Up-regulated CNTF plays a protective role for retrograde degeneration in the axotomized rat retina

Using reverse transcription-polymerase chain reaction and in situ hybridization, we investigated the expression and cellular localization of ciliary neurotrophic factor receptor alpha (CNTFRalpha) in the rat retina following optic nerve transection (ONT). Following ONT, a signal for CNTFRalpha mRNA appeared in a layer-specific and time-dependent manner. In the ganglion cell layer, the signal showed a peak value 1 day after ONT, and then gradually decreased. In the inner nuclear layer the signal reached a peak value at 14 days of about 500% of control level, but then decreased at 4 weeks. Our findings suggest that CNTF might play a protective role for the retrograde degeneration of retinal cells induced by ganglion cell death in the rat retina following ONT.

Upregulation of ciliary neurotrophic factor in reactive Müller cells in the rat retina following optic nerve transection

We have investigated the expression and cellular localization of ciliary neurotrophic factor (CNTF) in the rat retina following optic nerve transection. In the normal retina, CNTF immunoreactivity was restricted to profiles in the ganglion cell layer. Following optic nerve transection, immunoreactivity appeared in Müller cell somata and processes and its intensity increased between three and seven days post-lesion. Quantitative evaluation by immunoblotting confirmed that CNTF expression increased continuously up to 7 days after optic nerve transection (to 430% of control levels), but decreased again to 250% of controls at 4 weeks post-lesion. Our findings suggest that CNTF supplied by Müller cells may play a protective role for axotomized ganglion cells in the rat retina.

Differential regulation of ciliary neurotrophic factor and its receptor in the rat hippocampus following transient global ischemia

To investigate a potential role of ciliary neurotrophic factor (CNTF) in transient global ischemia, we have studied the postischemic regulatory changes in the expression of CNTF and its receptor, the ligand-binding alpha-subunit (CNTFRalpha). Immunoblot analysis demonstrated CNTF levels were slightly upregulated already during the first day after ischemia and then increased markedly by more than 10-fold until 2 weeks postischemia. Immunoreactivity for CNTF became detectable 1 day after ischemia and was localized in reactive astrocytes. The intensity of the immunolabeling was maximal in CA1 during the phase of neuronal cell death (days 3-7 postischemia) and in the deafferented inner molecular layer of the dentate gyrus. Upregulation of CNTF expression was less pronounced in CA3 and absent in the stratum lacunosum moleculare and the outer molecular layer of the dentate gyrus and thus did not simply correlate with astroliosis as represented by upregulation of glial fibrillary acidic protein (GFAP). As shown by in situ hybridization, expression of CNTFRalpha mRNA was restricted to neurons of the pyramidal cell and granule cell layers in control animals. Following ischemia, reactive astrocytes, identified by double labeling with antibodies to GFAP, transiently expressed CNTFRalpha mRNA with a maximum around postischemic day 3. This astrocytic response was most pronounced in CA1 and in the hilar part of CA3. These results show that CNTF and its receptor are differentially regulated in activated astrocytes of the postischemic hippocampus, indicating that they are involved in the regulation of astrocytic responses and the neuronal reorganizations occurring after an ischemic insult.

Increased expression of ciliary neurotrophic factor receptor alpha mRNA in the ischemic rat retina

Using in situ hybridization, we investigated the expression of ciliary neurotrophic factor receptor ((CNTFRalpha) mRNA in the rat retina rendered ischemic by elevation of the intraocular pressure (IOP). The IOP was increased to 120 mmHg and maintained for 60 min. The rats were sacrificed on the day of reperfusion (DRP) 1, 3, 7, 14, and 28. In the normal retina, the signal for CNTFRalpha mRNA was present in retinal cells in the inner nuclear layer (INL) and in the ganglion cell layer (GCL). On DRP 1, numerous cells in the INL and GCL showed a CNTFRalpha mRNA signal. From DRP 3 onwards, CNTFRalpha mRNA appeared in photoreceptor cells located in the outer part of the outer nuclear layer. The signal in these cells increased up to DRP 14 and then decreased at DRP 28. Our findings suggest that cells expressing CNTFRalpha mRNA may resist the degenerative processes induced by ischemic insult in the rat retina.

Selective neuronal survival and upregulation of PCNA in the rat inner retina following transient ischemia

In this study we investigated the extent and time course of neuronal cell death and the regulation of the proliferating cell nuclear antigen (PCNA) in the different retinal cell layers following ischemia-reperfusion injury. Retinal ischemia was induced by controlled elevation of the intraocular pressure for a duration of 60 min. Changes in thickness and cell numbers in the retinal cell layers were analyzed at various time points (1 h to 4 weeks) after reperfusion. In parallel, apoptotic cell death was determined by the TUNEL method and the expression of PCNA analyzed by immunocytochemistry. In addition, we tested whether PCNA is expressed in neurons by double immunocytochemistry. The reduction in thickness was found to be less pronounced in the inner nuclear layer (INL). Correspondingly, cell numbers decreased by only 33% in the inner retina, but by more than 80% in the outer nuclear layer (ONL). Alterations in glial cell numbers did not contribute significantly to postischemic changes in the INL and ONL as assessed by using immunocytochemical markers for microglial and Müller cells. The time course of cell death determined by the TUNEL technique also differed markedly in the retinal layers being rapid and transient in the inner retina but delayed and prolonged in the ONL. PCNA immunoreactivity was undetectable in the normal retina, but was specifically induced in neurons of the inner retina within 1 h after reperfusion and was sustained for at least 4 weeks. We conclude that in contrast to photoreceptors in the ONL, a significant proportion of inner retinal neurons is resistant to ischemic insult induced by transiently increased intraocular pressure and that PCNA may possibly play a role in the selective postischemic survival of these cells.

Expression of CNTF/LIF-receptor components and activation of STAT3 signaling in axotomized facial motoneurons: evidence for a sequential postlesional function of the cytokines

Several lines of evidence suggest that ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF) are important for the survival and regeneration of axotomized motoneurons. To investigate the role of CNTF/LIF signaling in regenerative responses of motoneurons, we studied the expression of the three receptor components, CNTF receptor alpha (CNTFRalpha), LIF receptor beta (LIFRbeta), and gp130, and the activation of the STAT3 signal transduction pathway in the rat facial nucleus following peripheral nerve transection. As shown by in situ hybridization and immunoblotting, axotomy resulted in a rapid down-regulation of CNTFRalpha mRNA expression within 24 h and a concomitant massive up-regulation of LIFRbeta mRNA and protein in the lesioned motoneurons. The altered mRNA levels were maintained for 3 weeks but had returned back to control levels by 6 weeks postlesion after successful regeneration. In contrast, mRNA levels remained in the lesioned state during the 6-week period studied, when regeneration was prevented by nerve resection. Significant lesion-induced changes in gp130 mRNA levels were not detectable. Rapid (within 24 h) and sustained (for at least 5 days) activation of STAT3 in axotomized facial motoneurons was revealed by demonstrating the phosphorylation and nuclear translocation of the protein using immunocytochemistry and immunoblotting. In agreement with previous studies showing a complementary regulation of CNTF and LIF in the lesioned facial nerve, our observations on the postlesional regulation of CNTF/LIF receptor components in the facial nucleus indicate a direct and sequential action of the two neurotrophic proteins on axotomized facial motoneurons.

