Three types of consciousness

It is useful to distinguish three senses of the word 'consciousness'. 'Minimal' consciousness is the occurrence of any mental activity, whether or not the subject is aware of this activity. 'Perceptual' consciousness is perceptual activity. Minimal and perceptual consciousness may be present, yet 'introspective' consciousness be lacking. Introspective consciousness is conceived as it was by Locke and Kant: as perception-like awareness of the subject's own current mental states and activities. It includes introspective consciousness of introspective consciousness itself. A useful model for demystifying and naturalizing introspective consciousness is the subject's proprioceptive awareness of bodily states and activities. Introspective consciousness may be further subdivided into 'reflex' introspective consciousness and 'introspection proper'. The distinction is one of degree: the degree of attention involved. We attach a quite special importance to introspective consciousness and are particularly unwilling to identify it with a purely physical process in the brain. It is suggested, however, that this springs from (a) the fact that what is introspected is taken to be a state or activity of a single thing, the self; and (b) the fact that event-memory is generally only possible if the event remembered was the object of introspective consciousness at the time. Without introspective consciousness, therefore, awareness of a self and the past history of that self is lacking.

Biochemical analysis of GABA(A) receptor subunits alpha 1, alpha 5, beta 1, beta 2 in the hippocampus of patients with Alzheimer's disease neuropathology

Alzheimer's disease (AD) is characterized by selective vulnerability of specific neuronal populations within particular brain regions. For example, hippocampal glutamatergic cell populations within the CA1/subicular pyramidal cell fields have been found to be particularly vulnerable early in AD progression. In contrast, hippocampal GABA-ergic neurons and receptors appear resistant to neurodegeneration. Despite relative sparing of GABA(A) receptors in AD, it is possible that the specific subunit composition of these receptors may undergo alterations with disease progression. In order to address this issue, we employed quantitative Western blot analysis to examine protein levels of GABA(A) receptor subunits alpha 1, alpha 5, beta 1, beta 2 in the hippocampus of subjects displaying increasing severity of AD neuropathology. Subjects were categorized into three groups based upon Braak staging pathologic criteria: pathologically mild (stages I/II, n=9); moderate (stages III/IV, n=8); and severe (stages V/VI, n=7). Across all subject groups, levels of subunit protein were heterogeneously distributed throughout the five hippocampal subregions analyzed (subiculum, CA1-3, dentate gyrus). Statistical analyses revealed differential preservation of GABA(A) receptor subunits in AD. In particular, alpha 1, beta 1, and beta 2 displayed little difference in protein levels among pathologically mild, moderate, and severe subject groups. In contrast, although relatively modest, protein levels of the alpha 5 subunit were significantly reduced between subjects with severe neuropathology compared with pathologically mild subjects (13.5% reduction). Collectively, our data provide evidence for heterogeneous distribution and relative sparing of GABA(A) receptor subunits in the hippocampus of AD patients.

Photothrombotic brain infarction results in seizure activity in aging Fischer 344 and Sprague Dawley rats

This study was designed to determine whether photothrombotic brain infarction could result in epileptic seizures in adult animals. Male Fischer 344 (F344) rats at 2, 6, 12, 24, and 30 months of age and male Sprague Dawley (SD) rats at 2 and 6 months of age underwent photothrombotic brain infarction with the photosensitive dye rose bengal by focusing a wide (6 mm) or narrow (3 mm) diameter white light beam on the skull overlying left hemisphere anterior frontal, midfrontal, frontoparietal, or parietal areas. Animals were monitored with video and EEG recordings. Morphological analysis of infarct size was performed with a computer-assisted image analysis system. The primary finding of this study was that epileptic seizures were recorded in post-mature rats 2 months after lesioning the frontoparietal cortex with large photothrombotic infarcts that extended to the cortical-subcortical interface. These seizures were characterized behaviorally by motor arrest, appeared to originate in the periinfarct area, and could be distinguished from inherited spontaneous bilateral cortical discharges by the morphology, frequency, duration, and laterality of the ictal discharges. Small cortical lesions were ineffective in producing seizures except for one animal that demonstrated recurrent prolonged focal discharges unaccompanied by behavioral change. Stage 3 seizures were observed in a small number of mid-aged and aged animals lesioned with large infarcts in anterior frontal and frontoparietal areas. These results suggest that the technique of photothrombosis can be used to produce neocortical infarction as a means to study mechanisms of secondary epileptogenesis.

Novel synthetic analogue of ACTH 4-10 (Semax) but not glycine prevents the enhanced nitric oxide generation in cerebral cortex of rats with incomplete global ischemia

This work investigates whether nitric oxide production and lipid peroxidation contribute to the pathophysiology of ischemia and whether glycine and a novel Russian compound, Semax are neuroprotective via a mechanism involving the regulation nitric oxide (NO) and lipid peroxidation. In brief, nitric oxide and indices of lipid peroxidation were elevated following global ischemia. While glycine proved ineffective in reducing NO levels or ameliorating the neurological deficits following global ischemia, Semax proved to be highly effective in abating the rise in nitric oxide and restoring neurologic functioning.

