The effects of methamphetamine self‐administration on cortical monoaminergic deficits induced by subsequent high‐dose methamphetamine administrations

Preclinical models suggest that repeated high‐dose methamphetamine (METH) exposures, administered in a “binge‐like” pattern, acutely decrease norepinephrine (NE), and acutely and persistently decrease serotonin (5‐hydroxytryptamine; 5HT) content in the frontal cortex. However, the impact of METH self‐administration on this region is unknown. Because of the importance of the monoaminergic neurons in the frontal cortex to a variety of cognitive and addictive processes, effects of METH self‐administration on cortical NE and 5HT content were assessed. Results revealed several novel findings. First, METH self‐administration decreased cortical NE content as assessed 24 h after last exposure. Consistent with previous preclinical reports after a binge METH regimen, this decrease was reversed 8 days after the final METH exposure. Second, and in contrast to our previous reports involving the hippocampus or striatum, METH self‐administration caused persistent decreases in 5HT content as assessed 8 days after the final METH exposure. Of note, the magnitude of this decrease (～20%) was less than that observed typically after a binge METH treatment. Third, prior METH self‐administration attenuated METH‐induced serotonergic deficits as assessed 7 days, but not 1 h, following a neurotoxic METH regimen. No protection was observed when the binge exposure occurred 15 days after the last self‐administration session. Taken together, these data demonstrate important and selective alterations in cortical serotonergic neuronal function subsequent to METH self‐administration. These data provide a foundation to investigate complex questions involving “resistance” to the persistent deficits caused by neurotoxic METH exposure and frontal cortical function. Synapse 67:875–881, 2013 . © 2013 Wiley Periodicals, Inc.     

Glutamic acid decarboxylase-67-positive hippocampal interneurons undergo a permanent reduction in number following kainic acid-induced degeneration of ca3 pyramidal neurons

Kainic acid (KA)-induced degeneration of CA3 pyramidal neurons leads to synaptic reorganization and hyperexcitability in both dentate gyrus and CA1 region of the hippocampus. We hypothesize that the substrate for hippocampal inhibitory circuitry incurs significant and permanent alterations following degeneration of CA3 pyramidal neurons. We quantified changes in interneuron density (N(v)) in all strata of the dentate gyrus and the CA1 and CA3 subfields of adult rats at 1, 4, and 6 months following intracerebroventricular (icv) KA administration, using glutamic acid decarboxylase-67 (GAD-67) immunocytochemistry. At 1 month postlesion, GAD-67-positive interneuron density was significantly reduced in all strata of every hippocampal region except stratum pyramidale of CA1. The reduction in GAD-67-positive interneuron density either persisted or exacerbated at 4 and 6 months postlesion in every stratum of all hippocampal regions. Further, the soma of remaining GAD-67-positive interneurons in dentate gyrus and CA3 subfield showed significant hypertrophy. Thus, both permanent reductions in the density of GAD-67-positive interneurons in all hippocampal regions and somatic hypertrophy of remaining GAD-67-positive interneurons in dentate gyrus and CA3 subfield occur following icv KA. In contrast, the density of interneurons visualized with Nissl in CA1 and CA3 regions was nearly equivalent to that in the intact hippocampus at all postlesion time points. Collectively, these results suggest that persistent reductions in GAD-67-positive interneuron density observed throughout the hippocampus following CA3 lesion are largely due to a permanent loss of GAD-67 expression in a significant fraction of interneurons, rather than widespread degeneration of interneurons. Nevertheless, a persistent decrease in interneuron activity, as evidenced by permanent down-regulation of GAD-67 in a major fraction of interneurons, would likely enhance the degree of hyperexcitability in the CA3-lesioned hippocampus.     

Cognitive deficits and degeneration of interneurons in HIV+ methamphetamine users

The cellular basis for cognitive deficits in HIV+ patients with and without a history of methamphetamine (METH) use is unclear. We found that HIV+ METH users had more severe loss of interneurons that was associated with cognitive impairment. Compared with other markers, loss of calbindin and parvalbumin interneurons in the frontal cortex was the most significant correlate to memory deficits, suggesting a role in neurobehavioral alterations of HIV+ METH users.     

