Rat brain cells in primary culture: visualization and measurement of catecholamines

Erythropoietin and erythropoietin receptor in the developing human central nervous system

We have previously shown the presence of erythropoietin (Epo) within the spinal fluid of normal preterm and term infants, and the presence of Epo receptor (Epo-R) in the spinal cords of human fetuses. It is not known, however: 1) whether cells within the fetal central nervous system (CNS) express Epo; 2) if so, whether this expression changes with development; 3) which cells within the CNS express Epo-R; 4) whether Epo-R expression within the CNS changes with development; and 5) whether Epo-R within the fetal CNS are functional. Expression of mRNA for Epo and Epo-R was sought by reverse transcription-PCR in mixed primary cultures of fetal spinal cords as well as NT2 and hNT cells, human cell lines of neuronal precursors and mature neurons, respectively. Epo was measured by ELISA in spent media from primary cell culture, and immunohistochemistry was used to identify Epo-R on neurons and glia in cell culture, and in brain sections. Developmental changes in Epo and Epo-R expression were sought in spinal cords and brains from fetuses of 7-24 wk postconception by semiquantitative PCR. To assess Epo-R function, NT2 cells were exposed to conditions which stimulate programmed cell death, and rescue from apoptosis by the addition of recombinant Epo was evaluated by nuclear matrix protein ELISA, cell counts, and by Klenow labeling of DNA fragments. Epo and Epo-R mRNA were expressed in mixed primary cultures of neural tissues and NT2 and hNT cells. Epo was detected by ELISA in media removed from mixed cell cultures, and immunohistochemical staining confirmed the presence of Epo-R on neurons and their supporting cells. Semiquantitative PCR revealed no significant change in expression of either Epo or Epo-R in spinal cords between 7 and 16 wk of gestation, with increased expression of Epo and Epo-R in brains from 8 to 24 wk of gestation. Epo mRNA expression from neurons doubled under conditions of hypoxia. Recombinant Epo decreased apoptotic cell death of neurons under conditions of hypoxia. Protein and mRNA for Epo and its receptor are expressed by human neurons and glial cells in spinal cord and brain during fetal development. These receptors appear to have a neuroprotective effect in conditions of hypoxia.

Increased agonist and antagonist sensitivity of N-methyl-D-aspartate stimulated calcium flux in cultured neurons following chronic ethanol exposure

Cortical cultures of rat brain neurons were exposed to ethanol (100 mM) for 4 days in order to examine whether the pharmacological characteristics of N-methyl-D-aspartate (NMDA) receptors expressed by these neurons were altered by this treatment. In fura-2 loaded control neurons, NMDA (plus 10 microM glycine) stimulated a dose-dependent increase in intracellular calcium concentrations with an estimated EC50 value of 6.8 microM. NMDA-stimulated increases in intracellular calcium reached a plateau at approximately 30 microM with no further increases observed at 100 microM. The EC50 value for NMDA in ethanol-exposed neurons was reduced to 1.8 microM with no alteration in the maximal response. Similarly, the EC50 value for glycine (tested with 100 microM NMDA) was reduced from 2.3 microM in control cultures to 0.67 microM in ethanol-treated cultures. Ifenprodil inhibited NMDA-stimulated increases in intracellular calcium in control cultures only at concentrations of 3 microM and above, with 100 microM producing approximately a 58% inhibition. In ethanol-treated cultures, 0.3 microM ifenprodil inhibited the NMDA response by approximately 60% with 100 microM ifenprodil producing a 72% inhibition. Over the concentration range of ifenprodil tested, half-maximal inhibition occurred at 1.4 microM and 0.18 microM, respectively, for control and ethanol-treated neurons. Although chronic ethanol treatment appeared to alter the sensitivity of neurons to NMDA agonists and antagonists, the inhibitory effects of 50 mM ethanol on NMDA-stimulated increases in intracellular calcium were not different between control (28% inhibition) and ethanol-treated neurons (27% inhibition). Finally, the changes in NMDA receptor sensitivity observed in ethanol-treated neurons were accompanied by an enhanced sensitivity to the neurotoxic effects of NMDA as measured by propidium iodide staining. These results suggest that chronic exposure of neurons to ethanol may result in an altered expression of agonist-sensitive/ifenprodil selective NMDA receptor subunits.

Differential effects of nitric oxide gas and nitric oxide donors on depolarization-induced release of [3H]norepinephrine from rat hippocampal slices

The NO-generating compounds sodium nitroprusside (NP), nitroglycerin (NTG), and isosorbide dinitrate (ISDN) all significantly inhibited N-methyl-D-aspartate (NMDA)-stimulated release of tritiated norepinephrine ([3H]NA) from preloaded hippocampal slices of adult male Sprague-Dawley rats with IC50's of 114 microM, 1.2 mM, and 1.7 mM respectively. NTG and ISDN also inhibited KCl-stimulated release, while NP had no significant effect on KCl-stimulated release. Although these results suggest that the inhibitory effects of these compounds were mediated by release of NO, NTG and ISDN did not generate detectable levels of NO, and iron-cyanide complexes similar in structure to NP but lacking NO also inhibited release. In contrast, both S-nitroso-N-acetyl-D,L-penicillamine (SNAP) and authentic NO gas significantly enhanced NMDA-stimulated release of [3H]NA (EC50's: 331 and 3.4 microM respectively). This enhancement was not selective for NMDA-stimulated release, since both SNAP and NO potentiated KCl-stimulated release as well. In addition, NO gas significantly enhanced NMDA-stimulated release of tritiated dopamine ([3H]DA) from striatal slices and [3H]NA from cortical and cerebellar slices. Analogs of cyclic guanosine monophosphate (cGMP) had no significant effect on NMDA-stimulated transmitter release, suggesting that the observed increase in release is via a cGMP-independent mechanism. While exogenous NO enhanced both NMDA- and KCl-stimulated neurotransmitter release, it appears that endogenous NO does not play a role in this depolarization-induced release since NO synthase inhibitors did not significantly reduce NMDA-stimulated [3H]NA release. The possibility remains that endogenous NO could modulate neurotransmitter release in other circumstances.

