Function Of Cholinergic Neurons Research Articles

Basal forebrain injections of the benzodiazepine partial inverse agonist FG 7142 enhance memory of rats in the double Y-maze

Cholinergic replacement strategies have achieved little success in the treatment of Alzheimer's disease. It has been suggested that the mnemonic function of cholinergic neurons may be enhanced by treatments that reduce GABA-ergic inhibition, while preserving the normal pattern of activity in the cholinergic neurons. Following on these suggestions, the present study investigated the mnemonic effects of intra-nucleus basalis magnocellularis (NBM) injections of the benzodiazepine receptor partial inverse agonist N-methyl-β-carboline-3-carboxamide (FG 7142). Rats were surgically implanted with bilateral cannulae in the NBM prior to training in a double Y-maze. Daily training sessions continued until reference and working memory choice performance stabilized to a criterion of - 91% correct. Rats ( n = 9) received FG 7142 bilaterally in doses of 0.2, 0.2 and 3.0 μg/0.5 μl per side, muscimol (a GABA A agonist) in a dose of 0.1 μg/0.5 μl per side, vehicle (345 μg 2-hydroxypropyl-β-cyclodextrin/0.5 μl saline per side) or no injection in a counterbalanced order with retraining to criterion between treatments. Muscimol impaired choice accuracy on both the reference and working memory components, but the effect was bigger for working memory, replicating our previous findings. Two doses of FG 7142 (0.2 and 2.0 μg/0.5 μl) enhanced choice accuracy on the working memory component. The present results suggest that benzodiazepine partial inverse agonists may enhance mnemonic function.

Defective cholinergic innervation in pyloric muscle of patients with hypertrophic pyloric stenosis

The etiology of hypertrophic pyloric stenosis (HPS) is not known. Many investigators have studied the myenteric plexus and muscle in HPS, but there are no reports of cholinergic nerve distribution in this condition. A histochemical technique for the detection of acetylcholinesterase (AChE) has been used to study cholinergic nerve distribution. Recently, it has been shown that the development and survival of cholinergic neurons in the peripheral and central nervous system depend on the presence of nerve growth factor (NGF) and its receptor (NGFR). We examined pyloric muscle from 18 patients with HPS and 10 controls using monoclonal antibody to NGFR and AChE histochemistry. Myenteric plexus displayed strong NGFR and AChE reactivity. Quantitative assessment of immunoreactivity in nerve fibres within pyloric muscle demonstrated selective absence of NGFR and AChE-positive nerve fibres in the circular and longitudinal muscle of HPS, whereas these fibres were in abundance in the muscle of controls. These findings suggest that NGFR is an important neurotrophic factor in the maintenance of cholinergic neuronal function and that NGFR deficiency, resulting in defective cholinergic innervation of pyloric muscle, may have an important role in the pathogenesis of HPS.

Stimulation of GABA B receptors in thebasal forebrain selectively impairs working memory of rats in the double Y-maze

The present experiments were conducted to evaluate the possible contribution of GABAergic inputs to the basal forebrain in the region of the nucleus basalis magnocellularis (nbm) to memory. In two experiments, rats implanted with bilateral intra-nbm guide cannulae were trained in the double Y-maze task to perform working- and reference-memory components. Animals were placed in one of two start arms of the first “Y” and the reference-memory component required travelling to its central stem for food. Access to the second “Y” then was given and the working-memory component for Expt. 1 required travelling to the goal arm diagonally opposite the start arm in the first “Y” of that trial. In Expt. 2, the working-memory component required travelling to the goal opposite to the goal arm entered in the second “Y” on the preceding trial, with 0- and 15-s delays between trials. In Expt. 1, pretrained rats ( n = 8) received the GABA A agonist, muscimol (0.1 μg in 0.5 μl), the GABA B agonist, R(+)-baclofen (0.01, 0.05 and 0.1 μg), and its less active enantiomer, S(−)-baclofen (0.1 μg), in a counterbalanced order with retraining to criterion between injections. In Expt. 2, pretrained rats( n = 9) received saline (0.5 μl), R(+)-baclofen (0.1 μg), the GABA B antagonist, phaclofen (1 μg), and R(+)-baclofen + phaclofen. Results of Expt. 1 revealed that intra-nbm muscimol and, in a dose-dependent manner, R(+)-baclofen differentially affected working but not reference memory. In Expt. 2, the differential mnemonic impairment produced by R(+)-baclofen was replicated and co-injection with phaclofen reversed this effect. A 15-s delay between trials significantly impaired working but not reference memory. Results suggest that both GABA A and GABA B receptors may be involved in modulating the possible mnemonic functions of nbm cholinergic neurons.