Ca2+ mobilization and capacitative Ca2+ entry regulate DNA synthesis in cultured chick retinal neuroepithelial cells

Release of Ca2+ from intracellular Ca2+ stores (Ca2+ mobilization) and capacitative Ca2+ entry have been shown to be inducible in neuroepithelial cells of the early embryonic chick retina. Both types of Ca2+ responses decline parallel with retinal progenitor cell proliferation. To investigate their potential role in the regulation of neuroepithelial cell proliferation, we studied the effects of 2,5-di-tert-butylhydroquinone (DBHQ), an inhibitor of the Ca2+ pump of intracellular Ca2+ stores, and of SK&F 96365, an inhibitor of capacitative Ca2+ entry, on DNA synthesis in retinal organ cultures from embryonic day 3 (E3) chicks and in dissociated cultures from E7 and E9 chick retinae. We demonstrate that both antagonists inhibit [3H]-thymidine incorporation in a dose-dependent manner without affecting cell viability or morphology. The inhibition of [3H]-thymidine incorporation by SK&F 96365 occurred in the same concentration range (IC50: approximately 4 microM) as the blockade of capacitative Ca2+ entry in the E3 retinal organ culture. At a concentration of 5 microM SK&F 96365. DNA synthesis was reduced by 71, 40 and 32% in the E3, E7 and E9 cultures, respectively. Application of DBHQ at concentrations which led to depletion of intracellular Ca2+ stores also inhibited [3H]-thymidine incorporation with IC50 values of 20-30 microM in the different cultures. Our results suggest the involvement of Ca2+ mobilization and capacitative Ca2+ entry in the regulation of DNA synthesis in the developing neural retina.

Involvement of P2 purinoceptors in the regulation of DNA synthesis in the neural retina of chick embryo

The activation of P2 purinoceptors induces Ca2+ mobilization in the early embryonic chick neural retina. This purinergic Ca2+ response declines parallel with the decrease in mitotic activity during retinal development. To investigate the role of P2 purinoceptors in the regulation of retinal cell proliferation, we studied the effects of the P2 purinoceptor antagonists suramin and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), and of the agonist ATP on DNA synthesis in retinal organ cultures from embryonic day 3 (E3) chick. Suramin inhibited [3H]-thymidine incorporation in a dose-dependent manner (IC50: approximately 70 microM). PPADS also reduced [3H]-thymidine incorporation with maximum inhibition of 46% at 100 microM. Exogenous ATP enhanced [3H]-thymidine incorporation in a dose-dependent manner to maximally 200% of control (EC50: approximately 70 microM). In dissociated retinal cultures from E7 chick, both antagonists showed similar inhibitory effects on [3H]-thymidine incorporation without affecting cell viability. In line with these observations, the presence of extracellular ATP was demonstrated both in vitro and in vivo. In the medium of E3 retinal organ cultures, the concentration of ATP increased 25-fold within 1 h of incubation and this concentration was kept for at least 24 h. In the chick amniotic fluid, the ATP concentration was nearly 3 microM at E3 and declined to 0.15 microM at E7. The results indicate that P2 purinoceptors activated by autocrine or paracrine release of ATP are involved in the regulation of DNA synthesis in the neural retina at early embryonic stages.

Expression of CNTF in Müller cells of the rat retina after pressure-induced ischemia

We have investigated the expression and cellular localization of ciliary neurotrophic factor (CNTF) in the rat retina following ischemia induced by transiently increasing the intraocular pressure. In the normal retina, CNTF immunoreactivity was restricted to profiles in the ganglion cell layer. Following ischemia and reperfusion, immunoreactivity appeared in Müller cell somata and processes and its intensity increased between 1 day and 2 weeks post-lesion. Quantitative evaluation by immunoblotting confirmed that CNTF expression continuously increased up to 2 weeks after ischemic injury (to 600% of control levels), but had declined again to 250% of controls at 4 weeks post-lesion. Our findings suggest that CNTF supplied by Müller cells has a protective function for lesioned neurons following transient ischemia.

A transient role for ciliary neurotrophic factor in chick photoreceptor development

Previous studies suggest that ciliary neurotrophic factor (CNTF) may represent one of the extrinsic signals controlling the development of vertebrate retinal photoreceptors. In dissociated cultures from embryonic chick retina, exogenously applied CNTF has been shown to act on postmitotic rod precursor cells, resulting in an two- to fourfold increase in the number of cells acquiring an opsin-positive phenotype. We now demonstrate that the responsiveness of photoreceptor precursors to CNTF is confined to a brief phase between their final mitosis and their terminal differentiation owing to the temporally restricted expression of the CNTF receptor (CNTFR alpha). As shown immunocytochemically, CNTFR alpha expression in the presumptive photoreceptor layer of the chick retina starts at embryonic day 8 (E8) and is rapidly down-regulated a few days later prior to the differentiation of opsin-positive photoreceptors, both in vivo and in dissociated cultures from E8. We further show that the CNTF-dependent in vitro differentiation of rods is followed by a phase of photoreceptor-specific apoptotic cell death. The loss of differentiated rods during this apoptotic phase can be prevented by micromolar concentrations of retinol. Our results provide evidence that photoreceptor development depends on the sequential action of different extrinsic signals. The time course of CNTFR alpha expression and the in vitro effects suggest that CNTF or a related molecule is required during early stages of rod differentiation, while differentiated rods depend on additional protective factors for survival.

Differential regulation of ciliary neurotrophic factor receptor-alpha expression in all major neuronal cell classes during development of the chick retina

Ciliary neurotrophic factor (CNTF) exerts a multiplicity of effects on a broad spectrum of target cells, including retinal neurons. To investigate how this functional complexity relates to the regulation of CNTF receptor alpha (CNTFR alpha) expression, we have studied the developmental expression of the receptor protein in chick retina by using immunocytochemistry. During the course of development, the receptor is expressed in all retinal layers, but three levels of specificity can be observed. First, the expression is regulated temporally with immunoreactivity observed in ganglion cells (embryonic day 8 [E8] to adult), photoreceptor precursors (E8-E12), amacrine cells (E10 to adult), bipolar cells (E12-E18), differentiated rods (E18 to adult), and horizontal cells (adult). Second, expression is restricted to distinct subpopulations of principal retinal neurons: preferentially, large ganglion cells; subpopulations of amacrine cells, including a particular type of cholinergic neuron; a distinctly located type of bipolar cell; and rod photoreceptors. Third, expression exhibits subcellular restriction: it is confined largely to dendrites in mature amacrine cells and is restricted entirely to outer segments in mature rods. These data correlate with CNTF effects on the survival of ganglion cells and mature photoreceptors, the in vitro differentiation of photoreceptor precursors and cholinergic amacrine cells, and the number of bipolar cells in culture described here or in previous studies. Thus, our results demonstrate an exceptional degree of complexity with respect to the regulation of neuronal CNTFR alpha expression in a defined model system. This suggests that the same signaling pathway is used to mediate a variety of regulatory influences, depending on the developmental stage and cell type.

Lesion-induced changes in the expression of ciliary neurotrophic factor and its receptor in rat optic nerve

There is evidence that ciliary neurotrophic factor (CNTF) is involved in reactive changes following lesions of the nervous system. To investigate, whether differences in the regulation of CNTF and CNTF receptor alpha (CNTFRalpha) contribute to the differences in PNS and CNS responses to injury, we have studied their expression on the mRNA and protein level in the rat optic nerve following a crush lesion to compare them with the situation in peripheral nerve. Seven days after the lesion, CNTF mRNA and protein levels were markedly decreased at the lesion site, concommitant with the disappearance of GFAP- and CNTF-immunopositive astrocytes. CNTF levels in proximal and distal parts were less affected. This was in contrast to the situation in the PNS, where CNTF was downregulated at and distal to the lesion site. Different from other CNS regions, optic nerve astrocytes expressed CNTFRalpha mRNA under normal conditions. Following lesion, CNTFRalpha was reduced substantially only in distal and proximal parts of the optic nerve but continued to be expressed at high levels at the lesion site, suggesting that GFAP-negative, CNTF-responsive cells are present there. Our results suggest that differences in lesion-induced changes in the optic and sciatic nerve reflect differences in the response to injury of astrocytes and Schwann cells. In the light of the known actions of CNTF in inducing astrogliosis, the expression pattern observed in the optic nerve indicates that CNTF and CNTFRalpha are involved in glial scar formation in the lesion area.

