RT Journal Article SR Electronic T1 Major Changes in the Brain Histamine System of the Ground Squirrel Citellus lateralis during Hibernation JF The Journal of Neuroscience JO J. Neurosci. FD Society for Neuroscience SP 1824 OP 1835 DO 10.1523/JNEUROSCI.19-05-01824.1999 VO 19 IS 5 A1 Tina Sallmen A1 Alexander L. Beckman A1 Toni L. Stanton A1 Krister S. Eriksson A1 Juhani Tarhanen A1 Leena Tuomisto A1 Pertti Panula YR 1999 UL http://www.jneurosci.org/content/19/5/1824.abstract AB Hibernation in mammals such as the rodent hibernatorCitellus lateralis is a physiological state in which CNS activity is endogenously maintained at a very low, but functionally responsive, level. The neurotransmitter histamine is involved in the regulation of diurnal rhythms and body temperature in nonhibernators and, therefore, could likely play an important role in maintaining the hibernating state. In this study, we show that histamine neuronal systems undergo major changes during hibernation that are consistent with such a role. Immunohistochemical mapping of histaminergic fibers in the brains of hibernating and nonhibernating golden-mantled ground squirrels (C. lateralis) showed a clear increase in fiber density during the hibernating state. The tissue levels of histamine and its first metabolitetele-methylhistamine were also elevated throughout the brain of hibernating animals, suggesting an increase in histamine turnover during hibernation, which occurs without an increase in histidine decarboxylase mRNA expression. This hibernation-related apparent augmentation of histaminergic neurotransmission was particularly evident in the hypothalamus and hippocampus, areas of importance to the control of the hibernating state, in whichtele-methylhistamine levels were increased more than threefold. These changes in the histamine neuronal system differ from those reported for the metabolic pattern in other monoaminergic systems during hibernation, which generally indicate a decrease in turnover. Our results suggest that the influence of histamine neuronal systems may be important in controlling CNS activity during hibernation.