Protein kinase C immunoreactivity in kitten visual cortex is developmentally regulated and input-dependent

Protein kinase C modulates ventilatory patterning in the developing rat

Protein kinase C (PKC) mediates important components of signal transduction pathways underlying neuronal excitability and modulates respiratory timing mechanisms in adult rats. To determine ventilatory effects of systemic PKC inhibition during development, whole-body plethysmographic recordings were conducted in 2-3-d (n = 11), 5-6-d (n = 19), 10-12-d (n = 14), and 20-21-d-old (n = 14) rat pups after treatment with vehicle and Ro 32-0432 (100 mg/kg, intraperitoneally). Ro 32-0432 decreased minute ventilation (V E) by 51.0 +/- 5.5% (mean +/- SEM) in youngest pups (p < 0.01) but only 19.1 +/- 6.8% in 20-21-d-old pups (p < 0.01). V E decreases were always due to frequency reductions with tidal volume (VT) remaining unaffected. Respiratory rate decreases primarily resulted from marked expiratory time (TE) prolongations being more pronounced in 2-3-d-old (115.5 +/- 28.9%) compared with 20-21-d old (36.6 +/- 10.9%; p < 0.002 analysis of variance [ANOVA] ). Expression of the PKC isoforms alpha, beta, gamma, delta, iota, and mu was further examined in brainstem and cortex by immunoblotting and revealed different patterns with postnatal age and location. We conclude that endogenous PKC inhibition elicits age-dependent ventilatory reductions which primarily affect timing mechanisms rather than changes in volume drive. This effect on ventilation abates with increasing postnatal age suggesting that the neural substrate mediating overall respiratory output may be more critically dependent on PKC activity in the immature animal.

Up-regulation of protein kinase C in regenerating optic nerve fibers of goldfish: immunohistochemistry and kinase activity assay

Protein kinase C (PKC) activation has been associated with synaptic plasticity in many projections, and manipulating PKC in the retinotectal projection strongly affects the activity-driven sharpening of the retinotopic map. This study examined levels of PKC in the regenerating retinotectal projection via immunostaining and assay of activity. A polyclonal antibody to the conserved C2 (Ca2+ binding) domain of classical PKC isozymes (anti-panPKC) recognized a single band at 79-80 kD on Western blots of goldfish brain. It stained one class of retinal bipolar cells and the ganglion cells in normal retina, as shown previously. Strong staining was not present in the optic fiber layer of retina or in optic nerve, optic tract, or terminal zone in tectum, with the exception of a single fascicle of optic nerve fibers that by their location and by L1 (E587) staining were identified as those arising from newly added ganglion cells at the retinal margin. Normal tectal sections showed dark staining of a subclass of type XIV neuron with somas at the top of the periventricular layer and an apical dendrite ascending to stratum opticum. In regenerating retina, swollen ganglion cells stained darkly and stained axons were seen in the optic fiber layer. In regenerating optic nerve (2-11 weeks postcrush), all fascicles of optic fibers stained darkly for both PKC and L1(E587). At 5 weeks postcrush, PKC staining could also be seen in the medial and lateral optic tracts and stratum opticum at the front half of the tectum and very lightly over the terminal zones. PKC activity was measured in homogenized tissues dissected from a series of fish with unilateral nerve crush from 1 to 5 weeks previously. Activity levels stimulated by phorbols and Ca2+ were measured by phosphorylation of a specific peptide and referred to levels measured in the opposite control side. Regeneration did not increase overall PKC activity in retina or tectum, but in optic nerve there was an 80% rise after the first week. The increased activity verifies that the increased staining in nerve represented an up-regulation of functional PKC during nerve regeneration.