Ultraprofound cerebral hypothermia and blood substitution with an acellular synthetic solution maintains neuronal viability in rat hippocampus

The acute effects of ultraprofound hypothermia and blood substitution (UHBS) on neuronal cell viability were examined in adult rat hippocampus, a brain region particularly vulnerable to ischemic cell death. UHBS was performed using either artificial cerebrospinal fluid (ACSF) or Hypothermosol, an "intracellular-type" hypothermic preservation solution. After the procedure, the hippocampus was sliced and tested for cellular viability using a combination of cellular fluorochromes that are markers for live cells (acridine orange) and dead cells (propidium iodide). UHBS with ACSF resulted in a variable degree of neuronal death within the hippocampal subfields CA1/CA3, and dentate granular layer and hilus (CA4). In contrast, UHBS with Hypothermosol consistently resulted in hippocampal slices with only mild neuronal death. Our results of preserved hippocampal neuronal viability with use of UHBS and Hypothermosol support the demonstrated central nervous system (CNS) protective effects of UHBS and Hypothermosol when used during prolonged cardiac arrest. The results of this study also suggest that UHBS and Hypothermosol may be useful in the preparation and maintenance of viable hippocampal tissue for physiological studies, especially those involving aged animals, which are particularly vulnerable to hypoxic-ischemic cellular injury

Age-related loss of the AMPA receptor subunits GluR2/3 in the human nucleus basalis of Meynert

Magnocellular cholinergic neurons in the basal forebrain have long been recognized as vulnerable to the pathology of Alzheimer's disease. Despite numerous anatomical, pharmacological, behavioral, and physiological investigations of these neurons the cellular mechanism that underlines their selective vulnerability remains unclear. As part of an ongoing investigation into the molecular mechanism(s) underlying neuronal vulnerability in Alzheimer's disease and normal aging, we employed immunocytochemical techniques and examined the cellular localization of the alpha-amino-3-hydroxy-5-methyl-4-isoaxolepropionate (AMPA) glutamate receptor subunits GluR1 and GluR2/3 in the basal forebrain of eight nondemented elderly human subjects (66-102 years). For each case we observed GluR1-positive magnocellular cells darkly labeled within all main divisions of the basal forebrain (Ch1-Ch4). Double-labeling immunohistochemical techniques confirmed that the overwhelming majority (94%) of these neurons were also positive for the p75NGFr antibody, thus substantiating the cholinergic nature of these neurons. In contrast, GluR2/3 immunolabeling upon magnocellular neurons was relatively faint or nonexistent. The latter observations were most apparent in cases of advanced age and in the posterior part of the nucleus basalis of Meynert (NBM) (i.e., Ch4). In contrast, in adjacent structures (e.g., globus pallidus), a number of robustly labeled GluR2/3-positive cells were observed. In addition to the eight elderly subjects, we examined GluR1 and GluR2/3 immunostaining in the NBM of five younger cases, 5, 33, 36, 47, and 48 years of age. Although practical considerations limited our observations to the Ch4 region, we observed both GluR1 and GluR2/3 labeling upon NBM neurons in this latter region. On average, the distribution of labeled cells and intensity of immunoreaction were comparable between GluR1 and GluR2/3. The presence of GluR2/3- and GluR1-labeled neurons in the Ch4 region of younger cases but primarily GluR1 in cases of advanced age suggests an age-related decrease in GluR2/3. Functionally, the loss of GluR2 from the AMPA receptor complex results in ion channels highly permeable to Ca(2+). These alterations in cation permeability of the AMPA receptor together with the occurrence of a number of other intrinsic and extrinsic events (i.e., decrease Ca(2+)-binding protein) likely contribute to the vulnerability of these neurons in aging and in AD.

Effects of post-mortem delay on subunits of ionotropic glutamate receptors in human brain

The effect of post-mortem delay on the stability of the protein subunits that combine to form NMDA and AMPA type glutamate receptors has been assessed in samples of human brain tissue. While most of the subunits (i.e. GluR1, GluR2/3, GluR4, NR1) appear to be stable for up to 18 h post-mortem, the NR2A and NR2B subunits appear to be proteolyzed rapidly following death. These results are consistent with the concept that the proteolytic products of NR2A and NR2B, although at smaller molecular sizes than the full-length protein, are all identifiable on Western blots. Thus, a method is proposed that allows for the estimation of the levels of these labile proteins even in samples obtained up to 18 h post-mortem. Using this method we have estimated the levels of all AMPA and NMDA receptor subunits in selected (i.e. hippocampus, frontal and entorhinal cortex) brain tissue samples obtained from control patients and patients who have died with Alzheimer's disease. Modest decreases in NMDA receptor subunits NR1, NR2A, and NR2B were found in the hippocampus and in frontal cortex while little or no change in any of these subunits were documented in entorhinal cortex. Subunits for AMPA receptors (GluR1, GluR2/3, and GluR4) appeared to show a generalized decrease in all these tissues. As a surrogate marker for overall decreases due to generalized neuronal cell death, levels of neuron-specific enolase were measured in all tissues and were found to be nearly identical in control and Alzheimer's brains.