Functional changes in cocultures of mesencephalon and striatal neurons from embryonic C57/BL6 mice due to low concentrations of 1-methyl-4-phenylpyridinium (MPP+)

1-Methyl-4-phenylpyridinium (MPP+), the active metabolite of 1-Methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP) is taken up into dopaminergic terminals and selectively destroys dopaminergic neurons, serving as a valuable tool in animal model of Parkinson's disease. Cocultures from ventral mesencephalon and neostriatum of embryonic C57/BL6 mouse brains were used to study the sensitivity of dopaminergic neurons to the toxic agent MPP+. Cultures were grown for 9 days in vitro and exposed to different concentrations of MPP+ for various times. Treatment with (0.1-1.0 microM) MPP+ for 24 hours decreased 3H-dopamine (3H-DA) uptake with an IC50 at 0.2 microM. Exposure of cells to 1 microM MPP+ over time decreased the 3H-DA uptake to 38% of controls within the first two hours of incubation and to 8% after 48 hours. Loss of tyrosine hydroxylase (TH) positive cells became evident at 0.1 microM MPP+ (80% of control) leading to maximal toxicity at 10 microM (20% of control). MPP+ reduced the dopamine content in the cultures in a dose dependent manner (IC50 at 0.1 microM) and failed to show reversibility in recovery studies. These findings provide evidence that exposure of MPP+ even at low concentrations and for short time in our coculture model results in irreversible toxicity for dopaminergic neurons.

Regulatory role of brain angiotensins in the control of physiological and behavioral responses

Considerable evidence now indicates that a separate and distinct renin-angiotensin system (RAS) is present within the brain. The necessary precursors and enzymes required for the formation and degradation of the biologically active forms of angiotensins have been identified in brain tissues as have angiotensin binding sites. Although this brain RAS appears to be regulated independently from the peripheral RAS, circulating angiotensins do exert a portion of their actions via stimulation of brain angiotensin receptors located in circumventricular organs. These circumventricular organs are located in the proximity of brain ventricles, are richly vascularized and possess a reduced blood-brain barrier thus permitting accessibility by peptides. In this way the brain RAS interacts with other neurotransmitter and neuromodulator systems and contributes to the regulation of blood pressure, body fluid homeostasis, cyclicity of reproductive hormones and sexual behavior, and perhaps plays a role in other functions such as memory acquisition and recall, sensory acuity including pain perception and exploratory behavior. An overactive brain RAS has been identified as one of the factors contributing to the pathogenesis and maintenance of hypertension in the spontaneously hypertensive rat (SHR) model of human essential hypertension. Oral treatment with angiotensin-converting enzyme inhibitors, which interfere with the formation of angiotensin II, prevents the development of hypertension in young SHR by acting, at least in part, upon the brain RAS. Delivery of converting enzyme inhibitors or specific angiotensin receptor antagonists into the brain significantly reduces blood pressure in adult SHR. Thus, if the SHR is an appropriate model of human essential hypertension (there is controversy concerning its usefulness), the potential contribution of the brain RAS to this dysfunction must be considered during the development of future antihypertensive compounds.

Opioid and cannabinoid receptor inhibition of adenylyl cyclase in brain

Both opioids and cannabinoids bind to G-protein-coupled receptors to inhibit adenylyl cyclase in neurons. These reactions were assayed in brain membranes, where maximal inhibitory activity occurred in the following regions: mu-opioid inhibition in rat thalamus, delta-opioid inhibition in rat striatum, kappa-opioid inhibition in guinea pig cerebellum, and cannabinoid inhibition in cerebellum. The inhibition of adenylyl cyclase by both cannabinoid and opioid agonists was typical of G-protein-linked receptors: they required GTP, they were not supported by non-hydrolyzable GTP analogs, and they were abolished (in primary neuronal cell culture) by pertussis toxin treatment. The immediate targets of this system were determined by assaying protein phosphorylation in the presence of receptor agonists and App(NH)p, a substrate for adenylyl cyclase. In striatal membranes, opioid agonists inhibited the phosphorylation of at least two bands of MW 85 and 63 kDa, which may be synapsins I and II, respectively. Other experiments determined the long-term effects of this second messenger system. In primary neuronal cultures, opioid-inhibited adenylyl cyclase attenuated forskolin-stimulated pro-enkephalin mRNA levels, thus providing a feedback regulation of opioid synthesis. Finally, in cerebellar granule cells, both cannabinoid and opioid receptors may exist on the same cells. In these cells, agonists which bind to different receptor types may produce similar biological responses.

