Capsaicin

Capasaicin is the active ingredient in hot peppers of the New World.

Some stubs to fill out:

chemical structure and related compounds (including antagonist)

acts on vanilloid TRPV1 receptor (Julius paper), which is a heat sensitive receptor

Althoughthe TRPV1 receptor is sensitive to heat and protons in both mammals and birds, only the mammalian receptor is sensitive to capsaicin due to a specific domain of the mammalian TRPV1 PMID 11853675

production by hot peppers appears to select for seed dispersal by birds, and discourages mammals because mammalian digestive system destroys seeds PMID 11473305

aposematic coloration by hot peppers -- relies on predators ability to learn association of color with ingestive effect (positive for birds, aversive for mammals)

A tarantula from the West Indies also produces a set of peptide toxins (vanillotoxins) in its venom that activate the TRPV1 receptor in the same manner as capsaicin, presumably in order to deter mammalian predators. PMID 17093448

why humans like to eat hot peppers (Paul Rozin work)

Lesions of the medial PBN block acquisition of sucrose/LiCl-mediated CTA, but not capsaicin/LiCl CTA -- Because capsaicin works through trigeminal somatosensory nerves, and not gustatory nerves, this result suggests that the medial PBN is required for gustatory-LiCl associations, but not somatosensory-LiCl associations. PMID 9517824