THURSDAY, May 27 (HealthDayNews) -- Brain cells that contain the chemical histamine are critical for waking, says a study by scientists at the Veterans Affairs' Neurobiology Research Laboratory and University of California, Los Angeles (UCLA) Neuropsychiatric Institute.

The study, which utilized dogs with the sleep disorder narcolepsy, found that cessation of activity in brain cells with histamine causes loss of consciousness during sleep. The findings may explain why antihistamine drugs cause drowsiness.

The researchers also found that cessation of activity in brain cells that contain the chemicals norepinephrine or serotonin causes loss of muscle tone during sleep.

The study appears in the May 27 issue of Neuron.

"Our findings greatly improve our understanding of the brain activity responsible for maintaining consciousness and muscle tone while awake," senior author Dr. Jerome Siegel, chief of neurobiology research at the VA Greater Los Angeles Health Care System in Sepulveda, said in a prepared statement.

"The findings should aid in the development of drugs to induce sleep and to increase alertness," Siegel said.

More information

The U.S. National Institute of Neurological Disorders and Stroke has more about sleep.