Substance P-immunoreactivity in the developing human retinogeniculate pathway

Substance P has been immunohistochemically localized in the human optic nerves and lateral geniculate nuclei during the prenatal period from 13-14 to 37 weeks of gestation. Substance P-immunoreactive fibres were present in the optic nerves and lateral geniculate nuclei in all these ages thereby providing direct evidence of this undecapeptide being associated with the retinogeniculate pathway. At 16-17 weeks, greater numbers of fibres were observed than in the later ages. It is likely that the reduction in number of optic nerve fibres seen quantitatively during prenatal life may partly be due to the loss of substance P fibres.