Selective degeneration of CA1 pyramidal cells by chronic application of bismuth

The heavy metal bismuth induces a new type of selective neuronal degeneration that shares some common aspects with that seen following hypoxia and ischemia. Continuous application of 3 μm bismuth to organotypic cultures of rat hippocampus resulted after 2–3 weeks in selective degeneration of CA1 pyramidal cells, while CA3 pyramidal cells, dentate granule cells, and subicular neurons were resistant. With 10 μm MK-801, a noncompetitive NMDA-antagonist, during the entire culturing period failed to prevent neuronal degeneration induced by 3 μm bismuth. GABA-immunoreactive interneurons were also affected by bismuth, but were generally less sensitive than CA1 pyramidal cells. Acute application of up to 100 μm bismuth did not change the electrophysiological properties of CA1 pyramidal cells. © 1994 Wiley-Liss, Inc.     

Changes in APP,PS1 and other factors related to Alzheimer's disease pathophysiology after trimethyltin-induced brain lesion in the rat

Trimethyltin (TMT) chloride induces limbic system neurodegeneration, resulting in behavioral alterations including cognitive deficits. Different factors related to Alzheimer's disease (AD) were studied after TMT lesion in Sprague-Dawley rats. The expression of amyloid precursor protein (APP) containing 695 amino acids (APP695), APP containing the Kuniz protease inhibitor domain (APP- KPI), presenilin 1 (PS1), c- fos and IL- 1Beta was investigated at different timepoints after a single TMT injection (7 mg/kg i.p.) using in situ hybridization and immunohistochemistry. After the TMT treatment, extensive degeneration of pyramidal neurons was observed in the CA3 region of the hippocampus, concomitant with neurodegeneration in the outer layer of the CA1 region and layer II of entorhinal and piriform cortex. The affected regions showed abundant condensed eosinophilic and TUNEL-positive neuronal cells, that were apparent at day 4 after TMT, increasing to day 7 and subsequently disappearing. In the affected regions the levels of APP695 mRNA gradually declined with time after the TMT injection. While there was no apparent alteration in the overall expression of APP- KPI or PS1 mRNA, detailed analysis of the CA3c region showed that the mRNA expression shifted from neurons to glial cells. Three days after TMT, neurons in the piriform cortex, the CA3 region and DG expressed high levels of c-fos mRNA that slowly declined to become normalized when analyzed at day 28. At day 7 after TMT a few distinct IL- 1Beta mRNA expressing glial cells were observed in the CA3c region. Thus, TMT exposure leads to alterations in the expresson of APP, APP- KPI, PS1, c-fos and IL- 1Beta in the limbic system. These findings suggest that TMT lesions, not only share certain key features of AD symptomatology and regional neurodegeneration, but also induce effects on important factors related to the pathophysiology of AD.     

Selective loss of pyramidal neurons in the pre-supplementary motor cortex in Parkinson's disease.

The nonprimary motor cortices have not previously been studied in Parkinson's disease, despite the selective pattern of dysfunction observed in these regions. In particular, the pre-supplementary motor region is consistently underactive, with successful treatments correlating with increased excitatory drive to nonprimary motor regions. This finding could suggest a primary cortical abnormality in the pre-supplementary motor area (pre-SMA) in Parkinson's disease. We analysed and compared neuronal number in the pre-SMA and dorsolateral premotor cortical regions in 5 cases of Parkinson's disease and 5 controls. For each cortical region, the total neuronal number as well as the estimated numbers of subpopulations of interneurons and pyramidal neurons was quantified using previously published unbiased techniques. The results showed a significant loss of cortico-cortical projecting pyramidal neurons in the pre-SMA with no loss of other pyramidal neurons or interneurons either in this region or in the dorsolateral premotor region. These findings indicate a highly selective loss of pyramidal cells in the pre-SMA in Parkinson's disease, consistent with previous imaging findings in this disease. Our results implicate the degeneration of the premotor projection from the pre-SMA, along with dopaminergic basal ganglia dysfunction, in the pathogenesis of Parkinson's disease.     