Developmental expression of alpha-, beta- and gamma-subspecies of protein kinase C in the dorsal corticospinal tract in the rat spinal cord

Developmental expression of alpha-, beta- and gamma-subspecies of protein kinase C in the dorsal corticospinal tract was immunohistochemically investigated at the cervical level of the postnatal rat spinal cord. On postnatal day 0, immunoreactivity for these subspecies was uniformly distributed throughout the posterior funiculus. On postnatal day 7, immunoreactivity for this enzyme in the posterior funiculus began to decline. On postnatal days 14 and 21, the immunoreactivity in the posterior funiculus became weak, while the dorsal corticospinal tract forming in the most ventral portion of the posterior funiculus exhibited strong immunoreactivity for these three subspecies of protein kinase C. Thereafter, immunoreactivity in the corticospinal tract rapidly declined, and on postnatal days 28 and 35, weak immunoreaction was demonstrated as very fine granular deposits in the tract. Expression of this enzyme in the dorsal corticospinal tract at these stages resembled that in the adult rat. Electron microscopically, growth cones and nascent axonal shafts were first noted on postnatal day 2 in the most ventral portion of the posterior funiculus, and thereafter, the axonal shaft gradually thickened and on postnatal day 14 some axons began to be myelinated. The growth cones and thin axonal shafts randomly exhibited weak immunoreactivity in the axoplasm. The thicker unmyelinated axonal shafts showed distinct immunoreactivity uniformly throughout the axoplasm and along the axolemma as granular deposits. In these developing axons, intensity and distribution of immunoreactivity for all three subspecies were principally similar. In the mature myelinated axons, the intensity and distribution of immunoreactivity for each subspecies of protein kinase C were quite different, i.e. immunoreactivity for alpha-subspecies was randomly distributed on some cytoskeletal elements, and that for beta-subspecies was uniformly detected on most of the cytoskeletal elements. In contrast, immunoreactivity for gamma-subspecies was distributed mainly on the endoplasmic reticulum. These findings suggest that in growing corticospinal axons protein kinase C might be involved in several important aspects of axonal development, and that in mature axons this enzyme might participate in different aspects of axonal function.

Expression of alpha-, beta-, and gamma-subspecies of protein kinase C in the motor neurons in the embryonic and postnatal rat spinal cord

Using polyclonal antibodies against alpha-, beta- and gamma-subspecies of protein kinase C, developmental changes in expression of these subspecies in the motor neurons in the rat cervical spinal cord were immunohistochemically investigated. On embryonic day-12, the motor neurons began to differentiate from undifferentiated neuroepithelial cells. On embryonic day-13, they began to express weak immunoreactivity for alpha- and beta-protein kinase C and slightly more evident immunoreactivity for gamma-protein kinase C. Immunoreactivity for protein kinase C in these neurons gradually became stronger, as the development progressed. Between embryonic day-18 and postnatal day-7, the motor neurons showed distinct immunoreactivity in the nucleus, perikaryal cytoplasm, axon and dendrites. At these stages, distribution and intensity of immunoreactivity for alpha-, beta- and gamma-protein kinase C were very similar. Thereafter, the expression of this enzyme in the nucleus gradually declined, while in the other structures, expression of each subspecies changed independently. On postnatal day-28 and 35, expression of beta-protein kinase C in the axons was stronger than that of alpha- and gamma-protein kinase C, and immunoreactivity for gamma-protein kinase C in the perikaryal cytoplasm and dendrites was slightly weaker than that for alpha- and beta-protein kinase C. Expression of this enzyme in the motor neurons at these stages was almost the same as in the adult animal. Electron microscopically, immunoreactivity for protein kinase C was randomly distributed in the nucleus, and in the perikaryal cytoplasm, often near the cisterns of the endoplasmic reticulum. Expression of protein kinase C in the growing axons was quite different from that in the mature axons. In the dendrites, immunoreactivity for protein kinase C was distributed randomly in the cytoplasm and at the postsynaptic densities. These findings suggest that protein kinase C might regulate not only the neural functions, but also several aspects of the differentiation process in the motor neurons.

