Differential regulation of cholinergic and peptidergic development in the rat striatum in culture

Effect of acrylamide on cerebellar astrocyte proliferation in vitro

Cerebellar astrocyte cultures derived from 7-day-old rats were exposed to acrylamide. Acrylamide dose-dependently inhibited the proliferation of astrocytes, 50% inhibition occurring at about 0.52 mm. Acrylamide reduced [(3)H]thymidine incorporation into DNA, but did not affect it when cytosine arabinoside was present. The main cause of the inhibition of astrocyte proliferation may be the suppression of mitosis. Interleukin-1, one of the factors that produce astrocyte proliferation after brain injury, increased [(3)H]thymidine incorporation into DNA in astrocyte cultures. Acrylamide was found to abolish this proliferative effect of interleukin-1 completely. It is suggested that acrylamide may influence the astrocytic response to brain injury and the regenerative process.

Neurochemical and electrophysiological characteristics of rat striatal neurons in primary culture

Neurons maintained in dispersed primary culture offer a number of advantages as a model system and are particularly well-suited for studies of the intrinsic electrical properties of neurons by patch clamp. We have characterized the immunocytochemical and electrophysiological properties of cultured rat striatal neurons as they develop in vitro in order to compare this model system with the known properties found in vivo. We found a high abundance of cells in vitro corresponding to the principal striatal output neuron, the medium spiny neuron. Immunocytochemical studies indicate that these cells have both dopamine-1 and dopamine-2 receptors and that there is overlap in their expression within the population of neurons. Semiquantitative analysis revealed bimodal distributions of dopamine receptor expression among the population of neurons. The principal peptide neurotransmitters substance P and enkephalin were present but at reduced levels compared with adult preparations. Other striatal markers such as calbindin, calretinin, and the cannabinoid-1 receptor were abundant. An immunocytochemical survey of voltage-gated K(+) channel subunits characteristic of adult tissue demonstrated the presence in vitro of Kv1.1, Kv1.4, Kv4.2, Kv4.3, and Kvbeta1.1, which have been associated with the rapidly inactivating currents. Electrophysiological studies employing voltage clamp revealed that outward currents had a large inactivating (A-type) component characteristic of mature basal ganglia. Current clamp studies reveal complex spontaneous firing patterns in a subset of neurons, including bursting behaviors superimposed on a slow depolarization. The inward rectifying channels Kir2.1 and Kir2.3, which are specific to particular compartments in adult striatum, were present in culture.

Agonist stimulation provokes dendritic and axonal dopamine D(1) receptor redistribution in primary cultures of striatal neurons

To investigate the influence of neurotransmitter on G-protein-coupled receptor trafficking and compartimentalization in neurons, we have developed a model of primary neuronal cultures from fetal rat striatum on which we have studied the cellular and subcellular distribution and trafficking of the D(1) dopaminergic receptor. This receptor is known to be somatodendritic and axonal targeted in vivo, mostly to extrasynaptic locations. Immunohistochemical studies at the light and electron microscopic levels showed that, in cultures, the D(1) dopaminergic receptor is expressed in the absence of dopamine stimulation. The pattern of D(1) dopaminergic receptor immunostaining after stimulation by the D(1) dopaminergic receptor agonist SKF 82958 (1 microM) is dramatically modified with a decrease of the number of labeled D(1) dopaminergic receptor puncta (-40%) and an increase of their size in both dendrites (+120%) and axons (+240%). Seven hours after removal of the agonist, return to normal pattern was observed. The D(1) dopaminergic receptor antagonist SCH 23390 (2 microM) abolishes the effect of SKF 82958. Electron microscopy demonstrated, in dendrites, a translocation of the labeling from the plasma membrane to endosomes. Axonal D(1) dopaminergic receptor redistribution after acute stimulation indicates that the D(1) dopaminergic receptor is membrane targeted and responsive to stimulation. These results validate primary culture of striatal neurons to study subcellular localization and intraneuronal trafficking of G-protein-coupled receptors. This preparation will be useful to address various questions concerning the behavior and the trafficking of these receptors in neurons in relation to the neurotransmitter environment.

Autoradiographic study of striatal dopamine re-uptake sites and dopamine D1 and D2 receptors in a 6-hydroxydopamine and quinolinic acid double-lesion rat model of striatonigral degeneration (multiple system atrophy) and effects of embryonic ventral mesencephalic, striatal or co-grafts

The influence of embryonic mesencephalic, striatal and mesencephalic/striatal co-grafts on amphetamine- and apomorphine-induced rotation behaviour was assessed in a rat model of multiple system atrophy/striatonigral degeneration type using dopamine D1 ([3H]SCH23390) and D2 ([3H]spiperone) receptor and dopamine re-uptake ([3H]mazindol) autoradiography. Male Wistar rats subjected to a sequential unilateral 6-hydroxydopamine lesion of the medial forebrain bundle followed by a quinolinic acid lesion of the ipsilateral striatum were divided into four treatment groups, receiving either mesencephalic, striatal, mesencephalic/striatal co-grafts or sham grafts. Amphetamine- and apomorphine-induced rotation behaviour was recorded prior to and up to 10 weeks following transplantation. 6-Hydroxydopamine-lesioned animals showed ipsiversive amphetamine-induced and contraversive apomorphine-induced rotation behaviour. Amphetamine-induced rotation rates persisted after the subsequent quinolinic acid lesion, whereas rotation induced by apomorphine was decreased. In 11 of 14 animals receiving mesencephalic or mesencephalic/striatal co-grafts, amphetamine-induced rotation scores were decreased by >50% at the 10-week post-grafting time-point. In contrast, only one of 12 animals receiving non-mesencephalic (striatal or sham) grafts exhibited diminished rotation rates at this time-point. Apomorphine-induced rotation rates were significantly increased following transplantation of mesencephalic, striatal or sham grafts. The largest increase of apomorphine-induced rotation rates approaching post-6-hydroxydopamine levels were observed in animals with striatal grafts. In contrast, in the co-graft group, there was no significant increase of apomorphine-induced rotation compared to the post-quinolinic acid time-point. Morphometric analysis revealed a 63-74% reduction of striatal surface areas across the treatment groups. Striatal [3H]mazindol binding on the lesioned side (excluding the demarcated graft area) revealed a marked loss of dopamine re-uptake sites across all treatment groups, indicating missing graft-induced dopaminergic re-innervation of the host. In eight (73%) of the 11 animals with mesencephalic grafts and reduced amphetamine-induced circling, discrete areas of [3H]mazindol binding ("hot spots") were observed, indicating graft survival. Dopamine D1 and D2 receptor binding was preserved in the remaining lesioned striatum irrespective of treatment assignment, except for a significant reduction of D2 receptor binding in animals receiving mesencephalic grafts. "Hot spots" of dopamine D1 and D2 receptor binding were observed in 10 (83%) and nine (75%) of 12 animals receiving striatal grafts or co-grafts, consistent with survival of embryonic primordial striatum grafted into a severely denervated and lesioned striatum. Our study confirms that functional improvement may be obtained from embryonic neuronal grafts in a double-lesion rat model of multiple system atrophy/striatonigral degeneration type. Co-grafts appear to be required for reversal of both amphetamine- and apomorphine-induced rotation behaviour in this model. We propose that the partial reversal of amphetamine-induced rotation asymmetry in double-lesioned rats receiving mesencephalic or mesencephalic/striatal co-grafts reflects non-synaptic graft-derived dopamine release. The changes of apomorphine-induced rotation following transplantation are likely to reflect a complex interaction of graft- and host-derived striatal projection pathways and basal ganglia output nuclei. Further studies in a larger number of animals are required to determine whether morphological parameters and behavioural improvement in the neurotransplantation multiple system atrophy rat model correlate.