Oxytocin receptors on cultured astroglial cells. Kinetic and pharmacological characterization of oxytocin-binding sites on intact hypothalamic and hippocampic cells from foetal rat brain

The ability of astroglial cells to exhibit oxytocin (OT)-binding sites has been investigated in embryonic hypothalamic and hippocampic astroglial cell cultures. The differential characteristics of binding of OT and [Arg8]vasopressin (AVP) agonists and antagonists to the OT-binding sites using the highly selective iodinated OT antagonist d(CH2)5-[Tyr(Me)2,Thr4,Tyr-NH2(9)]OVT ([125I]OTA) have been evaluated using intact cells maintained for 12 days in culture. The specific binding displayed features of reversibility. Computer analysis of the saturation studies using the LIGAND program indicated that, at 4 degrees C, the antagonist binds to a homogeneous population of sites with a Kd value of 0.02 nM and a low binding-site density of around 2 fmol/dish for hypothalamic cells and 6 fmol/dish for hippocampic cells. For hypothalamic cells, competition curves using unlabelled OT, AVP or V2 AVP agonist were characterized by a pseudo-Hill coefficient below unity (0.7), indicating possible heterogeneity among the binding sites. On the other hand, the dose-inhibition curves resulting from competition studies with hippocampic cells had a pseudo-Hill coefficient close to unity, except for OT. Computer analysis (LIGAND) indicated that the OT dose-inhibition curve was significantly better fitted to a two-site model, and this can be explained by two apparent forms of the receptor having high and low affinities for the displacing drug. The relative potencies of the peptides tested for binding to the high-affinity site were: AVP greater than OT greater than V1 AVP antagonist ([d(CH2)5-Tyr(Me)2]AVP) = V2 AVP agonist greater than AVP-Sar ([d(CH2)5-Sar7,Arg8]VP) in hypothalamic cultures, and OT = AVP greater than V1 AVP antagonist greater than V2 AVP agonist in hippocampic cultures. In addition, autoradiography allowed visualization of OT-binding sites, which are located on both soma and processes of astrocyte-like type of cells. In conclusion, these data provide evidence that glial cell cultures contain specific OT-binding sites which display pharmacological characteristics different from those already reported in neuronal cultures and in the adult rat brain.

Release of immunoreactive angiotensin II from neuronal cultures: adrenergic influences

The effects of adrenergic drugs on the release of immunoreactive angiotensin II (ANG II-ir) from brain cells in culture were examined. In neuronal cultures, basal release of Ang II-ir was 43.65 +/- 7.44 pg/5-min incubation period (n = 14 experiments; 52 individual determinations), and in astrocytic glial cultures, it was 21.76 +/- 5.7 pg (n = 8 experiments; 24 individual determinations) when cells were exposed to buffer alone. Incubation of neuronal cultures with the alpha 2-adrenergic antagonist yohimbine (0.1-50 microM, 5 min) caused concentration-dependent increases in ANG II-ir release above basal levels. Analysis of the released material by high-pressure liquid chromatography revealed that authentic ANG II was present. No increase in the release of ANG II-ir was seen from glial cells. Experiments using neuronal cultures revealed that the yohimbine-induced release of ANG II-ir may be secondary to increased norepinephrine (NE) release. Incubation of neuronal cultures with NE (10 nM-50 microM) caused concentration-dependent increases in the release of ANG II-ir. This effect of NE was not inhibited by the alpha 1-adrenergic blocker prazosin. However, a weaker release of ANG II-ir from neuronal cultures was stimulated by the beta-adrenergic agonist isoproterenol at 100 microM. These data show that ANG II-ir can be released from neuronal but not glial cell cultures by adrenergic receptor-mediated mechanisms.

An immunochemical and biochemical study of catecholaminergic activity in dissociated hypothalamic cultures

Dopamine (DA)-containing cells of the medial basal hypothalamus (MBH) were dissociated and maintained in culture for up to 9 days. Cultures were evaluated both biochemically and immunochemically for DA activity. DA biosynthesis was determined using incorporation of [3H]tyrosine and was analyzed by HPLC with electrochemical detection. Immunochemical studies were performed to identify tyrosine hydroxylase (TH)-positive and neuron-specific enolase (NSE)-positive cells. Morphometric analyses determined the cell size, density, process length and the percent of neurons which were catecholaminergic. TH-positive neurons ranged from 6 to 8% of the total neuronal population when examined over days 3-9 of culture and the length of TH-positive neurites was significantly greater than that of NSE-positive cells. There was incorporation of [3H]tyrosine into DA as evidenced by the presence of [3H]DA in both the media and tissue and the inhibition of synthesis with alpha-methyl-p-tyrosine. There was a greater amount of labeled DA in the media than in the tissue at every time point examined. On the other hand, biosynthesis of DA in fresh brain tissue revealed approximately equal levels of DA in the media and tissue. These studies indicate that DA continues to be synthesized in dissociated cultures of MBH as evidenced by both the biochemical and immunochemical analyses and that there appears to be some alteration in the ability of these neurons to store the newly synthesized amine.

