Variations in levels of substance P-encoding β-, γ-preprotachykinin and substance P receptor NK-1 transcripts in the rat hypothalamus throughout the estrous cycle: A correlation between amounts of β-preprotachykinin and NK-1 mRNA

Using a sensitive RNase protection assay, the simultaneous quantification of hypothalamic β-, γ-preprotachykinin (PPT) and SP receptor NK-1 transcripts was performed throughout the estrous cycle. The amounts of these 3 transcripts were up-regulated during diestrus II-proestrus night (2-, 1.5- and 1.3-fold, respectively). These levels returned to low values during the proestrous day in the case of γ-PPT mRNA and during the estrus-diestrus I night in the cases of β-PPT and NK-1 mRNAs. These results implicate a differential regulation in amounts of the two alternatively spliced PPT transcripts. The 160 hypothalami of this study had been previously assayed for amounts of substance P (SP) and neurokinin A (NKA) peptides. Variations in mRNA and peptide levels were compared by statistical analysis. Surprisingly, variations in SP level paralleled those in β-PPT mRNA level and variations in NKA level paralleled those of γ-PPT mRNA level, although β- and γ-PPT transcripts encode both SP and NKA. Furthermore, the level of NK-1 mRNA was positively correlated with the level of β-PPT mRNA (r = 0.90, P < 10^-58) and with the level of SP peptide (r = 0.30, P < 10^-3) but not with the level of NKA peptide. This analysis suggests that SP receptor NK-1 mRNA could be physiologically regulated by S9 peptide in the rat hypothalamus.