NMDA and non-NMDA receptor-mediated excitotoxicity are potentiated in cultured striatal neurons by prior chronic depolarization

The excitatory input from cortex and/or thalamus to striatum appears to promote the maturation of glutamate receptors on striatal neurons, but the mechanisms by which it does so have been uncertain. To explore the possibility that the excitatory input to striatum might influence glutamate receptor maturation on striatal neurons, at least in part, by its depolarizing effect on striatal neurons, we examined the influence of chronic KCl depolarization on the development of glutamate receptor-mediated excitotoxic vulnerability and glutamate receptors in cultured striatal neurons. Dissociated striatal neurons from E17 rat embryos were cultured for 2 weeks in Barrett's medium containing either low (3 mM) or high (25 mM) KCl. The vulnerability of these neurons to NMDA receptor agonists (NMDA and quinolinic acid), non-NMDA receptor agonists (AMPA and KA), and a metabotropic glutamate receptor agonist (trans-ACPD) was examined by monitoring cell loss 24 h after a 1-h agonist exposure. We found that high-KCl rearing potentiated the cell loss observed with 500 microM NMDA or 250 microM KA and yielded cell loss with 250 microM AMPA that was not evident under low KCl rearing. In contrast, neither QA up to 5 mM nor trans-ACPD had a significant toxic effect in either KCl group. ELISA revealed that chronic high KCl doubled the abundance of NMDA NR2A/B, AMPA GluR2/3, and KA GluR5-7 receptor subunits on cultured striatal neurons and more than doubled AMPA GluR1 and GluR4 subunits, but had no effect on NMDA NR1 subunit levels. These receptor changes may contribute to the potentiation of NMDA and non-NMDA receptor-mediated excitotoxicity shown by these neurons following chronic high-KCl rearing. Our studies suggest that membrane depolarization produced by corticostriatal and/or thalamostriatal innervation may be required for maturation of glutamate receptors on striatal neurons, and such maturation may be important for expression of NMDA and non-NMDA receptor-mediated excitotoxicity by striatal neurons. Striatal cultures raised under chronically depolarized conditions may, thus, provide a more appropriate culture model to study the role of NMDA or non-NMDA receptor subtypes in excitotoxicity in striatum.

GDNF induces the calretinin phenotype in cultures of embryonic striatal neurons

Glial cell line-derived neurotrophic factor (GDNF), a member of the transforming growth factor-beta (TGF-beta) superfamily, is a potent neurotrophic factor for several neuron populations in the central and peripheral nervous system. Members of the neurotrophin, neurokine, and TGF-beta families of growth factors can affect neurons beyond their capacity to promote survival. They can play instructive roles including the determination of a particular transmitter phenotype. Here, we show that GDNF enhances the number of calretinin (CaR)-positive neurons in serum-free cultures of striatal cells isolated from embryonic rats. The effect is dose-dependent, can be elicited with concentrations as low as 0.1 ng/ml, and is not accompanied by increased incorporation of 5-bromo-2'-desoxyuridine and appearance of glial fibrillary acidic protein-positive cells. Similar, but weaker effects can be elicited by brain-derived neurotrophic factor, neurotrophin-3 and -4, fibroblast growth factor-2. Ciliary neurotrophic factor, nerve growth factor, and TGF-beta 1 do not affect striatal CaR expression. GDNF can augment CaR-positive cells at any time point and with a minimal exposure of 18 hr, suggesting induction of the phenotype rather than increased survival. By reverse transcription polymerase chain reaction (RT-PCR), we show that GDNF is expressed in the E16 striatum and in cultures derived from this tissue. GDNF also protected striatal CaR-positive neurons against glutamate toxicity. We conclude that striatal GDNF, in addition to its retrograde trophic role for nigrostriatal dopaminergic neurons, may also act locally within the striatum (e.g., by inducing the CaR phenotype and protecting these cells against toxic insult).

An increase in intracellular levels of cyclic AMP produces trophic effects on striatal neurons developing in culture

Cyclic AMP-dependent kinases have been suggested to constitute signal transduction pathways involved in the regulation of neuronal development and survival. The present study examined whether elevated levels of cyclic AMP exhibit trophic activities on rat striatal neurons grown under serum-free culture conditions. Treatment with dibutyryl cyclic AMP, a permeable cyclic AMP, increased GABA uptake and immunocytochemically detectable levels of proteins such as c-Fos and calbindin-D28k. Neuronal survival was promoted by dibutyryl cyclic AMP only in lower density cultures. Chronic exposure of neurons to dibutyryl cyclic AMP enhanced the morphological development of calbindin-D28k-positive neurons. Furthermore, pretreatment with dibutyryl cyclic AMP afforded neuroprotection against N-methyl-D-aspartate-induced excitotoxicity. The dibutyryl cyclic AMP-induced trophic effects above were blocked by adenosine 3',5'-cyclic monophosphothioate, a specific inhibitor of cyclic AMP-dependent kinases. We also examined whether cyclic AMP is involved in trophic effects provided by membrane depolarization induced by high K+ and growth factors such as basic fibroblast growth factor and insulin-like growth factor-1. Depolarization, but not the growth factors, increased intracellular levels of cyclic AMP. Adenosine 3',5'-cyclic monophosphothioate diminished depolarization increases in GABA uptake, whereas it did not affect the trophic effect of the growth factors. Co-treatment with the growth factors and dibutyryl cyclic AMP produced additive effects on both increases in GABA uptake and neuroprotection against excitotoxicity. The present results indicate that cyclic AMP-dependent kinases play roles in mediating differentiation and survival of developing striatal neurons. Signalling pathways activated by either basic fibroblast growth factor or insulin-like growth factor-1 are independent of those involving cyclic AMP. In contrast, depolarization-induced trophic effects are mediated, at least in part, by cyclic AMP-dependent pathways. Protective actions of dibutyryl cyclic AMP against excitotoxic injury as well as the additive effects with the growth factors are of potential interest in the experimental therapy of acute or chronic neurodegenerative diseases.