Alpha 2-adrenergic receptors in neuronal and glial cultures: characterization and comparison

Membranes prepared from either neuronal or glial cultures contain alpha 2-adrenergic receptors as determined by the characteristics of [3H]yohimbine [( 3H]YOH) binding. The binding was rapid, reversible, saturable, dependent on the protein concentration used, and reached equilibrium by 5 min in membranes from both neuronal and glial cultures. Scatchard analyses of saturation isotherms revealed similar KD values of 13.7 +/- 1.35 nM (n = 10) for neuronal cultures and 18.42 +/- 2.34 nM (n = 10) for glial cultures. Glial cultures contained many more binding sites for [3H]YOH than neuronal cultures, having a Bmax of 1.6 +/- 0.33 pmol/mg protein (n = 10) compared with 0.143 +/- 0.018 pmol/mg protein (n = 10) in neurons. Drugs selective for alpha 2-adrenergic receptors were the most effective displacers of [3H]YOH binding in both neuronal and glial cultures, i.e., the alpha 2-adrenergic antagonists rauwolscine and yohimbine were better displacers than the other catecholamine antagonists prazosin, corynanthine, or propranolol. The agonists showed the same pattern with the alpha 2-selective drugs clonidine and naphazoline being the most effective competitors for the [3H]YOH site. GTP and its nonhydrolyzable analog. 5'-guanylyl-imidodiphosphate, were able to lower the affinity of the alpha 2-receptors for agonists but not antagonists in membranes from both neuronal and glial cultures, suggesting that the receptors are linked to a G protein in both cell types. The presence of alpha 2-adrenergic receptors in neuronal cultures was also substantiated by light microscopic autoradiography of [3H]YOH binding. In summary, we have demonstrated that both neuronal and glial cultures contain alpha 2-adrenoceptors.

Basic fibroblast growth factor promotes the survival and development of mesencephalic neurons in culture

Neuronotrophic effects of basic fibroblast growth factor (bFGF) have been reported for some central nervous system neurons. Here we report that also rat mesencephalic neurons are responsive to bFGF. bFGF produces a significant increase in the number of neurite-bearing cells, as well as in the degree of their fiber network. The present findings also provide the first evidence that bFGF can affect, in a concentration-dependent manner, at least two defined CNS neuronal populations, i.e., dopaminergic and gabaergic neurons. This effect was quantified by assessing the specific [3H]dopamine and [gamma-14C]aminobutyric acid uptakes with time in culture. Stimulation of uptake was more pronounced for dopaminergic neurons, suggesting a relative specificity in the actions of bFGF. These effects of bFGF were completely blocked by affinity-purified polyclonal antibodies. The possibility that bFGF plays a key role in normal nervous system development or function is discussed.

Increased expression of alpha 1-adrenergic receptors in the hypothalamus of spontaneously hypertensive rats

The specificity and molecular weights of alpha 1-adrenergic receptors in various tissues of spontaneously hypertensive (SH) rat were compared with normotensive controls (Wistar-Kyoto; WKY) with the use of [125I]HEAT and [125I]azidoprazosin, specific alpha 1-adrenergic receptor antagonists. Binding of [125I]HEAT to membranes prepared from SH rat brain hypothalamus was significantly higher, due to a 75% increase in the Bmax, than the WKY control. In contrast, the Bmax and Kd of [125I]HEAT binding to brainstem and liver membranes from SH rats were not significantly different from those of WKY controls. Competition-inhibition data suggested similar pharmacological specificity with potencies in the order of prazosin greater than yohimbine greater than propranolol for both WKY and SH rat membranes prepared from liver, hypothalamus, brainstem and neuronal cultures. Photoaffinity labeling of alpha 1-adrenergic receptors from hypothalamus, brainstem and neuronal cultures using [125I]azidoprazosin followed by SDS-PAGE and autoradiography showed the presence of one major band with a molecular weight (MW) of 105,000 Da for both WKY and SH rats. In contrast, labeling of liver alpha 1-adrenergic receptors revealed one major band with a MW of 60,000 Da. Quantitation of the 105,000-Da band from SH rat hypothalamic membranes demonstrated a 52% higher intensity compared with WKY controls. Neuronal cultures prepared from 1-day-old SH rats showed a similarly greater intensity of the 105,000-Da band compared with WKY controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Receptors for phorbol esters are primarily localized in neurons: comparison of neuronal and glial cultures

Binding of [3H]PDB has been measured in the present study to determine the levels of protein kinase C in the neuronal and astrocytic glial cells in culture from rat brain. Binding of [3H]PDB to homogenates of cultured neuronal cells from the brains of normotensive and hypertensive rats was time-dependent and specific. The relative potency for competition by various phorbol esters to [3H]PDB binding was TPA greater than beta-PDD greater than POE greater than alpha-PDD greater than or equal to 4 alpha phorbol. Scatchard analysis showed that neuronal cultures from normotensive rat brains contained 2-3 fold more phorbol ester receptors compared with the glial cultures from the same brains. No differences in the Kd and Bmax were observed between neuronal cultures from normotensive and spontaneously hypertensive rat brains. These studies suggest that the phorbol ester receptors are primarily localized in neuronal cells.

Phorbol esters inhibit agonist-stimulated phosphoinositide hydrolysis in neuronal primary cultures

The effects of phorbol esters on neurotransmitter-stimulated phosphoinositide (PI) hydrolysis in neurons in primary culture were investigated. Ten-day-old neuronal cultures were incubated with [3H]inositol for 2-3 days, exposed to phorbol esters, and the release of [3H]inositol phosphates was measured in the presence of 10 mM lithium. Pretreatment of the neuronal cultures with 1 microM phorbol myristate acetate (PMA) inhibited alpha 1, muscarinic, and glutamate receptor-mediated PI hydrolysis in a time-dependent manner with maximal inhibition observed after a 20-30 min preincubation. The active beta-phorbol didecanoate inhibited stimulated PI hydrolysis, but its stereo-isomer alpha-phorbol didecanoate was without effect at 1 microM. PMA was about 10 times more potent at inhibiting PI hydrolysis stimulated by norepinephrine and glutamate compared to carbachol. The order of potency of the various phorbol esters for inhibition of stimulated PI hydrolysis and the differences between active and inactive stereoisomers suggests that the activation of protein kinase C may mediate the inhibitory effects. Thus, stimulation of neuronal protein kinase C may represent a mechanism for the regulation of agonist-stimulated PI hydrolysis.

