Serum-free medium for cultures of the postnatal mouse cerebellum: only insulin is essential

PVN pathways controlling energy homeostasis

Research into the control of energy balance has tended to focus on discrete brain regions, such as the brainstem, medulla, arcuate nucleus of the hypothalamus, and neocortex. Recently, a larger picture has begun to emerge in which the coordinated communication between these areas is proving to be critical to appropriate regulation of metabolism. By serving as a center for such communication, the paraventricular nucleus of the hypothalamus (PVH) is perhaps the most important brain nucleus regulating the physiological response to energetic challenges. Here we review recent advances in the understanding of the circuitry and function of the PVH.

Developmental programming of energy balance and its hypothalamic regulation

Developmental programming is an important physiological process that allows different phenotypes to originate from a single genotype. Through plasticity in early life, the developing organism can adopt a phenotype (within the limits of its genetic background) that is best suited to its expected environment. In humans, together with the relative irreversibility of the phenomenon, the low predictive value of the fetal environment for later conditions in affluent countries makes it a potential contributor to the obesity epidemic of recent decades. Here, we review the current evidence for developmental programming of energy balance. For a proper understanding of the subject, knowledge about energy balance is indispensable. Therefore, we first present an overview of the major hypothalamic routes through which energy balance is regulated and their ontogeny. With this background, we then turn to the available evidence for programming of energy balance by the early nutritional environment, in both man and rodent models. A wealth of studies suggest that energy balance can indeed be permanently affected by the early-life environment. However, the direction of the effects of programming appears to vary considerably, both between and within different animal models. Because of these inconsistencies, a comprehensive picture is still elusive. More standardization between studies seems essential to reach veritable conclusions about the role of developmental programming in adult energy balance and obesity.

Peripheral nerve endoneurial microangiopathy and necrosis in rats with insulinoma

Peripheral nerve pathology related to chronic hyperinsulinemia and hypoglycemia has yet to be fully explored. Here we conducted a systematic quantitative analysis of morphological alterations in peripheral sensory and motor nerve fibers and endoneurial microvasculature in longstanding insulinoma-carrying rats (I-rats; n=12). Age-matched normal rats (n=6) served as controls. Over the 15-month observation period, two of I-rats developed paresis of the hind limbs when their blood glucose level fell below 1.7 mmol/l. These animals showed a massive myelinated fiber loss associated with active degeneration of residual myelinated fibers and multiple endoneurial microvascular occlusions at the sciatic nerve level. The rest of the non-paretic I-rats showed a decreased density of large myelinated fibers with axonal degeneration in the peroneal nerve and an increased density of small myelinated fibers with preserved morphology in the sural nerve. This was associated with endoneurial microangiopathic changes indicative of endoneurial ischemia/hypoxia in the sciatic and peroneal nerves, and an increase in endoneurial microvascular density in the sciatic and sural nerves. In conjunction with previous data, these findings suggest that the observed increase in endoneurial microvascular density may be a compensatory response to endoneurial ischemia/hypoxia induced by chronic hyperinsulinemia in I-rats without paresis. In conclusion, the present study showed characteristic morphological alterations in peripheral sensory and motor nerve fibers associated with microangiopathy indicative of endoneurial ischemia/hypoxia in the sciatic and peroneal nerves, and provides the first evidence for the occurrence of endoneurial necrosis in the sciatic nerve, to which the hind limb paresis can be ascribed in I-rats.

Neuronal necrosis inhibition by insulin through protein kinase C activation

In the serum-free culture of rat embryonic neurons, most neurons rapidly died by necrosis, which was revealed by propidium iodide (PI)-positive staining as early as 3 h after the start of culture and by marked membrane disruption and mitochondrial swelling in transmission electron microscopic (TEM) analysis. However, neither nuclear condensation/fragmentation stained with Hoechst 33342 nor activated caspase-3-like immunoreactivity was observed. In the serum-deprived culture, on the other hand, neurons showed apoptotic features, such as caspase-3 activation and nuclear damages in TEM analysis. Insulin at relatively higher concentrations, up to 100 microg/ml, ameliorated the rapid decrease in survival activity measured with 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt WST-8 assay and PI staining in the serum-free culture, despite the fact that brain-derived neurotrophic factor and insulin-like growth factor-I had no survival effect even at concentrations up to 100 microg/ml. Insulin-induced survival effects were abolished by the protein kinase C (PKC) inhibitor calphostin C but not by the phosphatidyl inositol-3-OH-kinase inhibitor wortmannin or the mitogen-activated protein kinase inhibitors PD98059 or U0126. Insulin significantly stimulated the PKC activity in cell lysates and suppressed the mitochondrial swelling and membrane disruption in TEM analysis in a calphostin C-reversible manner. All of these findings suggest that insulin inhibited the neuronal necrosis resistant to known neurotrophic factors under the serum-free culture through PKC mechanisms.