Antioxidant treatment protects striatal neurons against excitotoxic insults

It has been suggested that oxidative stress plays an important role in mediating excitotoxic neuronal death. We have therefore investigated the protective effects of antioxidants against excitotoxic injury in the rat on striatal neurons both in vitro and in vivo. In the first part of the study, we determined whether two different types of antioxidants, the spin trapping agent, alpha-phenyl-tert-butyl nitrone and an inhibitor of lipid peroxidation, U-83836E, could protect cultured striatal neurons against either hypoglycemic injury or N-methyl-D-aspartate-induced excitotoxicity. Dopamine- and cyclic AMP-regulated phosphoprotein, which is enriched in medium-sized spiny neurons, was chosen as a marker for striatal neurons. alpha-Phenyl-t-butyl nitrone and U-83836E both significantly reduced cell death induced by these insults as indicated by an increased number of surviving dopamine- and cyclic AMP-regulated phospho-protein-positive neurons. The two antioxidants also promoted the survival of cultured striatal neurons grown at low cell density under serum-free culture conditions. In an in vivo experiment systemically administered alpha-phenyl-t-butyl nitrone exerted neuroprotective effects in the rat striatum following injection of the excitotoxin quinolinic acid. Apomorphine-induced rotation tests revealed that alpha-phenyl-t-butyl nitrone-treated animals were significantly less asymmetric in their motor behavior than control rats. Treatment with alpha-phenyl-t-butyl nitrone significantly reduced the size of the quinolinic acid-induced striatal lesions, as assessed by the degree of sparing of dopamine- and cyclic AMP-regulated phospho-protein-positive and nicotinamide adenine dinucleotide phosphate-diaphorase-positive neurons, and of microtubule-associated protein-2-immunorective areas. Furthermore, lesion-induced morphological changes in the substantia nigra pars reticulate, i.e. loss of dopamine- and cyclic AMP-regulated phosphoprotein-positive afferent fibers and atrophic changes due to transsynaptic degeneration, were also less extensive in the alpha-phenyl-t-butyl nitrone-treated animals. The results support the hypothesis that oxygen-free radicals contribute to excitotoxic neuronal injury. The in vivo cytoprotective effects of alpha-phenyl-t-butyl nitrone against striatal excitotoxic lesions suggest that antioxidants could be used as potential neuroprotective agents in Huntington's disease, which has been suggested to involve excitotoxicity.

Reciprocal influences of nigral cells and striatal patch neurons in dissociated co-cultures

Our previous work has shown that the functional efficacy of nigral tissue transplants into dopamine (DA)-depleted rats is increased when embryonic striatal tissue is included (Costantini et al.: Exp Neurol 127:219-231, 1994). To examine further the influence of striatal patch neurons in this regard, we employed co-cultures of dissociated nigral and striatal cells taken from embryos at different ages. Striatal patch neurons were labeled by in vivo bromodeoxyuridine (BrdU) on embryonic day (E)13 and E14. The percentage of striatal cells that were BrdU labeled was greater in E14 striatal cultures (51.0%) compared with E16 (33.9%) and E20 (3.5%) striatal cultures at 1 day in vitro (DIV). The proportion of surviving BrdU-labeled cells in striatal cultures decreased over time. The inclusion of E14 nigral cells attenuated this decline. Similarly, the number of dopaminergic [tyrosine hydroxylase (TH)-immunoreactive] neurons in pure nigral cultures decreased with time in vitro (8.2% at 1 DIV to 3.5% at 12-15 DIV). The inclusion of E14 striatal tissue increased the number of TH-immunoreactive neurons at all time points, whereas E16 and E20 striatal tissue was somewhat less effective. Thus, the survival of nigral DA neurons and striatal patch neurons in culture appears to be enhanced in the presence of the other. These reciprocal influences on neuronal survival may be relevant to the in vivo development of the nigrostriatal system as well as the enhanced function of cells in co-transplants.

Ethanol neurotoxicity in culture: selective loss of cholinergic neurons

Studies from our laboratory have shown that in ovo exposure of chick embryos to ethanol decreases neuronal survival in culture, and shifts neurotransmitter phenotypic from cholinergic to catecholaminergic and GABAergic. In this study we attempted to determine if the shift from cholinergic expression is a result of selective loss of cholinergic neurons. Neuron-enriched primary cultures were prepared from 3-day-old whole chick embryos. Cells proliferating during the first 3 days in culture were labeled with BrdU, and one half of the cultures were exposed to 50 mM ethanol during the same time period. Selective survival in vitro of the cholinergic, catecholaminergic. GABAergic, glutamatergic, and somatostatinergic phenotypes was determined by counting cells double-stained for BrdU and either ChAT, TH, GAD, Glu, or SRIF. We found that ethanol exposure resulted in a significant reduction in neuronal survival within the cholinergic phenotype, both in the total number of ChAT+ cells and in the subpopulation born between 0-3 DIV. In addition, survival of glutamatergic neurons "born" between 0-3 days in vitro was significantly enhanced, while survival in catecholaminergic, GABAergic, and somatostatinergic phenotypes was also enhanced slightly. These results corroborate our earlier biochemical findings and suggest that the differential cholinotoxic effect of ethanol is due, at least in part, to enhancement of cell-death of cholinergic neuroblasts. This does not preclude the possibility that multipotent neuroblasts are also influenced to express alternative phenotypes, and analyses of these data, in fact, support this notion as well.

Phenotypic characterisation of rat striatal neurones in primary culture

The aim of this study was to determine to what extent the neuronal phenotypes present in primary cultures of rat striatal neurones correspond to those present in vivo. A large percentage of cultured striatal neurones contained relatively high levels of proenkephalin mRNA. In addition, a high level of expression was found for the prosomatostatin mRNA. Protachykinin mRNA and proneuropeptide Y mRNA were also expressed, but at a comparatively low level. No prodynorphin mRNA could be detected. Considerable numbers of neurones were also found to express NADPH-diaphorase activity, while a smaller number of neurones were positive for acetylcholinesterase. The NADPH-diaphorase and the acetylcholinesterase could be detected both in cell bodies, and in neuronal processes contacting groups of neighbouring neurones. Since nitric oxide does not require synaptic specialisations to exert its intercellular actions, this provides strong evidence that NADPH-positive neurones communicate with other cells in primary culture. These observations demonstrate that when striatal neurones are grown in primary culture, a range of neurochemical phenotypes are present which correspond closely to those present in the mature striatum in vivo. Together with the evidence for cell-cell interactions, this suggests that primary striatal cultures will provide a suitable model to study the molecular mechanisms controlling striatal function.

Cytokine-induced programmed death of cultured sympathetic neurons

Programmed cell death (PCD) of sympathetic neurons is inhibited by nerve growth factor. However, factors that induce PCD of these cells are unknown. Leukemia inhibitory factor (LIF) and ciliary neurotrophic factor, neuropoietic cytokines known to regulate sympathetic neuron gene expression, were examined for effects on survival of cultured sympathetic neurons. Treatment with LIF or ciliary neurotrophic factor caused neuronal death in a dose-dependent fashion. Inhibition of RNA or protein synthesis, or treatment with potassium, all of which prevent PCD after nerve growth factor deprivation, prevented LIF-induced death. The morphologic and ultrastructural characteristics of the neuronal death induced by LIF and by nerve growth factor deprivation were similar. Furthermore, LIF treatment resulted in DNA fragmentation with a characteristic "ladder" on Southern blot analysis. These observations suggest that neuron numbers may be regulated by factors which initiate PCD, as well as by factors which prevent it.

Retrograde factors in peripheral nerves

The relationship between the neuron and its target is explored and the possible mechanisms for achieving correct connections are analysed. The most plausible mechanism is the presence of a retrograde intra-axonal message from the target to the neuronal cell body. The molecular form of the message and the mechanisms to achieve this signal transduction are discussed and it is proposed that there are two types of neurotrophic factors. One has a short-acting second messenger, itself incapable of surviving for the time required for transport to the cell body and thus requiring the transport of the message-generating complex to the cell body. The other has a long-lasting second messenger complex which is well able to survive the transport to the cell body so that there is no need for the transport of the neurotrophic factor itself. Thus all neurotrophic factors do not themselves require retrograde axonal transport and such non-transportable factors may generate intricate messages due to associations of signal transduction molecules via binding sites such as phosphorylated tyrosines and the src homology domain 2.