Effect of vinconate, an indolonaphthyridine derivative, on metabolism and function of cerebral cholinergic neurons in rat

Effects of (+/-)-methyl 3-ethyl-2,3,3a,4-tetrahydro-1H-indolo [3,2,1,-de] [1,5] naphthyridine-6-carboxylate hydrochloride (vinconate), an indolonaphthyridine derivative, on the metabolism and function of cerebral cholinergic neurons were investigated using male Wistar rats. Single administration of vinconate (5, 50 and 200 mg/kg) decreased acetylcholine content in the striatum but not those in the cerebral cortex and hippocampus. The same treatment with vinconate (5, 50 and 200 mg/kg, p.o.) had no effect on the activities of choline acetyltransferase and acetylcholinesterase in these brain areas. Although the addition of vinconate (10(-7) - 10(-4) M) had no effect on the high affinity uptake of [3H]choline into striatal slices, it induced a concentration-dependent increase of a KCl(2 x 10(-2) M)-evoked endogenous acetylcholine release. The addition of (-)-sulpiride (10(-8) - 10(-6) M), a dopamine D2 receptor antagonist, also accentuated the KCl(2 x 10(-2) M)-evoked endogenous acetylcholine release form striatal slices. Furthermore, it was found that this (-)-sulpiride (10(-7) M)-induced increase of endogenous acetylcholine release was further augmented by the addition of vinconate (10(-5) M). These results suggest that vinconate may enhance the release of endogenous acetylcholine via the modulation of presynaptic dopamine heteroreceptor in the striatum.

Neural regulation of cerebral blood flow

The brain is encased in a rigid container, the skull, and thus the total volume of cerebral blood flow (CBF) per se is maintained at a stable level within very narrow ranges. The change in regional CBF (rCBF) has been considered to be broadly attributable to the rate of glucose metabolism by regional neurons. Although autonomic nerves have been proposed to contribute to maintenance of autoregulation of the CBF, the regulation of rCBF by metabolites produced in the regional cerebral tissues has received more attention. However, the fact that most blood vessels in the brain are innervated by fibers containing noradrenaline, acetylcholine, serotonin and some peptides, indicates a functional role for these neurons in the regulation of rCBF. Recently, Alzheimer's disease has become an important research target at both the clinical and neuroscientific levels. In this disease, degeneration of cells in the basal forebrain, e.g., cholinergic neurons originating in the nucleus basalis of Meynert (NBM) and projecting to the cerebral cortex, is quite striking. However, the function of these cholinergic neurons in the cerebral cortex has remained unclear until recently. Over the last few years, new evidence concerning the role of cortical and hippocampal cholinergic fibers has accumulated and revealed a physiological vasodilative function for these cholinergic fibers. I would like to introduce recent studies on vasodilative regulation of the cerebral cortex and hippocampus by these central cholinergic nerves originating in the NBM and septal complex. I shall also briefly introduce the related subjects of vasomotor regulation in the brain by other central noradrenergic, serotonergic, and dopaminergic fibers, and also by peripheral sympathetic and parasympathetic nerves.

