Transient Receptor Potential Protein (Trp) mRNA Expression in Rat Substantia Nigra

Abstract

Substantia nigra neurons produce dopamine in response to cholinergic stimuli that may involve receptor operated Ca²⁺ -entry that has been associated with the transient receptor potential (Trp) proteins. There were 6 Trp isoforms reported when I started this work. I set out to determine which isoforms of Trp mRNA were expressed in the substantia nigra using the whole brain for comparison. I initially used RT-PCR to determine the Trp mRNA expression. Subsequently, I used competitive RT-PCR for quantifying the major isoforms. Finally, I confirmed my results by Co-RT-PCR of the major isoforms. Trp3 and Trp6 were found to be the predominant forms expressed in the substantia nigra and whole brain, while the levels of Trps 1, 2, 4 and 5 were very low in both. Estimation of mRNA levels using competitive RT-PCR showed that the Trp6 mRNA levels in substantia nigra and the whole brain were similar while those for Trp3 were significantly lower in the substantia nigra than in the while brain. Thus substantia nigra differs from the whole brain in its Trp expression. Properties of Trps 3 and 6 are not fully known. Trp3 is regulated by IP₃-receptor activation but both Trp 3 and 6 can be activated by diacylglycerol. How this relates to the signal transduction events in substantia nigra remains to be determined.