Differential effects of insulin on choline acetyltransferase and glutamic acid decarboxylase activities in neuron-rich striatal cultures

We studied the effects of insulin, nerve growth factor (NGF), and tetrodotoxin (TTX) on cellular metabolism and the activity of glutamic acid decarboxylase (GAD) and choline acetyltransferase (ChAT) in neuron-rich cultures prepared from embryonic day 15 rat striatum. Insulin (5 micrograms/ml) increased glucose utilization, protein synthesis, and GAD activity in cultures plated over a range of cell densities (2,800-8,400 cells/mm2). TTX reduced GAD activity; NGF had no effect on GAD activity. Insulin treatment reversibly reduced ChAT activity in cultures plated at densities of greater than 4,000 cells/mm2, and the extent of this reduction increased with increasing cell density. The number of acetylcholinesterase-positive neurons was not reduced by insulin, suggesting that insulin acts by down-regulating ChAT rather than by killing cholinergic neurons. Insulin-like growth factor-1 (IGF-1) reduced ChAT activity at concentrations 10-fold lower than insulin, suggesting that insulin's effect on ChAT may involve the IGF-1 receptor. NGF increased ChAT activity; TTX had no effect on ChAT activity. These results suggest that striatal cholinergic and GABAergic neurons are subject to differential trophic control.

Postnatal development of cholinergic neurons in the rat: I. Forebrain

The postnatal development of cholinergic projection and local-circuit neurons in the rat forebrain was examined by use of choline acetyltransferase (ChAT) immunohistochemistry and acetylcholinesterase (AChE) histochemistry. Although regional nuances were apparent, a general trend emerged in which cholinergic projection neurons in the basal nuclear complex (i.e., medial septal nucleus, vertical and horizontal diagonal band nuclei, magnocellular preoptic field, substantia innominata, nucleus basalis, and nucleus of the ansa lenticularis) demonstrated ChAT-like immunoreactivity earlier in postnatal development than intrinsically organized cholinergic cells in the caudate-putamen nucleus and nucleus accumbens, although this disparity was less apparent for local circuit neurons in the olfactory tubercle and Islands of Calleja complex. Ontologic gradients of enzyme expression also existed in some regions. A lateral to medial progression of ChAT and AChE appearance was observed as a function of increasing postnatal age in the nucleus accumbens and rostral caudate-putamen nucleus. By comparison, a rostrocaudal gradient of expression of ChAT-like immunoreactivity was apparent within the basal nuclear complex. Moderate to intense ChAT positivity, for example, appeared first in the medial septal nucleus. Furthermore, compared to more caudal regions, a greater proportion of AChE-positive neurons in rostral aspects of the basal forebrain expressed ChAT immunoreactivity on postnatal day 1, a difference that was no longer present by postnatal day 5. Cholinergic neurons in all forebrain regions also underwent an initial stage of progressive soma and proximal-dendrite hypertrophy, which peaked during the third postnatal week, followed by a period of cell-body and dendritic shrinkage that persisted into the fifth postnatal week when adult configurations were reached. These soma and dendritic size increases and decreases were not correlated with the magnitude of postnatal ChAT expression, which increased progressively until adult levels were attained approximately by the third to fifth weeks after birth. Expression of AChE in putative cholinergic neurons appeared to precede that of ChAT, especially in the caudate-putamen complex. Staining intensity of AChE also incremented earlier than that of ChAT.

Characterization of rat ARPP-21 mRNA: sequence analysis, tissue distribution, and regulation

ARPP-21 (cyclic AMP-regulated phosphoprotein; Mr = 21,000) is a cytosolic neuronal phosphoprotein that is highly enriched in the striatum and in other dopaminoceptive regions of the brain. The state of phosphorylation of ARPP-21 is also regulated by vasoactive intestinal peptide in intact cells. We previously reported the sequence analysis of bovine ARPP-21 cDNA and have now characterized rat ARPP-21 cDNA to study further the molecular biology of this protein. The sequence of the coding region is 82 and 85% identical at the nucleotide and amino acid levels, respectively, between the two species. There are two major classes of clones, differing only in the lengths of their 3' untranslated ends, suggesting that the different ARPP-21 mRNAs are derived from the use of alternate polyadenylation sites. Both major mRNA species, 2.6 and 0.7 kb, are present at the highest concentration in the striatum, followed by the cortex, consistent with previous immunocytochemical results. Southern blot analysis reveals a simple hybridization pattern, consistent with the presence of a single rat gene encoding ARPP-21. The steady-state levels of the ARPP-21 mRNAs are developmentally regulated but, in the neonatal and mature animal, are not altered following 6-hydroxydopamine lesions of the substantia nigra or by pharmacologic treatments that up-regulate the D1- or D2-dopamine receptors.

Transient expression of somatostatin messenger RNA and peptide in the hypoglossal nucleus of the neonatal rat

The postnatal developmental expression of somatostatin mRNA and peptide in the rat hypoglossal nucleus was analyzed using immunocytochemical and in situ hybridization techniques. Both the neuropeptide and its cognate mRNA were found to be transiently present within a subpopulation of hypoglossal motoneurons during the neonatal period. At the day of birth, a large population of perikarya situated in caudal, ventral regions of the hypoglossal nucleus expressed somatostatin. By postnatal day 7, the number of hypoglossal somata which expressed somatostatin had diminished considerably, and by 2 weeks postnatal, only few such cell bodies were found. By 3-4 weeks postnatal, somatostatin peptide- and mRNA-containing hypoglossal motoneurons were rarely observed, and in the adult, they were never detected, despite the use of colchicine. A double-labeling co-localization technique was used to demonstrate that somatostatin, when present perinatally, always coexisted with calcitonin gene-related peptide in hypoglossal motoneurons. The latter peptide, in contrast to somatostatin, was expressed in large numbers of somata throughout the entire hypoglossal nucleus and persisted within the motoneurons throughout development into adulthood. These results demonstrate that somatostatin is transiently expressed in motoneurons of the caudal, ventral tier of the hypoglossal nucleus in the neonatal rat. The developmental disappearance of somatostatin is most likely not due to cell death; hypoglossal somata continue to express calcitonin gene-related peptide, with which somatostatin coexisted perinatally, a high levels throughout development. Thus, it appears that the regulation of somatostatin expression in hypoglossal neurons occurs at the level of gene transcription or mRNA stability/degradation.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium-dependent regulation of the enkephalin phenotype by neuronal activity during early ontogeny

Genetic components of the neuronal phenotype are regulated by epigenetic factors--trophic molecules and neuronal activity--during neurodifferentiation. Developing neurons in dissociated cultures of embryonic mouse spinal cord show spontaneous electrical activity after one week in culture. We now report that the blockade of this spontaneous electrical activity for two days with tetrodotoxin (TTX) causes virtually complete down-regulation of preproenkephalin A gene transcripts in embryonic spinal cord cultures. This TTX-induced down-regulation is fully reversed upon reinitiation of neuronal activity (removal of TTX from cultures). This reversible, tetrodotoxin-induced down-regulation of enkephalin mRNA is confined to a restricted period of early neurodevelopment (days 7 to 21 in culture). Since depolarization triggers calcium entry through voltage-activated calcium channels, we have investigated the involvement of calcium in the mechanism of this activity- and age-dependent regulation of preproenkephalin A expression. The selective activation of the L-type of voltage-sensitive calcium channels by a dihydropyridine derivative [(+) 202-791] prevented this TTX-induced down-regulation without reducing methionine enkephalin secretion. This effect was observed only when the drug was applied to electrically active cultures, prior to the addition of TTX. Simultaneous application of (+) 202-791 and TTX, or pretreatment with TTX, failed to prevent TTX-induced down-regulation. Thus, activity-dependent phenotypic plasticity of met-enkephalinergic neurons in spinal cord is: 1) maximum at an early age of neuronal development (less than 10 days in culture) and becomes less apparent in old cultures (greater than 30 days); 2) reversible throughout; and 3) mediated by calcium entry through L-type channels.