Use of cell ELISA for the screening of neurotrophic activities on minor cell populations in retinal monolayer cultures

In this study we describe a large-scale screening cell ELISA protocol which is suitable for the characterization of exogenic factor effects in mixed central nervous system (CNS) culture. The main novelty of the assay is that it permits the measurement of cellular responses in populations comprising as little as 2-4% of the total cell number. For standardization of the assay, we employed antibodies against opsin and microtubule-associated protein (MAP2) which label distinct retinal cell classes. Embryonic chick retinal neurons were grown in microtiter plates and directly processed for detection of antibody binding on the same plate. Binding of the antibodies was saturable and the ELISA signal was proportional to the number of immunoreactive cells comprising 2-4% and 16% of the total cell number with opsin and MAP2 antibodies, respectively. A minimum of 2000 opsin-positive cells could be reliably determined. Using our cell ELISA protocol, we demonstrate a developmental increase of both cell markers which reflected an increase in the number of opsin-positive cells but an enhanced expression per cell in the case of MAP2. We also show that growth-promoting activity-the presumed chick ciliary neurotrophic factor (CNTF)-stimulated the expression of opsin in retinal cultures (EC50; 2.3 pM) and that a corresponding activity is specifically expressed in the developing retina. Our results show that the cell ELISA protocol allows the rapid screening for distinct, low-percentage cell populations responding to exogenous factors in mixed CNS cultures.

Evidence for multiple, local functions of ciliary neurotrophic factor (CNTF) in retinal development: expression of CNTF and its receptors and in vitro effects on target cells

There is increasing, although largely indirect, evidence that neurotrophic factors not only function as target-derived survival factors for projection neurons, but also act locally to regulate developmental processes. We studied the expression of ciliary neurotrophic factor (CNTF) and the CNTF-specific ligand-binding alpha-subunit of the CNTF receptor complex (CNTFR alpha) in the rat retina, a well-defined CNS model system, and CNTF effects on cultured retinal neurons. Both CNTF and CNTFR alpha (mRNA and protein) are expressed during phases of retinal neurogenesis and differentiation. Retina-specific Müller glia are immunocytochemically identified as the site of CNTF production and CNTFR alpha-expressing, distinct neuronal cell types as potential CNTF targets. Biological effects on corresponding neurons in culture further support the conclusion that locally supplied CNTF plays a regulatory role in the development of various retinal cell types including ganglion cells and interneurons.

Transient up-regulation of ciliary neurotrophic factor receptor-alpha mRNA in axotomized rat septal neurons

Using non-radioactive in situ hybridization we investigated the effect of fimbria-fornix transection on the expression of ciliary neurotrophic factor receptor alpha (CNTFR alpha) mRNA in axotomized septohippocampal neurons of the rat septal complex. Whereas CNTFR alpha expression was undetectable in the medial septal nucleus/diagonal band complex (MSDB) of control animals, specific up-regulation was observed in MSDB neurons after fimbria-fornix transection. CNTFR alpha expression was maximal 7-10 days after the lesion and had returned to control levels after 3 weeks. Following unilateral fimbria-fornix transection, CNTFR alpha up-regulation was restricted to the MSDB ipsilateral to the lesion. When cholinergic septal neurons were selectively eliminated by immunolesioning with 192 IgG-saporin prior to fimbria-fornix transection, the lesion-induced expression of CNTFR alpha was still observed in many medial septal nucleus neurons. These results demonstrate that after fimbria-fornix transection CNTFR alpha expression is transiently induced in axotomized, non-cholinergic neurons of the medial septal nucleus, suggesting a postlesion function of locally supplied CNTF.

Expression of ciliary neurotrophic factor receptor-alpha messenger RNA in neonatal and adult rat brain: an in situ hybridization study

Ciliary neurotrophic factor is a pleiotropic molecule thought to have multiple functions in the developing and adult nervous system. To investigate the role of ciliary neurotrophic factor in the developing and mature brain by defining putative target cells the expression of the ligand-binding alpha-subunit of the ciliary neurotrophic factor receptor was studied in neonatal and adult rat brains using a digoxygenin-labelled probe for in situ hybridization. Neuronal populations expressing ciliary neurotrophic factor receptor-alpha messenger RNA were found in many functionally diverse brain areas including the olfactory bulb (mitral cells and other neurons) neocortex (layer V) and other cortical areas (pyramidal cell layers in the piriform cortex and hippocampus, granule cell layer of the dentate gyrus) and distinct nuclei in the thalamus, hypothalamus and brainstem. In the latter, reticular nuclei and both cranial motor and sensory nerve nuclei showed intense hybridization signals in the neonatal brain. The nucleus ruber, substantia nigra pars reticularis, deep cerebellar nuclei and a subpopulation of cells in the internal granular layer of the cerebellum were also labelled. In many areas (e.g. in thalamic, midbrain and pontine nuclei) ciliary neurotrophic factor receptor-alpha expression became undetectable with maturation; however, there were other areas (e.g., olfactory bulb, cerebral cortex and hypothalamus) where expression was higher in the adult. The neuroepithelium of the neonatal rat displayed a highly selective expression of ciliary neurotrophic factor receptor-alpha in areas which are known to exhibit high rates of postnatal cell proliferation in the germinal zones. Generally, neurons which have been reported to respond to exogenous ciliary neurotrophic factor were labelled by the ciliary neurotrophic factor receptor-alpha probe. This was not the case, however, for striatal and septal neurons. The results of this study suggest that ciliary neurotrophic factor receptor-alpha ligands have even broader functions than previously thought, acting on different neuronal populations in the developing and mature brain, respectively.

Differential regulation of ciliary neurotrophic factor (CNTF) and CNTF receptor alpha expression in astrocytes and neurons of the fascia dentata after entorhinal cortex lesion

Neurotrophic factors have been implicated in reactive processes occurring in response to CNS lesions. Ciliary neurotrophic factor (CNTF), in particular, has been shown to ameliorate axotomy-induced degeneration of CNS neurons and to be upregulated at wound sites in the brain. To investigate a potential role of CNTF in lesion-induced degeneration and reorganization, we have analyzed the expression of CNTF protein and CNTF receptor alpha (CNTFR alpha) mRNA in the rat dentate gyrus after unilateral entorhinal cortex lesions (ECLs), using immunocytochemistry and nonradioactive in situ hybridization, respectively. In sham-operated as in normal animals, CNTF protein was not detectable by immunocytochemistry. Starting at 3 d after ECL, upregulation of CNTF expression was observed in the ipsilateral outer molecular layer (OML). Expression was maximal at around day 7, and at this stage immunoreactivity could be specifically localized to astrocytes in the ipsilateral OML. By day 14 postlesion, CNTF immunoreactivity had returned to control levels. CNTFR alpha mRNA was restricted to neurons of the granule cell layer in controls. Three days postlesion, prominent CNTFR alpha expression was observed in the deafferented OML. A similar but less prominent response was noticed in the contralateral OML. After 10 d, CNTFR alpha expression had returned to control levels. Double labeling for CNTFR alpha mRNA and glial fibrillary acidic protein (GFAP) showed that upregulation of CNTFR alpha occurred in reactive, GFAP-immunopositive astrocytes of the OML. A substantial reduction of CNTFR alpha expression in the deafferented granule cells was transiently observed at 7 and 10 d postlesion. Our results suggest a paracrine or autocrine function of CNTF in the regulation of astrocytic and neuronal responses after brain injury.

CNTF exerts opposite effects on in vitro development of rat and chick photoreceptors

Effects of ciliary neurotrophic factor (CNTF) on photoreceptor development in dissociated cultures of embryonic chick and newborn rat retina were studied using opsin immunoreactivity to characterize photoreceptor differentiation. In the presence of CNTF, the number of photoreceptors was increased by up to 200% in chick cultures, but was reduced by 82-99% in rat cultures. The EC50 determined for CNTF effects in chick and rat cultures were 0.06 ng ml-1 and 0.02 ng ml-1, respectively. By studying the time course of in vitro development we showed that CNTF transiently stimulated the generation of photoreceptors from opsinnegative precursor cells of chick retina, but completely prevented the same process in rat cultures. These results suggest that CNTF is involved in the regulation of photoreceptor development, but that it can have different actions in the two species, at least in vitro.