Developmental changes in the expression of alpha-, beta- and gamma-subspecies of protein kinase C at synapses in the ventral horn of the embryonic and postnatal rat spinal cord

Developmental changes in expression of alpha-, beta- and gamma-subspecies of protein kinase C (PKC) at synapses in the ventral horn of the rat spinal cord were immunocytochemically investigated. On embryonic day 15, a few synapses were found in the ventral horn, and they gradually increased in number until postnatal day 21 or 28. During the embryonic period, immunoreactivity (IR) for all three subspecies was demonstrated in both the pre- and postsynaptic regions. In the former, IR was detected mainly along the outer surface of the synaptic vesicles, and in the latter, along the postsynaptic membranes. At these stages, synapses were morphologically immature, having a faint postsynaptic density and a few round synaptic vesicles. After birth, IR for PKCs at the postsynaptic densities became stronger, but gradually disappeared in most of the presynaptic regions. In adult, IR for PKCs was detected only at the postsynaptic densities. At the later postnatal stages, the synapses were fully mature, having a thick postsynaptic density, a great number of synaptic vesicles and a distinct synaptic cleft as those in adult animals. In addition, the developmental changes in expression of these subspecies of PKC in the presynaptic regions were quite different. These findings suggest that the increase in expression of PKC at postsynaptic densities might be closely related with the development of synaptic functions, and also that each subspecies of PKC may take part in different aspects of synaptogenesis.

NGF and BDNF are differentially modulated by visual experience in the developing geniculocortical pathway

Neuronal activity and trophic factors have been implicated in shaping the connectivity of functional synaptic circuits. We studied the development and regulation by sensory input of the neurotrophins NGF, BDNF and NT-3 in the developing rat visual system. In the occipital cortex, NT-3 mRNA was transiently expressed in the neonate. In contrast, BDNF and NGF mRNA's increased during postnatal development, and reached mature levels around 3 weeks of age. BDNF mRNA was ten times more abundant than NGF mRNA. In the lateral geniculate nucleus (LGN), NT-3 mRNA was also transiently expressed, whereas NGF and BDNF mRNA's did not vary significantly during development. The high-affinity neurotrophin receptors trkB and trkC were expressed both in the developing LGN and occipital cortex. These receptors for BDNF and NT-3, respectively, were expressed at birth, with little change during development. In contrast, trkA mRNA, which encodes the high-affinity NGF receptor, was undetectable in either region. Visual experience differentially modulated expression of NGF and BDNF mRNA's. NGF mRNA was slightly increased after 3 weeks of light-deprivation. In contrast, BDNF mRNA expression in visual cortex was significantly lower than normal in rats dark-reared from birth. Decreased BDNF expression after sensory deprivation was reversible by exposure to light. Thus, all three neurotrophins were detected in visual cortex and LGN. Differences in abundance developmental profiles, and regulation imply distinct functions for each factor in the visual system.

Postnatal development of inositol 1,4,5-trisphosphate receptors: a disparity with protein kinase C

Ligand-stimulated phosphoinositide hydrolysis activates a bifurcating second messenger system, releasing inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DG), which activates protein kinase C (PKC). Yet, in developing cat visual cortex and hippocampus, high levels of [3H]PDBu binding (labelling PKC) appear much earlier than do [3H]IP3 labelled sites. Binding distributions for the two ligands also appear to be complimentary in both brain regions. Moreover, early surgical removal of input to the visual cortex increases [3H]PDBu binding without affecting that of [3H]IP3. Our results suggest that, (1) at certain developmental stages, IP3 and PKC may act individually or complimentarily rather than synergistically in the visual cortex and hippocampus; (2) in neonatal cortex, IP3 metabolites rather than IP3 itself may act as second messengers; (3) although both IP3 receptors and PKC are localized in intracortical cells, their expression is regulated by different mechanisms during development.