Age-dependent increase in infarct volume following photochemically induced cerebral infarction: putative role of astroglia

This study demonstrates that the photochemically induced model of stroke is an extremely viable method of inducing cerebral infarction in old animals. The lesions are reproducible both in terms of location and size and compatible with long-term survival of the animal. With this model we demonstrated, one week following surgery, a significantly larger infarct in rats 20 and 24 months of age compared to 4-month-old rats. The older rats also sustained greater neurologic deficits as assessed on a rotarod task. Older rats also were characterized by a glial response that was far less intense than in young animals. While the precise relationship between glia activation and cerebral damage remains to be determined, it would appear that a better understanding of those factors that contribute to the astrocytic response in the aged rat may be of particular benefit in designing therapeutic strategies aimed at reducing the pathologic consequences of cerebral infarction in elderly humans.

Distribution of glutamate receptor subunit NMDAR1 in the hippocampus of normal elderly and patients with Alzheimer's disease

Immunocytochemical techniques were employed to study the distribution and cytological features of NMDAR1-immunoreactive elements in the human hippocampal formation. Subjects with Alzheimer's disease (AD), presenting with a wide range of neuropathology and classified into six Braak stage (I-VI), and nondemented age-matched controls were examined. In control cases, the most intense NMDAR1 immunoreactivity was observed within the soma and dendrites of granule cells in the dentate gyrus and pyramidal neurons in Ammon's horn. Whereas small variations in the pattern of immunoreactivity were noted in control cases, AD subjects were characterized with intersubject variability which in most instances correlated with neuropathologic severity. For example, AD cases, particularly those with mild/modest pathology (Braak I-III), were indistinguishable from controls in the overall pattern of immunolabeling. In contrast, in those more severe AD cases (Braak IV-VI) the intensity of immunolabeling within the CA fields was greater than observed in controls and those with mild AD pathology. In addition, in pathologically severe cases numerous NMDAR1-positive pyramidal neurons were characterized by unique morphologic features including long and often tortuous apical dendrites. These latter findings were most prevalent in the CA1 region and subiculum. In contrast to the marked increase in immunolabeling in the CA fields, in the dentate gyrus we observed a reduction in NMDAR1 labeling particularly within the outer molecular layer (i.e., termination zone of the perforant pathway). This latter region was also the site of a number of NMDAR1-labeled plaques. Notably, the overall pattern of NMDAR1 immunoreactivity is distinct from that observed with antibodies against AMPA receptor subunits and suggests a differential role of various inotropic glutamate receptors in hippocampal plasticity in AD.

Central regulation of motor cortex neuronal responses to forelimb nerve inputs during precision walking in the cat

1. The responses of neurones in forelimb motor cortex to impulse volleys evoked by single pulse electrical stimulation (at 1.5 or 2 times the threshold for most excitable nerve fibres) of the superficial radial (SR) and ulnar (UL) nerves of the contralateral forelimb were studied in awake cats both resting quietly and walking on a horizontal ladder. Nerve volley amplitude was monitored by recording the compound action potential elicited by the stimulus. 2. In the resting animal 34/82 (41%) cells yielded statistically significant responses to SR stimulation, and 20/72 (28%) responded to UL stimulation. Some responses were confined to or began with an increase in firing probability ('excitatory' responses) and others with a decrease in firing ('inhibitory' responses), typically including a brief interruption of the spike train (zero rate). Cells responding to both nerves usually yielded responses similar in type. Most (78%) response onset latencies were less than 30 ms. Responses involved the addition or subtraction of from 3.4 to 0.1 impulses stimulus-1 (most <1 impulse stimulus-1). The distribution of response sizes was continuous down to the smallest values, i.e. there was no 'gap' which would represent a clear separation into 'responsive' and 'unresponsive' categories. Responses were commonest in the lateral part of the pericruciate cortex, and commoner among pyramidal tract neurones (PTNs) than non-PTNs. 3. During ladder walking most cells generated a rhythmic step-related discharge; in assessing the size of responses to nerve stimulation (20 studied, from 13 cells) this activity was first subtracted. Response onset latencies (90% <30 ms) and durations showed little or no change. Although most cells were overall more active than during rest both 'excitatory' and 'inhibitory' responses in both PTNs and non-PTNs were often markedly reduced in large parts of the step cycle; over some (usually brief) parts responses approached or exceeded their size during rest, i.e. response size was step phase dependent. Such variations occurred without parallel change in the nerve compound action potential, nor were they correlated with the level of background firing at the time that the response was evoked. When responses to both nerves were studied in the same neurone they differed in their patterns of phase dependence. 4. The findings are interpreted as evidence for central mechanisms that, during 'skilled', cortically controlled walking, powerfully regulate the excitability of the somatic afferent paths from forelimb mechanoreceptors (including low threshold cutaneous receptors) to motor cortex. Retention (or enhancement) of responsiveness often occurred (especially for ulnar nerve) around footfall, perhaps reflecting a behavioural requirement for sensory input signalling the quality of the contact established with the restricted surface available for support.