Rapid method for culturing embryonic neuron-glial cell cocultures

A streamlined, simple technique for primary cell culture from E17 rat tissue is presented. In an attempt to standardize culturing methods for all neuronal cell types in the embryo, we evaluated a commercial medium without serum and used similar times for trypsinization and tested different surfaces for plating. In 1 day, using one method and a single medium, it is possible to produce robust E17 cultures of dorsal root ganglia (DRG), cerebellum, and enteric plexi. Allowing the endogenous glial cells to repopulate the cultures saves time compared with existing techniques, in which glial cells are added to cultures first treated with antimitotic agents. It also ensures that all the cells present in vivo will be present in the culture. Myelination commences after approximately 2 weeks in culture for dissociated DRG and 3-4 weeks in cerebellar cultures. In enteric cultures, glial wrapping of the enteric neurons is seen after 3 weeks (2 weeks in ascorbic acid), suggesting that basal lamina production is important even for glial ensheathment in the enteric nervous system. No overgrowth of fibroblasts or other nonneuronal cells was noted in any cultures, and myelination of the peripheral nervous system and central nervous system cultures was very robust.

Increased sensitivity to N-methyl-D-aspartate receptor-induced excitotoxicity in cerebellar granule cells from interleukin-1 receptor type I-deficient mice

The effects of chronic exposure to excitatory amino acids (EAAs) were examined in cultured cerebellar granule cells (CGCs) from wild type (WT) and interleukin-1 receptor type I (IL-1RI)-deficient mice. After 8 days in culture, the cells were exposed to 100 microM glutamate or 300 microM N-methyl-D-aspartate (NMDA) for 24 h. Analysis of cell viability, as assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay and phase-contrast microscopy revealed that CGCs from IL-1RI-deficient mice were more vulnerable to EAAs as compared to the WT controls. The results indicate that IL-1RI signalling is important for neuronal survival. The effect of glutamate on the CGCs from IL-1RI-deficient mice was decreased by the non-competitive NMDA-receptor antagonist MK-801, supporting the involvement of NMDA receptors in the glutamate-induced excitotoxicity.

Excessive hexosamines block the neuroprotective effect of insulin and induce apoptosis in retinal neurons

In addition to microvascular abnormalities, neuronal apoptosis occurs early in diabetic retinopathy, but the mechanism is unknown. Insulin may act as a neurotrophic factor in the retina via the phosphoinositide 3-kinase/Akt pathway. Excessive glucose flux through the hexosamine biosynthetic pathway (HBP) is implicated in the development of insulin resistance in peripheral tissues and diabetic complications such as nephropathy. We tested whether increased glucose flux through the HBP perturbs insulin action and induces apoptosis in retinal neuronal cells. Exposure of R28 cells, a model of retinal neurons, to 20 mm glucose for 24 h attenuated the ability of 10 nm insulin to rescue them from serum deprivation-induced apoptosis and to phosphorylate Akt compared with 5 mm glucose. Glucosamine not only impaired the neuroprotective effect of insulin but also induced apoptosis in R28 cells in a dose-dependent fashion. UDP-N-acetylhexosamines (UDP-HexNAc), end products of the HBP, were increased approximately 2- and 15-fold after a 24-h incubation in 20 mm glucose and 1.5 mm glucosamine, respectively. Azaserine, a glutamine:fructose-6-phosphate amidotransferase inhibitor, reversed the effect of 20 mm glucose, but not that of 1.5 mm glucosamine, on attenuation of the ability of insulin to promote cell survival and phosphorylate Akt as well as accumulation of UDP-HexNAc. Glucosamine also impaired insulin receptor processing in a dose-dependent manner but did not decrease ATP content. By contrast, in L6 muscle cells, glucosamine impaired insulin receptor processing but did not induce apoptosis. These results suggest that the excessive glucose flux through the HBP may direct retinal neurons to undergo apoptosis in a bimodal fashion; i.e. via perturbation of the neuroprotective effect of insulin mediated by Akt and via induction of apoptosis possibly by altered glycosylation of proteins. The HBP may be involved in retinal neurodegeneration in diabetes.