Regulation of hippocampal muscarinic receptor function by chronic nerve growth factor treatment in adult rats with fimbrial transections

Effects of chronic intraventricular administration of recombinant human nerve growth factor on hippocampal muscarinic receptor densities and muscarinic receptor-linked second messenger systems were determined in adult rats 21 days following partial or full unilateral fimbrial transections. First, autoradiographic analysis of muscarinic receptors was carried out using [ 3H]quinuclidinyl benzilate for total muscarinic receptors, [ 3H]pirenzepine for M1 receptors and [ 3H]AF-DX 384 for M2 receptors. Partial fimbrial transections did not significantly alter the density of these muscarinic receptor populations in the dorsal or ventral hippocampus and there was no effect of chronic (1 /gmg every other day, 21 days) recombinant human nerve growth factor treatment. In contrast, in animals receiving full fimbrial transections which by themselves did not alter muscarinic receptor density, recombinant human nerve growth factor treatment increased the density of [ 3H]quinuclidinyl benzilate binding sites. M1 receptors, and M2 receptors by approximately 40% in the CA1 region. Secondly, we determined the effect of chronic recombinant human nerve growth factor treatment on muscarinic receptor-mediated second messenger production in rats with either partial or full unilateral fimbrial transections. In partially fimbriectomized rats, oxotremorine-induced inositol triphosphate production by hippocampal slices was increased by 81% on the lesioned side of animals treated with a control protein. This lesion-induced supersensitivity of M1 muscarinic receptor function was prevented by chronic recombinant human nerve growth factor treatment. In recombinant human nerve growth factor-treated animals, inositol triphosphate production was similar to values on unlesioned control sides. The muscarinic receptor-mediated increase in cyclic GMP levels was not altered by fimbrial transections or recombinant human nerve growth factor treatment. In animals with full unilateral fimbrial transections, oxotremorine-induced inositol triphosphate production was increased by 99% on the lesioned side of animals treated with a control protein and treatment with recombinant human nerve growth factor did not alter this denervation-induced supersensitivity of muscarinic receptor transduction signal. Chronic recombinant human nerve growth factor treatment did not affect the levels of inositol triphosphate on the contralateral unlesioned side of either partial or full fimbriectomized animals. Earlier studies indicate that chronic nerve growth factor treatment increases the presynaptic function of hippocampal cholinergic neurons surviving partial fimbrial transections. The findings of the present study indicate that these presynaptic effects translate into functional changes at the level of postsynaptic muscarinic receptors in the hippocampus. In addition, our studies suggest that a presynaptic cholinergic component is necessary to observe recombinant human nerve growth factor-induced enhancements of cholinergic receptor function in the hippocampus, since in animals receiving full unilateral transections muscarinic receptor-mediated responses are not attenuated following recombinant human nerve growth factor treatment.

Effects of concomitant cholinergic and adrenergic stimulation on learning and memory performance by young and aged monkeys.

The beneficial effects of physostigmine and other centrally acting AChE inhibitors on learning and memory processes have been documented in several studies. Some of these compounds are currently being examined for their potential in the treatment of Alzheimer's disease. However, the ability to employ this class of agents alone is limited by the potential for debilitating and dangerous side effects. In addition, a growing body of evidence also suggests a role for a number of other transmitter systems in this disorder. Agents such as clonidine that address adrenergic deficits have recently been demonstrated to enhance memory performance in monkeys. Clonidine also inhibits the function of cholinergic neurons in specific brain regions and reduces certain side effects of physostigmine. This evidence provided the impetus to evaluate a combination of physostigmine and clonidine in a learning and memory paradigm in monkeys. Seven young adult and three aged macaque monkeys performing a delayed matching-to-sample task received regimens of increasing doses of clonidine and physostigmine on separate occasions to determine the optimal dose of each agent in terms of enhanced memory performance. The optimal dose of clonidine was combined with a series of physostigmine doses and performance was compared to that using the two drugs alone. The best combination regimen of clonidine and physostigmine was more effective than either drug alone in enhancing memory performance. Part of the benefit may have been due to the ability of the animals to tolerate significantly higher doses of physostigmine in the combination regimen.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain and cerebrospinal fluid cholinesterases in Alzheimer's disease, Parkinson's disease and aging. A critical review of clinical and experimental studies.

