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A study was made of the distribution of Substance P-immunoreactive fibers in chick cornea and uvea in whole mount preparation, using the indirect immunofluorescence technique. The development of these fibers during embryogenesis was also investigated. SP-fibers were present in all chick eye structures, in the various prenatal and postnatal stages examined. Their distribution was comparable with that observed by other workers in mammals. Transformation of the iris musculature from smooth to striated, during development, is not accompanied by significant changes in SP-ergic innervation.

This paper reports immunofluorescence data concerning fibronectin distribution in chick embryo striated muscle buds, i.e. myotomes and heart bud, in stages following their differentiation. At earliest developmental stages (12-15 HH) no fibronectin could be observed between the still poorly differentiated myoblasts of myotomes and of the splanchnopleure. Fibronectin, however, was observed among differentiated myoblasts of the myocardial ventral portion. In myotomes at later stages (16-18 HH), a few thin strands of fibronectin were observed between the myotomal and dermatomal laminae; this pattern became more marked between stages 17 and 26 HH. It is concluded that during myogenesis, fibronectin is absent at the earliest differentiation stages. A faint fibronectin-containing matrix is detectable at later stages and becomes more evident only in mature muscle tissue. This pattern is consistent with a role of fibronectin in the process of tissue organization.

Localization and development of chick heart peptidergic innervation (Substance P, VIP and Somatostatin) were investigated by means of immunofluorescence technique. The peptidergic component of the heart innervation was observed, for the first time, in older than 11 day chick embryos, i.e., subsequently to the appearance of the cholinergic component. The peptidergic structures achieve nearly full development in about 16-17 day embryos. Substance P is the most represented of the three peptides. It is localized both in nerve bundle fibers and in isolated fibers within the myocardium, the pericardium, the vessel walls; it is also present in fibers of some heart base ganglia. VIP is mostly contained in some thick single fibers travelling along the vessel walls of the heart base, the myocardium and the pericardium. Some VIP immunoreactive cells were also observed in the base ganglia. Somatostatin is mostly contained in some ganglia cells, whilst thin Somatostatin-immunoreactive fibers form a rich plexus among the atrial and ventricular myofibers, without contacting the vessel walls.

Serial sections of stage 18-27 HH (3-5 days of incubation) chick embryo myotomes were investigated by electron microscope. Two morphologically different types of contractile elements (myoblasts and myotubes) with an exact and constant localization were identified. Myotome sections of other chick embryos in the same stages were examined with the immunofluorescence technique, after treatment with antisera directed against fast and slow adult myosins. As from stage 24 HH, some contractile elements react positively with anti-fast adult myosin antiserum, others with anti-slow antiserum. A very precise correspondence was constantly found between the ultrastructural and immunohistochemical findings. An identical pattern was observed in the buds of the fast-twitching pectoralis major and posterior latissimus dorsi and slow-twitching anterior latissimus dorsi muscles.

Substance P-immunoreactive neurons were demonstrated in chick embryonic and adult trigeminal ganglion and jugular-superior ganglionic complex using FITC-immunohistochemical methods. Both small-size and large ganglion cells exhibited SP immunoreactivity, without apparent changes during embryonic and post-hatching development. SP-positive fibers could be detected in a good number in the sympathetic cranial cervical ganglion, either during embryonic development or in adult chick. No immunoreactive perikarya were observed in this ganglion. In the ciliary ganglion, both choroidal and ciliary neurons were SP-negative, whereas SP immunoreactive fibers surrounded the perikarya of both cell populations.