Insulin rescues retinal neurons from apoptosis by a phosphatidylinositol 3-kinase/Akt-mediated mechanism that reduces the activation of caspase-3

The ability of insulin to protect neurons from apoptosis was examined in differentiated R28 cells, a neural cell line derived from the neonatal rat retina. Apoptosis was induced by serum deprivation, and the number of pyknotic cells was counted. p53 and Akt were examined by immunoblotting after serum deprivation and insulin treatment, and caspase-3 activation was examined by immunocytochemistry. Serum deprivation for 24 h caused approximately 20% of R28 cells to undergo apoptosis, detected by both pyknosis and activation of caspase-3. 10 nm insulin maximally reduced the amount of apoptosis with a similar potency as 1.3 nm (10 ng/ml) insulin-like growth factor 1, which acted as a positive control. Insulin induced serine phosphorylation of Akt, through the phosphatidylinositol (PI) 3-kinase pathway. Inhibition of PI 3-kinase with wortmannin or LY294002 blocked the ability of insulin to rescue the cells from apoptosis. SN50, a peptide inhibitor of NF-kappaB nuclear translocation, blocked the rescue effect of insulin, but neither insulin or serum deprivation induced phosphorylation of IkappaB. These results suggest that insulin is a survival factor for retinal neurons by activating the PI 3-kinase/Akt pathway and by reducing caspase-3 activation. The rescue effect of insulin does not appear to be mediated by NF-kappaB or p53. These data suggest that insulin provides trophic support for retinal neurons through a PI 3-kinase/Akt-dependent pathway.

Activation of glycogen synthase kinase 3 beta (GSK-3beta) by platelet activating factor mediates migration and cell death in cerebellar granule neurons

Children with vertically acquired HIV-1 can present with a rapidly progressive encephalopathy and neuronal apoptosis in the first 12-18 months of life. Furthermore, abnormal prenatal platelet activating factor (PAF) signalling may result in lissencephaly, a disorder of neuronal migration. PAF, produced from human immunodeficiency virus type 1 (HIV-1) -infected brain-resident macrophages, induces neuronal apoptosis in cultured cerebellar granule neurons (CGNs) in part by activating glycogen synthase kinase 3 beta (GSK-3beta). However, PAF can also inhibit migration of CGNs that are dispersed and allowed to reaggregate. Therefore, we investigated the biological effects following activation of GSK-3beta by PAF, and whether these effects were dependent on the culture conditions of the CGNs. We show here that activation of neuronal GSK-3beta by PAF is receptor-specific, with similar kinetics of activation in both monolayer cultures of CGNs that have ceased to migrate and reaggregate cultures of CGNs that are actively migrating. However, PAF receptor activation in reaggregated CGNs inhibits neuronal migration and induces approximately half the level of neuronal apoptosis compared with PAF-treated CGN cultures that have ceased to migrate. PAF-mediated inhibition of neuronal migration in reaggregated CGNs or induction of apoptosis in CGNs that have ceased to migrate can be reversed by either PAF receptor antagonists, or the GSK-3beta inhibitors lithium or valproic acid, in a dose-dependent manner. Abnormal PAF signalling that results in GSK-3beta overactivation may represent a common mechanism for pathological defects in neuronal migration in the prenatal period and neuronal apoptosis in the postnatal period.

