Why would anyone immobilise a caterpillar with thin strips of cling film and drip caffeine into its head? To help it to pass an exam? To enable it to make that gallery opening after work? No: in the name of science, of course. John Glendinning and colleagues of Columbia University, New York have been doling out the insect-equivalent of double espressos in an effort to shed light on the complex issue of taste sensitisation. Caterpillars, you see, are a bit of an open book when it comes to recording neural responses to taste, and caffeine is a useful bitter-tasting compound.
Just as people who eat a lot of chillies or sugary foods seem to become almost immune to them, "chronic exposure to specific compounds can [also] profoundly alter subsequent behavioural responsiveness to chemical stimuli in both vertebrates and invertebrates," as Glendinning's group explain in Journal of Experimental Biology [July 1999]. But what is not yet clear is where exactly these exposure-induced sensitivity changes occur in the 'taste pathway' which joins an animal's sensory organs with its brain.
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