NADPH diaphorase-containing striatal or cortical neurons are resistant to apoptosis

The Role of Voltage-Gated Calcium Channels in Basal Ganglia Neurodegenerative Disorders

Calcium (Ca2+) plays a central role in regulating many cellular processes and influences cell survival. Several mechanisms can disrupt Ca2+ homeostasis to trigger cell death, including oxidative stress, mitochondrial damage, excitotoxicity, neuroinflammation, autophagy, and apoptosis. Voltage-gated Ca2+ channels (VGCCs) act as the main source of Ca2+ entry into electrically excitable cells, such as neurons, and they are also expressed in glial cells such as astrocytes and oligodendrocytes. The dysregulation of VGCC activity has been reported in both Parkinson's disease (PD) and Huntington's (HD). PD and HD are progressive neurodegenerative disorders (NDs) of the basal ganglia characterized by motor impairment as well as cognitive and psychiatric dysfunctions. This review will examine the putative role of neuronal VGCCs in the pathogenesis and treatment of central movement disorders, focusing on PD and HD. The link between basal ganglia disorders and VGCC physiology will provide a framework for understanding the neurodegenerative processes that occur in PD and HD, as well as a possible path towards identifying new therapeutic targets for the treatment of these debilitating disorders.

Microelectrode implants, inflammatory response and long-lasting effects on NADPH diaphorase neurons in the rat frontal cortex

At present, one of the main therapeutic challenges comprises the development of technologies to improve the life quality of people suffering from different types of body paralysis, through the reestablishment of sensory and motor functions. In this regard, brain-machine interfaces (BMI) offer hope to effectively mitigate body paralysis through the control of paralyzed body parts by brain activity. Invasive BMI use chronic multielectrode implants to record neural activity directly from the brain tissue. While such invasive devices provide the highest amount of usable neural activity for BMI control, they also involve direct damage to the nervous tissue. In the cerebral cortex, high levels of the enzyme NADPH diaphorase (NADPH-d) characterize a particular class of interneurons that regulates neuronal excitability and blood supply. To gain insight into the biocompatibility of invasive BMI, we assessed the impact of chronic implanted tungsten multielectrode bundles on the distribution and morphology of NADPH-d-reactive neurons in the rat frontal cortex. NADPH-d neuronal labeling was correlated with glial response markers and with indices of healthy neuronal activity measured by electrophysiological recordings performed up to 3 months after multielectrode implantation. Chronic electrode arrays caused a small and quite localized structural disturbance on the implanted site, with neuronal loss and glial activation circumscribed to the site of implant. Electrodes remained viable during the entire period of implantation. Moreover, neither the distribution nor the morphology of NADPH-d neurons was altered. Overall, our findings provide additional evidence that tungsten multielectrodes can be employed as a viable element for long-lasting therapeutic BMI applications.

Factor XII protects neurons from apoptosis by epidermal and hepatocyte growth factor receptor-dependent mechanisms

BACKGROUND

Factor XII (FXII) is a serine protease that participates in the intrinsic coagulation pathway. Several studies have shown that plasma FXII exerts a deleterious role in cerebral ischemia and traumatic brain injury by promoting thrombo-inflammation. Nevertheless, the impact of FXII on neuronal cell fate remains unknown.

OBJECTIVES

We investigated the role of FXII and FXIIa in neuronal injury and apoptotic cell death.

METHODS

We tested the neuroprotective roles of FXII and FXIIa in an experimental model of neuronal injury induced by stereotaxic intracerebral injection of N-methyl-D-aspartic acid (NMDA) in vivo and in a model of apoptotic death of murine primary neuronal cultures through serum deprivation in vitro.

RESULTS

Here, we found that exogenous FXII and FXIIa reduce brain lesions induced by NMDA injection in vivo. Furthermore, FXII protects cultured neurons from apoptosis through a growth factor--like effect. This mechanism was triggered by direct interaction with epidermal growth factor (EGF) receptor and subsequent activation of this receptor. Interestingly, the "proteolytically" active and two-chain form of FXII, FXIIa, exerts its protective effects by an alternative signaling pathway. FXIIa activates the pro-form of hepatocyte growth factor (HGF) into HGF, which in turn activated the HGF receptor (HGFR) pathway.