Neuroprotective actions of dipyridamole on cultured CNS neurons

We report that dipyridamole is neuroprotective for a variety of rat embryonic CNS neurons cultured in serum-free basal medium lacking trophic factors or other additives. We also describe the mechanism underlying this action. Neurons died rapidly in basal medium but were rescued in large measure by 10 microM dipyridamole. The protective action of dipyridamole seems to be attributable to its antioxidant property. Vitamin E and N-acetylcysteine provided comparable neuroprotection in basal medium, whereas an array of compounds that mimic other actions of dipyridamole (inhibition of phosphodiesterases, blockade of nucleoside and chloride transport, interference with the multidrug resistance protein, and enhancement of prostacyclin synthesis) failed to promote survival. Thus, a major cause of neuronal death in this system seems to be oxidative stress that is relieved by dipyridamole. Iron plays a significant role in generation of such stress, as indicated by the observations that addition of apotransferrin or iron chelators to basal medium or use of iron-free medium also afforded protection. Although oxidative stress was a major determinant of neuronal death, it was not the only factor. Dipyridamole or other antioxidant measures did not provide sustained neuroprotection. However, provision of insulin, which was not protective alone in basal medium, along with dipyridamole significantly enhanced long-term neuronal survival. Hence, optimal protection requires both trophic support and relief from oxidative stress. These findings lend credence to the potential use of dipyridamole or its derivatives in prevention and/or treatment of CNS injuries and degenerative disorders in which oxidative stress is a significant component.

Transient induction of apoptosis in serum-starved glioma cells by insulin and IGF-1

Insulin has a wide variety of biological effects. One of them is a mitogen-like activity whereby cell proliferation is stimulated. In this study we found a heretofore unreported insulin-elicited transient apoptosis of glioma cells. When serum-starved glioma cells were fed with a fresh regular medium, in the 6- to 12-h post-starvation period, the growth rate as determined by cell number was significantly suppressed by insulin, although cell cycle progression and DNA synthesis were actually accelerated. Increase in apoptosis in those growth-retarded cultures was demonstrable by Hoechst staining, detection of histone-associated DNA fragment, and in situ cell death detection. Apoptosis occurred among cells in all stages of cell cycle. After 24 h post-starvation, insulin increased the total cell number like a typical growth-promoting mitogen. In this regard, IGF-1, but not EGF nor TGF-beta 1, behaved like insulin.

A teratocarcinoma-derived neurotrophic activity

In a search for nerve growth factor (NGF) in tissue extracts of a murine transplantable teratocarcinoma that harbours immature neural tissue in abundance, a trypsin-sensitive and heat labile neurotrophic activity was identified. The final protein fraction obtained by cation exchange chromatography contained five proteins with mol. wts ranging from 52 to 72 kD. It supported the growth and differentiation of immature neurones in neonatal rat cerebellar cultures but had no effect on embryonic chick dorsal root ganglia which are the classical targets for NGF.

An in vitro model to study diabetic neuropathy

Adult dorsal root ganglion (DRG) neurons from diabetic and normal C57BL mice were cultured and compared for survival and neurite extension. Neurons from diabetic mice have improved their survival and neurite extension when the insulin concentration was increased but it was never as good as that of controls. The increase of glucose concentration in serum-free media to ten times higher than normal improved both survival and neurite extension of neurons from diabetic animals.

The role of taurine in the survival and function of cerebellar cells in cultures of early postnatal cat

The role of taurine and beta-alanine was analyzed in kitten cerebellar cultures. Since in contrast to mouse, cats (and primates including man) cannot synthesize sufficient taurine to maintain their body pools, we considered the cat an ideal species for the analysis of the role of taurine during early postnatal cerebellar development under controlled conditions. Unexpectedly, we found that the presence of taurine was toxic to neurons but that compounds, considered to be competitors for the beta-amino acid uptake system, support cell survival and cell function in vitro, the opposite of the results found in mice. This could be explained by the finding that only minute amounts of [3H]taurine were taken up by both cat neurons and glial cells under optimal culture conditions but that in the presence of the taurine analogues beta-alanine and guanidinoethane sulfonic acid (GES) significant amounts of taurine were found in all cell types. These differences between mouse cerebellar cells and cat cerebellar cells in vitro suggest that a re-evaluation of the mechanisms that control taurine function in cats and primates is warranted.