Ciliary neurotrophic factor promotes chick photoreceptor development in vitro

Previous in vitro studies have convincingly demonstrated the involvement of diffusible factors in the regulation of photoreceptor development. We now provide evidence that ciliary neurotrophic factor (CNTF) represents one of these regulatory molecules. In low density monolayer cultures prepared from embryonic day 8 chick retina, photoreceptor development was studied using the monoclonal antiopsin antibody rho-4D2 as a differentiation marker. The number of cells acquiring opsin immunoreactivity, determined after 3 days in vitro, was increased up to 4-fold in the presence of CNTF to maximally 10.5% of all cells. Basic fibroblast growth factor or taurine both of which have been reported to stimulate opsin expression in rat retinal cultures and other neurotrophic factors tested (nerve growth factor, brain derived neurotrophic factor) had no effect. The EC50 of the CNTF effect (2.6 pM) was virtually identical to that measured for other CNTF receptor mediated cellular responses. Conditioned medium produced by cultured retinal cells (most likely glial cells) exhibited opsin stimulating activity identical to that of CNTF. Stimulation of opsin expression was specific for morphologically less mature photoreceptors and obviously restricted to rods, since changes in the number of identifiable cone photoreceptors expressing opsin immunoreactivity (10% of all cones) were not detectable. Measurement of the kinetics of the CNTF response revealed that the factor acted on immature opsin-negative progenitors and that CNTF effects were unlikely to reflect enhanced cell survival. Proliferation of photoreceptors was also unaffected, as demonstrated by [3H]thymidine autoradiography. With prolonged culture periods a gradual decrease in the number of opsin-positive cells was observed both in controls and in the continuous presence of CNTF. This decrease could be partly prevented by the addition of 1 mM taurine. Our results suggest that CNTF acted as an inductive signal for uncommitted progenitor cells or during early stages of rod photoreceptor differentiation, whereas other extrinsic stimulatory activities seemed to be required for further maturation.

Expression of ciliary neurotrophic factor receptor mRNA and protein in the early postnatal and adult rat nervous system

We have used reverse transcription/polymerase chain reaction (RT-PCR) and Western blotting with an anti-peptide antibody to study the expression of the alpha-component of the receptor for ciliary neurotrophic factor (CNTFR alpha) in rat nervous tissue. At the early postnatal stage CNTFR alpha protein could be detected in all parts of the nervous system studied (and also in muscle and liver). It was particularly abundant in pons, cerebellum, spinal cord, retina and sciatic nerve. In adult tissues the content was dramatically reduced except for olfactory bulb and cortex, where CNTFR alpha protein was upregulated during development. Only in part of the tissues, expression of CNTFR alpha mRNA and its developmental regulation paralleled that of the protein. These differences are partly explainable by the different cellular localization of mRNA and the membrane associated receptor protein, but, in addition, they suggest the existence of different regulatory mechanisms for CNTFR alpha. Our results support the idea that CNTF plays an important role during the development of the nervous system and that CNTF actions may be found in many brain regions and target cells.

Early in vitro development of voltage- and transmitter-gated currents in GABAergic amacrine cells

It has been shown in previous studies that a subpopulation of neurons in monolayer cultures prepared from immature embryonic chicken retina acquired a series of functional properties which characterized them as GABAergic amacrine cells after 1 week in vitro. In the present study, we demonstrate that immature precursors of these cells were already identifiable by morphological criteria after 2 days in vitro (DIV). Using the whole cell patch-clamp technique we have studied the time-course of the expression of voltage-dependent and of glutamate and GABA receptor-associated conductances in these identified retinal interneurons developing in vitro. Recordings after 2 DIV revealed a very homogeneous pattern of membrane conductances. In all cells tested, whole cell responses to depolarizing voltage steps consisted solely of a sustained outward potassium current and 100% of the cells responded to the glutamate receptor agonist kainic acid (KA) and to GABA. Fast activating inward sodium currents first appeared after 3 DIV, whereas a transient component of outward potassium currents was not detectable before day 4 in vitro. N-Methyl-D-aspartate (NMDA)-evoked currents were first observed at 3 DIV in the GABAergic neurons. Only 1 day later they were found in all of the GABAergic neurons. Expression of responses to quisqualic acid (QU) started at 3 DIV, but remained restricted to a subpopulation of the GABAergic cells even at later stages (59% at 4 DIV, 63% at 6-9 DIV). Antagonistic effects of QU on KA responses, however, were detectable in all cells tested, independent of the developmental stage and the presence of QU-evoked currents.(ABSTRACT TRUNCATED AT 250 WORDS)

Diversity of neuronal phenotypes expressed in monolayer cultures from immature rabbit retina

We have used monolayer cultures prepared from early postnatal rabbit retinae (days 2-5) by the sandwich technique to study the capacity of immature neurons to express specific neuronal phenotypes in a homogeneous in vitro environment. Applying morphological, immunocytochemical, and autoradiographic criteria, we demonstrate that a variety of phenotypes could be distinguished after 7-14 days in vitro, and correlated with known retinal cell types. Bipolar cell-like neurons (approximately 4% of total cell number) were identified by cell type-specific monoclonal antibodies (115A10) and their characteristic bipolar morphology. Small subpopulations (about 1%) of GABA-immunoreactive neurons acquired elaborate morphologies strikingly similar to those of A- and B-type horizontal cells. Amongst putative amacrine cells several different subpopulations could be classified. GABA-immunoreactive amacrine-like neurons (6.5%), which also showed high affinity [3H]-GABA uptake, comprised cells of varying size and shape and could be subdivided into subpopulations with respect to their response to different glutamate receptor agonists (NMDA, kainic acid, quisqualic acid). In addition, a small percentage of [3H]-GABA accumulating cells with large dendritic fields showed tyrosine-hydroxylase immunoreactivity. Presumptive glycinergic amacrine cells (18.5%) were rather uniform in shape and had small dendritic fields. Release of [3H]-glycine from these neurons was evoked by kainic and quisqualic acid but not by NMDA. Small [3H]-glutamate accumulating neurons with few short processes were the most frequent cell type (73%). This cell type also exhibited opsin immunoreactivity and probably represented incompletely differentiated photoreceptor cells. Summing the numbers of characterized cells indicated that we were able to attribute a defined retinal phenotype to most, if not all of the cultured neurons. Thus, we have demonstrated that immature neuronal cells growing in monolayer cultures, in the absence of a structured environment, are capable of maintaining or producing specific morphological and functional properties corresponding to those expressed in vivo. These results stress the importance of intrinsic factors for the regulation of neuronal differentiation. On the other hand, morphological differentiation was far from perfect indicating the requirement for regulatory factors.

Voltage-gated currents of rabbit A- and B-type horizontal cells in retinal monolayer cultures

In monolayer cultures prepared from immature early postnatal rabbit retina, small populations of neurons can be demonstrated to differentiate into apparently mature A- and B-type horizontal cells. Using whole-cell, single-channel, patch-clamp recording techniques, we have analyzed the pattern of voltage-gated conductances expressed by mammalian horizontal cells under these conditions. A total of six different voltage-dependent ionic currents were recorded. Tetrodotoxin-sensitive fast sodium inward currents (INa) were found in 81% of the A-type and 90% of the B-type cells. Inward calcium currents could be demonstrated in all cells tested after blockade of other conductances. Two types of outward potassium currents with properties of the 4-aminopyridine-sensitive transient IA and the tetraethylammonium sensitive delayed rectifier IK, respectively, could be characterized in whole-cell recordings. An inward rectifying potassium current (Ianom) typical for horizontal cells was activated in response to hyperpolarizing voltage steps. These types of currents have also been described in dissociated adult horizontal cells from lower vertebrates and cat. With single-channel recordings on inside-out patches excised from B-type cells, an additional Ca(2+)-dependent current (IK(Ca)) was observed which, so far, has not been described in horizontal cells developing in situ. Our results demonstrate that cultured rabbit horizontal cells express a set of voltage-gated currents which largely, but not completely, corresponds to that described in situ for horizontal cells of other species. The culture system will allow further investigation of developmental and functional aspects of mammalian horizontal cells.