Localization of the two protein kinase C beta-mRNA subtypes in cat visual system

Protein kinase C (PKC) consists of a family of different subtypes encoded by different PKC genes. We investigated the distribution of PKC beta 1 and PKC beta 2 in the visual system of the adult cat by in situ hybridization using oligonucleotide probes complementary to the PKC beta 1 and PKC beta 2 mRNAs, two splicing variants of the same gene transcript. In the primary visual cortex PKC beta 1 and PKC beta 2 were both present. The laminar distribution patterns found for the two PKC subtypes were identical. A remarkable finding was the difference between the laminar distribution of the PKC beta s in areas 17 and 18 when compared with area 19. In all three areas the highest expression levels were found in layer VI, moderately high levels were found in layers II, III and V, while layer I was devoid of signal. In area 17 and 18 layer IV stood out by its low PKC beta signal. In sharp contrast, layer IV of area 19 was indiscernible from the superficial layers because of an evenly high signal. In the dLGN of the adult cat PKC beta 1 and PKC beta 2 mRNAs were distributed rather homogeneously over the different layers, but the expression levels for PKC beta 1 were clearly higher than those for PKC beta 2.

Development and regulation of alpha adrenoceptors in kitten visual cortex

Alpha-1 and alpha-2 adrenergic receptors were localized in developing cat visual cortex by using [3H]prazosin and [3H]rauwolscine, respectively as selective ligands. The effects of neuronal input on the development of the two receptor subtypes were also studied in animals with lesions at various sites within the central visual pathways. Binding densities for both ligands increased during the first few postnatal weeks and declined thereafter. For both receptor subtypes, the highest concentration of binding sites was found in the subplate zone of the cortex in neonatal animals. Both ligands showed their highest concentrations in cortical layer IV beginning at postnatal day 30 and in the superficial cortical layers in adulthood. However, the developmental redistribution of alpha-1 receptors began at earlier ages than that of the alpha-2 sites. The alpha-1 sites were still concentrated in the subplate zone up to 60 days postnatal, while the alpha-2 sites in this region disappeared much earlier. Receptor binding densities were also examined in animals with quinolinic acid lesions within cortex, lesions of the lateral geniculate nucleus and lesions of the optic tract. The results indicate that both alpha-adrenoceptor subtypes were mainly located on cortical cells, and that the absence of neuronal activity during development resulted in a reduction of the binding density for both subtypes in the visual cortex. An additional major reduction in alpha-2 but not alpha-1 binding sites was observed following the lateral geniculate nucleus lesion, suggesting that the development of alpha-2 receptors is also dependent on input from the lateral geniculate nucleus. Removal of the lateral geniculate nucleus early in life resulted in a significant increase in alpha-1 receptors in the subplate region, indicating that receptor densities in this zone may be negatively regulated by the lateral geniculate nucleus afferents. These results show that adrenergic receptors reorganize during postnatal cortical development with a strong temporary concentration in the subplate zone. The reorganization process is heavily influenced by cortical inputs.

Immunocytochemical localization of the alpha-, beta I-, beta II- and gamma-subspecies of protein kinase C in the monkey visual pathway

We examined the distribution of alpha-, beta I-, beta II- and gamma-subspecies of protein kinase C (PKC) in the monkey visual pathway, including the retina, the lateral geniculate nucleus (LGN) and the visual cortex (area 17). In the retina, alpha-PKC immunoreactivity was found in cone photoreceptor and in bipolar cells. beta I-PKC immunoreactivity was present in the ganglion cell layer and the optic nerve fibers. The beta II- and gamma-PKCs were not found in the retina. In the LGN, intense gamma-PKC immunoreactivity was found in a part of magno and parvo cells. The LGN was negative for the alpha-, beta I- and beta II-PKC. All four PKC subspecies were present in the visual cortex but the distribution was distinct. The beta I-PKC immunoreactive cells were scattered in all layers, while the alpha-PKC immunoreactive cells were prominent in layers II, III, IVb, IVc and VI, and the beta II-PKC immunoreactive cells were found in layers II, III, IVb and VI. The intense gamma-PKC immunoreactivity was present in the neuropils in layers I, IVa, IVc and VI and also in soma and dendrites in layers II and VI. It thus seems likely that each subspecies plays a specific role in neuronal transmission in the visual pathway.