Acetylcholinesterase (AChE), an enzyme responsible for the break-down of acetylcholine, is found both in cholinergic and non-cholinergic neurons in the central nervous system. In addition to its role in the catabolism of acetylcholine, AChE have other functions in brain, e.g. in the processing of peptides and proteins, and in the modulation of dopaminergic neurons in the brain stem. Several clinical and experimental studies have investigated AChE in brain and cerebrospinal fluid (CSF) in aging and dementia. The results suggest that brain AChE and its molecular forms show interesting changes in dementia and aging. However, CSF-AChE activity is not a very reliable or sensitive marker of the integrity and function of cholinergic neurons in the basal forebrain complex. Additional work is needed to clarify the role of AChE abnormality in the formation of pathology changes in patients with Alzheimer's disease.

Involvement of the cholinergic system in the effects of nefiracetam (DM-9384) on carbon monoxide (CO)-induced acute and delayed amnesia

The effects of N-(2,6-dimethylphenyl)-2-(2-oxo-1-pyrrolidinyl)-acetamide (DM-9384, nefiracetam), a cyclic derivative of GABA, were investigated in the carbon monoxide (CO)-induced amnesia model in the mice using the passive avoidance task. Memory deficiency occurred when mice were exposed to CO before memory was completely consolidated after training (acute amnesia), at 7 days before training and 7 days after training (delayed amnesia). DM-9384 prolonged the step-down latency in mice with CO-induced amnesia. Scopolamine blocked the anti-amnesic effect of DM-9384 on delayed amnesia that had been induced by pre- or post-training exposure to CO. Bicuculline had a tendency to antagonize the anti-amnesic effect of DM-9384, but this tendency was not significant. Under these conditions, no significant change in the activity of choline acetyltransferase and glutamic acid decarboxylase was observed in the frontal cortex, striatum and hippocampus. These results suggest that DM-9384 potentiates cholinergic neuronal function and that it may modify acquisition and/or consolidation of memory.

Effects of estrogen and fimbria/fornix transection on p75 NGFR and ChAT expression in the medial septum and diagonal band of Broca

NGF receptor-expressing cells located in the basal forebrain have recently been shown to contain estrogen (E) receptors (Toran-Allerand and MacLusky. 1989. Soc. Neurosci. Abstr. 15: 954) . In the present study, we have examined the effects of E-treatment on p75 NGFR and choline acetyltransferase (ChAT) expression by neurons in the medial septum (MS) and the vertical (VDB) and horizontal (HDB) limbs of the diagonal band of Broca using immunocytochemical and in situ hybridization techniques. First, since E-treatment has been shown to affect neuronal survival and to stimulate synaptic reorganization and growth within various regions of the brain, we hypothesized that E-treatment might attenuate the loss of p75 NGFR immunoreactivity (IR) which occurs in the MS and VDB following transection of the fimbria/fornix. Contrary to our hypothesis, E-treatment did not attenuate the effects of fimbria/fornix transection. In fact, E-treatment alone produced a significant decrease in the number of p75 NGFR-IR cells detected in the MS. Subsequent experiments confirmed that chronic E-treatment produces a down-regulation of both p75 NGFR-IR and p75 NGFR mRNA in the MS and VDB. In the MS, estrogen appeared to affect a subpopulation of p75 NGFR-expressing neurons which were also affected by fimbria/fornix transection since the effects of these two treatments were not additive. In addition, effects of E-treatment on p75 NGFR-IR were sex-specific (observed in females but not in males) and were reversible in the MS after 2 weeks, but not after 4 weeks (allowing 2 weeks recovery), of E-treatment. A time-course analysis revealed that effects of E-treatment on p75 NGFR-IR were not observed until after 16 days (MS) or 30 days (VDB) of E-treatment and were preceded by a significant and transient increase in ChAT expression in both the MS and VDB. The data are consistent with the possibility that continuous, long-term exposure to gonadal steroids may contribute to a loss of p75 NGFR-expressing neurons with age. In addition, the data suggest that p75 NGFR expression may play a role in regulating the functioning of specific basal forebrain cholinergic neurons. Different mechanisms by which E-treatment might influence ChAT and p75 NGFR expression in brain are discussed.