CONCLUSION

This study describes two novel mechanisms of action of FXII and identifies neurons as target cells for the protective effects of single and two-chain forms of FXII. Therefore, inhibition of FXII in neurological disorders may have deleterious effects by preventing its beneficial effects on neuronal survival.

Leigh syndrome: neuropathology and pathogenesis

Leigh syndrome (LS) is the most common pediatric presentation of a defined mitochondrial disease. This progressive encephalopathy is characterized pathologically by the development of bilateral symmetrical lesions in the brainstem and basal ganglia that show gliosis, vacuolation, capillary proliferation, relative neuronal preservation, and by hyperlacticacidemia in the blood and/or cerebrospinal fluid. Understanding the molecular mechanisms underlying this unique pathology has been challenging, particularly in view of the heterogeneous and not yet fully determined genetic basis of LS. Moreover, animal models that mimic features of LS have only been created relatively recently. Here, we review the pathology of LS and consider what might be the molecular mechanisms underlying its pathogenesis. Data from a wide range of sources, including patient samples, animal models, and studies of hypoxic-ischemic encephalopathy (a condition that shares features with LS), were used to provide insight into the pathogenic mechanisms that may drive lesion development. Based on current data, we suggest that severe ATP depletion, gliosis, hyperlacticacidemia, reactive oxygen species, and potentially excitotoxicity cumulatively contribute to the neuropathogenesis of LS. An intimate understanding of the molecular mechanisms causing LS is required to accelerate the development of LS treatments.

Protective effect of apelin on cultured rat bone marrow mesenchymal stem cells against apoptosis

Bone marrow-derived mesenchymal stem cells (BMSCs) have shown great promise for ischemic tissue repair. However, poor viability of transplanted BMSCs within ischemic tissues has limited their therapeutic potential. Apelin, an endogenous peptide, whose level is elevated following ischemia, has been shown to enhance survival of cardiomyocytes and neuronal cells during ischemia. We hypothesized that apelin-13 protects BMSCs from apoptotic death. In this paper we determined the potential mechanism of apelin-13 effects using cultured BMSCs from adult rats. Apoptosis was induced by the specific apoptotic insult serum deprivation (SD) for up to 36 h. Apoptotic cell death was measured using immunostaining and Western blotting in the presence and absence of apelin-13 (0.1 to 5.0 nM) co-applied during SD exposure. SD-induced apoptosis was significantly reduced by apelin-13 in a concentration-dependent manner. SD-induced mitochondrial depolarization, cytochrome c release, and caspase-3 activation were largely prevented by apelin-13. The apelin-13 anti-apoptotic effects were blocked by inhibiting the MAPK/ERK1/2 and PI3K/Akt signaling pathways. Taken together, our findings indicate that apelin-13 is a survival factor for BMSCs and its anti-apoptotic property may prove to be of therapeutic significance in terms of exploiting BMSC-based transplantation therapy.

Mitochondrial UCP4 mediates an adaptive shift in energy metabolism and increases the resistance of neurons to metabolic and oxidative stress

