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We investigated immunohistochemically the distribution of γ-aminobutyric acid (GABA) and the calcium-binding protein parvalbumin (PV) in postnatal rat retina. At birth, GABA was found in the ganglion cell layer and in some cells in the nuclear layer that differentiate to amacrine cells and horizontal cells, while PV appeared in some cells in the outer portion of the nuclear layer that differentiates to horizontal cells. At P7, when the inner and outer nuclear layers were divided by outer plexiform layer, both GABA and PV were observed in some cells in the ganglion cell layer, amacrine cells, and horizontal cells. As the postnatal day advanced, GABA and PV were observed in some cells in the ganglion cell layer and amacrine cells. PV has been present in the horizontal cells after its appearance, however, the immunoreactivity of GABA was gradually weaker as the postnatal day advanced. Since GABA existed transiently in the horizontal cells in the early postnatal period, it seems that GABA may have some specific function for differentiation of horizontal cells. However, PV has existed in the horizontal cells since they differentiated in the retina, suggesting that PV may be one of the specific marker of horizontal cells.

Development of extraocular muscles of rat was studied immunohistochemically using antibodies against three molecular markers of muscle differentiation: brain type (CK-B) and muscle type (CK-M) creatine kinase isoenzymes and muscle type enolase isoenzyme (β-enolase). The time of innervation of extraocular muscles was also studied immunohistochemically using antibody against neuron specific enolase (NSE). Periodic acid-Schiff (PAS) and PAS after diastase digestion stainings was used for the demonstration of glycogen. At embryonic day (E) 15, when muscle primordium of each extraocular muscle appears, β-enolase and glycogen were observed in all muscle primordia, while CK-B was immunoreactive only in lateral rectus (LR), superior rectus (SR), inferior rectus (IR) and inferior oblique (IO) muscle primordia. CK-B immunoreactivity appeared in superior oblique (SO) and medial rectus (MR) muscles at E17 and E18, respectively. By E18-19, CK-M immunoreactivity became positive in all muscles. NSE immunoreactive nerve fibers were first observed in LR, SR, IR and IO at E15, in SO at E16, and in MR at E17. Consequently, β-enolase immunoreactivity and glycogen appeared in all extraocular muscles at E15, while CK-M at E18. LR, SR, IR and IO muscles became immunoreactive to CK-B antibody at E15; however, SO and MR muscles became immunoreactive at E17 and E18, respectively. The sequence and time of appearance of CK-B in extraocular muscles were similar to those of NSE-immunoreactive nerve fibers. These findings suggest that in rats the expression of CK-B in each extraocular muscle coincides with the innervation of that muscle, while CK-M is expressed only after innervation.

Developmental changes in the distribution of parvalbumin immunoreactivity in the rat reticular thalamic nucleus from embryonic day 18 to adult were studied using immunohistochemistry. Neurons containing parvalbumin immunoreactivity in their cell somata were first detected at embryonic day 18. By embryonic day 20, many cells extended parvalbumin-positive fibers into the ventral thalamic nucleus. During development of the ventral thalamic nucleus, these fibers increased in number and thickness and ran in various directions. By postnatal day 16, these fibers became thinner and less well-stained. Neurons in the reticular thalamic nucleus extended their parvalbumin-positive axons into other nuclei of the thalamus, but in these other nuclei, parvalbumin-positive terminal and fibers developed primarily postnatally. In the reticular thalamic nucleus, the distribution of GABA-like immunoreactivity was very similar to that of parvalbumin at embryonic day 20 with cells extending fibers which contained immunoreactivity for GABA into the ventral thalamic nucleus. Thus parvalbumin immunoreactivity appears in the neurons of the reticular thalamic nucleus early in development of this nucleus, first in cell somata of neurons, then in their axons and dendrites. Apart from the ventral thalamic nucleus, the innervation by parvalbumin containing neurons in the reticular thalamic nucleus of the rest of the thalamus, showed a variable developmental pattern with different nuclei being innervated at different times, presumably reflecting the separate development of individual thalamic nuclei.