Effects of concomitant cholinergic and adrenergic stimulation on learning and memory performance by primates

Physostigmine and other centrally-acting acetylcholinesterase inhibitors are currently being examined for their potential in the treatment of Alzheimer's Disease. The ability to employ this class of agents is limited by the potential for debilitating and dangerous side effects. Clonidine and related drugs have recently been demonstrated to enhance memory performance in monkeys. Clonidine also inhibits the function of cholinergic neurons in specific brain regions and reduces certain side effects of physostigmine. Seven adult macaque monkeys performing a delayed matching-to-sample (DMTS) task received regimens of increasing doses of clonidine and physostigmine on separate occasions to determine the ‘best dose’ of each agent in terms of enhanced memory performance. The best doses were combined as a single administration and performance compared to that using the two drugs alone. The combination regimen of clonidine and physostigmine was more effective than either drug alone in enhancing memory performance. Part of the benefit may have been due to the ability to employ significantly higher doses of physostigmine on the combination regimen. A single injection of the combination resulted in enhanced performance both on the day of administration as well as on the following day. These results are consistent with the ability of clonidine to limit the expression or intensity of certain physostigmine-induced autonomic side effects, while allowing the cognitive beneficial effects of the cholinesterase inhibitor.

The effect of the acetylcholine transport blocker vesamicol on central cholinergic pressor neurons

Vesamicol (AH5183) inhibits the uptake of acetylcholine into cholinergic neuronal storage vesicles. Earlier in vitro studies have demonstrated that such inhibition can lead to a failure of transmission, particularly in peripheral cholinergic tissues. The present study was designed to determine whether vesamicol could inhibit central cholinergic transmission in conscious freely moving rats. Central (lateral cerebroventricular) injection of 20 micrograms of vesamicol significantly reduced the hypertensive and bradycardic response to subsequent central injection of physostigmine in spontaneously hypertensive rats. Inhibition of the pressor response was greatest when physostigmine was administered 1 hr after vesamicol. Acetylcholine and choline levels were determined in three brain regions derived from rats treated one hr earlier with either vehicle or vesamicol. Acetylcholine levels were found to be unaltered after vesamicol treatment, although choline levels were significantly higher in two brain regions. These results are consistent with the ability of vesamicol to inhibit the function of central cholinergic cardiovascular regulatory neurons. The mechanism for this inhibition is not related to depletion of total brain acetylcholine content but may be due to depletion of a small critical pool of transmitter.

Redox reactive reagents inhibiting and inactivating choline acetyltransferase

3-Trimethylammoniomethyl catechol and N,N-dimethylepinephrine (catecholine) are redox reactive reagents which possess quarternary ammonium functional groups and the capacity to inhibit or inactivate choline binding macromolecules which mediate cholinergic neuronal function. Earlier studies reported the synthesis of 3-trimethylammoniomethyl catechol and demonstrated its redox-dependent covalent inactivation of the nicotinic acetylcholine receptor [Nickoloff et al., Biochemistry 24, 999–1007 (1985)]. Here we present the synthesis of catecholine and show that both 3-trimethylammoniomethyl catechol and catecholine are weak noncompetitive inhibitors (K i = 15 ± 6 and 25 ± 4 mM, respectively) of choline acetyltransferase (EC 2.3.1.6). Both agents irreversibly inactivate the enzyme.

Discriminative stimulus properties of nicotine: mechanisms of transduction.

