Release of preprotachykinin-A mRNA from rabbit iris upon C-fibre stimulation

It is usually said that axons and nerve terminals do not contain messenger RNA (mRNA) and that peptide transmitters are packaged in granules and transported towards the periphery of the neuron. However, several recent reports challenge this view by showing evidence of the existence of mRNA in axons. In the present study, we demonstrate the existence of mRNA coding for gamma-preprotachykinin-A in rabbit iris by Northern blot analysis and Southern blot analysis of the polymerase chain reaction (PCR)-amplified products. Interestingly, mRNA coding for gamma-preprotachykinin-A was detected also in aqueous humor from eyes exposed to injury (infrared irradiation of the iris or retrobulbar injection of the C-fibre excitant capsaicin), but not from contralateral eyes and normal eyes of untreated rabbits. Our results suggest that the mRNA coding for gamma-preprotachykinin-A occurs in C-fibres in the iris and that it is released into the aqueous humor together with tachykinins in response to C-fibre stimulation.