Intra-hippocampal tonic inhibition influences formalin pain-induced pyramidal cell suppression,but not excitation in dorsal field CA1 of rat

It has been hypothesized that intra-hippocampal GABAergic inhibitory interneurons mediate formalin pain-induced suppression of dorsal hippocampal CA1 pyramidal cell discharge. The present study performed on anaesthetized rats tested the hypothesis by disrupting GABAergic mechanisms with intra-hippocampal administration of the GABA_A receptor antagonist bicuculline methiodide, applied either dorsally into the pyramidal cell layer and stratum oriens (dorsal-bicuculline) or ventrally into the region of apical dendrites (ventral-bicuculline). It was found that ventral-, but not dorsal-bicuculline attenuated formalin-induced suppression of pyramidal cell extracellular discharge. The antagonism was selective in such a way that the excitation of pyramidal cell was unaffected. Interestingly, ventral-bicuculline strongly disinhibited CA1 pyramidal cells and shifted the distribution of their spontaneous discharge to values higher than the control group. However, dorsal-bicuculline disinhibited the local CA1 interneurons that were strongly excited on injection of formalin. Overall, the findings favour the notion that tonic GABA_A receptor mechanisms located in the region of apical dendrites facilitate formalin-induced pyramidal cell suppression by masking the background excitatory drive impinging on the pyramidal cells. Interestingly, both the attenuation of formalin-induced inhibition and facilitation of basal discharge of CA1 pyramidal cells by ventral-bicuculline are similar to the effects seen previously with the destruction of medial septal cholinergic neurons. This convergence of effects strengthens the proposal that the network of medial septal cholinergic neurons and hippocampal GABAergic interneurons influence formalin pain-induced CA1 pyramidal cell suppression. In addition, the data point to a non-overlapping excitatory drive whose strength is unaffected by the inhibitory drive that underpins formalin suppression.     

Mild metabolic stress is sufficient to disturb the formation of pyramidal cell ensembles during gamma oscillations

Disturbances of cognitive functions occur rapidly during acute metabolic stress. However, the underlying mechanisms are not fully understood. Cortical gamma oscillations (30–100 Hz) emerging from precise synaptic transmission between excitatory principal neurons and inhibitory interneurons, such as fast-spiking GABAergic basket cells, are associated with higher brain functions, like sensory perception, selective attention and memory formation. We investigated the alterations of cholinergic gamma oscillations at the level of neuronal ensembles in the CA3 region of rat hippocampal slice cultures. We combined electrophysiology, calcium imaging (CamKII.GCaMP6f) and mild metabolic stress that was induced by rotenone, a lipophilic and highly selective inhibitor of complex I in the respiratory chain of mitochondria. The detected pyramidal cell ensembles showing repetitive patterns of activity were highly sensitive to mild metabolic stress. Whereas such synchronised multicellular activity diminished, the overall activity of individual pyramidal cells was unaffected. Additionally, mild metabolic stress had no effect on the rate of action potential generation in fast-spiking neural units. However, the partial disinhibition of slow-spiking neural units suggests that disturbances of ensemble formation likely result from alterations in synaptic inhibition. Our study bridges disturbances on the (multi-)cellular and network level to putative cognitive impairment on the system level.     

Selective sparing of hippocampal CA3 cells following in vitro ischemia is due to selective inhibition by acidosis

A brief global ischemic insult to the brain leads to a selective degeneration of the pyramidal neurons in the hippocampal CA1 region while the neurons in the neighbouring CA3 region are spared. The reason for this difference is not known. The selective vulnerability of CA1 neurons to ischemia can be reproduced in vitro in murine organotypic slice cultures, if the ion concentrations in the medium during the anoxic/aglycemic insult are similar to that in the brain extracellular fluid during ischemia in vivo. As acidosis develops during ischemia, we studied the importance of extracellular pH for selective vulnerability. We found that cell death in the CA1 and CA3 regions was equally prevented by removal of calcium from the medium or following blockade of the N-methyl-D-aspartate (NMDA) receptor by D-2 amino-5-phosphonopentanoic-acid (D-APV). On the other hand, damage to the CA3 neurons markedly decreased with decreasing pH following in vitro ischemia, while the degeneration of CA1 neurons was less pH dependent. Patch-clamp recordings from pyramidal neurons in the CA1 and CA3 regions, respectively, revealed a pronounced inhibition of NMDA-receptor mediated excitatory postsynaptic currents (EPSCs) at pH 6.5 that was equally pronounced in the two regions. However, when changing pH from 6.5 to 7.4 the recovery of the EPSCs was significantly slower in the CA3 region. We conclude that acidosis selectively protects CA3 pyramidal neurons during in vitro ischemia, and differentially affects the kinetics of NMDA receptor activation, which may explain the difference in vulnerability between CA1 and CA3 pyramidal neurons to an ischemic insult.     

