Traumatic brain injury results in mast cell increase and changes in regulation of central histamine receptors

Experimental fluid-percussion models produce brain injury by rapidly injecting saline into the closed cranium of rats. In this study our purpose was to determine how the central histaminergic system, which controls excitability and neurotransmitter release through G-protein coupled receptors, is affected by the pathophysiology of traumatic brain injury. We found that mast cell infiltration, as a result of the trauma, occurred primarily in the injured cortex and did not proceed beyond the fimbria of the hippocampus. In comparing injured animals with controls we found that H-3 receptor binding densities are significantly decreased bilaterally in the cortex but are significantly increased bilaterally in the thalamus. H-3 receptor binding densities may well be affected by mast cell secretion of mediators (i.e. histamine, heparin, leukotrienes), evidenced by detection of a cosecreted enzyme (mast cell tryptase) in the extracellular region. Moreover, we detected significant decreases in H-1 and H-3 receptor mRNA as well as Cu/Zn-dependent superoxide dismutase (SOD) mRNA in the thalamic region closest to the trauma. These significant decreases delineate the extent of cellular damage because of trauma and may underlie sustained cognitive and motor deficits displayed by these animals.