Factors regulating the expression of acetylcholinesterase-containing neurons in striatal cultures: effects of chemical depolarization

The influence of chemical depolarization on the survival and differentiation of acetylcholinesterase (AChE)-containing neurons was examined in primary rat striatal cultures, maintained in different types of media (serum-free and serum-supplemented) and substrate (poly-ornithine and astrocyte monolayer). Chronic application of 5 microM veratridine resulted in a significant loss of neurites by AChE-positive cells, while a higher concentration (20 microM) reduced the number of stained cell bodies. These effects appeared to be selective with regard to AChE-positive cells, as indicated by morphological observations of the cells in the treated cultures and receptor binding measurements. Similarly, elevation of extracellular KCl levels (20-60 mM) produced a dose-dependent neurite loss by AChE-containing cells. Blockers of voltage-sensitive Ca2+ channels--verapamil (1 microM) and nifedipine (1 microM)--did not affect the veratridine-induced neurite loss, while tetrodotoxin (0.1 microM) had a partial effect. When cultures treated with 5 microM veratridine were allowed to recuperate for several days, the number of AChE-positive cells possessing neurites returned close to control values, thus indicating the reversibility of the effect of chemical depolarization. The possibility that chronic neuronal depolarization in the striatum might play a role in regulation of the neuronal processes outgrowth by AChE-containing cells is discussed.

Loss of striatal somatostatin neurons following prenatal methylazoxymethanol

Prenatal administration of methylazoxymethanol acetate (MAM), which kills neuroblasts undergoing mitosis, was used to lesion striatal somatostatin neurons. Previous [3H]thymidine autoradiographic studies had indicated that striatal somatostatin neurons undergo their final mitotic division at Gestational Days (G) 15 and 16. Therefore, pregnant Sprague-Dawley rats received an intraperitoneal injection of MAM (25 mg/kg) on G15. Neurochemical and histological examination of the mature offspring indicated the loss of half the striatal aspiny interneurons in which somatostatin, neuropeptide Y, and NADPH diaphorase coexist, with relative sparing of the cholinergic interneurons and medium spiny projection cells. This prenatal MAM treatment was without apparent effect on the patch-matrix organization of the striatum.

Characterization of opioid receptors in cultured neurons

The appearance of mu-, delta-, and kappa-opioid receptors was examined in primary cultures of embryonic rat brain. Membranes prepared from striatal, hippocampal, and hypothalamic neurons grown in dissociated cell culture each exhibited high-affinity opioid binding sites as determined by equilibrium binding of the universal opioid ligand (-)-[3H]bremazocine. The highest density of binding sites (per mg of protein) was found in membranes prepared from cultured striatal neurons (Bmax = 210 +/- 40 fmol/mg protein); this density is approximately two-thirds that of adult striatal membranes. By contrast, membranes of cultured cerebellar neurons and cultured astrocytes were devoid of opioid binding sites. The opioid receptor types expressed in cultured striatal neurons were characterized by equilibrium binding of highly selective radioligands. Scatchard analysis of binding of the mu-specific ligand [3H]D-Ala2,N-Me-Phe4,Gly-ol5-enkephalin to embryonic striatal cell membranes revealed an apparent single class of sites with an affinity (KD) of 0.4 +/- 0.1 nM and a density (Bmax) of 160 +/- 20 fmol/mg of protein. Specific binding of (-)-[3H]bremazocine under conditions in which mu- and delta-receptor binding was suppressed (kappa-receptor labeling conditions) occurred to an apparent single class of sites (KD = 2 +/- 1 nM; Bmax = 40 +/- 15 fmol/mg of protein). There was no detectable binding of the selective delta-ligand [3H]D-Pen2,D-Pen5-enkephalin. Thus, cultured striatal neurons expressed mu- and kappa-receptor sites at densities comparable to those found in vivo for embryonic rat brain, but not delta-receptors.

DARPP-32 development in the caudate nucleus is independent of afferent input from the substantia nigra

DARPP-32, a dopamine- and adenosine 3':5'-monophosphate regulated neuronal phosphoprotein, Mr 32 kDa, is a phenotypic marker of the medium-size spiny neurons of the mammalian caudate-putamen. In the present study, we examined the ontogeny of DARPP-32 protein and mRNA, and compared it to the ontogeny of tyrosine hydroxylase and synapsin I, a synaptic-vesicle phosphoprotein. In vivo, the amount of DARPP-32 protein per mg total protein increased throughout the first three postnatal weeks, and then declined to plateau at adult levels. The mRNA level closely paralleled the protein, except that its rise preceded that of the protein. Tyrosine hydroxylase levels rose throughout the first 4 postnatal weeks, and synapsin I levels rose steadily during the same period. Primary reaggregate cultures containing cells from the caudate-putamen expressed DARPP-32 with a time course similar to that seen in vivo. The level of expression was not altered by coculturing with dopaminergic neurons from the rostral mesencephalic tegmentum. Thus, the postnatal increase in DARPP-32 levels in the caudate-putamen appears to be independent of transsynaptic or end-organ influences from the substantia nigra.

Characterization and mechanism of glutamate neurotoxicity in primary striatal cultures

Excitatory amino acids may play a role in the pathogenesis of cell death in neurodegenerative diseases, including Huntington's disease (HD). In an attempt to develop a tissue culture model for HD, the toxicity of glutamate was examined in primary striatal cultures derived from newborn rats. Morphological criteria were used to determine the toxic effects of glutamate in 6-, 12-, and 18-day-old cultures which were examined before and after 1-3 h of exposure to glutamate. Although younger cultures demonstrated little susceptibility to glutamate relative to controls, the number of neurons in older cultures was significantly depleted in the presence of glutamate. Glutamate toxicity was dose-dependent, with an ED50 of approximately 300 microns glutamate, and a maximal effect was observed within 3 h of initial exposure. Affected neurons demonstrated somal swelling within 1 h of glutamate exposure and disruption of neuritic processes and somal integrity within 3 h. Cell death was significantly increased by raising the extracellular calcium concentration and could be decreased by the addition of magnesium to the incubation medium. Moreover, the N-methyl-D-aspartate (NMDA) receptor agonist, quinolinic acid, showed a toxicity profile similar to that of glutamate. The NMDA receptor competitive antagonist, 2-amino-5-phosphonovalerate (APV) significantly reduced toxicity, albeit incompletely. An additional component of glutamate mediated toxicity in striatal cultures could be explained by activation of non-NMDA receptor subtypes. These in vitro studies indicate that glutamate is toxic to a subset of mature striatal neurons in the absence of a glutamatergic afferent input, and that this toxicity is mediated partially by the NMDA receptor, with an additional component due to non-NMDA receptors.