Expression of horizontal cell phenotypes in monolayer cultures from immature rabbit retina

Using the sandwich culture technique introduced by Brewer and Cotman we have studied the in vitro differentiation of A- and B-type horizontal cells which represent two well characterized cell types of the rabbit retina. Neurons from immature (postnatal day 3) rabbit retinae were dissociated and grown on inverted coverslips for up to 5 weeks in a chemically defined medium. On the basis of morphological criteria and the staining pattern for several immunocytochemical and autoradiographic horizontal cell markers we have examined to what extent expression of a distinct mature neuronal phenotype can take place under the artificial conditions of monolayer cultures. After 14 days in vitro neurons could be identified which had acquired elaborate morphological features closely resembling those of A- and B-type horizontal cells, respectively. Axonless A-like cells had 2-4 stout primary dendrites. In agreement with in situ observations these cells showed immunoreactivity for neurofilament proteins (68 kDa, 200 kDa), calbindin-28 kDa and less strongly for vimentin. B-like neurons reached varying states of development. Ideally, they had dendritic trees with 6-8 primary processes extending radially from the soma and a single axon-like process which branched extensively to form a profuse neuritic arbor strikingly similar to axon terminal systems of B-type cells in the intact retina. B-like cells also stained for vimentin, calbindin-28 kDa and unexpectedly also for neurofilament proteins. Interestingly, however, neurofilaments became redistributed during in vitro development eventually resulting in their restricted localization in the 'axon terminal system'. This apparently reflects a developmental process which has escaped detection in situ so far. Both cell types were intensely labelled with antibodies to gamma-aminobutyric acid (GABA), the presumed horizontal cell transmitter, but high affinity uptake of this transmitter was practically undetectable by [3H]-GABA autoradiography. This was in agreement with observations in intact retinae. These results support the notion that once a neuron has reached a certain developmental state further differentiation and maintenance of its particular morphological and functional properties are primarily governed by intrinsic factors, but do not exclude that extrinsic signals have important modulatory functions.

Voltage-gated currents of putative GABAergic amacrine cells in primary cultures and in retinal slice preparations

To analyze the voltage-dependent ionic conductances of putative GABAergic amacrine cells developing in vitro, whole cell patch clamp recordings were carried out on identified neurons in monolayer cultures from embryonic chick retinae. These recordings were directly compared with those performed on amacrine cells in chick retinal slice preparations. Current responses to depolarizing voltage steps observed in cultured neurons could be separated into at least four different components. A small tetrodotoxin-sensitive sodium inward current was observed in approximately 50% of the cells. The considerably larger outward potassium current consisted of a transient 4-aminopyridine-sensitive component and a sustained component. The latter was reduced in the presence of both tetraethylammonium chloride and Co2+ and thus was probably composed of two conductances. In addition, a Ca(2+)-carried inward current of small amplitude could be identified. Voltage-sensitive currents measured in amacrine cells of retinal slices were very similar. Again, only about half of the cells exhibited sodium currents. Potassium currents contained the above components, but their contributions to the whole cell current seemed to be different. Together with previous findings these results suggest that immature retinal neurons in dissociated cultures undergo a differentiation process similar to that occurring in vivo.

Transmitter-gated currents of GABAergic amacrine-like cells in chick retinal cultures

A subpopulation of cells developing in dissociated neuronal cultures prepared from 8-day-old embryonic chick retinae can be identified as putative in vitro counterparts of GABAergic amacrine cells by immunocytochemical and autoradiographic markers and by their electrophysiological responses to transmitter agonists. In the present study, transmitter-gated conductances expressed by these neurons were examined using the whole-cell patch-clamp technique. At negative holding potentials, the excitatory amino acid agonists N-methyl-D-aspartate (NMDA), kainate quisqualate, and glutamate induced inward currents with reversal potentials close to 0 mV in most of the cells selected for recording. NMDA-evoked responses were selectively blocked by the noncompetitive inhibitor MK 801 and by Mg2+ (in a voltage-dependent manner) and were potentiated in the presence of submicromolar concentrations of glycine. Glutamate apparently interacted with both NMDA and non-NMDA type receptors. All cells tested responded to the inhibitory transmitters GABA and glycine. Both inhibitory agonists could be shown to activate chloride conductances. Responses to GABA and glycine were specifically inhibited in the presence of bicuculline and strychnine, respectively. Thus, GABAergic neurons in retinal cultures express at least two different excitatory amino acid receptors--NMDA and non-NMDA--and two different inhibitory amino acid receptors--the GABAA and the glycine receptor. The results demonstrate the ability of the cultured neurons to develop an apparently mature phenotype and contribute to the understanding of the functional properties of GABAergic amacrine cells in the vertebrate retina.

Release of gamma-amino[3H]butyric acid from cultured amacrine-like neurons mediated by different excitatory amino acid receptors

The release of preaccumulated gamma-amino[3H]butyric acid ([3H]GABA) from putative GABAergic amacrine cells was studied in neuronal monolayer cultures made from embryonic chick retina. Release was specifically stimulated by excitatory amino acid agonists. N-Methyl-D-aspartate (NMDA; EC50, 19.1 +/- 5.0 microM), kainic acid (EC50, 15.6 +/- 2.3 microM), and the presumptive endogenous ligand glutamate (EC50, 3.6 +/- 0.5 microM) showed the same efficacy. Quisqualic acid, although the most potent agonist (EC50, 0.56 +/- 0.12 microM), was only half as efficacious. The time course of [3H]GABA release and autoradiographic visualization of responsive GABA-accumulating cells suggest that approximately 50% of the [3H]GABA-accumulating cells possess no or very low responsiveness to quisqualic acid. Depolarization (56 mM KCl)-induced release was fivefold lower than the maximal effect elicited by excitatory amino acids. Release of [3H]GABA and of endogenous GABA was entirely independent of extracellular Ca2+ but was completely abolished after replacement of Na+ by choline or Li+. The effects of NMDA and low concentrations of glutamate (up to 10 microM) were blocked by 2-amino-5-phosphonovaleric acid, by MK 801, and (in a voltage-dependent manner) by Mg2+. The reduction of NMDA responses by kynurenic acid was reversed by D-serine, and quisqualic acid competitively inhibited kainic acid-evoked release. Our results show that the cultured [3H]GABA-accumulating neurons, which probably represent the in vitro counterparts of GABAergic amacrine cells, express at least two types of excitatory amino acid receptors (of the NMDA and non-NMDA type), both of which can mediate a Ca2(+)-independent but Na2(+)-dependent release of GABA.

Identification of GABAergic amacrine cell-like neurons developing in chick retinal monolayer cultures

Purified neuronal monolayer cultures were prepared from embryonic chick retinae. Using immunocytochemistry for GABA and autoradiographic demonstration of [3H]muscimol uptake as markers, approximately 32% of the cells were identified as putative in vitro counterparts of gamma-aminobutyric acidergic (GABAergic) amacrine cells. Whole cell patch clamp recordings revealed close similarities between identified [3H]GABA accumulating neurons in culture and amacrine cells recorded in retinal slices, with respect to voltage-dependent membrane currents and to ion channels gated by exitatory (N-methyl-D-aspartate, kainate, quisqualate, glutamate) and inhibitory (GABA, glycine) amino acid agonists. The results demonstrate that retinal neurons are able to differentiate in dissociated retinal cultures. Such cultures may thus serve as a model system to study development and function of CNS neurons.