Intra-hippocampal tonic inhibition influences formalin pain-induced pyramidal cell suppression, but not excitation in dorsal field CA1 of rat

It has been hypothesized that intra-hippocampal GABAergic inhibitory interneurons mediate formalin pain-induced suppression of dorsal hippocampal CA1 pyramidal cell discharge. The present study performed on anaesthetized rats tested the hypothesis by disrupting GABAergic mechanisms with intra-hippocampal administration of the GABA(A) receptor antagonist bicuculline methiodide, applied either dorsally into the pyramidal cell layer and stratum oriens (dorsal-bicuculline) or ventrally into the region of apical dendrites (ventral-bicuculline). It was found that ventral-, but not dorsal-bicuculline attenuated formalin-induced suppression of pyramidal cell extracellular discharge. The antagonism was selective in such a way that the excitation of pyramidal cell was unaffected. Interestingly, ventral-bicuculline strongly disinhibited CA1 pyramidal cells and shifted the distribution of their spontaneous discharge to values higher than the control group. However, dorsal-bicuculline disinhibited the local CA1 interneurons that were strongly excited on injection of formalin. Overall, the findings favour the notion that tonic GABA(A) receptor mechanisms located in the region of apical dendrites facilitate formalin-induced pyramidal cell suppression by masking the background excitatory drive impinging on the pyramidal cells. Interestingly, both the attenuation of formalin-induced inhibition and facilitation of basal discharge of CA1 pyramidal cells by ventral-bicuculline are similar to the effects seen previously with the destruction of medial septal cholinergic neurons. This convergence of effects strengthens the proposal that the network of medial septal cholinergic neurons and hippocampal GABAergic interneurons influence formalin pain-induced CA1 pyramidal cell suppression. In addition, the data point to a non-overlapping excitatory drive whose strength is unaffected by the inhibitory drive that underpins formalin suppression.     

Loss of calbindin-immunoreactivity in CA1 hippocampal stratum radiatum and stratum lacunosum-moleculare interneurons in the aged rat

Alterations in hippocampal circuitry may underly age-related learning and memory impairment. We showed in a previous study that the GABA_B-mediated slow inhibitory postsynaptic potential (IPSP) induced in CA1 pyramidal neurons by electrical stimulation of stratum radiatum, is depressed in the hippocampus of the aged rat. This could be due to alterations in GABAergic interneuron functions. We report in this study that the number of hippocampal calbindin-immunoreactive (CaBP-IR) GABAergic interneurons is decreased in the aged rat. The mean number of CaBP-IR interneurons per slice decreases by 50% in the aged rat. The most severe loss was observed in the stratum radiatum of CA1 (78%), with a less consistent loss of immunoreactivity in CA3 (35%). In contrast, the mean number of interneurons containing parvalbumin (PV), was not significantly decreased in the aged rat. Our results show a loss of CaBP immunoreactivity in a population of GABAergic interneurons, which might be related to an altered function of these interneurons and consequently of GABAergic synaptic transmission in the aged rat. In contrast, PV immunoreactivity in interneurons located close to the pyramidal layer does not decrease in the hippocampus of the aged rat.     

Somatosensory stimulation suppresses the excitability of pyramidal cells in the hippocampal CA1 region in rats

The hippocampal region of the brain is important for encoding environment inputs and memory formation. However, the underlying mechanisms are unclear. To investigate the behavior of indi-vidual neurons in response to somatosensory inputs in the hippocampal CA1 region, we recorded and analyzed changes in local ifeld potentials and the ifring rates of individual pyramidal cells and interneurons during tail clamping in urethane-anesthetized rats. We also explored the mechanisms underlying the neuronal responses. Somatosensory stimulation, in the form of tail clamping, chan-ged local ifeld potentials into theta rhythm-dominated waveforms, decreased the spike ifring of py-ramidal cells, and increased interneuron ifring. In addition, somatosensory stimulation attenuated orthodromic-evoked population spikes. These results suggest that somatosensory stimulation sup-presses the excitability of pyramidal cells in the hippocampal CA1 region. Increased inhibition by local interneurons might underlie this effect. These ifndings provide insight into the mechanisms of signal processing in the hippocampus and suggest that sensory stimulation might have thera-peutic potential for brain disorders associated with neuronal hyperexcitability.     