Immunohistochemical study of GABAA receptor alpha1 subunit in the hippocampal formation of aged brains with Alzheimer-related neuropathologic changes

Immunocytochemical techniques were employed to examine the distribution of the gamma-aminobutyric acid (GABA)A receptor alpha1 subunit within the hippocampus of 19 elderly subjects with Alzheimer-related neuropathologic changes. In mild cases (i.e., Braak stages I and II), the most intense neuropil immunolabeling was observed in the molecular layer of the dentate gyrus, the stratum pyramidale of the CA1 subregion and subiculum, while the weakest labeling was observed in the CA3 subfield. In CA4 region, the proximal dendrites and cell bodies of mossy cells were intensely alpha1 positive. Throughout the hippocampus, we observed a number of alpha1 labeled interneurons. These cells consisted of both large and small multipolar cells as well as small bipolar neurons. In moderate cases (i.e., Braak stages III and IV), the pattern and intensity of alpha1 immunolabeling appeared indistinguishable from mild cases. In severe cases (i.e., Braak stages V and VI), we observed a marked decrease in neuropil immunolabeling within the CA2, CA1 subregions and prosubiculum, while the labeling of the molecular layer of the dentate gyrus, subiculum proper and presubiculum was indistinguishable from mild and moderate cases. These data together with our previous immunocytochemical study in which we demonstrated a marked preservation of the GABAA receptor subunit beta2/3 suggest that responses of selected GABAA receptor subunits to AD pathology are variable with the alpha1 subunit displaying a high degree of vulnerability.

GABAA receptor beta 2 and beta 3 subunits mRNA in the hippocampal formation of aged human brain with Alzheimer-related neuropathology

Our work on the role of glutamate in Alzheimer's disease (AD)-related neuronal vulnerability and death provided significant insight into the potential contribution of the gamma-aminobutyric acid (GABA) neurotransmitter system as it participates in countering the neurotoxic effects of excessive glutamate receptor stimulation. Our previous studies demonstrate that beta2/3 GABAA receptor subunit immunoreactivity is relatively well preserved in hippocampi with AD pathology. To further elucidate the molecular basis for this observation, we employed in situ hybridization histochemistry to examine the levels of beta2 and beta3 receptor subunit mRNAs in the hippocampus of 19 elderly subjects presenting with a broad range of pathologic severity (i.e., Braak stage I-VI). Semi-quantitative analysis with film autoradiograms revealed that beta2 mRNA signal was highest in the granule cell layer, CA2 and CA1 subfields, while beta3 mRNA hybridization was highest in the granule cell layer, followed by CA2>/=CA3>/=CA1 regions. No significant difference in beta2 mRNA expression was detected among the pathologically mild, moderate or severe groups. In contrast, levels of beta3 mRNA in the pathologically severe group was significantly decreased compared to the mild group within all subregions examined except CA4. Our data suggest that alterations in the expression of GABAA receptor subunits in the AD hippocampus differ between specific receptor subunits with the amount of beta2 mRNA being relatively well-preserved, while beta3 mRNA levels were decreased.

Zonal organization of cortico-nuclear and nucleo-cortical projections of the paramedian lobule of the cat cerebellum. 1. the C1 zone