Development and plasticity of adrenal chromaffin cells: cues based on in vitro studies

Neural crest derived precursors of the sympathoadrenal cell lineage give rise to two major cell types that differ in a number of morphological, ultrastructural, and biochemical characteristics: principal sympathetic neurons and chromaffin cells of the adrenal medulla. The present article reviews experimental studies performed on cultured adrenal medullary cells and designed to unravel the nature of epigenetic signals governing the developmental choice between the endocrine chromaffin and the neuronal sympathetic phenotype. Emphasis is placed on the role of glucocorticoids in initiation, development, and maintenance of the endocrine chromaffin phenotype and apparently antagonistic influences exerted by nerve growth factor (NGF) in vitro, resulting in the acquisition of neuronal properties by differentiated chromaffin cells. Experimental data from in vitro studies are compatible with the following conclusions. Glucocorticoids represent the decisive signal for the initial induction of endocrine differentiation. Moreover, high steroid hormone concentrations, as present in the adrenal medulla, are a prerequisite for the maturation of chromaffin cells. Even in a differentiated state, the endocrine phenotype is unstable in the absence of glucocorticoids, and the cells seem to reenter the neuronal developmental pathway. Under these conditions, cellular survival and differentiation into sympathetic neurons become NGF-dependent, as in normal sympathetic development. Thus, the effects of NGF survival, neurite outgrowth, and transmitter synthesis of cultured chromaffin cells probably do not reflect the induction of a specific phenotype, but they may be interpreted as a general neurotrophic support observable with other responsive cell types.

The neuro-endocrine ambiguity of sympathoadrenal cells

This introductory article presents a survey of the principle cellular constituents of the sympathoadrenal section in the peripheral autonomic nervous system, their development and plasticity and factors that govern the expression of particular morphologic and transmitter phenotypes. The article focuses on results obtained in cell culture studies with isolated chromaffin cells that have permitted the analysis of molecular signals possibly serving as environmental cues during the development of sympathoadrenal cells.

Ciliary neuronotrophic factor stimulates choline acetyltransferase activity in cultured chicken retina neurons

It has been demonstrated that cultured cholinergic retinal neurons from 8-day-old chicken embryos respond to a polypeptide factor present in retinal cell-conditioned medium (RCM) and in retinal extracts. Compared with control cultures, the activity of acetyl-CoA:choline O-acetyltransferase (EC 2.3.1.6; ChAT) is enhanced more than twofold in neuronal retinal cultures grown for 7 days in the presence of RCM. The present study demonstrates that both ciliary neuronotrophic factor (CNTF), which is characterized by its trophic activity on parasympathetic ciliary neurons, and RCM exhibit identical stimulatory effects on ChAT activity in retinal monolayer cultures. Similarly, RCM supports the in vitro survival of ciliary neurons to the same extent as CNTF. The active species in RCM has a molecular weight (20,900 +/- 1,000) identical to that of CNTF, as determined by preparative sodium dodecyl sulfate gel electrophoresis. The results indicate that cholinergic retinal neurons represent a central neuronal target for CNTF or a closely related protein.

Development of cholinergic retinal neurons from embryonic chicken in monolayer cultures: stimulation by glial cell-derived factors

In recent years evidence has indicated that, like the PNS, the development of the CNS is influenced by neuronotrophic polypeptide factors. In the present study, cultures of dissociated retinal neurons from 8-d-old chicken embryos were used to investigate the role of neuronotrophic factors (NTF) in the development of the neural retina. CAT, which in vivo is located in amacrine cells of the retina, served as a marker for studying the in vitro development of cholinergic retinal neurons. Differentiation of cholinergic cells under control conditions was indicated by a 10-fold increase of enzyme activity during a 7-d culture period. Addition of media conditioned by high-density retinal cultures resulted in a further stimulation of CAT activity by 100-400%. The CAT-stimulating activity was associated with a high-molecular-weight component of the retina conditioned medium (RCM) and was sensitive to protease treatment, but was not affected by other hydrolytic enzymes. The putative cholinergic factor was secreted by retinal cultures virtually free of neurons, suggesting that it is mainly produced by Müller cells. CAT-stimulating activity was also present in extracts from embryonic chicken retinae and medium conditioned by rat retinal cultures. NGF, anti-NGF antiserum, extracts from chicken brain tissues, and a number of other extracts and conditioned media, all known to contain neuronotrophic activities, were found to have no influence on cholinergic development in chicken retinal cultures. An extract from non-retinal eye tissue containing ciliary neuronotrophic factor (CNTF) stimulated CAT activity to the same extent as did RCM.(ABSTRACT TRUNCATED AT 250 WORDS)

Tetanus toxin binding to isolated and cultured rat retinal glial cells

The presence of immunocytochemically detectable membrane receptors for tetanus toxin, supposedly composed of higher gangliosides, is widely accepted as a marker of neuronal cells. We now demonstrate that Müller cells, a unique glial cell type of the vertebrate retina, possess specific tetanus toxin (TT)-binding sites. Single cell suspensions were prepared from adult rat retina by a gentle dissociation method, and the Müller cells, unequivocally identified by their morphology, could be immunocytochemically double-labeled by antisera to vimentin and to TT. The expression of complex gangliosides by identified Müller cells was also demonstrated by immunofluorescence labeling with the monoclonal antibody A2B5. Using the double-immunolabeling method for the identification of Müller cells we show that specific tetanus toxin binding is acquired by these cells during postnatal maturation both in vivo and in vitro. In vivo the percentage of tetanus toxin-positive Müller cells increases from 0% in 4-day-old animals to 10% on postnatal day 8, reaching the adult level of about 95-100% around day 30. In retinal monolayer cultures prepared from newborn rats, the majority (65%) of vimentin-positive non-neuronal cells became TT-positive during a 2-week culture period, indicating that this population of non-neuronal cells represents differentiating Müller cells. Again, comparable results were obtained with A2B5, supporting the conclusion that Müllerian glia expresses surface molecules, which are normally regarded as neuronal markers.

Characterization and partial purification of a novel neuronotrophic factor from bovine seminal vesicle

Extracts from bovine seminal vesicles have been shown to contain high concentrations of nerve growth factor (NGF)-like biological activity and of the NGF protein with properties corresponding to that of NGF from other sources. We now demonstrate that a second neuronotrophic protein, termed seminal vesicle-derived neuronotrophic factor (SVNF), is present in seminal vesicle extracts (SVEs), which could not be distinguished from NGF on the basis of biological activity. SVNF has neuronotrophic activity on NGF target cells like embryonic chicken-sensory and sympathetic neurons, sympathetic neurons, and chromaffin cells from neonatal rats, but it is inactive on embryonic chicken ciliary or neonatal rat nodose ganglion neurons. It also stimulates fiber outgrowth from rat pheochromocytoma (PC 12) cells. In gel filtration chromatography on Biogel A 1.5 m, the activity is eluted with an apparent molecular weight of 40 kilodaltons, and by preparative isoelectric focusing, the isoelectric point was determined to be in the neutral range (6.8-7.8). The biological activity of SVNF, in contrast to that of NGF, is partially retained after preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis and can be electrophoretically eluted with an apparent molecular weight of 16-20 kilodaltons. Electrophoretically purified SVNF is not inhibited by antisera to mouse NGF, but its activity is increased greater than 10-fold in the presence of very low concentrations of NGF. For partially purified SVNF, a specific activity of 2.9-5.8 X 10(5) biological units/mg of protein was determined in the presence of subthreshold NGF concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-dependent differences in 125I-nerve growth factor binding properties of rat adrenal chromaffin cells

Nerve growth factor (NGF) has been shown to influence survival, morphology, and transmitter phenotype of young postnatal rat chromaffin cells in vitro. Significant differences in NGF responses of chromaffin cells from newborn rats compared to 8-10-day-old ones have been reported. For this reason we studied equilibrium binding and dissociation kinetics of 125I-NGF on newborn (D1) and 10-day-old (D10) rats. Under equilibrium conditions no differences were found between the two cell types, with respect to dissociation constant (approximately 2.5 X 10(-9) M) and receptor number (10-22,000 per cell). In dissociation experiments D10 chromaffin cells exhibited two classes of NGF receptors, similar to those found in other NGF-responsive cells. From fast receptors 125I-NGF was released rapidly both at 4 degrees C and at 37 degrees C, whereas dissociation from "slow" receptors was observed only at 37 degrees C. The slow receptor class was not found on D1 cells. Instead, more than 50% of specifically bound 125I-NGF did not dissociate in the presence of excess unlabeled NGF at 37 degrees C. These age-dependent differences seem to indicate regulatory developmental changes in NGF-binding properties of rat chromaffin cells.