Action of tachykinins in the rat hippocampus: modulation of inhibitory synaptic transmission

Substance P and other neuropeptides of the tachykinin family can powerfully excite CA1 hippocampal interneurons present in the CA1 region. In the present work we show that, by exciting hippocampal interneurons, tachykinins can indirectly inhibit pyramidal neurons. We found that tachykinins caused a decrease in the inhibitory synaptic current interval and an increase in the inhibitory synaptic current amplitude in almost all pyramidal neurons tested. This effect was tetrodotoxin sensitive. Tachykinins did not alter the frequency or amplitude of miniature inhibitory synaptic currents and were without effect on evoked inhibitory synaptic currents. Thus, these neuropeptides acted at the somatodendritic membrane of GABAergic interneurons, rather than at their axon terminals. The effect of substance P on spontaneous inhibitory synaptic currents could be mimicked by a selective agonist of NK1 receptors, but not by selective agonists of NK2 and NK3 receptors. It was suppressed by an NK1 receptor antagonist. In CA1 interneurons located in stratum radiatum, substance P generated a sustained tetrodotoxin-insensitive inward current or induced membrane depolarization and action potential firing. This direct excitatory action was mediated by NK1 receptors. Current-voltage relationships indicate that the net tachykinin-evoked current reversed in polarity at or near the K+ equilibrium potential, suggesting that a suppression of a resting K+ conductance was involved. By increasing the excitability of CA1 GABAergic interneurons, tachykinins can powerfully facilitate the inhibitory synaptic input to pyramidal neurons. This indirect inhibition could play a role in regulating short-term and/or long-term synaptic plasticity, promoting neuronal circuit synchronization or, in some physiopathological situations, influencing epileptogenesis.     

Loss of interneurons innervating pyramidal cell dendrites and axon initial segments in the CA1 region of the hippocampus following pilocarpine-induced seizures

In the pilocarpine model of chronic limbic seizures, vulnerability of GABAergic interneurons to excitotoxic damage has been reported in the hippocampal CA1 region. However, little is known about the specific types of interneurons that degenerate in this region. In order to characterize these interneurons, we performed quantitative analyses of the different populations of GABAergic neurons labeled for their peptide or calcium-binding protein content. Our data demonstrate that the decrease in the number of GAD mRNA-containing neurons in the stratum oriens of CA1 in pilocarpine-treated rats involved two subpopulations of GABAergic interneurons: interneurons labeled for somatostatin only (O-LM and bistratified cells) and interneurons labeled for parvalbumin only (basket and axo-axonic cells). Stratum oriens interneurons labeled for somatostatin/calbindin or somatostatin/parvalbumin were preserved. The decrease in number of somatostatin- and parvalbumin-containing neurons was observed as early as 72 hours after the sustained seizures induced by pilocarpine injection. Many degenerating cell bodies in the stratum oriens and degenerating axon terminals in the stratum lacunosum-moleculare were observed at 1 and 2 weeks after injection. In addition, the synaptic coverage of the axon initial segment of CA1 pyramidal cells was significantly decreased in pilocarpine-treated animals. These results indicate that the loss of somatostatin-containing neurons corresponds preferentially to the degeneration of interneurons with an axon projecting to stratum lacunosum-moleculare (O-LM cells) and suggest that the death of these neurons is mainly responsible for the deficit of dendritic inhibition reported in this region. We demonstrate that the loss of parvalbumin-containing neurons corresponds to the death of axo-axonic cells, suggesting that perisomatic inhibition and mechanisms controlling action potential generation are also impaired in this model.     

Nitric oxide synthase-containing neurons in the hippocampus are preserved in trimethyltin intoxication

We studied the effects of trimethyltin (TMT) (9 mg/kg, p.o.) on the nitric oxide synthase (NOS)-containing neurons in the rat hippocampus by NADPH-diaphorase histochemistry and a biochemical assay of NOS activity. TMT exposure caused the typical behavioral changes and a loss of the CA3/4 pyramidal cells, which were NADPH diaphorase-negative. The scattered interneurons and the CA1 pyramidal cells, which were NADPH diaphorase-positive, were spared. Hippocampal NOS activity showed no reduction in the TMT-treated rats compared with the controls. These results provide evidence of the preservation of the NOS-containing neurons in TMT intoxication.     