The high-metabolic demand of neurons and their reliance on glucose as an energy source places them at risk for dysfunction and death under conditions of metabolic and oxidative stress. Uncoupling proteins (UCPs) are mitochondrial inner membrane proteins implicated in the regulation of mitochondrial membrane potential (Deltapsim) and cellular energy metabolism. The authors cloned UCP4 cDNA from mouse and rat brain, and demonstrate that UCP4 mRNA is expressed abundantly in brain and at particularly high levels in populations of neurons believed to have high-energy requirements. Neural cells with increased levels of UCP4 exhibit decreased Deltapsim, reduced reactive oxygen species (ROS) production and decreased mitochondrial calcium accumulation. UCP4 expressing cells also exhibited changes of oxygen-consumption rate, GDP sensitivity, and response of Deltapsim to oligomycin that were consistent with mitochondrial uncoupling. UCP4 modulates neuronal energy metabolism by increasing glucose uptake and shifting the mode of ATP production from mitochondrial respiration to glycolysis, thereby maintaining cellular ATP levels. The UCP4-mediated shift in energy metabolism reduces ROS production and increases the resistance of neurons to oxidative and mitochondrial stress. Knockdown of UCP4 expression by RNA interference in primary hippocampal neurons results in mitochondrial calcium overload and cell death. UCP4-mRNA expression is increased in neurons exposed to cold temperatures and in brain cells of rats maintained on caloric restriction, suggesting a role for UCP4 in the previously reported antiageing and neuroprotective effects of caloric restriction. By shifting energy metabolism to reduce ROS production and cellular reliance on mitochondrial respiration, UCP4 can protect neurons against oxidative stress and calcium overload.

Early involvement of small inhibitory cortical interneurons in Alzheimer's disease

Work on acute models of cortical injury has revealed a population of small GABAergic interneurons that are induced to increase their low constitutive expression of neuronal nitric oxide (NO) synthase (nNOS). In some cases, this activation may play a role in NO-mediated degeneration of pyramidal neurons. In this report, we explore the anatomy of various classes of cortical nNOS (+) (nitrergic) neurons, with emphasis on small interneurons, in the medial temporal lobe of subjects with Alzheimer's disease (AD) from two well-characterized cohorts, the Baltimore Longitudinal Study on Aging (BLSA) and the Religious Order Study (ROS). We find that small calbindin (+) cortical interneurons are induced to high levels of NADPHd/nNOS reactivity early in AD and abound in areas with emerging neurofibrillary pathology, that is, in entorhinal cortex in the beginning of the limbic stage of Braak, in hippocampal CA1 in the mature limbic stage and in temporal neocortex in the late limbic stage. This pattern was robust and significant in the younger of the two AD cohorts studied (BLSA), but persisted as a trend in the older cohort (ROS). In optimally prepared material, we find a significant correlation between numbers of these interneurons and markers of neuronal cell death, for example, caspase-3 activation. Our results show that small cortical inhibitory interneurons represent an extensive signaling system that is induced to higher levels of NADPHd/nNOS expression early in the paralimbic-limbic-neocortical sequence of AD progression. We propose that nNOS/NO signaling initiated in these interneurons can serve as a marker of early cortical injury in AD. The specific role played by inhibitory interneurons and NO in the elaboration of specific neuropathologies associated with AD, that is, Abeta and neurofibrillary deposits and cell death deserves further exploration in experimental animal models.

Neuropeptide Y protects against methamphetamine-induced neuronal apoptosis in the mouse striatum

Methamphetamine (METH) is an illicit drug that causes neuronal apoptosis in the mouse striatum, in a manner similar to the neuronal loss observed in neurodegenerative diseases. In the present study, injections of METH to mice were found to cause the death of enkephalin-positive projection neurons but not the death of neuropeptide Y (NPY)/nitric oxide synthase-positive striatal interneurons. In addition, these METH injections were associated with increased expression of neuropeptide Y mRNA and changes in the expression of the NPY receptors Y1 and Y2. Administration of NPY in the cerebral ventricles blocked METH-induced apoptosis, an effect that was mediated mainly by stimulation of NPY Y2 receptors and, to a lesser extent, of NPY Y1 receptors. Finally, we also found that neuropeptide Y knock-out mice were more sensitive than wild-type mice to METH-induced neuronal apoptosis of both enkephalin- and nitric oxide synthase-containing neurons, suggesting that NPY plays a general neuroprotective role within the striatum. Together, our results demonstrate that neuropeptide Y belongs to the class of factors that maintain neuronal integrity during cellular stresses. Given the similarity between the cell death patterns induced by METH and by disorders such as Huntington's disease, our results suggest that NPY analogs might be useful therapeutic agents against some neurodegenerative processes.