Effects of pre- and postnatal administration of antibodies to nerve growth factor on the morphological and biochemical development of the rat adrenal medulla: a reinvestigation

Whether or not adrenal medullary (chromaffin) cells which respond to nerve growth factor (NGF) both in vitro and in vivo require NGF for their normal development is controversial. Systemic deprivation of endogenous NGF by injection of anti-NGF antibodies into rat fetuses or by transfer of anti-NGF to the offspring of autoimmunized mothers has provided conflicting results. We have reinvestigated the effects of a specific antiserum to NGF on the morphology, catecholamine (CA) and neuropeptide (Met-enkephalin, Met-ENK; substance P, SP) content, and choline acetyltransferase (ChAT) activity of the rat adrenal medulla. Fetuses were injected with anti-NGF antibodies on day 17 of gestation and postnatally at daily intervals for 7 days. The histological appearance of adrenal medullae of anti-NGF injected animals was not altered as compared to controls. Ultrastructurally, no degenerative changes or developmental retardation of chromaffin cells could be detected. However, numbers of chromaffin granules per micron 2 of cytoplasmic area were greater and the mean diameters of the cores of adrenaline storage granules were smaller in antibody-treated than in control animals. CA and SP content, ratios of adrenaline to noradrenaline and ChAT activities were identical in anti-NGF-treated and control animals. Anti-NGF antibodies caused a reduction of adrenal Met-ENK by 40% as compared to controls. Superior cervical ganglia from the same animals were used to document immunosympathectomy induced by the antiserum. They displayed the well-established structural alterations and a marked reduction of the CA content. We conclude that administration of anti-NGF antibodies to embryonic and early postnatal rats induces only subtle changes in the ultramorphology of chromaffin cells without altering the development of normal CA levels. The small, yet significant effects of anti-NGF antibodies on adrenal Met-ENK, however, may suggest a role for endogenous NGF in the regulation of opioid peptide metabolism in developing chromaffin cells.

Embryonic rat adrenal glands in organ culture: effects of dexamethasone, nerve growth factor and its antibodies on pheochromoblast differentiation

In the present study we sought to determine the developmental potentialities and restrictions of adrenal medullary cells (pheochromoblasts) by investigating their morphological and biochemical response to nerve growth factor (NGF), anti-NGF antibodies and dexamethasone (DEX) after explantation into culture at different embryonic stages. With the exception of explants taken at embryonic day 15 (E 15) cultures of embryonic adrenal glands showed neurite outgrowth, which was not influenced by the addition of NGF, anti-NGF antibodies or DEX to the culture medium during the 4-day-culture period. Pheochromoblasts in E 17 + 4 explants showed spontaneous ultramorphological and biochemical maturation in terms of an increase in the number of catecholamine storage vesicles (CSVs) per micron 2 of cytoplasmic area, diameters of the cores of CSVs, percentages of electron-lucent cores of CSVs indicative of increased storage of adrenaline, overall catecholamine (CA) content and relative amount of adrenaline. NGF did not significantly affect this maturational process. Anti-NGF antibodies slightly decreased the proportion of adrenaline. The most pronounced maturation was seen in response to DEX and DEX plus NGF, although a maturational state equivalent to the E 21 stage was not achieved. E 21 + 4 explants showed neither spontaneous nor drug-induced biochemical maturation. Medullary cells in NGF-treated E 21 explants frequently retained the morphological features of pheochromoblasts. Treatment with anti-NGF antibodies significantly reduced the portion of adrenaline as compared to any other treatment. We conclude that under the culture conditions employed (1) a few pheochromoblasts spontaneously express a neuronal phenotype, (2) differentiation of pheochromoblasts towards chromaffin cells is enhanced by glucocorticoids but not by NGF, and (3) anti-NGF antibodies do not impair spontaneous neuritic growth and morphological maturation of pheochromoblasts, but cause a small reduction in the relative amount of adrenaline.

Nerve growth factor and dexamethasone specify the catecholaminergic phenotype of cultured rat chromaffin cells: dependence on developmental stage

Antibodies to epinephrine (E) and bovine phenylethanolamine N-methyltransferase (PNMT) have been used to monitor the regulation of the E- and PNMT-immunoreactive chromaffin cell phenotypes by dexamethasone (DEX) and nerve growth factor (NGF). The cells were isolated from 1-, 10- and 30-day-old (D1, D10 and D30) rat adrenal glands and grown for 4 days on a polyornithine substratum. DEX (10(-5)M) supported the survival of 90% of the cells from all postnatal ages studied. In contrast, only 45% (D1), 33% (D10) and 60% (D30) of the chromaffin cells had survived after 4 days in control cultures or when treated with NGF (100 ng/ml). Throughout this study numbers of E-immunoreactive cells were approximately 10% larger than those of cells stained by anti-PNMT antibodies irrespective of the treatments applied. 55% of the cells isolated at D1 and 79% of the cells at D10 were stained by anti-E antibodies. The proportion of E-positive cells was constant in D1 cultures carried for 4 days, while E-immunoreactive cells dropped to 63% in cultures from D10. At D1 and D10 DEX and NGF had opposite effects on the portions of E-positive cells, DEX increasing and NGF decreasing their relative numbers, 66% of the chromaffin cells isolated at D30 displayed E-specific immunoreactivity. DEX caused a significant increase (to 74%), while both NGF-treated and control cultures exhibited a decrease in the relative numbers of E-immunoreactive cells.(ABSTRACT TRUNCATED AT 250 WORDS)

C6 glioma cell-conditioned medium induces neurite outgrowth and survival of rat chromaffin cells in vitro: comparison with the effects of nerve growth factor

The effects of medium conditioned by rat C6 glioma cells (C6-CM) on the survival, neurite formation, and catecholamine content of adrenal medullary cells in culture were investigated and compared with the effects of nerve growth factor (NGF). Adrenal medullary cells were isolated from 10-day-old rats and the proportions of surviving and neurite-extending cells were determined after 8 days in culture. In the presence of C6-CM virtually all seeded cells survived and 50% developed neuritic processes. In contrast, NGF did not support survival above control levels (30%) and induced neurite formation from approximately one-third of the surviving cells. C6-CM and NGF had no additive effects on neurite outgrowth. C6-CM-mediated fiber outgrowth was not inhibited by physiological concentrations of glucocorticoids which abolished the NGF-induced neurite formation. Both C6-CM and NGF increased the catecholamine content of the cultures and reduced the relative content of epinephrine. However, in view of its substantial effect on cell survival as compared to NGF, C6-CM caused a reduction of the catecholamine content per cell. We conclude that adrenal medullary cells, like other members of the sensory-sympathetic cell lineage of the neural crest, respond to glial-conditioned medium. This response differs both quantitatively and qualitatively from that mediated by NGF.

