Mammals capsaicin

FIGURE 13.1 Methyl anthranilate deters birds from feeding and stimulates feeding in mammals. Capsaicin deters mammals from feeding but stimulates birds. 

Capsaicin is what makes chili peppers hot. It is an irritant, for mammals, but not for birds. This may be because birds spread the seeds better than mammals. It causes a burning sensation in any mammalian tissue with which it comes in contact. 

Further examples of the importance of functional groups for behavior are the responses of simfish to steroids in beetles, their prey reactions of birds and mammals to capsaicin-related compounds and fear behavior of rats when exposed to sulfur compoimds from fox urine and feces. 

Capsaicin analogues that differ in only one functional group affect birds and mammals differently. A change from an acidic phenolic hydroxyl group in vanil-lyl acetamide to a methoxy group in veratryl acetamide reverses the effect on starlings and rats. The first was aversive to starlings, but attractive to rats, while the opposite was true for veratryl acetamide (Mason etal., 1991). 

Birds may have a trigeminal receptor for o-aminoacetophenone and methyl anthranilate, analogous to the capsaicin receptor in mammals (Clark and Shah, 1994). 

Jancso, G., Kiraly, E., Such, G., Joo, F., Nagy, A. (1987). Neurotoxic effect of capsaicin in mammals. Acta Physiol. Hung. 69 295-313. 

Birds and squirrels at capsaicin-treated food. Top Bluejay (Cyanocitta cristata) feeds on capsaicin-treated birdseed, while gray squirrel (Sciurus cadrolinensis) simultansously feeds on untreated birdseed. Bottom Simultaneously, bluejay feeds on birdseed treated with capsaicin (a mammal repellent), and a gray squirrel feeds on birdseed treated with methyl anthrandate, a bird repellent... 

It has been proposed that capsaicin serves chili peppers by selectively deterring predators. Birds, productive vectors for seed dispersion, do not respond to capsaicin. In contrast, mammals are predatory but are deterred by the capsaicin (with the exception of humans) [26], The molecular basis of the differential capsaicin sensitivity between birds and mammals can be traced to VR1 [27]. The avian homolog of VR1, like its mammalian counterpart, is responsive to heat but unlike its mammalian counterpart, avian VR1 does not respond to capsaicin. 

Perhaps more remarkable than the ability to use the differences between chick (insensitive) and rat (sensitive) to construct a mutant insensitive rat VR1, was the use of the rat receptor to guide the construction of a capsaicin-sensitive chick receptor. Building the binding pocket required more than a point mutation the active construct borrowed 45 amino acids from the rVRl inserted into the correct position in the cVRl. Essentially, the molecular basis of this selective deterrence causing birds, but not mammals, to consume chili peppers is explained by a biochemical change in ligand specificity, induced by a few amino acids in mammal versus avian VR1. 

TRP channels, named for their role in Drosophila phototransduction, are a family of hexas-panning receptors with a pore domain between the fifth and sixth transmembrane segments and a common 25-amino acid TRP box C-terminal of the sixth transmembrane domain these channels are found across the phylogenetic scale from bacteria to mammals. Members of the TRPV subfamily serve as the receptors for endogenous cannabinoids, such as anandamide, and the hot pepper toxin, capsaicin. 

The molecule that makes hot peppers so spicy is called capsaicin (see its chemical structure below). This molecule behaves as an irritant to humans and other mammals, but some of us still really like its flavor ... 

Of these receptor sites, it is the distinct subsets of thermoreceptors in combination with nociceptors that give the sensations of heat and cooling by chemical stimulus in the mouth. In mammals it is proposed that a set of ion channels, called transient receptor potential (TRP) channels, are the primary molecular transducers of thermal stimuli. One such molecular transducer is the vanilliod receptor (VRl) channel, which is an ion-gated channel that is activated by temperatures above 43°C and by chemical irritants, such as, capsaicin and acidic pH [34]. Vanilliod receptor. 

Mammals find capsaicin hot, but not birds. If you don t want the squirrels to get the seeds or nuts that you put out for the birds, coat them with capsaicin the squirrels will leave them well alone, but the birds will still tuck in. 

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