The immunohistochemical localization of neuronal nitric oxide synthase in the basal forebrain of the dog

The present work describes for the first time the anatomical distribution of neuronal nitric oxide synthase (nNOS) immunoreactivity and NADPH-d activity in the basal forebrain of the dog. As in other species, small, intensely nNOS-immunoreactive cells were seen within the olfactory tubercle, caudate nucleus, putamen, nucleus accumbens and amygdala. In addition, a population of mixed large and small nNOS positive cells was found in the medial septum, diagonal band and nucleus basalis overlapping the distribution of the magnocellular cholinergic system of the basal forebrain. Our results show that the distribution of NOS containing neurons in these nuclei in the dog is more extensive and uniform than that reported in rodents and primates. When double labeling of nNOS and NADPH-d was performed in the same tissue section most neurons were double labeled. However, a considerable number of large perikarya in the diagonal band and nucleus basalis appeared to be single labeled for nNOS. Thought a certain degree of interference between the two procedures could not be completely excluded, these findings suggest that NADPH-d histochemistry, which is frequently used to show the presence of NOS, underestimates the potential of basal forebrains neurons to produce nitric oxide. In addition, a few neurons mainly localized among the fibers of the internal capsule, appeared to be labeled only for NADPH-d. These neurons could be expressing a different isoform of NOS, not recognized by our anti-nNOS antibody, as has been reported in healthy humans and AD patients.

Creatine and neurotrophin-4/5 promote survival of nitric oxide synthase-expressing interneurons in striatal cultures

Nitric oxide (NO) mediates a variety of physiological functions in the central nervous system and acts as an important developmental regulator. Striatal interneurons expressing neuronal nitric oxide synthase (nNOS) have been described to be relatively spared from the progressive cell loss in Huntington's disease (HD). We have recently shown that creatine, which supports the phosphagen energy system, induces the differentiation of GABAergic cells in cultured striatal tissue. Moreover, neurotrophin-4/5 (NT-4/5) has been found to promote the survival and differentiation of cultured striatal neurons. In the present study, we assessed the effects of creatine and NT-4/5 on nNOS-immunoreactive (-ir) neurons of E14 rat ganglionic eminences grown for 1 week in culture. Chronic administration of creatine [5mM], NT-4/5 [10ng/ml], or a combination of both factors significantly increased numbers of nNOS-ir neurons. NT-4/5 exposure also robustly increased levels of nNOS protein. Interestingly, only NT-4/5 and combined treatment significantly increased general viability but no effects were seen for creatine supplementation alone. In addition, NT-4/5 and combined treatment resulted in a significant larger soma size and number of primary neurites of nNOS-ir neurons while creatine administration alone exerted no effects. Double-immunolabeling studies revealed that all nNOS-ir cells co-localized with GABA. In summary, our findings suggest that creatine and NT-4/5 affect differentiation and/or survival of striatal nNOS-ir GABAergic interneurons. These findings provide novel insights into the biology of developing striatal neurons and highlight the potential of both creatine and NT-4/5 as therapeutics for HD.

Neuroprotection and aging of the cholinergic system: a role for the ergoline derivative nicergoline (Sermion)

The aging brain is characterized by selective neurochemical changes involving several neural populations. A deficit in the cholinergic system of the basal forebrain is thought to contribute to the development of cognitive symptoms of dementia. Attempts to prevent age-associated cholinergic vulnerability and deterioration therefore represent a crucial point for pharmacotherapy in the elderly. In this paper we provide evidence for the protective effect of nicergoline (Sermion) on the degeneration of cholinergic neurons induced by nerve growth factor deprivation. Nerve growth factor deprivation was induced by colchicine administration in rats 13 and 18 months old. Colchicine induces a rapid and substantial down-regulation of choline acetyltransferase messenger RNA level in the basal forebrain in untreated adult, middle-aged and old rats. Colchicine failed to cause these effects in old rats treated for 120 days with nicergoline 10 mg/kg/day, orally. Moreover, a concomitant increase of both nerve growth factor and brain-derived neurotrophic factor content was measured in the basal forebrain of old, nicergoline-treated rats. Additionally, the level of messenger RNA for the brain isoform of nitric oxide synthase in neurons of the basal forebrain was also increased in these animals. Based on the present findings, nicergoline proved to be an effective drug for preventing neuronal vulnerability due to experimentally induced nerve growth factor deprivation.