Development of the dendritic fields of layer 3 pyramidal cells in the kitten's visual cortex

The cat's visual cortex is immature at birth and undergoes extensive postnatal development. For example, cells of layers 2 and 3 do not complete migration until about 3 weeks after birth. Despite the importance of dendritic growth for synaptic and functional development, there have been few studies of dendritic development in the cat's visual cortex to correlate with numerous studies of functional and synaptic development. Accordingly, we used the Golgi method to study the development of the dendrites of layer 3 pyramidal cells in the visual cortex of a series of cats ranging in age from 2 days to 3 years. Blocks of visual cortex were impregnated by the Golgi-Kopsch method and sectioned in the tangential plane. Layer 3 pyramidal cells were drawn with a camera lucida and analyzed by Sholl diagrams and vector addition. In kittens < 1 week old, these cells were very immature, with only an apical dendrite and no basal dendrites. Basal dendrites appeared during the second week. By 2 weeks, all of the basal dendrites had emerged from the soma, but they had few branches and were tipped with growth cones. By 4 weeks, they had finished branching but continued to grow in length until, by 5 weeks, they reached their adult size. Examination of the basal dendritic fields in the tangential plane revealed that their dendritic fields were more elongated at 2 weeks than at later ages, perhaps because of their smaller size. The distribution of dendritic field orientations was uniform at all ages except 3 and 4 weeks, when there was a preponderance of fields oriented in the rostrocaudal direction. Because dendritic growth and branching occurred very rapidly over a period that precedes and overlaps with the peak periods of synaptogenesis and of sensitivity to the effects of early visual experience, they may depend on afferent visual activity. The early emergence of primary dendrites, however, suggests that this process is independent of afferent activity. The coincident timing of dendritic branching with the presence of dendritic growth cones suggests that branching may occur at growth cones.

Transient expression of calbindin-D28k immunoreactivity in layer V pyramidal neurons during postnatal development of kitten cortical areas

Calbindin-D28k is a 28 kDa calcium binding protein that has been shown to colocalize with a specific subpopulation of gamma-aminobutyric acid inhibitory interneurons in mammalian neocortex. We have examined the ontogeny of calbindin in neonatal kitten cortex in areas 17,18,19,7, medial and lateral suprasylvian visual areas, splenial visual area and cingulate cortex from the day of birth (P0) through maturation of the brain (P101). Transient staining of immature layer V pyramidal cells was seen in kittens six weeks old and younger. This transient staining of pyramidal cells was most intense and the stained neurons were most numerous in cingulate cortex. Apical dendrites of pyramidal cells in cingulate cortex were prominently stained and could be followed to layer I, where they were seen to branch extensively. There were very few calbindin immunoreactive pyramidal cells in primary cortical areas postnatally. Transient staining in extrastriate visual cortical areas disappeared first from the lateral suprasylvian areas, and persisted longest in area 7. Pyramidal neurons in the cingulate gyrus expressed calbindin longest, but calbindin expression by pyramidal neurons ceased by the sixth postnatal week in all areas of the brain.

Protein kinase C-epsilon is a developmentally regulated, neuronal isoform in the chick embryo central nervous system

Protein kinase C (PKC) is expressed as many isoforms and in high quantities in the central nervous system (CNS), which suggests an important role for this enzyme in neuronal development and function. We used specific antibodies to investigate the expression of the known PKC isoforms in extracts from chick major CNS areas during embryogenesis, from day 3 (E3) of incubation to day 1 post-hatching (P1). PKC-epsilon was the predominant isoform and was expressed from E6 onward in all brain regions, except retina (E12 and on). PKC-alpha/beta and -zeta isoforms were expressed at lower levels prior to PKC-epsilon expression and throughout embryogenesis. No other isoforms were detected in neural tissue preparations. We then used neural culture systems derived from the chick CNS to study the expression of PKC isoforms in neuroblasts, cortical neurons, and cortical glial cells. Western blotting and immunostaining of neuroblast-enriched cultures, derived from E3 CNS, showed only the Ca(2+)-dependent PKC-alpha/beta to be present. Studies on neuronal cultures derived from E6 cerebral hemispheres revealed only the Ca(2+)-independent PKC-epsilon to be expressed in neurons, as predicted by the developmental studies on tissue homogenates. PKC-epsilon immunoreactivity was seen intracellularly in differentiating neurons, regardless of their neurotransmitter phenotypes, and it correlated well with the level of neuronal activity. Furthermore, PKC-alpha/beta immunoreactivity was verified on glia cells, as the glial lineage emerges in E15 cortical cultures. These data suggest that PKC-epsilon expression is associated with the final neuroblast division in neurons, and the correlation of PKC isoform expression and neural cell lineage is discussed.