Our thinking about how nicotine might be inducing DS control of behavior has changed drastically in the past 25 years. Our first inclination was that nicotine was mimicking ACh at a variety of specific and select n-AChRs. Then several nicotine researchers suggested that nicotine might be acting via specific and select noncholinergic receptors. At present, we seem to have returned to the view that nicotine may have pronounced effects at the n-AChR (figure 1), at least in some specific cases such as in the development of tolerance and in rats trained to discriminate nicotine (figure 6). The endogenous ligand has not changed, but the mechanism of how it affects presynaptic and postsynaptic receptors appears to have been rediscovered. The concept of rapid ACh-induced desensitization at the n-AChR is not new and appears basic to cholinergic neuronal function (figure 5). The desensitization concept has been revitalized by several investigators who also consider this mechanism important to how nicotine might act in protecting DA neurons from neurotoxicity of chemicals such as 6-OHDA or MPTP (Janson et al. 1988). The overall concept suggests that n-AChR desensitization at presynaptic DA sites may reduce neuronal accessibility to select exogenous neurotoxins and thus attenuate neuronal destruction. This hypothesis has also been partially validated in relation to the cholinergic neuron by providing preliminary evidence that nicotine was able to reduce cholinergic neuron destruction (measured by brain ACh levels) via the intraventricular administration of the neurotoxin AF64A, an ACh nitrogen mustard (Villanueva et al. 1990). Thus, nicotine or compounds acting like nicotine could possibly be beneficial to patients exhibiting the select neurological problems observed in Parkinson's and Alzheimer's diseases. The process of desensitization might also be useful to understanding why humans choose to smoke tobacco products. Perhaps the ability of nicotine to induce such neuronal effects at a specific n-AChR makes it reinforcing (or aversive) to behavior. Such a mechanism of action might explain why nicotine appears to both increase and decrease arousal levels in animals (or humans) exhibiting differential basal level of excitability (Hendry and Rosecrans 1982), or why some people never become dependent on nicotine. How nicotine alters the n-AChR may also be beneficial to our understanding of the subtle nature of cholinergic neuronal function in learning, memory, and other behavioral states. The ability of ACh (or nicotine) to induce an activation or attenuation of some cholinergic or noncholinergic neuron or both may be important to these brain processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of 1,3-di-n-butyl-7-(2-oxopropyl)-xanthine (denbufylline) on metabolism and function of cerebral cholinergic neurons.

Effect of denbufylline, a low Km phosphodiesterase inhibitor, on cerebral cholinergic neurons was investigated using male Wistar rats. Single administrations of denbufylline (3, 10 and 30 mg/kg, p.o.) decreased cerebral cortical, hippocampal and striatal acetylcholine (ACh) contents in a dose-dependent manner. However, denbufylline (30 mg/kg, p.o.) had no effect on the activities of ACh synthesizing and degrading enzymes in these brain areas. In vitro addition of denbufylline (10(-8)-10(-4) M) produced no significant change in [3H]choline uptake in striatal slices, while denbufylline (10(-4) M) increased high (20 mM) potassium-evoked endogenous ACh release from striatal slices. Denbufylline (30 mg/kg, p.o.) increased cyclic AMP (cAMP) contents in the cerebral cortex, hippocampus and striatum. In vitro addition of dibutyryl cAMP (5 x 10(-3) M) also accentuated the high (20 mM) potassium-evoked endogenous ACh release from striatal slices. These results suggest that denbufylline may induce the facilitation of ACh turnover by enhancing endogenous ACh release via the increase of cAMP content in the brain.

Effect of l,3-Di-n-Butyl-7-(2-Oxopropyl)-Xanthine (Denbufylline) on Metabolism and Function of Cerebral Cholinergic Neurons

Effect of denbufylline, a low Km phosphodiesterase inhibitor, on cerebral cholinergic neurons was investigated using male Wistar rats. Single administrations of denbufylline (3, 10 and 30 mg/kg, p.o.) decreased cerebral cortical, hippocampal and striatal acetylcholine (ACh) contents in a dose-dependent manner. However, denbufylline (30 mg/kg, p.o.) had no effect on the activities of ACh synthesizing and degrading enzymes in these brain areas. In vitro addition of denbufylline (10-8-10-4 M) produced no significant change in [3H]choline uptake in striatal slices, while denbufylline (10-4 M) increased high (20 mM) potassium-evoked endogenous ACh release from striatal slices. Denbufylline (30 mg/kg. p.o.) increased cyclic AMP (cAMP) contents in the cerebral cortex, hippocampus and striatum. In vitro addition of dibutyryl cAMP (5 × 10-3 M) also accentuated the high (20 mM) potassium-evoked endogenous ACh release from striatal slices. These results suggest that denbufylline may induce the facilitation of ACh turnover by enhancing endogenous ACh release via the increase of cAMP content in the brain.