Identification of an insulin-like factor in astrocyte conditioned medium

Survival of dissociated 19-day fetal rat telencephalic neurons in a hormone-free defined medium required the addition of insulin at pharmacological concentrations. However, survival of astrocytes cultured from the cerebral cortex of newborn rats in the same medium did not require insulin. When fetal neurons were incubated with astrocyte conditioned medium or plated on a monolayer of astrocytes, their survival was significantly increased in the absence of insulin. This effect of astrocyte conditioned medium was visibly inhibited by affinity chromatography on an anti-insulin protein A agarose column. A 5-30 kDa ultrafiltration fraction of astrocyte conditioned medium also increased neuronal survival. In addition, the 5-30 kDa fraction stimulated [3H]leucine incorporation into the TCA insoluble material from cultured neurons and competed for [125I]insulin binding to intact neuronal cultures. These results indicate that cultured astrocytes produce a factor with biological and immunological properties similar to those of insulin. This factor may in part mediate the observed neurotrophic effects of astrocyte conditioned medium and may play a role in the normal development and differentiation of central nervous system neurons.

Insulin and insulinlike growth factor receptors regulating neurite formation in cultured human neuroblastoma cells

The functional role of brain insulin and insulinlike growth factor (IGF) receptors is being sought. Recently it has been found that these ligands are members of a newly identified family of neuritogenic polypeptides. We studied the relationship between 125I-insulin and 125I-IGF binding and their capacity to enhance neurite formation in cultured human neuroblastoma SH-SY5Y cells. The binding of 125I-insulin was temperature-dependent and heterogeneous. The Scatchard plot and dissociation rate were both consistent with the presence of two types of sites. There appeared to be about 900 high affinity sites per cell with a Kd of about 3 nM. This compared favorably with the half-maximal concentration of 4 nM for enhancement of neurite formation. The type I IGF sites were also present. Physiologic concentrations of insulin clearly enhanced neurite formation through the insulin sites, whereas physiologic concentrations of IGF-I and IGF-II enhanced through the IGF sites. Cross-occupancy of sites was observed at supraphysiologic concentrations, providing a reasonable explanation for the broad dose-response curves for these ligands. These results support the suggestion that one function of insulin and IGF receptors in neural tissues may be to modulate neurite formation.

The cellular neurobiology of neuronal development: the cerebellar granule cell

Cerebellar granule cells in vivo and in vitro have been widely used in the study of the cellular neurobiology of neuronal development. We have described the basic neuroanatomical data on the granule cell in the developing and mature cerebellum. The importance of the cytoskeleton in determining the morphology of the granule cell and in process outgrowth and cell migration has been described. Extensive information is now available on the composition of the granule cell cytoskeleton. Cell surface glycoproteins are thought to be involved in the control of cell adhesion and cellular interactions during development. A number of surface molecules belonging to either the N-CAM or the Ng-CAM groups of glycoproteins have been studied in detail in the cerebellum. The role of these proteins in cell adhesion and in granule cell-astroglial interactions during granule cell migration has been reviewed. The survival and differentiation of neurones is controlled by soluble trophic factors. Several factors have been described which act as trophic factors for granule cells in vitro and may do the same in vivo. The numerous studies that have been carried out on the cerebellar granule cell have allowed us to describe certain aspects of the cellular neurobiology of this class of neurones as an example with general significance for the understanding of neuronal differentiation and function.

Synapse formation and development of neurotransmitter functions in neuronal cells from chick brain cultured in a serum-free, defined medium

Cells dissociated from cerebral hemispheres of 8-day-old chick embryos were seeded on poly-L-lysine coated Petri dishes in serum-containing medium. After 24 hr the culture medium was switched to a serum-free, chemically defined medium. These cultures contain mainly neuronal cells until day 14, characterized by the presence of acetylcholinesterase activity and neurofilament proteins. After 2 weeks glial cells progressively contaminated the neuronal culture. Cultures were maintained for a period of 4 weeks. From day 6 on numerous synapses with clear vesicles were observed. The activity of choline acetyltransferase remained low throughout the culture period, while GABA levels increased in parallel with synaptogenesis. Our observations indicate that chick cerebral hemisphere neuronal cultures grown in serum-free, chemically defined medium contain GABAergic neurons that undergo maturation.