Cellular Mechanisms of Desynchronizing Effects of Hypothermia in an In Vitro Epilepsy Model

Hypothermia can terminate epileptiform discharges in vitro and in vivo epilepsy models. Hypothermia is becoming a standard treatment for brain injury in infants with perinatal hypoxic ischemic encephalopathy, and it is gaining ground as a potential treatment in patients with drug resistant epilepsy. However, the exact mechanism of action of cooling the brain tissue is unclear. We have studied the 4-aminopyridine model of epilepsy in mice using single- and dual-patch clamp and perforated multi-electrode array recordings from the hippocampus and cortex. Cooling consistently terminated 4-aminopyridine induced epileptiform-like discharges in hippocampal neurons and increased input resistance that was not mimicked by transient receptor potential channel antagonists. Dual-patch clamp recordings showed significant synchrony between distant CA1 and CA3 pyramidal neurons, but less so between the pyramidal neurons and interneurons. In CA1 and CA3 neurons, hypothermia blocked rhythmic action potential discharges and disrupted their synchrony; however, in interneurons, hypothermia blocked rhythmic discharges without abolishing action potentials. In parallel, multi-electrode array recordings showed that synchronized discharges were disrupted by hypothermia, whereas multi-unit activity was unaffected. The differential effect of cooling on transmitting or secreting γ-aminobutyric acid interneurons might disrupt normal network synchrony, aborting the epileptiform discharges. Moreover, the persistence of action potential firing in interneurons would have additional antiepileptic effects through tonic γ-aminobutyric acid release.

Electronic supplementary material

The online version of this article (doi:10.1007/s13311-011-0078-5) contains supplementary material, which is available to authorized users.     

Methamphetamine-induced gene expression profiles in the striatum of male rat pups exposed to the drug in utero

Methamphetamine is a neurotoxic pychostimulant which affects monoaminergic and non-monoaminergic systems in the brain. Clinical studies in humans have found that exposure to methamphetamine in the developing embryo can cause significant behavioral and cognitive anomalies later in life. Exposure of animals to methamphetamine (METH) in utero can cause neurobehavioral effects that do not become apparent until young adulthood. In the present study, we sought to determine the effects of in utero METH exposure on the striata of perinatal rat pups using a recently developed 17 k cDNA microarray. We found that METH administration caused alterations in 913 genes according to strict criteria. These alterations include changes in genes that participate in signal transduction, heat shock responses and neuronal development. The majority of the changes in gene expression were more prominent at the 7-day time point. These observations suggest that in utero METH exposure might initiate molecular programs that significantly impact gene expression during the developmental period long after the last exposure to this drug. Thus, during development, METH exposure in utero might cause significant long-term changes in gene expression that might constitute, in part, some of the substrates for the behavioral and cognitive anomalies reported in the literature.     

Immunocytochemical investigation of L-glutamic acid decarboxylase in the rat hippocampal formation: the influence of transient cerebral ischemia

The hippocampus is especially vulnerable to ischemic damage. Neurons in the CA3c region and dentate hilus demonstrate fast progressive damage while CA1 pyramidal cells demonstrate delayed neuronal damage. The delayed CA1 pyramidal cell loss could be caused by postischemic neuronal hyperactivity if hippocampal interneurons are lost after ischemia. Therefore we have counted the L-glutamic acid decarboxylase (GAD)-immunoreactive neurons in the hippocampus from control rats and rats surviving 4 or 11 days after 20 minutes of cerebral ischemia. All rats were injected intraventricularly with colchicine before they were killed. The hippocampal cell counts showed an increase in GAD-immunoreactive somata visualized on the fourth postischemic day. Eleven days after ischemia, the number of GAD-immunoreactive neurons visualized in the hippocampus CA1 and CA3c region decreased. GAD-immunoreactive baskets were visualized in the pyramidal cell layer and the granule cell layer in controls and 4 days after ischemia, but not in the CA1 and CA3c pyramidal cell layer 11 days after ischemia. We suggest the number of GAD-immunoreactive neurons visualized on the fourth postischemic day increases because somatal GAD accumulation increases and, therefore, ischemia may enhance GAD production. Our previous counts of CA1 interneurons 21 days after ischemia in toluidine-stained semithin sections demonstrated no interneuron loss. Therefore we suggest that the decreased number of CA1 and CA3c GAD-immunoreactive neurons visualized 11 days after ischemia is related to a decreased GAD production. It is possible at this stage after ischemia that the interneurons have decreased their GAD production because they have lost their input and/or target cells. We conclude that our counts of GAD-immunoreactive neurons visualized after ischemia express changes in the content of somatal GAD rather than the actual number of GAD-immunoreactive somata. Finally, we conclude that the delayed loss of CA1 pyramidal cells seen 4 days after ischemia is not preceded by loss of hippocampal GAD-immunoreactive neurons.     

