Somatostatinergic neurones of the developing human and cat retinae.

We have examined somatostatin-immunoreactive (S-IR) neurones in developing retinae of the human and cat. At 14 and 16 weeks' gestation (G14 and G16) in the human, S-IR cells were only found close to the putative fovea centralis, but by 18 weeks' gestation (G18), they were located in all retinal regions. By adulthood, the majority of S-IR cells were restricted to inferior retina. In the developing cat retina, two classes of S-IR cells were recognized. S1-IR cells were similar in morphology and distribution to adult cells: they had small round somata which were only found in inferior retina and gave rise to beaded processes which traversed the inner plexiform layer (IPL) and nerve fibre layer (NFL). S2-IR cells had larger somata located in the ganglion cell layer (GCL) and the label was compartmentalized within their cytoplasm. Most S2-IR cells had lost immunoreactivity by P (postnatal day) 25 and may have been alpha-ganglion cells transiently expressing somatostatin in association with their retention of plasticity into postnatal life.