Norepinephrine metabolism in neuronal cultures is increased by angiotensin II

In this study we have examined the actions of angiotensin II (ANG II) on catecholamine metabolism in neuronal brain cell cultures prepared from the hypothalamus and brain stem. Neuronal cultures prepared from the brains of 1-day-old Sprague-Dawley rats exhibit specific neuronal uptake mechanisms for both norepinephrine (NE) and dopamine (DA), and also monoamine oxidase (MAO) and catechol O-methyltransferase (COMT) activity. Separate neuronal uptake sites for NE and DA were identified by using specific neuronal uptake inhibitors for each amine. In previous studies, we determined that ANG II (10 nM-1 microM) stimulates increased neuronal [3H]NE uptake by acting at specific receptors. We have confirmed these results here and in addition have shown that ANG II (1 nM-10 microM, 10-120 min) has no significant effects on neuronal [3H]DA uptake. These results suggest that the actions of ANG II are restricted to the NE transporter in neuronal cultures. It is possible that ANG II stimulates the intraneuronal metabolism of at least part of the NE that is taken up, because the peptide stimulates MAO activity, an effect mediated by specific ANG II receptors. ANG II had no effect on COMT activity in neuronal cultures. Therefore, the use of neuronal cultures of hypothalamus and brain stem we have determined that ANG II can specifically alter NE metabolism in these areas, while apparently not altering DA metabolism.

Soluble striatal extracts enhance development of mesencephalic dopaminergic neurons in vitro

Recent studies have suggested that diffusible factors released by neural target tissues enhance survival, growth, and differentiation of neurons within the central, as well as the peripheral, nervous system. In this report, we use catecholamine cytofluorescence to demonstrate that a soluble factor from the striatum produces a 4-fold increase in number of catecholamine cytofluorescent-positive dopaminergic neurons in dissociated mesencephalon cultures prepared from embryonic 14-day-old rats. The same soluble extract enhances the number of neurites per cell and the length of neurites, and also produces a greater than 3.5-fold stimulation of high affinity dopamine uptake into neurons. Such stimulation is significantly reduced following trypsin treatment. The trophic effects on dopaminergic neurons are maximal in extracts of the striatum, but are also found in extracts of the hippocampus-entorhinal cortex-amygdaloid nucleus and the cerebral cortex, although they are less in extracts of the cerebellum, negligible in the olfactory bulb, and absent in the liver. With molecular sieving chromatography, the soluble factors stimulating high affinity dopamine uptake are partially separable from the factors stimulating neuronal high affinity GABA uptake. The approximate molecular weight of the factors influencing dopaminergic neurons is 1500-2200 Da.

Alpha 1-adrenergic receptors in neuronal cultures from rat brain: increased expression in the spontaneously hypertensive rat

Neuronal cells in primary culture from 1-day-old brains of normotensive, Wistar-Kyoto strain (WKY) and spontaneously hypertensive (SH) rats have been utilized to study the expression of alpha 1-adrenergic receptors. Binding of a selective alpha 1 antagonist, [125I]2-[beta-(4-hydroxy-3-iodophenyl)-ethylaminomethyl]-tetralone ([125I]HEAT) to neuronal membranes prepared from primary brain cultures of WKY and SH rats was 75-80% specific, rapid, and time-dependent although the binding was 1.5-2 times higher in neuronal membranes from SH rat brain cultures. Kinetic analysis of the association and dissociation data demonstrated no significant differences between rat strains. Competition-inhibition experiments provided IC50 values for various antagonists and agonists in the following order: prazosin less than phentolamine less than yohimbine less than phenylephrine less than norepinephrine less than propranolol, suggesting that [125I]HEAT bound selectively to alpha 1-adrenergic receptors. Scatchard analysis of the binding data provided straight lines for both strains of rats, indicating the presence of a homogeneous population of binding sites. It also showed that the increase in the binding in neuronal cells from SH rat brains over those from normotensive WKY controls was a result of an increase in the number of alpha 1-adrenergic receptors. Incubation of neuronal cultures from both strains of rats with phenylephrine, an alpha 1-adrenergic agonist, caused a time- and dose-dependent decrease in the binding of [125I]HEAT. This decrease was due to a decrease in the number of alpha 1-adrenergic receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha 1-adrenergic receptor-mediated downregulation of angiotensin II receptors in neuronal cultures

Previous evidence has suggested that brain catecholamine levels are important in the regulation of central angiotensin II receptors. In the present study, the effects of norepinephrine and 3,4-dihydroxyphenylethylamine (dopamine) on angiotensin II receptor regulation in neuronal cultures from rat hypothalamus and brainstem have been examined. Both catecholamines elicit significant decreases in [125I]angiotensin II-specific binding to neuronal cultures prepared from normotensive rats, effects that are dose dependent and that are maximal within 4-8 h of preincubation. Saturation and Scatchard analyses revealed that the norepinephrine-induced decrease in the binding is due to a decrease in the number of angiotensin II receptors in neuronal cultures, with little effect on the receptor affinity. Norepinephrine has no significant actions on [125I]angiotensin II binding in cultures prepared from spontaneously hypertensive rats. The downregulation of angiotensin II receptors by norepinephrine or dopamine is blocked by alpha 1-adrenergic and not by other adrenergic antagonists, a result suggesting that this effect is initiated at the cell surface involving alpha 1-adrenergic receptors. This is further supported by our data indicating a parallel downregulation of specific alpha 1-adrenergic receptors elicited by norepinephrine. In summary, these results show that norepinephrine and dopamine are able to alter the regulation of neuronal angiotensin II receptors by acting at alpha 1-adrenergic receptors, which is a novel finding.