The cortico-nuclear (C-N) and nucleo-cortical (N-C) projections of the C1 cortical zone in pars anterior (pa) and pars copularis (pc) of the paramedian lobule (PML) in the posterior lobe of the cat cerebellum were investigated with a combined electrophysiological and neuroanatomical technique. In each experiment the mediolateral boundaries of the zone were located on the cortical surface by recording field potentials mediated via climbing fibres and evoked in the zone by activity elicited in spino-olivocerebellar paths through percutaneous stimulation of fore- and hindlimbs; a small (15-30 nl) injection of WGA-HRP was then made into the zone. The distributions in the deep cerebellar nuclei were determined (with light microscopy) both for terminal labelling due to anterograde axonal transport by Purkinje cells and for cell bodies labelled due to retrograde transport in N-C axons. The extent to which injection sites were confined to the C1 zone was assessed both by comparing injection site and zone widths and by determining the distributions of retrogradely labelled neurones within the contralateral inferior olive. The C-N projection from the part of the zone in PML pa (a forelimb part) terminates almost exclusively (perhaps exclusively) in nucleus interpositus anterior (NIA), primarily in caudal and dorsal parts, where it overlaps heavily with the C-N projections from the lobule V parts (also forelimb parts) of the C1 and C3 zones as previously defined. The C-N projection from the part of the zone in PML pc (a hindlimb part) also terminates virtually exclusively in NIA but primarily in almost all parts of the medial third of the nucleus. There is, nevertheless, sufficient overlap between the PML pa and PML pc projections that approximately one third of the termination territory of each projection overlaps that of the other. The PML pc part of the zone is almost entirely lacking in a N-C projection, as previously found for the lobule V part of the C1 zone (and C3 zone). However, the PML pa part of the zone receives N-C projections that arise, in descending order of size, from nucleus interpositus posterior (NIP), from NIA, from the NIA/nucleus lateralis (NL) fusion area and (perhaps) NL. The projection from NIP is similar in size to that provided by the nucleus to the C2 zone in lobule V of the anterior lobe. The findings are discussed, with particular emphasis on their implications for the hypothesis that the cerebellum is divisible into a number of olivo-cortico-nuclear complexes or compartments.

Zonal organization of cortico-nuclear and nucleo-cortical projections of the paramedian lobule of the cat cerebellum. 2. the C2 zone

The cortico-nuclear (C-N) and nucleo-cortical (N-C) projections of the C2 cortical zone in pars anterior (pa) and pars posterior (pp) of the paramedian lobule (PML) in the posterior lobe of the cat cerebellum were investigated with a combined electrophysiological and neuroanatomical technique. In each experiment the mediolateral boundaries of the zone were localized on the cortical surface by recording field potentials mediated via climbing fibres and evoked in the zone by activity elicited in spino-olivocerebellar paths through percutaneous stimulation of the fore- and hindlimbs; a small (15-30 nl) injection of 1-2% WGA-HRP was then made into the zone. Distributions in the deep cerebellar nuclei were determined with light microscopy both for C-N terminal labelling due to anterograde axonal transport by Purkinje cells and for cell bodies labelled due to retrograde transport in N-C axons. The extent to which retrogradely labelled olivary neurones were confined to the part of the rostral medial accessory olive that innervates the C2 zone was estimated to provide an indication of the degree to which the injected tracer might have spread beyond the boundaries of the zone. The C-N projection from the part of the C2 zone in PML pa terminates almost exclusively (probably exclusively) in nucleus interpositus posterior (NIP) at all medio-lateral levels of the nucleus but most extensively at middle and lateral levels. At most levels the C-N termination territory forms a crescent with its outer curve following the caudal, dorsal and rostral borders of the nucleus and as a result it is mainly in the dorsal half of the nucleus. There is heavy overlap with the projection from the lobule V part of the C2 zone previously studied by us. The projection from the C2 zone in PML pp terminates entirely in NIP, but although at middle medio-lateral levels in the nucleus there is substantial overlap with the PML pa and lobule V projections, the projection territory is confined to the medial half of the nucleus. Evidence was obtained compatible with the view that throughout the C2 zone its lateral and medial parts project to different parts of NIP. In both PML pa and pp the C2 zone receives N-C projections from NIP. Most of the N-C cells concerned are in the dorsal half of NIP and the great majority lie within the corresponding C-N projection territory. However, the N-C projection to PML pa appears c. 6 times heavier than that to PML pp and the PML pa part of the zone also receives a minor additional projection from nucleus lateralis (NL). The findings are discussed in relation to the hypothesis of olivo-cortico-nuclear complexes or compartments, with particular reference to the internal organization of the C2 complex.

Numerical aspects of pontine, lateral reticular, and inferior olivary projections to two paravermal cortical zones of the cat cerebellum

Two different olivo-cortico-nuclear zones in the cat cerebellum have been compared quantitatively as regards the numbers of cells projecting to them from within several sources of mossy fibres (MFs), namely the basal pontine nuclei (BPN), nucleus reticularis tegmenti pontis (NRTP), and the ipsilateral lateral reticular nucleus (LRN). The zones chosen were the C3 zone in lobule V of the anterior lobe and the C1 zone in pars copularis of the paramedian lobule (PMLpc), localised by recording climbing fibre-mediated potentials evoked on their surface as a result of volleys set up in their spino-olivocerebellar paths. The zones were injected with fluorescent-labelled latex microspheres and cell bodies, retrogradely labelled in the MF source nuclei and in the contralateral inferior olive, were counted and mapped. Evidence was obtained that tracer efficiency was very high in both the MF projections and the olivo-cerebellar projection and that each olivocerebellar axon may provide only one climbing fibre to the upper part of a lobule V folium but an average of nearly two to the same part of a PML folium. When the numbers of labelled cells in each MF source nucleus were expressed as a percentage of the total number of labelled pontine cells, the biggest source for lobule V was the contralateral BPN, followed by LRN, contralateral NRTP, ipsilateral BPN, and ipsilateral NRTP. For PMLpc, the order was similar except that ipsilateral BPNs exceeded contralateral NRTPs, but the dominance of contralateral BPN as a source was much greater. Cell totals were converted into projection densities (i.e., numbers of cells labelled per square millimetre of cortical sheet involved in the injection site); densities for PMLpc were found to be almost three times greater than those for lobule V for contralateral BPN but the two densities were not significantly different for ipsilateral BPN. The three other MF sources projected at higher densities to lobule V than to PML. These findings indicate that two cortical zones, both of which receive climbing fibres from the rostral part of the dorsal accessory olive and project to nucleus interpositus anterior, nevertheless differ markedly in regard to both the relative and the absolute sizes of the projections they receive from several of their most important sources of MFs.