Protein kinase C-delta in rat brain: association with sensory neuronal hierarchies

Originally characterized as the calcium- and phospholipid-dependent protein kinases, the protein kinases C include at least eight separate isoforms, some of which are calcium-independent and all of which are highly enriched in brain. Of the calcium-independent isoforms, the delta subspecies of protein kinase C has the most restricted complement of lipid activators and substrate specificity, suggesting that it may have a unique role in cell signalling pathways. Using immunocytochemistry, we report that the distribution of protein kinase C-delta immunoreactivity in rat brain is also restricted, being present in all sensory systems. Moreover, it is found in alternating hierarchies of sensory pathways: in all sensory systems except auditory, it is found in first- and third-order neurons, while in the auditory system, it is found in second- and fourth-order neurons. Thalamocortical systems are intensely immunoreactive, including barrel fields of the rat parietal cortex. Outside of sensory systems, protein kinase C-delta is present in cerebellum within longitudinal stripes in Purkinje neurons, and in the caudate-putamen, it appears to be associated with the striosome (patch) compartment. In contrast to all other protein kinase C isoforms, protein kinase C-delta is absent from hippocampus. These findings suggest that protein kinase C-delta may have a unique role in signal transduction in the central nervous system (CNS), especially in sensory systems.

Regulation of protein kinase C activity by sensory deprivation in the olfactory and visual systems

Environmental regulation of sensory function has provided an important model of plastic mechanisms mediating neural information processing. To define potential commonalities in information processing in different systems, we investigated molecular changes elicited by sensory deprivation in the developing rat olfactory and visual systems. Protein kinase C (PKC), an intracellular messenger implicated in synaptic plasticity and memory, was analyzed. Initial, developmental studies indicated that PKC activity in the soluble and particulate fractions of the olfactory bulb increased three- to fourfold from birth to 3 months of age. Unilateral olfactory deprivation prevented the developmental increase in both soluble and particulate PKC activities in the ipsilateral olfactory bulb and piriform cortex, the second-order relay. Phorbol ester binding localized PKC to intrinsic neuronal populations and their dendrites in the control and deprived bulbs. Moreover, PKC was similarly lower in the visual cortex of dark-reared rats than in light-reared controls. The changes in PKC were region specific, as activity was unchanged by either treatment in the parietal cortex, a control area that does not process primary olfactory or visual information. Our results suggest that the important intracellular messenger, PKC, is similarly regulated in entirely different sensory systems by different environmental stimuli. Consequently, different sensory systems may use common molecular mechanisms to process information.

Differential regulation of substance P and somatostatin in Martinotti cells of the developing cat visual cortex