Brain development in relation to fetal weight and maternal glucose tolerance during normal gestation

Parameters of brain development were studied in near term guinea-pigs in relation to fetal weight and maternal glucose tolerance during normal gestation. Seven litters (22 fetuses) were studied. Fetal weight ranged from 43 to 94 g (119% variability) and the maternal glucose index (sum of the 7 serum glucose levels during the oral glucose tolerance tests) from 921 to 1,528 mg/dl (66% variability). The weights of the cerebrum and cerebellum were less affected by changes of fetal weight compared to other fetal organs. Significant correlations were observed between the maternal glucose index and brain cell number (DNA) and myelination (cerebroside-sulfatide). These variables did not correlate with fetal weight. Liver weight (% fetal weight) and cell number also correlated with the maternal glucose index. It is speculated that the amount of glucose available to the brain could be responsible for the relative protection of the brain to fetal malnutrition and also for the link between maternal glucose index and parameters of fetal brain development.

Tissue culture analysis of neurite outgrowth in the presence and absence of serum: possible relevance for central nervous system regeneration

A tissue culture model has been developed to examine the hypothesis that axons can only regenerate when their growing tips are surrounded by extracellular fluid containing proteins derived from the blood. Fetal rat cerebral explants were cultured in serum medium for 10 days, followed by serum-free (SF) medium (from which serum had been removed) until 18 days in vitro (DIV). All explants cultured in serum medium for 0-10 DIV exhibited greater than 77% neurite viability (neurite viability ratio, NVR, 3.10). This degree of neurite viability was maintained for those explants exposed to serum until 18 DIV (NVR 2.82 at 18 DIV). By contrast, explants maintained in SF medium from 10-18 DIV had a much lower NVR, which, by 18 DIV, had declined to 0.30 (7.5% viability). Transmission electron microscopic analysis of explants fixed at 18 DIV confirmed these phase-contrast results and also showed a predominance of axonal profiles within the neurite population. In the center of explants, tissue viability was in excess of 75% in both the serum and SF media, suggesting that serum is of primary importance for axonal extension rather than neuronal survival. These data strengthen the hypothesis that blood-derived proteins may be needed for prolonged regeneration.

Dependence of food intake on acute and chronic ventricular administration of insulin

Several lines of evidences indicate that insulin affords short- and long-term neuroendocrine signals to modulate ingestive behavior. To further study a possible role of insulin in the control of food intake, male Wistar rats were subjected to various intra-third cerebro-ventricular applications of saline and insulin. Infusion of 2.0 mIU/rat of insulin at 1100 and 1900 decreased food intake in a 23.5 hr test period. Infusion of 0.5 mIU/rat of insulin between 1100 and 1200 decreased nighttime food intake during the 1st and 2nd days. Infusion of 2.0 mIU/rat/24 hr of insulin from osmotic minipumps decreased nighttime food intake throughout the active pump period and the effect persisted into the post-pump period. The results support the notion that insulin is involved in the regulation of food intake in the rat.

Effect of insulin, proinsulin and pancreatic extract on myelination and remyelination in organotypic nerve tissue in culture

The effect of insulin, proinsulin and crude pancreatic extract was studied in organotypic nerve tissue cultures, principally in relation to the development of myelin. Cultures were exposed to media supplemented with these substances beginning on the first day of explantation. By 4 days in vitro, there was a good neuritic outgrowth from all the fragments. That from the insulin and pancreatic extract-fed were more profuse and extended further than from the control group. By 8-12 days in vitro it was also possible to observe more myelinated axons in these treated groups. The pattern of changes in the myelin associated enzyme activity, 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNPase) paralleled the differential increase in myelination. Insulin-fed cultures showed a more rapid increase in CNPase activity, which, after 21 days in vitro reached a plateau about 30-50% over that of the controls. Cultures treated with pancreatic extract showed a similar pattern of increased activity, while in proinsulin-treated explants the activity was only significantly higher after 21 days in vitro. To study the effect of these substances on remyelination, well myelinated cultures were completely demyelinated by exposure to anti-white matter antiserum and were subsequently exposed to the same normal control or supplemented media. The amount of myelin and concomitantly the CNPase activity increased rapidly and in the same proportion between the various groups as was observed previously during primary myelination. Insulin as well as crude pancreatic extract and, to some extent, proinsulin demonstrated a marked effect on the time of onset and principally on the total amount of myelin developed by treated cultures as compared to those maintained in normal nutrient medium.