Mineralocorticoids modulate central angiotensin II receptors in rats

The effect of chronic administration of deoxycorticosterone acetate (DOCA) on the regulation of angiotensin II (AII) receptors in the brains of adult rats was compared with their drinking and pressor responsiveness to both peripheral and central administration of AII. Analysis of AII receptor binding in a block of tissue containing the hypothalamus, thalamus and septum (HTS) after treatment for 8 weeks with DOCA-salt (240 micrograms/kg/day) revealed a significant increase in the number of AII-binding sites compared to salt-loaded controls (Bmax 9.65 vs 6.80 fmol/mg protein) and no change in binding affinity (Kd). Significant increases in the drinking responses to peripheral (200 micrograms/kg) and central (10 ng) administration of AII were observed in these rats. Additional studies indicated that the pressor responses to either centrally (25 ng) or peripherally (20 micrograms/kg, s.c.) administered AII were augmented in DOCA-treated rats. The effect of mineralocorticoids on AII-binding sites was also investigated in primary neuronal cultures from the brains of one-day-old rats. Pretreatment of these cultures with either DOCA or aldosterone (ALDO) induced a time- and concentration-dependent increase in the specific binding of [125I]AII. Maximal increases in AII binding of 53 and 62% above control values were observed when cultures were treated with 500 pg of either ALDO or DOCA per milliliter of culture medium. Scatchard analysis of specific binding of [125I]AII in neuronal cultures treated with DOCA revealed a significant increase in Bmax but no change in Kd. Thus, mineralocorticoid hormones induce an increase in the number of AII-receptor binding sites in the HTS of rats which parallels physiological responses to both central and peripheral administration of AII. This relationship may be independent of the concentration of AII in the blood, since an increase in the number of AII binding sites was also observed in neurons cultured from the brains of one-day-old rats which had been treated with mineralocorticoid hormones.

Insulin is released from rat brain neuronal cells in culture

Depolarization of neuronal cells in primary culture from the rat brain by potassium ions in the presence of calcium or by veratridine caused a greater than three-fold stimulation of release of immunoreactive insulin. HPLC of the released insulin immunoreactivity from the neuronal cultures comigrated with the two rat insulins. The depolarization-induced release of insulin was inhibited by cycloheximide and was specific for neuronal cultures since potassium ions failed to cause the release in comparably prepared astrocytic glial cells from the rat brain. Prelabelling of neuronal cultures with [3H]leucine followed by depolarization resulted in the release of radioactivity that immunoprecipitated with insulin antibody. The release of [3H]insulin was biphasic. These observations suggest that neuronal cells from the brain have the capacity to synthesize insulin that could be released under depolarization conditions.

Sodium increases angiotensin II receptors in neuronal cultures from brains of normotensive and hypertensive rats

Neuronal cultures from one-day-old brains of Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats were used to determine the effect of sodium ions on angiotensin II (Ang II) receptors in order to understand the mechanism of action of sodium at the cellular level. Incubation with sodium chloride of neuronal cultures from WKY rats caused a rapid and dose-dependent increase in the specific binding of 125I-Ang II to its receptors. A 260% increase in the binding was observed with 150 mM NaCl. Neuronal cultures from SH rat brains showed a similar sodium-stimulated increase in Ang II binding; however this increase was 150% greater than that observed in neuronal cultures from WKY rat brain. Kinetic studies of the effects of sodium ions on both WKY and SH neuronal cultures showed an increase in the dissociation of 125I-Ang II from its receptors in the presence of sodium ions. In addition, Scatchard analysis revealed that the increase in binding caused by sodium was due to an increase in the number of Ang II receptors. These observations indicate that sodium ions increase the number of Ang II specific receptors in intact neuronal cells and that this stimulation was more pronounced in neuronal cells from SH rat brains compared with WKY controls.

Angiotensin II stimulates norepinephrine uptake in hypothalamus-brain stem neuronal cultures