Catecholamine and Acetylcholine in the, Rat Cerebral Cortex with Special Reference to, Pathogenetic Mechanisms of Alzheimer’s Disease

A direct synapse between catecholamine fibers and neuropeptide Y-containing neurons is demonstrated in rat cerebral cortex using an immunohistochemical double-staining method under the electron microscope. A new method to produce a selective reduction in cholinergic neurons in the basal forebrain without damage to the non-cholinergic neurons, passing fibers or other cholinergic systems, is described. This animal model seems to be very useful to analyze the pathogenesis of Alzheimer's disease and to examine the function of cholinergic neurons of the basal forebrain.

An Investigation of Aluminium Neurotoxicity using some In Vitro Systems

It has been shown that acute exposure in vitro to high concentrations of aluminium chloride does not appear to perturb neural function in terms of the electrophysiological properties of lower vertebrate leech neurones. Longer term exposure in vitro, however, both non-specifically inhibits cellular differentiation and also produces neural cytotoxicity in the rat midbrain micromass, mixed cell culture model. Furthermore, previous studies from this laboratory have demonstrated a reduction of cholinergic neuronal function in brain organotypic reaggregate cultures following long-term, but not short-term, exposure. More-immature neural cells appear to be most sensitive to the effects of aluminium. Relating these data to the tiered in vitro test system for neurotoxicants previously proposed by Atterwill (13), it is apparent that the neurotoxic effects of aluminium are detectable in a first-stage procedure using the micromass culture model, but not following acute exposure in freshly isolated, ex vivo leech neurones. Functional cholinergic toxicity was also detected in the organotypic reaggregate cultures proposed as a second level screen.

Brain-derived neurotrophic factor increases survival and differentiated functions of rat septal cholinergic neurons in culture

Brain-derived neurotrophic factor (BDNF) was found to promote the survival of Ell 7 rat embryo septal cholinergic neurons in culture, as assessed by a histochemical stain for acetylcholinesterase (AChE). A 2.4-fold increase in neuronal survival was achieved with 10 ng/ml BDNF After initial deprivation of growth factor for 7 days, BDNF failed to bring about this increase, strongly suggesting that BDNF promotes cell survival and not just induction of AChE. BDNF was also found to increase the levels of cholinergic enzymes; choline acetyltransferase (ChAT) and AChE activities were increased by approximately 2-fold in the presence of 50 ng/ml BDNF BDNF produced a 3-fold increase in the number of cells bearing the NGF receptor, as detected by the monoclonal antibody IgG-192. Although NGF had no additive effect with BDNF in terms of neuronal survival, suggesting that both act on a similar neuronal population, the combination of both produced an additive response, approximately a 6-fold increase, in ChAT activity.

Evidence for a physiological role of nerve growth factor in the central nervous system of neonatal rats

Forebrain cholinergic neurons have been shown to respond in vivo to administration of nerve growth factor (NGF) with a prominent and selective increase of choline acetyltransferase (ChAT) activity. This has suggested that NGF can act as a trophic factor for these neurons. To test this hypothesis directly, anti-NGF antibodies (and their Fab fragments) were intracerebroventricularly injected into neonatal rats to neutralize endogenously occurring NGF. The anti-NGF antibody adminstration produced a decrease of ChAT activity in the hippocampus, septal area, cortex, and striatum of rat pups. This finding was substantiated by a concomitant decrease of immunopositive staining for ChAT in the septal area. These effects indicate that the occurrence of endogenous NGF in the CNS is physiologically relevant for regulating the function of forebrain cholinergic neurons.