Selective alterations in the cellular distribution of apolipoprotein E immunoreactivity following transient cerebral ischaemia in the rat

The aim of this study was to examine the cellular localization and alterations of apolipoprotein E (apoE) following a transient ischaemic insult using immunohistochemistry. Transient cerebral ischaemia was induced in Wistar rats by occlusion of both carotid arteries with hypotension followed by reperfusion for 4 h (n = 5), 24 h (n = 5) or 72 h (n = 6). In sham-operated animals (n=9), the carotids were not occluded. In this model, ischaemia for 15 min results in selective neuronal damage in the caudate nucleus and neocortex (24 h after reperfusion) and the hippocampal CA1 pyramidal cells (72 h after reperfusion) while there is minimal damage in other areas such as the CA3 hippocampal region. In sham animals, apoE immunoreactivity was confined to astrocytes and their processes. ApoE immunoreactivity was not altered at 4 h post-ischaemic reperfusion. At 24 h reperfusion, intense apoE staining of the cytoplasm of astrocytes and neuropil within the caudate and neocortex was observed and at 72 h reperfusion apoE stained neuronal cell bodies within these regions. Within the CA1 region at 24 h reperfusion, there was increased immunoreactivity of the cytoplasm of astrocytes and the neuropil was more intensely stained compared with sham animals. At 72 h reperfusion, intense apoE staining of pyramidal cell bodies and dendrites was consistently observed in the CA1 region of the hippocampus. In contrast, at 72 h reperfusion, apoE staining of astrocytic processes was dramatically reduced in the CA1 region although GFAP staining indicated their preservation. The results demonstrate that following an ischaemic insult apoE is localized to degenerating neurons and their processes. This may indicate an inherent protective response of cells to injury. Alternatively, the results are consistent with the hypothesis that apoE is synthesized and released by astrocytes and taken up by neurons following injury.     

Persistent cognitive and dopamine transporter deficits in abstinent methamphetamine users

BACKGROUND: Studies in abstinent methamphetamine (METH) users have demonstrated reductions in brain dopamine transporter (DAT) binding potential (BP), as well as cognitive and motor deficits, but it is not yet clear whether cognitive deficits and brain DAT reductions fully reverse with sustained abstinence, or whether behavioral deficits in METH users are related to dopamine (DA) deficits. This study was conducted to further investigate potential persistent psychomotor deficits secondary to METH abuse, and their relationship to brain DAT availability, as measured using quantitative PET methods with [(11)C]WIN 35428. METHODS: Twenty-two abstinent METH users and 17 healthy non-METH using controls underwent psychometric testing to test the hypothesis that METH users would demonstrate selective deficits in neuropsychiatric domains known to involve DA neurons (e.g., working memory, executive function, motor function). A subset of subjects also underwent PET scanning with [(11)C]WIN 35428. RESULTS: METH users were found to have modest deficits in short-term memory, executive function, and manual dexterity. Exploratory correlational analyses revealed that deficits in memory, but not those in executive or motor function, were associated with decreases in striatal DAT BP. CONCLUSIONS: These results suggest a possible relationship between DAT BP and memory deficits in abstinent METH users, and lend support to the notion that METH produces lasting effects on central DA neurons in humans. As METH can also produce toxic effects on serotonin (5-HT) neurons, further study is needed to address the potential role of brain 5-HT depletion in cognitive deficits in abstinent METH users.