Abstract
The recent development of the olfactory conditioning of the sting extension response (SER) has provided new insights into the mechanisms of aversive learning in honeybees. Until now, very little information has been gained concerning US detection and perception. In the initial version of SER conditioning, bees learned to associate an odor CS with an electric shock US. Recently, we proposed a modified version of SER conditioning, in which thermal stimulation with a heated probe is used as US. This procedure has the advantage of allowing topical US applications virtually everywhere on the honeybee body. In this study, we made use of this possibility and mapped thermal responsiveness on the honeybee body, by measuring workers' SER after applying heat on 41 different structures. We then show that bees can learn the CS-US association even when the heat US is applied on body structures that are not prominent sensory organs, here the vertex (back of the head) and the ventral abdomen. Next, we used a neuropharmalogical approach to evaluate the potential role of a recently described Transient Receptor Potential (TRP) channel, HsTRPA, on peripheral heat detection by bees. First, we applied HsTRPA activators to assess if such activation is sufficient for triggering SER. Second, we injected HsTRPA inhibitors to ask whether interfering with this TRP channel affects SER triggered by heat. These experiments suggest that HsTRPA may be involved in heat detection by bees, and represent a potential peripheral detection system in thermal SER conditioning.
Highlights
In associative learning, animals associate sensory stimuli or their own behavioral responses with particular outcomes, possessing a positive or negative hedonic value for the animal
This map reveals that responses are symmetrical between body sides, that body structures are more sensitive than the appendages and it shows a gradual decrease in thermal sensitivity from the head to the abdomen
We demonstrated that heat application does not need to be located on specific structures to serve as an aversive US in sting extension response (SER) conditioning
Summary
Animals associate sensory stimuli or their own behavioral responses with particular outcomes, possessing a positive or negative hedonic value for the animal. Sucrose is detected by dedicated sugar receptors (AmGr1) on gustatory neurons within specific sensilla on the bees’ antennae, mouthparts and tarsi (de Brito Sanchez, 2011; Jung et al, 2015) These neurons project to the subesophageal ganglion, where they are thought to directly or indirectly contact a single octopaminergic neuron, VUM-mx (ventral unpaired median neuron 1 of the maxillary neuromere), which represents the appetitive reinforcement in the bee brain (Hammer, 1993). Such response is reminiscent of the SER probability increase observed from room temperature until 65◦C in worker bees (Junca et al, 2014) To this day, HsTRPA represents the best candidate for thermal detection involved in aversive thermal conditioning. We injected HsTRPA inhibitors to ask whether interfering with this TRP channel affects SER triggered by heat
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