In order to determine their morphological development and ontogenetic fate, Martinotti neurons immunoreactive for substance P and somatostatin have been analysed in the cat visual cortex. Martinotti neurons are located in layers V and VI. They are multipolar to bitufted, and most dendrites remain in layers V and VI. Their typical features is the ascending axon, which emerges from an apical dendrite or from the upper pole of the soma. A number of collaterals branch off in layer V, forming a local terminal plexus. The axon then branches into 2-8 collaterals, which ascend as a bundle to layers III and II, where a second terminal plexus is formed. Some collaterals ascend to layer I where they adopt a horizontal course. Horizontal collaterals in the terminal layers V, III, II, and in layer I may reach up to 400 microns in length. Martinotti neurons begin to differentiate perinatally. The quantitative analysis reveals that the initial time course of differentiation of Martinotti cells is very similar in material stained for substance P and for somatostatin. Double immunofluorescence then confirms that the two peptides are colocalized in Martinotti cells of layers V and VI during the early postnatal period. Further, substance P is colocalized with GABA. Substance P expression in Martinotti cells can be observed only in the immature visual cortex. After postnatal day 15, the Martinotti neuron system becomes less and less detectable by substance P immunoreactivity. It declines to virtually undetectable levels after the third postnatal month. The adult visual cortex is almost devoid of substance P-immunoreactive cell bodies, processes and axon terminals. In situ hybridization confirms this finding, revealing beta-preprotachykinin mRNA-expressing cell bodies in layers V and IV at postnatal day (P)6 and P12, but not in the adult cortex. This suggests a downregulation of the substance P expression at the transcriptional level. In contrast, somatostatin-immunoreactive Martinotti cells, most of which have coexpressed substance P during early postnatal life, can still be observed in the adult cortex. Thus, the Martinotti neurons constitute a persisting cell type, although many individual neurons of this type disappear during the second postnatal month by degeneration and cell death. In summary, while somatostatin is permanently expressed in Martinotti neurons in the cat visual cortex, substance P peptide and mRNA are transiently expressed during an early postnatal period, and apparently are downregulated later in development.

Histochemical localization of synaptic zinc in the developing cat visual cortex

The terminal boutons of many neurons in the telencephalon are known to contain a vesicle-bound, chelatable pool of zinc (Zn2+) that can be selectively visualized with histochemical procedures. In this paper, the normal laminar, areal, and ultrastructural distribution of histochemically reactive zinc in the visual cortex of the adult cat as well as its development from birth are described. In the adult cat visual cortex, intense zinc staining was found in layers I, II, III, and V, with layer VI staining only lightly. The primary geniculostriate input zone, layer IV, was conspicuously distinguished by the relative absence of zinc. This distinct pattern was restricted only to areas 17 and 18 and differentiated them from adjacent cortical area 19 laterally and the subadjacent cingulate cortex. The earliest zinc-positive staining in visual cortical areas 17 and 18 was first apparent by postnatal day 2 (P2) and was characterized by staining of a thin layer at the bottom of the cortical plate. By P10, and continuing through P20, synaptic zinc formed a trilaminar pattern of dense staining in areas 17 and 18, which included the top of layer I, and layers III and V. The laminar pattern of synaptic zinc in visual cortex appeared mature by P30, except that the distribution of zinc in layer IV was not uniform. This was most apparent around P50 in tangential sections through layer IV from opened and flattened cortex, where columnar patches of increased zinc staining were apparent in area 17. These columns were approximately 400 microns in diameter, with a centre-to-centre spacing of approximately 900 microns. The distribution of synaptic zinc apparently reflects the process of synaptic maturity of the cat visual cortex and appears to demarcate a particular form of columnar organization in visual cortex.

Changes of drebrin expression in the visual cortex of the cat during development

The expression of and developmental changes in drebrin were studied in cat visual cortex using immunohistochemistry and immunoblot analysis. Drebrin is a developmentally regulated brain protein which in the chicken has characteristic changes in expression related to developmental stage. A monoclonal antibody (MAb M2F6) raised against drebrin, was found to label the neuropil of the kitten visual cortex in the early postnatal period. At 1-3 weeks of age, the staining was prominent in layer IV of the visual cortex. The immunoreactivity, however, was found to be dramatically decreased around the end of the sensitive period for ocular dominance plasticity (approximately 3 months of age). In the adult visual cortex, almost no immunostaining was observed. These developmental changes revealed by an immunohistochemical method were confirmed using immunoblot analysis. Upon immunoblot analysis after SDS-PAGE of protein from the kitten visual cortex, MAb M2F6 was found to recognize two protein bands with molecular weights of 130 kDa (drebrin E) and 140 kDa (drebrin A). The developmental profile of the intensity of the two bands of the drebin closely parallels in time the postnatal changes in cortical susceptibility to visual deprivation. These results indicate that the expression of drebrin in kitten visual cortex is restricted to the early postnatal period and suggest that it may play an important role in the experience-dependent modification of cortical circuitry during the sensitive period.