In this study we have characterized the uptake of [3H]norepinephrine (NE) into neuronal co-cultures of rat hypothalamus and brain stem and have examined the effects of angiotensin II (ANG II) on this uptake. Neuronal co-cultures prepared from the brains of 1-day-old Sprague-Dawley (SD) or Wistar-Kyoto (WKY) rats exhibited sodium-dependent and sodium-independent portions of the total [3H]NE uptake. The sodium-dependent uptake was abolished by blockers such as maprotiline, desmethylimipramine, and xylamine (0.1-100 microM) and is presumably neuronal uptake. The sodium-independent uptake was unaffected by these drugs and is presumably non-neuronal, since nonneuronal co-cultures from SD rats exhibited no significant sodium-dependent or blocker-sensitive uptake. In SD or WKY neuronal co-cultures, ANG II (0.1 nM-10 microM) caused increased [3H]NE uptake during short-term incubations (1-5 min). This stimulatory effect of ANG II was on neuronal NE uptake. Furthermore, it was inhibited by preincubation with saralasin (1-10 microM). Construction of saturation curves and kinetic analyses revealed that ANG II caused an increase in the maximal velocity of uptake of neuronal [3H]NE, but the affinity of the transporter for NE was not altered. With longer-term incubations (15-30 min), ANG II caused a reduction in neuronal [3H]NE uptake. This effect was also blocked by saralasin. However, reliable kinetic analysis was not possible with the longer-term incubations, and it is likely that the inhibitory action of the peptide represents a stimulation of NE release. Therefore, using neuronal co-cultures, we have identified a previously unseen stimulatory action of ANG II on neuronal [3H]NE uptake, which precedes the already documented inhibitory actions.

Different developmental schedules of dopaminergic and noradrenergic neurons in dissociation culture of fetal rat midbrain and hindbrain

The development of dopaminergic and noradrenergic neurons in dissociation cultures of mesencephalon and rhombencephalon obtained from 18-day-old rat fetuses was characterized by their capacity to take up and release catecholamines. In both types of cultures, uptake of [3H]dopamine and [3H]noradrenaline was obtained which could be inhibited by reserpine. Autoradiographic studies demonstrated an almost exclusive neuronal localization of the labeled catecholamines. The transmitters could be released by depolarization with K+ in a Ca2+-dependent manner during the entire cultivation period. In contrast, catecholamine uptake by cultures of neocortex was minimal, could not be inhibited by reserpine, and the accumulated radioactivity could not be released upon depolarization. These points provide evidence for an active accumulation of the exogenous transmitters and for the presence of stimulus-secretion coupling in a distinct population of neurons of both brain stem cultures. Striking differences between the two brain stem cultures concerned their sensitivity to desmethylimipramine and benztropine as well as the time course of the development of the uptake capacity. Desmethylimipramine inhibited the uptake of both catecholamines in rhombencephalic, but not in mesencephalic cultures. The reverse was true for benztropine. It is concluded that cultures of rhombencephalon contain predominantly noradrenergic, and those of mesencephalon dopaminergic cells. Comparison of the uptake behaviour suggested that noradrenergic neurons mature considerably later than dopaminergic neurons. The results show that dissociation cultures of mid- and hindbrain, inspite of their heterogeneous composition, can serve as valuable models for the study of development and function of dopaminergic and noradrenergic neurons, respectively.

Cell and tissue culture of the central nervous system: recent developments and current applications

A survey of methods for cell and tissue culture of the central nervous system (CNS) is given. This includes a brief historical outline and description of methods in current use. Recent methodological improvements are emphasized, and it is shown how these are applied in modern neurobiological research. Both monolayer cell cultures and three-dimensional organ culture systems are widely used, each having advantages and limitations. In recent years, there has been considerable improvement of culture for prolonged periods in chemically defined media. Brain tissue from a wide spectrum of species have been used, including different types of human brain cells which can be propagated for several months. At present, these culture systems are employed for dynamic studies of the developing, the adult and ageing brain. It is possible to select neurons and the different classes of glial cells for culture purposes. Cell culture of the CNS has given new insights into the biology of brain tumours. Culture systems for experimental tumour therapy in vitro are also available. Recently, it has been shown that organ cultures of brain tissue can be used as targets for invasive glioma cells, enabling a direct study of the interactions between tumour cells and normal tissue to take place.

Receptor-mediated inositide hydrolysis is a neuronal response: comparison of primary neuronal and glial cultures

Cholinergic and adrenergic receptor-stimulated inositide hydrolysis was studied in neuronal and glial cells cultured from brains of 1-day-old Wistar-Kyoto rats. Incubation of the cells with [3H]inositol led to the incorporation of radioactivity specifically into inositol phospholipids. Labeling of the membrane lipids reached a maximum in 2-3 days. Receptor-stimulated breakdown of inositides was determined by following the accumulation of inositol phosphates after incubation of the labeled cells for 60 min with carbachol or norepinephrine in the presence of 10 mM lithium. Carbachol (1 mM) stimulated inositol phosphate production in neurons 30 times higher than that seen in glia. The response stimulated by norepinephrine (75 microM) was 6 times higher in neurons than glia. The response to carbachol was blocked by atropine, and the norepinephrine-induced response was inhibited by prazosin suggesting that the receptors mediating the responses were muscarinic and alpha 1-adrenergic, respectively. These results suggest that muscarinic cholinergic and alpha 1-adrenergic stimulated inositide hydrolysis is primarily a neuronal response and that this biochemical event may be important for transmembrane signaling which occurs during neurotransmission.

