferences, the specialist Aglais urticae and the generalist Polygonia c-album. The butterflies responded with stimulus-specific combinations of activated glomeruli to single plant-related compounds and to extracts of host and non-host plants. In general, responses were similar between the species. However, the specialist A. urticae responded more specifically to its preferred host plant, stinging nettle, than P. c-album. In addition, we found a species-specific difference both in correlation between responses to two common green leaf volatiles and the sensitivity to these compounds. Our results indicate that these butterflies have the ability to detect and to discriminate between different plant-related odorants.

A behavioural operant discrimination model for assessment and pharmacological manipulation of visual function in rats.

A large number of commercially available drugs are known to cause visual side effects in humans. Therefore, it would be advantageous to screen for alterations in visual function at a pre-clinical stage. Available methods, however, lack control for motivational and motoric side effects. The aim of the present study was therefore to develop a behavioural test to detect and quantify drug-induced visual side effects while simultaneously controlling for other side effects. We here present a novel model based on operant conditioning methodology with a food rewarded two-choice design to assess visual acuity and contrast sensitivity in rats. Rats were trained to discriminate between computer-generated sine-wave gratings and homogenous grey stimuli of equal luminance. They were subsequently tested with novel stimuli differing to training stimuli according to either spatial frequency or contrast. Finally, we tested how visual acuity was affected by oral administration of quinine HCl, a compound known to affect visual function in man. The rats learned to discriminate visual stimuli within 4-5weeks of twice daily training. A training procedure with moving stimuli achieved faster learning than with static stimuli. The visual detection threshold for discrimination of grating patterns decreased as a function of the contrast level, ranging from a spatial frequency of 0.8cycles/degree (c/d) at 100% contrast to 0.2c/d at 12.5%. Administration of quinine HCl was shown to affect the visual acuity threshold in a dose- and time dependent manner. In addition, response rate was affected by quinine administration but temporally isolated from the attenuation of visual acuity demonstrating that this model can separate the visual effects from motoric and motivational side effects.

Time and space are complementary encoding dimensions in the moth antennal lobe.

The contribution of time to the encoding of information by the nervous system is still controversial. The olfactory system is one of the standard preparations where this issue is empirically investigated. For instance, output neurons of the antennal lobe or the olfactory bulb display odor stimulus induced temporal modulations of their firing rate at a scale of hundreds of milliseconds. The role of these temporal patterns in the encoding of odor stimuli, however, is not yet known. Here, we use optical imaging of the projection neurons of the moth antennal lobe to address this question. First, we present a biophysically derived model that provides an accurate description of the calcium response of projection neurons. On the basis of this model, we subsequently show that the calcium response of the projection neurons displays a stimulus specific temporal structure. Finally, we demonstrate that an encoding scheme that includes this temporal information boosts classification performance by 60% as compared to a purely spatial encoding. Although the putative role of combinatorial spatio-temporal encoding strategies has been the subject of debate, our results for the first time establish quantitatively that such an encoding strategy is used by the insect brain.