Phenotypic plasticity of cultured bovine chromaffin cells. II. Fiber outgrowth induced by elevated potassium: morphology and ionic requirements

Chromaffin cells isolated from the adult bovine adrenal medulla extend neurite-like processes in culture in response to a variety of agents. In the present study we investigated the effect of chronic depolarization by high potassium on fiber outgrowth and its ionic requirements. Elevated K+ in the culture medium induced process formation of isolated bovine chromaffin cells in a dose-dependent fashion, and so did veratridine. Short-term depolarization by acetylcholine or carbachol caused increased flattening out of the cells, but no outgrowth of neurite-like processes. Formation of processes was accompanied by a significant reduction of endogenous catecholamines in cultured cells after 18 h and 8 days and a relative shift towards storage of primary amines after 8 days. K+-induced fiber outgrowth was dependent on the presence of Ca2+ in the medium and Ca2+-influx into the cells: the effect was inhibited by EDTA, EGTA, CoCl2 and verapamil and mimicked by the Ca2+ ionophore A 23187. Tetrodotoxin, tetraethylammonium, amiloride and ouabain, which interfere with Na+- and K+-fluxes, did not inhibit K+-induced process formation nor did any of them by itself evoke fiber outgrowth. Fiber outgrowth required de novo protein synthesis as shown by the inhibitory effect of cycloheximide. K+-induced formation of processes was not affected by dexamethasone and dbcAMP, both of which inhibit NGF-induced neurite formation of early postnatal rat chromaffin cells in vitro. These results document that chronic depolarization may induce de novo formation of neurite-like processes of bovine chromaffin cells in vitro by a Ca2+- and protein synthesis-dependent mechanism.

Catecholaminergic innervation of the chicken ovary. With special reference to the follicular wall

The innervation of the chicken ovary was investigated with special emphasis on adrenergic nerves in the follicular wall. Quantitative determinations of catecholamines (CA) by high-performance liquid chromatography and electrochemical detection (hplc-ed) revealed 15.4 +/- 3.3 ng/mg protein of norepinephrine (NE) and 3.14 ng/mg protein of epinephrine (E), with even larger amounts in the cranial part of the ovary close to the adrenal gland. Serial sections that had been processed for the visualisation of aminergic nerves (Falck-Hillarp- or glyoxylic acid techniques) showed CA localized in nerve-fibre bundles; cell bodies of chromaffin and sympathetic neurons were only found at the ovarian-adrenal junction suggesting that ovarian nerves stored considerable quantities of E. An antiserum against bovine phenylethanolamine N-methyltransferase (PNMT, the E-synthesizing enzyme) produced no immunostaining in chicken ovary or adrenal gland, due to a lack of cross-reactivity between the antiserum and chicken PNMT. Serial sections processed alternately for the visualisation of aminergic nerves and myosin (from chicken gizzard) immunoreactivity revealed a scarce nerve supply of contractile cells in the theca externa compared to an extraordinarily dense innervation of the endocrine interstitial tissue of the theca interna. This distribution pattern of nerve fibres in the follicular wall was confirmed by electron microscopy in ovarian tissue that had been pretreated with 5- or 6-hydroxydopamine (HDA). More than 90% of the terminal axons were specifically labeled by these false adrenergic transmitters. Many of these terminals were seen in close contact (20 nm) with steroidogenic cells suggesting a neuromodulatory function of CA in hormone synthesis and/or release. It is yet unclear whether E and NE are stored in separate or identical axon moieties and within the same organelles. Choline acetyltransferase activity, which was taken as a measure for a cholinergic nerve component in the ovary, amounted to only 7% of its adrenal activity. It is suggested that the chicken ovary may serve as an excellent model to investigate the modulatory role of nerves in the endocrine function of the ovary.

Phenotypic plasticity of cultured bovine chromaffin cells. I. Morphological changes induced by non-chromaffin cells and organ extracts, but not by mouse and bovine nerve growth factor

Adult bovine chromaffin cells are known to show process outgrowth in culture, similar to that seen with rat chromaffin and pheochromocytoma cells after exposure to nerve growth factor (NGF). To determine whether bovine chromaffin cells respond to NGF or NGF-like factors, dissociated adrenal medullary cells from adult cattle were cultured for up to 4 weeks in the presence or absence of NGF (from mouse submaxillary glands and bovine seminal vesicles, respectively), adrenal non-chromaffin cells and various organ extracts. Chromaffin cells that had been freed from non-chromaffin cells by differential plating and/or gamma-irradiation showed virtually no fiber outgrowth. In the presence of adrenal non-chromaffin cells (NCC), cell-free extracts obtained from these cells or medium conditioned by them, chromaffin cells formed processes. Extracts from bovine seminal vesicles (SVE), but not from other organs including bovine brain, heart, liver, kidney, adrenal glands and male mouse submaxillary glands, also elicited fiber outgrowth. Extension of processes induced by NCC and SVE could not be blocked by administration of monospecific anti-NGF antibodies directed against NGF from mouse submaxillary glands. Purified NGF from mouse submaxillary glands and SVE did not elicited a response. We conclude that adult bovine chromaffin cells in culture show structural plasticity similar to that shown by cultured chromaffin cells from other species, but do not respond to NGF. Neurite outgrowth promoting activities appear to reside with macromolecular constituents of bovine adrenal non-chromaffin cells and SVE.

Evidence for the association of villin with core filaments and rootlets of intestinal epithelial microvilli

Villin, a 95,000 dalton polypeptide of intestinal brush border which is known to bundle or sever actin filaments in a Ca++-dependent manner, was localized in rat and chicken intestinal epithelium by means of immunocytochemistry at the light- and electron-microscopic levels. Specific antibodies to villin were raised in rabbits immunized with villin purified from chicken intestinal epithelium. Anti-villin bound selectively to the microvillus filament bundle from its tip down to the rootlets. These findings indicate that the well-known stability of rootlet filaments towards elevated Ca++ ion concentrations cannot be explained by the absence of villin. Therefore additional factors must exist which prevent the rootlets from Ca++-villin mediated disassembly.

Nerve growth factor requirement of postnatal rat adrenal medullary cells in vitro for survival, aggregate formation and maintenance of extended neurites

Rat adrenal medullary cells, taken at different postnatal stages (1, 4, 10 and 14 days), were cultured in serum-containing medium with and without nerve growth factor (NGF 2.5 S, 50 ng/ml) to investigate their dependence on NGF for survival and maintenance of extended neurites. It was found that medullary cells depend on NGF for survival at day 1 and, to a lesser extent, at day 4. Neurite-like processes extended in response to NGF treatment breakdown when NGF is withdrawn. NGF-treated adrenal medullary cells displayed a pronounced tendency to form aggregates. It was also shown that plating adrenal medullary cells at higher cell densities, which largely increased the numbers of fibroblast-like cells present, may substitute for NGF with respect to survival.

Distribution of nerve growth factor in the submandibular gland of the male and female mouse. A re-examination by use of an improved immunohistochemical procedure

Nerve growth factor (NGF) was localized in the mouse submandibular gland by means of indirect immunofluorescence applied to 0.5 micron-thick sections of freeze-dried, plastic-embedded tissue. The antibody to NGF (IgG-fraction) was raised in rabbits immunized with pure 2.5 S NGF from submandibular glands of adult male mice. In the male gland anti-NGF bound selectively to the secretory granules was present in the cells of the granular ducts. Immunoreactive granules extended from the perinuclear region toward the apical pole. In the female gland immunoreactive cells and granules were considerably less abundant than in males. Immunofluorescence was confined to individual secretory cells located in the wall of the granular striated duct. In the present study no support was found for the hypothesis suggesting that immunoreactive NGF is formed within the secretory granules during their transport from the perinuclear region to the apical pole.

Specific labeling of a phosphate-transporting protein from rat-liver mitochondria by [203Hg]mersalyl

1. A highly specific labeling of a phosphate-transporting protein from rat-liver mitochondria was obtained with [203Hg]mersalyl under the following conditions: (a) labeling of mitoplasts, isolated by the French-Press procedure; (b) washing of the isolated inner membranes with NaCl/octylglucoside. 2. The concentration-dependent labeling of the protein with mersalyl showed a biphasic saturation which correlated well with the protection and inhibition of phosphate transport. 3. The molecular weight (Mr 31000) and the amount of labeled carrier protein (24 nmol/g mitochondrial protein) at 100% protection correlated well with published data from the literature. 4. Gel filtration of the labeled protein in the presence of non-ionic detergents showed a molecular weight of at least twice of that obtained by gel electrophoresis in the presence of sodium dodecylsulfate.