NMDA antagonists exacerbate neuronal death caused by proteasome inhibition in cultured cortical and striatal neurons

The proteasome is involved in multiple cellular processes including control of the cell cycle, apoptosis and intracellular signalling; loss of proteasome function has been postulated to participate in the pathogenesis of triplet repeat diseases. We examined the vulnerability of central neurons to proteasome inhibition and tested the ability of anti-excitotoxic and anti-apoptotic treatments to attenuate proteasome inhibition-induced neuronal death. Exposure of murine neocortical cultures to proteasome inhibitors (0.1-10 microm clasto-lactacystin beta-lactone or MG-132) for 48 h resulted in widespread neuronal death associated with a reduction in intracellular free calcium; higher inhibitor concentrations killed astrocytes. Cultured striatal neurons were more vulnerable than cortical neurons. Within each population, the NADPH diaphorase-positive neuronal subpopulation was more vulnerable than the general neuronal population. Enhancing calcium entry with S(-)BayK8644 or kainate, or blocking apoptosis with cycloheximide, actinomycin D or Z-VAD.FMK attenuated neuronal death, whereas, reducing calcium entry with NMDA antagonists or R(+)BayK8644 potentiated neuronal death. These findings suggest that proteasome inhibition can induce selective neuronal apoptosis associated with intracellular calcium starvation, and point to manipulation of intracellular calcium as a specific therapeutic strategy. In particular, concern is raised that glutamate receptor antagonists might exacerbate, rather than attenuate, proteasome inhibition-induced neuronal death.

Quantitative changes in reduced nicotinamide adenine dinucleotide phosphate-diaphorase-reactive neurons in the brain of Octodon degus after periodic maternal separation and early social isolation

The influence of preweaning maternal separation and postweaning social isolation on the development of reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase-reactive neurons in prefrontal cortical areas, in subdivisions of the nucleus accumbens and in the corpus callosum was quantitatively investigated in the precocious rodent Octodon degus. Forty-five-day-old degus from three animal groups were compared: (i) degus that were reared under normal undisturbed social conditions; (ii) degus that were repeatedly separated from their mothers during the first three postnatal weeks and thereafter reared with their family; and (iii) degus that remained undisturbed with the family until weaning (postnatal day 21) and thereafter were reared in social isolation. Preweaning maternal separation led to a significant decrease in NADPH-diaphorase-containing neurons in the corpus callosum in both genders (down to 33%) compared with the social control group. No significant changes were found in the subregions of the medial prefrontal cortex and nucleus accumbens. Postweaning social isolation led to a reduced density of NADPH-diaphorase-containing neurons in the corpus callosum in both genders (down to 52%) compared with the social control group. Furthermore, in the precentral medial cortex of female pups, a significant reduction in NADPH-diaphorase-reactive neurons (down to 72%) was detectable. All other regions of the medial prefrontal cortex and the nucleus accumbens remained unchanged. The observed deprivation-induced changes may reflect either an excessive reduction in NADPH-diaphorase-positive neurons or a down-regulation of the enzyme in neurons that normally express it.Our results indicate a link between early adverse socio-emotional experience and the maturation of NADPH-reactive neurons. Further studies are required to analyse the functional implications of this experience-induced brain pathology.

