Heterozygous HDC-Cre mice are viable and fertile, expressing an internal ribosome entry site (IRES)-iCre fusion protein from the histidine decarboxylase (Hdc) promoter/enhancer elements. Hdc encodes the catalyzing enzyme involved in the formation of histamine which is released during allergic reactions and acts as a neurotransmitter in the brain. Histaminergic neurons regulate sleep-wake cycle. When Hdc is induced, cre recombinase is expressed in tuberomammillary nucleus (TMN) of the hypothalamus as well as other areas of the brain, mast cells, gastric mucosa, and fetal liver. When these mice are bred with mice containing loxP-flanked sequence, Cre-mediated recombination will result in deletion of the floxed sequences in the Hdc-expressing cells of the offspring. The donating investigator has not attempted to generate homozygous mice to date (March 2013).
For example when bred to STOCK Gabrg2tm1Wul/J mice (Stock No. 021197), GABAA receptors in these GABAA receptor γ2 subunit deficient histaminergic neurons exhibit increased excitability with no effect on the sleep-wake cycle.