Neuronal activity in the lateral cerebellum of the cat related to visual stimuli at rest, visually guided step modification, and saccadic eye movements

1. The discharge patterns of 166 lateral cerebellar neurones were studied in cats at rest and during visually guided stepping on a horizontal circular ladder. A hundred and twelve cells were tested against one or both of two visual stimuli: a brief full-field flash of light delivered during eating or rest, and a rung which moved up as the cat approached. Forty-five cells (40%) gave a short latency response to one or both of these stimuli. These visually responsive neurones were found in hemispheral cortex (rather than paravermal) and the lateral cerebellar nucleus (rather than nucleus interpositus). 2. Thirty-seven cells (of 103 tested, 36%) responded to flash. The cortical visual response (mean onset latency 38 ms) was usually an increase in Purkinje cell discharge rate, of around 50 impulses s-1 and representing 1 or 2 additional spikes per trial (1.6 on average). The nuclear response to flash (mean onset latency 27 ms) was usually an increased discharge rate which was shorter lived and converted rapidly to a depression of discharge or return to control levels, so that there were on average only an additional 0.6 spikes per trial. A straightforward explanation of the difference between the cortical and nuclear response would be that the increased inhibitory Purkinje cell output cuts short the nuclear response. 3. A higher proportion of cells responded to rung movement, sixteen of twenty-five tested (64%). Again most responded with increased discharge, which had longer latency than the flash response (first change in dentate output ca 60 ms after start of movement) and longer duration. Peak frequency changes were twice the size of those in response to flash, at 100 impulses s-1 on average and additional spikes per trial were correspondingly 3-4 times higher. Both cortical and nuclear responses were context dependent, being larger when the rung moved when the cat was closer than further away. 4. A quarter of cells (20 of 84 tested, 24%) modulated their activity in advance of saccades, increasing their discharge rate. Four-fifths of these were non-reciprocally directionally selective. Saccade-related neurones were usually susceptible to other influences, i.e. their activity was not wholly explicable in terms of saccade parameters. 5. Substantial numbers of visually responsive neurones also discharged in relation to stepping movements while other visually responsive neurones discharged in advance of saccadic eye movements. And more than half the cells tested were active in relation both to eye movements and to stepping movements. These combinations of properties qualify even individual cerebellar neurones to participate in the co-ordination of visually guided eye and limb movements.

Alterations of GABA(A)beta2/3 immunoreactivity in the dentate gyrus after perforant pathway lesion

Immunocytochemical techniques were employed to examine the changes in the GABA receptor subunits beta2/3 within the dentate gyrus of the rat brain 1, 3, 7, 14, 30 and 90 days after a unilateral perforant pathway lesion. Three days post-lesion we observed a decrease in beta2/3 immunolabeling in the inner molecular layer of the dentate gyrus followed by a comparable decrease in the outer molecular layer 7 days post-lesion. These decreases were transient; 30 and 90 days post-lesion, beta2/3 immunolabeling appeared similar to controls in the inner portion of the molecular layer, while in the outer region the labeling was increased. In this latter region we also observed a dense band of AChE fibers. Following survival times of 3 days we observed a diffuse staining of the neuropil in the hilar region, and a dense amorphous accumulation of peroxidase reaction product in the polymorphic region. These responses were transient and by 14 days the hilar/polymorphic region appeared indistinguishable from controls. These data suggest a unique pattern of immunoabeling in the molecular and polymorphic region in response to perforant pathway lesion. A putative explanation for this response is discussed.