Light and electron microscopic analysis of insulin binding sites on neurons in dissociated brain cell cultures

The distribution of insulin binding sites on primary cultured neurons and glia from the fetal rat was examined by the immunoperoxidase method using a specific insulin receptor antiserum. Light and electron microscopic analysis revealed a homogenous distribution of insulin binding sites on selective neuron-like cells of the dissociated cell culture system. To determine the influence of medium insulin on the distribution of insulin binding sites, dissociated cell cultures were maintained in the presence or absence of porcine insulin for varying time periods. We observed a significant increase in the number of insulin stained neuron-like cells maintained in insulin free defined medium compared to neuron-like cells maintained in insulin supplemented defined medium. Further, we examined the distribution of insulin binding sites after incubation with the antibody, which has agonistic properties in peripheral tissues, for varying time periods prior to fixation. Under these conditions, the light microscopic analysis revealed a heterogeneous (patchy) distribution of immunoreactive insulin binding sites, suggesting that the ligand receptor complex migrates. These results demonstrate the presence and distribution of insulin binding sites on neurons maintained in vitro, and provide morphological evidence to support a functional role for insulin in CNS tissues.

Growth and myelination of explant cultures in defined medium

The purpose of this study was to compare the development of organotypic cultures in defined medium versus nutrient containing serum and embryo extract (EE). Explant cultures of cerebellum with or without locus ceruleus were grown in the Maximow system and monitored in the living state and with histological stains. Thinner explants, fibronectin and a more frequent feeding schedule were required to overcome the growth differences encountered using a defined medium. The final medium formulation was arrived at by evaluation of living cultures and consisted of a basal medium (Dulbecco's minimal essential medium), a number of hormones and other supplements, and a final glucose concentration of 750 mg%. Using a Golgi stain and histofluorescence, it was shown that the three major types of neurons - Purkinje, deep nuclear, and locus ceruleus - developed similarly in the defined medium and in serum-EE cultures. Myelination occurred in virtually all cerebellar cultures in defined medium and the onset was earlier than in serum-EE cultures. These results indicate that differentiation of oligodendroglia and maturation of neurons occur in a defined medium. Elimination of thyroid hormone delayed the maturation of the cultures, both neurons and myelin, by 3-4 days.

Gliotoxic effects of alpha-aminoadipic acid on monolayer cultures of dissociated postnatal mouse cerebellum

The cytotoxic effects of DL-, D- and L-alpha-aminoadipic acid, a six-carbon homologue of glutamate, were investigated in cell cultures of dissociated postnatal mouse cerebellum. Treatment with alpha-aminoadipic acid resulted in rapid nuclear and cytoplasmic swelling and, after longer periods of exposure, karyopyknosis of astrocytes, identified by indirect immunofluorescence labelling with anti-human glial fibrillary acidic protein antiserum. The number of astrocytes with pyknotic nuclei depended on the concentration of alpha-aminoadipic acid as well as on the duration of drug action. The presence of 0.21 mM DL-alpha-aminoadipic acid or 0.10 mM L-alpha-aminoadipic acid for 40 h caused karyopyknosis in 50% of the astrocytes. In contrast, D-alpha-aminoadipic acid, had little gliotoxic activity. None of the cytotoxic effects of DL-alpha-aminoadipic acid or L-alpha-aminoadipic acid observed for astrocytes were seen for the neurons present in the cultures when the drug was added after 4 days in vitro. Neurotoxic effects were evident, however, when alpha-aminoadipic acid was included in the culture medium at plating. These results indicate that alpha-adminoadpic acid can be used to substantially reduce the number of astroglia in cerebellar cultures and that dissociated cell cultures will provide a useful model with which to study the mechanisms of alpha-aminoadipic acid induced glial toxicity.

Cerebellar macroneurons in serum-free cultures: evidence for intrinsic neuronotrophic and neuronotoxic activities

Cerebellar macroneurones survive and differentiate for at least 10 days in Eagle's minimum essential medium with insulin as the only supplement when cultured either as microexplants or in high-density dissociated cultures, while they do not survive if cultured in low density. The survival is related to the extracellular release of neuronotrophic factor(s). Using a quantitative bioassay of the neuronotrophic effect, it is possible to demonstrate that the effect is concentration dependent. The analysis of the dose-response curves suggests that the neuronotrophic activity is associated with a neuronotoxic activity. The two activities can be segregated using a simple physical method, allowing direct demonstration of the neuronotoxic activity.