sentences:  Mammals and insects have different composition of the receptor subunits and the structures of the receptors.Because most neonicotinoids bind much more strongly to insect neuron receptors than to mammal neuron receptors, these insecticides are more toxic to insects than mammals.The low mammalian toxicity of imidacloprid has been explained by its inability to cross the blood–brain barrier because of the presence of a charged nitrogen atom at physiological pH.