Immunohistochemical study of GABA(A) receptor beta2/3 subunits in the hippocampal formation of aged brains with Alzheimer-related neuropathologic changes

In AD, it is hypothesized that one factor contributing to the vulnerability of neurons is a delicate balance of excitatory and inhibitory inputs. To examine this hypothesis we have initiated a number of studies examining the role of the excitatory neurotransmitter glutamate and the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) in the neurodegeneration of AD. As an initial investigation into the GABAergic system in AD, we employed immunocytochemical techniques and examined the distribution and density of the GABAA receptor subunits beta2/3 within the hippocampus of 13 subjects with a clinical diagnosis of AD and 6 nondemented elderly subjects. Collectively, these 19 subjects presented with a broad range of pathologic severity (i.e., Braak stages I-VI). Density measurements of nine hippocampal regions demonstrated highest levels of beta2/3 immunolabeling in the inner molecular layer of the dentate gyrus > CA1 > CA2, while the lowest levels were found in the granular layer of the dentate gyrus < or = CA4 < CA3 field. Despite these regional variations no significant difference in the mean density of beta2/3 immunolabeling was observed when comparing the pathologically mild (stages I and II), moderate (stages III and IV), and severe (stages V and VI) groups. These data suggest that in the hippocampus receptor subunits associated with GABAergic neurotransmission are relatively maintained even until the terminal stages of the disease.

Alterations of AMPA-selected glutamate subtype immunoreactivity in the dentate gyrus after perforant pathway lesion

Immunocytochemical techniques were employed to examine the changes in immunolabeling of the alpha-amino-3-hydroxy-5-methyl-4-isoaxolepropionate (AMPA) receptor subunits GluR1 and GluR2/3 within the dentate gyrus 1, 3, 7, 14, 30, and 90 days after a unilateral perforant pathway lesion in the rat brain. Completeness of the lesion was confirmed following examination of Nissl-stained tissue sections at all times post-lesion and acetylcholinesterase (AChE)-stained sections 14, 30 and 90 days post-lesion, the latter providing evidence of compensatory sprouting of cholinergic fibers in the outer molecular layer of the dentate gyrus. Compared to the non-lesioned hippocampus there was no difference in the staining pattern of AMPA receptor subunits in the dentate gyrus of the deafferented hippocampus 1, 3, 7 and 14 days following lesioning of the perforant pathway. In contrast, 30 and 90 days post-lesion, GluR1 immunolabeling was increased in the outer molecular layer of the dentate gyrus (i.e., deafferented zone) ipsilateral to lesion. Likewise, GluR2/3 immunolabeling was increased within the same region although the intensity of the response was less than that which was observed for GluR1. These data suggest that the loss of the perforant pathway fibers results in a compensatory increase in GluR1 and to a lesser extent GluR2/3 immunolabeling of the outer molecular layer at 30 and 90 days post-lesion and further suggest that AMPA receptor subunits play a role in perforant pathway signal transduction.

The loss of GluR2(3) immunoreactivity precedes neurofibrillary tangle formation in the entorhinal cortex and hippocampus of Alzheimer brains

Double-immunolabeling techniques were employed to examine the distribution of GluR2(3) subunits and markers of early cytoskeletal changes (mab MC1) within the entorhinal cortex (EC) and hippocampus of cases with varying degrees of Alzheimer disease (AD) pathology (stages I-VI by Braak and Braak). In addition near-adjacent tissue sections were double-immunolabeled using antibodies against GluR2(3) and a marker of normal neuronal cytoskeleton (MAP2). In those cases classified as stages I-II, most layer II neurons of the EC and pyramidal neurons in the CA1/subiculum were double-labeled with GluR2(3) and MAP2. An occasional MC1-labeled cell was observed, yet in no instance were these neurons double-labeled with GluR2(3). In cases with moderate AD pathology (stages III-IV), layer II of the EC and CA1/subiculum were characterized by a substantial loss of GluR2(3)-labeled neurons, while many were still immunoreactive to MAP2. Notably, the loss of GluR2(3) immunolabeling was accompanied by an increasing number of MC1-positive neurons. In no instance were GluR2(3) and MC1 co-localized within the same neuron. In cases with severe AD pathology (stages V-VI), the EC and CA1/subiculum were almost completely devoid of GluR2(3)-positive neurons. MAP2-labeled neurons also were reduced in number. In contrast, both regions contained an abundance of MC1-positive cells. That GluR2(3) and MC1 are not observed in the same neuron, together with the observation that the number of GluR2(3)-labeled neurons decreases as the number of MC1-positive cells increases, suggest that a loss of GluR2(3) immunolabeling precedes the appearance of MC1 immunolabeling.

AMPA-selective glutamate receptor subtype immunoreactivity in the hippocampal dentate gyrus of patients with Alzheimer disease. Evidence for hippocampal plasticity

Immunocytochemical techniques were employed in order to examine the distribution and relative intensity of immunolabeling of the alpha-amino-3-hydroxy-5-methyl-4-isoaxolepropionate (AMPA) receptor subunits GluR1 and GluR2/3 within the hippocampal formation of patients with Alzheimer disease (AD). Within sectors of the hippocampus that are particularly vulnerable to AD pathology (i.e., CA1, subiculum), we observed a variable loss of GluR1 and GluR2/3 immunolabeling correlating with the extent of cell loss and neurofibrillary pathology. In contrast, in less vulnerable sectors of the hippocampus (i.e., CA2/3, dentate gyrus), the intensity of immunolabeling was markedly increased in AD cases, particularly in the molecular and polymorphic layers of the dentate gyrus. Importantly, these latter regions correspond to termination zones of glutamatergic perforant pathway axons and mossy fiber collaterals, respectively. The increase in immunolabeling within these projection fields is hypothesized to occur in response to the deafferentation of selected glutamatergic pathways, and suggests a critical role for AMPA receptor subunits in hippocampal plasticity.

