Recent immunocytochemical studies indicate the existence of several classes of peptide- (PRGC) and catecholamine-containing retinal ganglion cells in anurans, birds, and mammals. Different classes of PRGC project to discrete and seemingly unique layers in the retino-recipient portion of the anuran and avian optic tectum. Peptide-containing retinofugal projections to the frog tectum originate early in development, and are reestablished by some classes of PRGC during regeneration of the optic nerve. These findings indicate that chemically specific, parallel retinofugal pathways presumably subserve different functional aspects of vision in vertebrates. Exciting prospects for research include the correlation of physiologically with immunocytochemically defined classes of retinal ganglion cells, the analysis of the possible role of neuroactive peptides in retinofugal transmission, and the pharmacological manipulation of putative peptidergic retinofugal pathways to analyze their role in visual function.
Recent postmarketing reports and a US Food and Drug Administration analysis have documented uncommon persistent sexual and nonsexual side-effects in a subset of younger men who have taken finasteride 1 mg for androgenic alopecia. While the mechanisms of the sexual side-effects in humans is incompletely understood, one study found lower cerebrospinal fluid concentrations of dihydrotestosterone, progesterone, dihydroprogesterone and allopregnanolone, and higher levels of testosterone, 5α-androstane-3α,17β-diol and pregnenolone. Another study found up-regulation of the androgen receptor in the human foreskin with a mean of 5 years after finasteride discontinuation.