TRANSPLANTED SWEAT GLANDS FROM MATURE AND AGED DONORS DETERMINE CHOLINERGIC PHENOTYPE AND ALTERED DENSITY OF HOST SYMPATHETIC-NERVES (VOL 58, PG 153, 1996)

Contact with sweat gland acini causes sympathetic neurons to switch fr om a catecholaminergic to a cholinergic phenotype during development a nd following experimental manipulations. Substantial reductions of cho linergic innervation have been shown in the sweat glands of ageing rat s and humans. Using in oculo transplantation, we have now studied whet her sweat gland target tissues retain the capacity to regulate changes in the phenotype of sympathetic neurons observed in maturity and old age, including a switch from catecholaminergic to cholinergic characte rs. Markers have been used which indicate changes in nerve fibre morph ology (the pan-neuronal marker, PGP9.5) as well as neurotransmitter ex pression (acetylcholinesterase (AChE), vasocative intestinal polypepti de (VLP) and tyrosine hydroxylase (TH)). Sweat glands from young and o ld donor rats became reinnervated by an organotypic pattern of choline rgic host nerves. Surgical sympathectomy demonstrated that these choli nergic nerve fibres originate from sympathetic neurons of the host sup erior cervical ganglion (SCG). Retrograde tracing combined with staini ng for VIP (a marker associated with cholinergic phenotype in neurons supplying sweat glands) showed that SCG neurons projecting to irises w ith sweat gland implants may be induced to express VIP. We hypothesise that these neurons have been switched from their normal catecholamine rgic phenotype to a cholinergic one by contact with the sweat gland im plants. Transplants from old donors attracted a density of reinnervati on by young host nerves which was appropriate to the age of the donor, thus old sweat glands received a significantly reduced density of inn ervation compared to young glands. Despite the reduced density of inne rvation, there was no obvious difference in the ability of young and o ld implants to induce the switch to a cholinergic phenotype, suggestin g that different mechanisms regulate nerve growth and neurotransmitter phenotype.