Retinoic acid-mediated enhancement of the cholinergic/neuronal nitric oxide synthase phenotype of the medial septal SN56 clone: establishment of a nitric oxide-sensitive proapoptotic state

It is unclear what mechanisms lead to the degeneration of basal forebrain cholinergic neurons in Alzheimer's or other human brain diseases. Some brain cholinergic neurons express neuronal nitric oxide (NO) synthase (nNOS), which produces a free radical that has been implicated in some forms of neurodegeneration. We investigated nNOS expression and NO toxicity in SN56 cells, a clonal cholinergic model derived from the medial septum of the mouse basal forebrain. We show here that, in addition to expressing choline acetyltransferase (ChAT), SN56 cells express nNOS. Treatment of SN56 cells with retinoic acid (RA; 1 microM) for 48 h increased ChAT mRNA (+126%), protein (+88%), and activity (+215%) and increased nNOS mRNA (+98%), protein (+400%), and activity (+15%). After RA treatment, SN56 cells became vulnerable to NO excess generated with S-nitro-N-acetyl-DL-penicillamine (SNAP) and exhibited increased nuclear DNA fragmentation that was blocked with a caspase-3 inhibitor. Treatment with dexamethasone, which largely blocked the RA-mediated increase in nNOS expression, or inhibition of nNOS activity with methylthiocitrulline strongly potentiated the apoptotic response to SNAP in RA-treated SN56 cells. Caspase-3 activity was reduced when SNAP was incubated with cells or cell lysates, suggesting that NO can directly inhibit the protease. Thus, whereas RA treatment converts SN56 cells to a proapoptotic state sensitive to NO excess, endogenously produced NO appears to be anti-apoptotic, possibly by tonically inhibiting caspase-3.

Constitutive and inducible nitric oxide synthases after dynorphin-induced spinal cord injury

It has recently been demonstrated that selective inhibition of both neuronal constitutive and inducible nitric oxide synthases (ncNOS and iNOS) is neuroprotective in a model of dynorphin (Dyn) A(1-17)-induced spinal cord injury. In the present study, various methods including the conversion of 3H-L-arginine to 3H-citrulline, immunohistochemistry and in situ hybridization are employed to determine the temporal profiles of the enzymatic activities, immunoreactivities, and mRNA expression for both ncNOS and iNOS after intrathecal injection of a neurotoxic dose (20 nmol) of Dyn A(1-17). The expression of ncNOS immunoreactivity and mRNA increased as early as 30 min after injection and persisted for 1-4 h. At 24-48 h, the number of ncNOS positive cells remained elevated while most neurons died. The cNOS enzymatic activity in the ventral spinal cord also significantly increased at 30 min 48 h, but no significant changes in the dorsal spinal cord were observed. However, iNOS mRNA expression increased later at 2 h, iNOS immunoreactivity and enzymatic activity increased later at 4 h and persisted for 24-48 h after injection of 20 nmol Dyn A(1-17). These results indicate that both ncNOS and iNOS are associated with Dyn-induced spinal cord injury, with ncNOS predominantly involved at an early stage and iNOS at a later stage.

Maternal separation and early social deprivation in Octodon degus: quantitative changes of nicotinamide adenine dinucleotide phosphate-diaphorase-reactive neurons in the prefrontal cortex and nucleus accumbens

The influence of postnatal socio-emotional deprivation on the development of nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase-reactive neurons in prefrontal cortical areas and in subdivisions of the nucleus accumbens was quantitatively investigated in the precocious rodent Octodon degus. Forty-five-days-old O. degus from two animal groups were compared: (i) degus which were repeatedly separated from their mothers during the first three postnatal weeks and after weaning reared in complete isolation; and (ii) degus which were reared under normal undisturbed social conditions. Socially-deprived animals displayed a significant decrease of NADPH-diaphorase-containing neurons in anterior cingulate cortex (85.5%), the same tendency was observed in the infralimbic, precentral medial and prelimbic prefrontal areas. Similarly, the core region of nucleus accumbens expressed reduced NADPH-diaphorase-reactive neuron numbers in deprived animals (70%), whereas the shell region remained unchanged. Since during normal postnatal development the number of NADPH-diaphorase-reactive neurons gradually decreases in all prefrontal cortical and accumbal regions, the observed deprivation-induced changes may reflect either an excessive reduction of NADPH-diaphorase-positive neurons or a down-regulation of the enzyme in neurons that normally express it. Since some NADPH-diaphorase-containing neurons in the prefrontal cortex have been shown to be GABAergic, it is tempting to speculate that a reduction of these inhibitory neurons in the anterior cingulate cortex may result in an enhanced excitatory output activity of disinhibited projection neurons in this cortical region, including those that project to the core region of the nucleus accumbens. Our results indicate a link between early adverse socio-emotional experience and the maturation of NADPH-reactive neurons and further studies are required to analyse the functional implication for this experience-induced brain pathology.

