Heterogeneity of histamine H3 receptor genomic expression in the cerebral cortex of spontaneously hypertensive rat.

Specific binding of [3H]-N-alpha-methylhistamine to homogenates from cerebral cortex tissue was analyzed in aged Wistar Kyoto (WKY) and Spontaneously Hypertensive rats (SHR). Scatchard plot analysis of [3H]-N-alpha-methylhistamine binding of the H3 receptor in the cerebral cortex from aged (6, 9, 12, and 16 week) SHR animals indicated that Bmax increased, respectively, 38.05 +/- 1.58, 59.63 +/- 2.48, 79.17 +/- 5.02, and 84.41 +/- 3.72 fmol/mg of protein. Binding studies using tissue from WKY rats indicated that maximal binding (Bmax) of the ligand to the receptor was not significantly altered. The analyses also yielded Kd values of 5, 7.2, 6.3 and 3.8 nM in SHR tissue respectively. Primers based on the sequence of the third intracellular loop of the H3 receptor were amplified at 35 cycles yielding several amplicons. These amplicons expressed sizes 875, 485, and 280 bp in 6 and 9 week cortical tissue from WKY animals where as in cortical tissue from 6 and 9 week SHR animals only two amplicons were expressed, 485 and 280 bp, respectively. Differences in gene expression for 12 and 16 week WKY and SHR rats were also compared using identical primers. Five amplicons were expressed in cortical tissue from 12 and 16 week WKY rats with 1000, 900, 821, 485, and 430 bp where as in 12 and 16 week SHR animals only one amplicon was expressed at 485 bp. The present results imply (1) that H3 receptor density in cortical tissue of SHR animals increases with age where as the number of the expressed amplicons of the detected H3 receptor decreases; and (2) even though a decrease in number of expressed amplicons of the H3 receptor were observed, an increase in expression of the larger amplicon (~500 bp) is evident.