Ontogeny of mu-, delta- and kappa-opioid receptors mediating inhibition of neurotransmitter release and adenylate cyclase activity in rat brain

The ontogeny was examined of functional opioid receptors mediating presynaptic inhibition of neurotransmitter release and inhibition of dopamine (DA)-sensitive adenylate cyclase in the rat brain, using highly selective agonists for mu-, delta- and kappa-receptors. On gestational day 17 (E17) strong inhibitory effects of the selective mu-agonist DAGO on the electrically evoked release of [3H]noradrenaline from cortical slices and of the selective kappa-agonist U-50,488 on the electrically evoked release of [3H]DA from striatal slices were found. Electrically evoked release of [3H]acetylcholine from striatal slices was not detectable before postnatal day 7 (P7), but on that day it was already strongly inhibited by the selective delta-agonist DPDPE. Although mu- and delta-opioid receptors coupled to DA-sensitive adenylate cyclase in the striatum are likely to be physically associated in an opioid receptor complex in the adult, they were found to develop asynchronously. Whereas selective activation of mu-receptors with DAGO resulted in an inhibition of D1 dopamine receptor-stimulated adenylate cyclase activity on E17, activation of delta-receptors with DPDPE was not effective until P14. This study confirms the early appearance of mu- and kappa-opioid receptors and the relatively late development of delta-opioid receptors in the rat brain. Most importantly, it shows that in an early stage of development opioids are already able to mediate modulation of noradrenergic (via activation of mu-receptors) and dopaminergic (via activation of mu- and kappa-receptors) neurotransmission processes. Therefore, these opioid receptor types could play a role in brain development and/or developmental disturbances.

Regulation of cholinergic expression in cultured spinal cord neurons

Factors regulating development of cholinergic spinal neurons were examined in cultures of dissociated embryonic rat spinal cord. Levels of choline acetyltransferase (CAT) activity in freshly dissociated cells decreased rapidly, remained low for the first week in culture, and then increased. The decrease in enzyme activity was partially prevented by increased cell density or by treatment with spinal cord membranes. CAT activity was also stimulated by treatment with MANS, a molecule solubilized from spinal cord membranes. The effects of MANS were greatest in low-density cultures and in freshly plated cells, suggesting that the molecule may substitute for the effects of elevated density and cell-cell contact. CAT activity in ventral (motor neuron-enriched) spinal cord cultures was similarly regulated by elevated density or treatment with MANS, whereas enzyme activity was largely unchanged in mediodorsal (autonomic neuron-enriched) cultures under these conditions. These observations suggest that development of cholinergic motor neurons and autonomic neurons are not regulated by the same factors. Treatment of ventral spinal cord cultures with MANS did not increase the number of cholinergic neurons detected by immunocytochemistry with a monoclonal CAT antibody, suggesting that MANS did not increase motor neuron survival but rather stimulated levels of CAT activity per neuron. These observations indicate that development of motor neurons can be regulated by cell-cell contact and that the MANS factor may mediate the stimulatory effects of cell-cell contact on cholinergic expression.

M1 muscarinic acetylcholine receptor in cultured rat neostriatum regulates phosphoinositide hydrolysis

Muscarinic acetylcholine receptor expression and function in cultured rat neostriatal neurons were examined. All experiments were performed on intact neurons grown in vitro for 12-14 days. The muscarinic antagonist N-[3H]methylscopolamine [( 3H]NMS) binds to a single site in cultures with a KD of 89 pM and a Bmax of 187 fmol/mg of protein, or 32,000 sites/neuron. Competition studies using [3H]NMS were performed to determine what receptor subtypes were present. Nonlinear analysis of competition curves was best described with a single binding site for atropine, pirenzepine, and AF-DX 116 (11-[[2-[(diethylamino)-methyl]-1-piperidinyl]acetyl]-5,11-dihydro- 6H-pyrido[2,3-b][1,4]benzodiazepine-6-one), with Ki values of 0.6, 62, and 758 nM, respectively. These results indicate that the muscarinic receptors present in neostriatal cultures are of the M1 subtype, having high affinity for pirenzepine and low affinity for AF-DX 116. In contrast with antagonists, carbachol displaced [3H]NMS from two sites with Ki values of 6.5 and 147 microM, with the higher-affinity form predominant (83% of sites). The M1 receptor subtype was linked to phosphoinositide turnover. Carbachol stimulated the formation of phosphoinositides with an EC50 of 37 microM and was antagonized by atropine. At equimolar doses, pirenzepine was more potent than AF-DX 116 at antagonizing the response.

Synaptic potentials in the rat neostriatum in dissociated embryonic cell culture

Neostriatal cells of embryonic days 19-21 were grown in dissociated cell culture. To test whether the cultures contained predominantly neostriatal cells, a glyoxylic acid staining procedure was used which, after dopamine loading, stained neostriatal cells but not neurons of embryonic neocortical tissue. Whole cell current clamp recording was performed in the neurons after 1-2 weeks in cell culture. Although cells could be driven to discharge by direct depolarization, spontaneous activity was low. All cells responded to gamma-aminobutyric acid (GABA) (0.1-0.5 mM), and the majority of them responded to glutamate (Glu) (0.1 mM). Only about 50% were depolarized by acetylcholine (ACh) (0.1-0.5 mM). Atropine (1-10 microM) did not block this depolarization. Barrages of postsynaptic potentials (PSPs) were induced by applications of Glu or ACh, even if the neuron under observation was not depolarized. All PSPs were depressed by bicuculline (50 microM), indicating their mediation by GABAergic receptors. Exclusively GABAergic PSPs were also observed in cultures raised in the presence of nerve growth factor. The study indicates that neostriatal cells form GABAergic, but not excitatory cholinergic synapses when cultured at this embryonic age under our conditions, resembling the pattern of development observed in slices obtained from neonatal rats.

The development of cholinergic neurons

Motoneuron precursors acquire some principles of their spatial organization early in their cell lineage, probably at the blastula stage. A predisposition to the cholinergic phenotype in motoneurons and some neural crest cells is detectable at the gastrula to neurula stages. Cholinergic expression is evident upon cessation of cell division. Cholinergic neurons can synthesize ACh during their migration and release ACh from their growth cones prior to target contact or synapse formation. Neurons of different cell lineages can express the cholinergic phenotype, suggesting the importance of secondary induction. Early cholinergic commitment can be modified or reversed until later in development when it is amplified during interaction with target. Motoneurons extend their axons and actively sort out in response to local environmental cues to make highly specific connections with appropriate muscles. The essential elements of the matching mechanism are not species-specific. A certain degree of topographic matching is present throughout the nervous system. In dissociated cell culture, most topographic specificity is lost due to disruption of local environmental cues. Functional cholinergic transmission occurs within minutes of contact between the growth cone and a receptive target. These early contacts contain a few clear vesicles but lack typical ultrastructural specializations and are physiologically immature. An initial stabilization of the nerve terminal with a postsynaptic AChR cluster is not prevented by blocking ACh synthesis, electrical activity, or ACh receptors, but AChR clusters are not induced by non-cholinergic neurons. After initial synaptic contact, there is increasing deposition of presynaptic active zones and synaptic vesicles, extracellular basal lamina and AChE, and postjunctional ridges over a period of days to weeks. There is a concomitant increase in m.e.p.p. frequency, mean quantal content, metabolic stabilization of AChRs, and maturation of single channel properties. At the onset of synaptic transmission, cell death begins to reduce the innervating population of neurons by about half over a period of several days. If target tissue is removed, almost all neurons die. If competing neurons are removed or additional target is provided, cell death is reduced in the remaining population. Pre- or postsynaptic blockade of neuromuscular transmission postpones cell death until function returns.(ABSTRACT TRUNCATED AT 400 WORDS)

Insulin-like growth factor II in the rat choroid plexus

In situ hybridization histochemistry has been used to demonstrate the expression of the mRNA for insulin-like growth factor II (IGF-II) in the adult rat choroid plexus. IGF-II mRNA was found in the choroid plexus cells by using two different probes specific for different parts of IGF-II sequence. Parallel studies on consecutive sections showed that message for a choroid plexus marker transthyretin mRNA was also localized in the same choroid plexus cells.