Altered norepinephrine uptake in neuronal cultures from spontaneously hypertensive rat brain

Uptake of [3H]norepinephrine (NE) has been characterized and compared in neuronal cultures prepared from the brains of 1-day-old normotensive (Wistar-Kyoto, WKY) and spontaneously hypertensive (SH) rats. In cultures from both strains total [3H]NE uptake consisted of a sodium-dependent portion and a sodium-independent portion. The sodium-dependent [3H]NE uptake was inhibited by NE uptake blockers such as maprotiline or desmethylimipramine (both at 0.5-100 microM). This sodium-dependent, NE uptake blocker-sensitive portion of the uptake was also stereospecific, preferring the l-isomer of NE. In contrast, the sodium-independent uptake was not sensitive to maprotiline or desmethylimipramine. Autoradiograms of cultures incubated with [3H]NE showed label concentrated in certain, but not all, neurites and in a few neuronal cell bodies. Cultures incubated with label in sodium-free buffer did not show any such localization of grains but instead showed a diffuse pattern. Incubation of neuronal WKY or SH brain cultures with various concentrations of l-[3H]NE and unlabeled l-NE in the presence or absence of sodium enabled the construction of saturation curves for sodium-dependent uptake in each culture type. In WKY cultures, Km and maximal velocity of uptake (Vmax) values of 0.37-0.45 microM and 0.58-0.69 pmol X mg protein-1 X min-1, respectively, were obtained for sodium-dependent uptake. In contrast, the Km and Vmax values for [3H]NE uptake in SH neuronal cultures were 1.4 microM and 1.31 pmol X mg protein-1 X min-1, respectively. Kinetic analyses of the results show that in SH neuronal cultures the [3H]NE uptake sites are of lower affinity but higher capacity compared with those in WKY neuronal cultures.

Increased angiotensin II receptors in neuronal cultures from hypertensive rat brain

Binding of 125I-angiotensin II (ANG II) to neuronal cultures made from the brains of 1-day-old normotensive (Wistar-Kyoto, WKY) and spontaneously hypertensive (SH) rats was time dependent, saturable, reversible, and 90-95% specific. Neuronal cultures from SH rats bound 50-70% more 125I-ANG II compared with their WKY controls. Scatchard analysis revealed that the increase in the specific binding of ANG II to SH rat neuronal cultures was due to an increase in the number of binding sites per cell rather than change in the affinity of receptors for ANG II. Light-microscopic autoradiographic analysis showed that ANG II specific binding sites were located on neuronal cell bodies and neurites. Treatment of neuronal cultures from both strains of rats with alpha-methyl-p-tyrosine caused a 50-60% decrease in the endogenous levels of norepinephrine (NE) and dopamine (DA). This decrease was associated with increases in the specific binding of 125I-ANG II in neuronal cultures from WKY rat brain. In contrast, ANG II binding in neuronal cultures from SH rat brain failed to respond to changes in NE and DA levels. These observations suggest that ANG II specific receptors are increased and that they are not under a negative-feedback control by catecholamines in SH rat brain neuronal cultures.

Angiotensin II in neuronal cultures from brains of normotensive and hypertensive rats

Primary neuronal cultures from 1-day-old rat brains, which contain angiotensin II (ANG II) immunoreactivity within the neurons and are capable of de novo synthesis of this immunoreactivity, have been used in this study to determine the nature of this immunoreactivity by high-performance liquid chromatography (HPLC). Neuronal cultures from the brains of normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats were found to contain ANG II immunoreactivity, which co-migrated with authentic ANG II on HPLC. The angiotensin detected in brain cultures was not derived from the growth medium, and its level was significantly decreased by incubating the cultures with captopril. A 71% decrease in the levels of ANG II was observed in neuronal cultures of SH rat brains compared with those from WKY controls. These observations show that differences in brain angiotensin between SH and WKY are present before differences in blood pressure are manifested.

Catecholamine-angiotensin II receptor interaction in primary cultures of rat brain

Neuron-enriched primary cultures from 1-day-old rat brains have been used to study the influence of catecholamines on angiotension II receptors. Treatment of cultures with alpha-methyl-p-tyrosine caused a time- and concentration-dependent increase in the specific binding of 125I-angiotensin II and a decrease in neuronal norepinephrine and dopamine contents. A maximum increase of 75% in the binding and a decrease of 67% in catecholamine content was observed with 400 microM alpha-methyl-p-tyrosine. Removal of alpha-methyl-p-tyrosine from cultures resulted in the recovery of catecholamine levels and decrease in 125I-angiotensin II binding to control levels. In contrast, treatment of cultures with pargyline caused decreases in the binding of 125I-angiotensin II and increases in catecholamine levels in neuronal cultures. Scatchard analysis demonstrated that an increase in 125I-angiotensin II binding by alpha-methyl-p-tyrosine was due to an increase in the affinity of receptors for angiotensin II without changes in the number of angiotensin II binding sites. The results obtained here indicate that angiotensin II binding to neuron-enriched cultures is reciprocally related to the levels of neuronal catecholamines.

Effects of insulin and tunicamycin on neuronal insulin receptors in culture

We have examined the effect of insulin and tunicamycin, which cause decreases in cell surface insulin receptor numbers in peripheral tissues, on insulin receptors in neuron-enriched brain cell cultures. Incubation with 0.016-0.83 microM insulin for 24 h failed to decrease the specific binding of 125I-insulin in neuron-enriched cultures prepared from whole brains of 1-day-old rats. In contrast, these concentrations of insulin produced a dose-dependent decrease in the binding of 125I-insulin in fibroblastic cultures. Tunicamycin, an antibiotic which inhibits glycosylation of proteins and greatly reduced insulin binding via a reduction in apparent receptor numbers in fibroblastic cultures, caused no decrease in the binding of 125I-insulin in neuron-enriched cultures. These results indicate that brain insulin receptors are not down regulated by insulin and that glycosylation of insulin receptors may not be an important step in the regulation of their surface expression in the brain.