Neuronal death in cultured murine cortical cells is induced by inhibition of GAPDH and triosephosphate isomerase

Polyglutamine-containing proteins expressed in the CAG repeat diseases Huntington's disease and dentatorubralpallidoluyisian atrophy have recently been suggested to inhibit the key glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). To examine the consequences of GAPDH inhibition upon neuronal survival, we exposed murine neocortical cell cultures to the inhibitor of GAPDH and triosephosphate isomerase, alpha-monochlorohydrin. Cultures exposed to 6-15 mM alpha-monochlorohydrin for 48 h exhibited an increase in dihydroxyacetone phosphate and a decrease in neuronal ATP that was followed by progressive neuronal death; some glial death occurred at high drug concentrations. The neuronal death was characterized by cell body shrinkage and chromatin condensation and was sensitive to cycloheximide and to the caspase inhibitors Z-Val-Ala-Asp fluoromethylketone and tert-butoxycarbonyl-Asp fluoromethylketone. Neurons in striatal cell cultures were more vulnerable to death induced by exposure to alpha-monochlorohydrin, except that NADPH-diaphorase(+) neurons were selectively spared. Repeated addition of the glycolytic endpoint metabolite pyruvate to the bathing medium attenuated both the drop in neuronal ATP and the neuronal cell death.

Differential expression of NADPH-diaphorase between electrophysiologically-defined classes of pyramidal neurons in rat ventral subiculum, in vitro

The subiculum is the major output region of the hippocampal formation. We have studied pyramidal neurons in slices of rat ventral subiculum to determine if there is a correlation between nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) activity and electrophysiological phenotype. The majority of NADPH-d-positive pyramidal neurons were found in the superficial cell layer (i.e. nearest to the hippocampal fissure) of the subiculum and appreciable NADPH-d activity was absent from pyramidal neurons in area CA1. This distribution of NADPH-d activity was mimicked by that of immunoreactivity for the neuronal isoform of nitric oxide synthase. Subicular pyramidal neurons were classified, electrophysiologically, as intrinsically burst-firing or regular spiking. After electrophysiological characterization, neurons were filled with Neurobiotin and revealed using fluorescence immunocytochemistry. The slices containing these neurons were also processed for NADPH-d. NADPH-d activity was found in six out of eight regular spiking neurons but was not found in any of 13 intrinsically burst-firing neurons (P=0.0008, Fisher's Exact Test). We conclude that in rat ventral subiculum, NADPH-d activity is present in a proportion of pyramidal neurons and indicates the presence of the neuronal isoform of nitric oxide synthase. Furthermore, amongst pyramidal neurons, NADPH-d activity is distributed preferentially to those with the regular spiking phenotype. The distribution of regular spiking neurons suggests that they may not be present to the same extent in all subicular output pathways. Thus, the actions of nitric oxide may be relatively specific to particular hippocampal connections.

Apoptosis, neurotrophic factors and neurodegeneration

Apoptosis is an active process of cell death characterized by distinct morphological features, and is often the end result of a genetic programme of events, i.e. programmed cell death (PCD). There is growing evidence supporting a role for apoptosis in some neurodegenerative diseases. This conclusion is based on DNA fragmentation studies and findings of increased levels of pro-apoptotic genes in human brain and in in vivo and in vitro model systems. Additionally, there is some evidence for a loss of neurotrophin support in neurodegenerative diseases. In Alzheimer's disease, in particular, there is strong evidence from human brain studies, transgenic models and in vitro models to suggest that the mode of nerve cell death is apoptotic. In this review we describe the evidence implicating apoptosis in neurodegenerative diseases with a particular emphasis on Alzheimer's disease.