The expression of gamma-aminobutyric acid and Leu-enkephalin immunoreactivity in primary monolayer cultures of rat striatum

Primary monolayer cultures of rat striatum were examined for gamma-aminobutyric acid (GABA) and leucine-enkephalin (L-ENK) immunoreactivity. Cultures were established on polycation-treated glass coverslips from the striata of gestational day 17 rat embryos using a serum and insulin-supplemented medium. The proportion of GABA-immunoreactive (GABA-IR) neurons increased during the first week in vitro from approximately one third to nearly one half and remained relatively constant thereafter. On the other hand, the proportion of L-ENK-IR neurons increased gradually over the culturing period, increasing from about one-fifth of the neurons initially to one-half after 3-4 weeks in vitro. The changes in the proportions of GABA- and L-ENK-IR neurons appeared to be largely a consequence of the death of non-immunoreactive neurons, not delayed expression or induction of GABA or L-ENK traits. Light microscopic analysis of somatic-proximal neuritic morphology led to a partitioning of the neuronal population into 4 groups. GABA- and L-ENK-IR groups were heterogeneous in this regard and differed only modestly.

A novel way of removing quiescent astrocytes in a culture of subcortical neurons grown in a chemically defined medium

A new method has been described for removing a very small number of contaminating astrocytes in neuronal cultures (derived from the septal-diagonal band region of 17-day-old embryonic rat brain) grown in a chemically defined medium. The proportion of these glial fibrillary acidic protein (GFAP)-positive cells was usually less than 1.5% up to 10 days, but thereafter their number increased rapidly reaching 10-15% by 22 days in vitro. A prolonged exposure to normally used concentration of cytosine arabinoside (Ara-C; 10 microM) was toxic to both astroglial and neuronal cells, while a brief treatment (48 h) with a low level (4 microM) of Ara-C failed to eliminate these astrocytes, as judged by glutamine synthetase activity and GFAP-positive cell count. However, these quiescent astroglial cells could be easily eliminated if they were induced to proliferate by epidermal growth factor before exposure to Ara-C. The combined treatment with these agents had no effect on the number of acetylcholinesterase-positive cells, and on the development of cholinergic and GABA-ergic neurons, as measured in terms of choline acetyltransferase and glutamate decarboxylase activity, respectively.

The influence of neuronal cells on the development of glutamine synthetase in astrocytes in vitro

The influence of neurons on the development of astroglial cells was examined in vitro using glutamine synthetase (GS) activity as an index of metabolic maturation. The GS activity in forebrain astrocytes was significantly increased (about 70%) when they were co-cultured with forebrain neuronal cells. A similar effect was also observed when astrocytes from the immature septum, hippocampus or cerebellum were co-cultured with neurons derived from the septal-diagonal band region. The magnitude of the effect was not uniform; the cerebellar astrocytes, with relatively low GS activity, showed a greater (about 290%) quantitative response to the subcortical nerve cells than did the septal (about 115%) or the hippocampal (about 120%) astroglial cells. The addition of conditioned medium derived from neuronal cultures or plating the cells on a substratum of heat-killed nerve cells, elevated the GS activity of astroglial cells by 33% and 39%, respectively. Our results indicate that a trophic factor secreted by neurons and direct contact with the nerve cell matrix, are both involved in the regulation of the differentiation of astrocytes.

Effect of depolarization on the maturation of cerebellar granule cells in culture

The effect of depolarization on the maturation of granule cells derived from cerebella of 8-day-old rats can be studied in cultures in chemically defined media because their survival is not dependent on elevated K+ as it is when they are grown in serum-containing media. As an index of maturation, stimulus-coupled transmitter release was examined. This was chosen because it is closely associated with the neuronal phenotype and, in contrast to granule cells grown under depolarizing conditions in serum-containing media, it has not been known whether this property is expressed during the development of serum-free cells in culture. Veratrine-induced release of preloaded D-[3H]aspartate (Asp), an analogue of glutamate (Glu; the transmitter of the granule cells), was not detectable in the serum-free cells at a time (8-12 days in vitro) when this property was fully developed in cells grown in a medium containing serum and 25 mM K+ (reference cultures). This finding may be related to the failure of the expression of voltage-sensitive calcium channels in the serum-free granule cells. However, in comparison with reference cultures, voltage-sensitive 45Ca2+ entry was only transiently retarded in the serum-free cells. Furthermore, in contrast to the exogenous D-[3H]Asp, stimulated release of endogenous Glu was detectable, although it was substantially lower than in the reference cultures. Autoradiographic studies indicated that the failure to elicit evoked release of the exogenous amino acid was due to a severe retardation of the expression of the acidic amino acid carrier in the serum-free granule cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholinergic neurons in cultures derived from three-, six- or eight-day-old chick embryo: a biochemical and immunocytochemical study

Cultures were prepared by dissociating 3-day-old whole chick embryos, or 6- or 8-day-old chick embryo cerebral hemispheres. The dispersed cells were plated onto poly-L-lysine coated dishes in Dulbecco's modified Eagle's medium fortified with 10% fetal bovine calf serum. Immunocytochemistry, histochemistry and biochemistry were used to characterize the cholinergic neurons in these cultures. Double staining for acetylcholinesterase (AChE) and neurofilament revealed that a high percentage of neurons also contained AChE; fewer neurons though were positive for choline acetyltransferase (ChAT). The presence of AChE in non-cholinergic neurons was interpreted to be indicative of 'cholinoceptive' neurons in culture. The developmental profile for ChAT activity in cultures derived from 3-day-old whole chick embryos was previously described; we have reported that activity reached high levels by 7 days in culture. In this study we found that in cultures derived from 6-day-old chick embryos ChAT activity increased slowly up to 6 days in culture and rose markedly thereafter; in contrast, in cultures derived from 8-day-old chick embryos activity was low until day 9 and rose moderately thereafter. The differences in ChAT expression between cultures derived from chick embryos of different developmental stages may reflect a loss of plasticity of the cholinergic population with age.

Solubilization of a membrane factor that stimulates levels of substance P and choline acetyltransferase in sympathetic neurons

The choice of which neurotransmitters will be produced by a developing neuron is influenced by the microenvironment of the neuron. In this study we show that neuronal contact with membrane-associated molecules promotes expression of peptidergic and cholinergic traits. Treatment of cultured neonatal rat sympathetic neurons with plasma membranes derived from adult rat spinal cord or sympathetic ganglia induced expression of the peptide transmitter substance P and increased levels of the cholinergic biosynthetic enzyme choline acetyltransferase. The transmitter-stimulating activity could be solubilized from spinal cord membranes by the detergent octyl glucoside but not by Triton X-100. The choline acetyltransferase- and substance P-stimulating activity also could be extracted from spinal cord membranes by 4 M sodium chloride, suggesting that the active material is membrane associated rather than an intrinsic structural membrane molecule. Trypsin or heat treatment of the extract destroyed the transmitter-stimulating activity, indicating that the factor contains a protein. Activity also was destroyed by hyaluronidase treatment, suggesting that the active material may contain a glycosaminoglycan. The choline acetyltransferase-stimulating activity in the 4 M NaCl extract was eluted in a single peak from a calibrated Sephadex G-75 column with a retention time slightly less than that of a 25-kDa standard. NaDodSO4/polyacrylamide gel electrophoresis of the active peak revealed a predominant band at 29 kDa. Thus, contact-mediated stimulation of substance P and choline acetyltransferase activity in sympathetic neurons results from neuronal exposure to a 29-kDa membrane-associated factor.

An interaction between thyroid hormone and nerve growth factor in the regulation of choline acetyltransferase activity in neuronal cultures, derived from the septal-diagonal band region of the embryonic rat brain

Culture conditions have been established for growing neurons from the medial frontal part of the forebrain, containing the septum and the diagonal band of Broca, of 17-day-old rat embryos in a chemically defined medium. At 10 days in vitro, the cultures contained more than 96% nerve cells of which about 18% were cholinergic neurons, while the proportion of astrocytes was less than 1%. The majority of the cells that stained for acetylcholinesterase were bipolar but with different sizes and shapes. During development both the specific activity of choline acetyltransferase (ChAT) and the amount of protein increased markedly in the cholinergic cultures, ChAT activity rising much more than the protein content. Exposure of the cultures to nerve growth factor (NGF) or 3,3',5-triiodo-L-thyronine (T3) enhanced the expression of ChAT activity in a dose-dependent manner. The elevation of ChAT activity was due to an increase in the amount of enzyme per cholinergic cell, since, during the experimental period studied, neither treatment with NGF nor with T3 had significant effects on the total protein content of the cultures or on the number of cells, including the cholinergic neurons. When cultures were supplemented with both agents at maximal effective concentrations, the stimulation in ChAT activity was much greater than the sum of the individual effects. The observations indicate that subcortical cholinergic neurons, which are affected in Alzheimer's disease and in Down's syndrome, are subject to regulation by an interaction between thyroid hormone and local humoral factors such as NGF.

Insulin stimulates choline acetyltransferase activity in cultured embryonic chicken retina neurons

The effect of insulin on the appearance of the enzyme choline acetyltransferase (ChoAcT; acetyl-CoA:choline O-acetyltransferase, EC 2.3.1.6) in embryonic chicken retina neurons cultured in defined medium was studied. In the presence of a minimal level of insulin (1 ng/ml), ChoAcT activity increased with time in culture. A correspondence between the insulin concentration in the defined medium (1-100 ng/ml) and both the rate of increase and maximum attained level of ChoAcT activity was observed. Maximal ChoAcT activity was 2- to 3-fold greater in cells cultured in the presence of 100 ng of insulin per ml than in cells cultured in the presence of 1 ng of insulin per ml. To elicit maximum ChoAcT activity, insulin at 100 ng/ml was required in the medium for only the first 4 days of the culture period, at which time insulin could be reduced to maintenance levels (10 ng/ml) without affecting ChoAcT activity. Insulin binding assays performed during a 7-day culture period revealed that irrespective of the insulin concentration in the medium during culture, cell-surface insulin receptors decreased by approximately 90% between 4 and 7 days in culture. This decrease in insulin binding corresponded to the observed decrease in the sensitivity of ChoAcT activity to insulin. Our findings suggest that insulin plays a role in mediating cholinergic differentiation in the embryonic chicken retina.

Ontogeny of glutamic acid decarboxylase, tyrosine hydroxylase, choline acetyltransferase, somatostatin and substance P in monkey cerebellum

The enzyme activities of glutamic acid decarboxylase (GAD), tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) and concentrations of substance P (SP) and somatostatin were determined in the cerebellum of macaque monkey (Macaca fuscata fuscata) at 3 different ages, embryonic 4 months, embryonic 5.5 months (full-term) and adult. Similar graded increases in the activities of GAD and TH were observed during development. In contrast, ChAT activity was relatively high at embryonic 4 months, increased about twofold between embryonic 4 months and 5.5 months, but did not change between embryonic 5.5 months and adult. These findings suggest that noradrenergic terminals develop synchronously with GABAergic interneurons. On the other hand, the innervation by ChAT-containing fibers is completed during the prenatal period. The concentrations of somatostatin and SP were high at embryonic 4 months, and decreased to, respectively, about 1/18 and 1/4 (expressed per g weight) in adult animals. Several interpretations of the decrease of the two neuropeptides in cerebellar tissue during ontogeny are discussed.

Deficiency of a cholinergic differentiating factor in fibroblasts of patients with Alzheimer's disease

Skin fibroblasts from patients with Alzheimer's disease and from apparently normal control subjects were compared for their production of a cholinergic differentiating factor. The factor's activity was assayed by measuring the induction of choline acetyltransferase (CAT) activity in cultured sympathetic neurons. Culture medium conditioned by exposure to normal human fibroblasts induced substantial levels of CAT activity in sympathetic neurons, indicating that human fibroblasts produce a soluble factor that promotes cholinergic expression. In contrast, medium conditioned by Alzheimer fibroblasts induced only about one-third as much CAT activity, a highly significant reduction (p less than 0.01). These observations suggest that Alzheimer fibroblasts may be deficient in their secretion of a cholinergic factor and raise the possibility that the pathophysiology of the disease is related to a defect in the release of this factor. The fibroblast abnormalities suggest that Alzheimer's disease may be a systemic disease involving nonneuronal cells that are outside as well as within the brain.

Isolated plasma membranes regulate neurotransmitter expression and facilitate effects of a soluble brain cholinergic factor

The choice of which transmitter will be expressed by a neuron is influenced by diffusible differentiating factors produced by a variety of nonneuronal cells. In this study we show that human, bovine, and rat brains contain a soluble heparin-binding factor that stimulates cholinergic and peptidergic expression. We also show that neuronal contact with other cell membranes influences neurotransmitter development and acts synergistically with the effects of the soluble brain factor. Exposure of cultured sympathetic neurons to purified plasma membranes derived either from cultured Schwann cells or from cultured sympathetic neurons promoted expression of choline acetyltransferase (CAT), a cholinergic trait, and of substance P (SP). CAT activity and SP were also stimulated by a 50-kDa soluble protein that was purified 14,000-fold from human, calf, and rat brain by heparin-Sepharose affinity chromatography. CAT activity after concurrent treatment with plasma membranes and the soluble factor far exceeded the sum of the enzyme activities after the individual treatments, suggesting that membrane molecules and the factor facilitated each other. Thus, cell-surface molecules, which have been shown previously to influence neuronal morphogenesis and neurite elongation, may also help determine the transmitter phenotype of the neuron. Moreover, cell-surface molecules may modulate the effects of diffusible differentiating factors.