Distribution of AMPA receptor subunits in the nucleus basalis of Meynert in aged humans: implications for selective neuronal degeneration

Immunocytochemical techniques using polyclonal antibodies directed against GluR1 and GluR2/3 subunits of the AMPA-selective receptor complex were used to examine the distribution of these receptor subunits within the nucleus basalis of Meynert (NBM) of non-demented elderly humans. Both somata and processes of magnocellular neurons within the NBM were intensely immunoreactive to GluR1 antibodies. In contrast, within the same region GluR2/3 immunolabeling was largely absent, although GluR2/3-positive neurons were abundantly distributed within adjacent brain regions (i.e., amygdala, entorhinal cortex and hippocampus). These data suggest that NBM neurons may be unique compared to those of other brain regions, in their response to glutamatergic excitation as mediated via non-NMDA receptors and be particularly vulnerable to glutamate excitotoxicity via a mechanism involving the destabilization of intracellular calcium.

Role of the cerebellum and motor cortex in the regulation of visually controlled locomotion

An account is given of the current state of knowledge of the contributions of the cerebellum and the forelimb motor cortex (MC) to the neural control of walking movements in the cat. The main emphasis is on information obtained by recording from single MC and cerebellar neurones in chronically instrumented cats engaged in walking on the rungs of a horizontal ladder, a form of locomotion that is heavily dependent on visual input and for which the integrity of MC is essential. Evidence from the authors' laboratory and from other studies is presented which establishes that MC neurones, including pyramidal tract neurones, show higher levels of activity during ladder walking than during overground walking (i.e., when less constraint exists over the locus of footfall) and that this increase is greatest in late swing-early stance in the contralateral forelimb, consistent with one role of MC being to help determine the locus of footfall. However, many MC neurones develop peak activity at other times in the step cycle, and a comparison with recordings during treadmill walking suggests MC may also help regulate stance duration when walking speed is an important performance variable. Recordings from Purkinje cells and cerebellar nuclear neurones show that during ladder walking step-related activity is widespread in the vermal, paravermal, and crural regions of cortex and in the interposed and dentate nuclei. Nuclear cell activity is so timed that it could be contributing to producing the locomotor rhythms evident in MC cells, although this is not yet proven. Results are also presented and discussed relating to MC and cerebellar neuronal responses that occur when a step onto an unstable rung results in an unexpected external perturbation of the forelimb step cycle. MC responses begin with onset latency as short as 20 ms so that MC may assist spinal reflex mechanisms to produce a post hoc compensatory change in motor output. However, work in progress suggests that corresponding responses in paravermal cerebellum are weak and infrequent, so provisionally it seems that the MC responses are initiated via pathways that do not pass through the cerebellum. By contrast, current work involving a paradigm in which a ladder rung is motor driven to a new position as the animal approaches (thereby providing a visual cue that an adaptive change in gait will soon be required) is revealing in lateral cerebellar neurones, including dentate neurones, changes in discharge that are time locked to the execution of an adapted pace. In addition, there are prominent earlier responses, which begin at short latency after the onset of rung movement. These apparently visual responses have characteristics that encourage the speculation that they may represent a cerebellar signal that "primes for action" other more directly motor regions of the central nervous system.

Functional evidence for the presence of nitric oxide synthase in the dorsal motor nucleus of the vagus

BACKGROUND & AIMS

Histochemical studies indicate that reduced nicotinamide adenine dinucleotide phosphate diaphorase, the nitric oxide synthase-related enzyme, is present in the dorsal motor nucleus of the vagus of the cat. We have previously shown in vitro that NO synthase is present in this nucleus in the rat and that the excitatory effect of N-methyl-D-aspartate on these neurons is in part caused by NO formation. The aim of this study was to obtain functional evidence for the presence of NO synthase in the cat dorsal motor nucleus of the vagus.

METHODS

L-Glutamate, L-arginine, D-arginine, the NO donor S-nitroso-N-acetyl-penicillamine, and the NO synthase inhibitor NG-nitro-L-arginine-methyl ester were unilaterally microinjected into the rostral dorsal motor nucleus of anesthetized cats, and antral and pyloric motility were monitored using extraluminal force transducers.

RESULTS

Microinjection of L-arginine increased gastric motility, whereas D-arginine had no effect. Vagotomy eliminated the L-arginine-induced increases. Microinjection of S-nitroso-N-acetyl-penicillamine increased antral motility. NG-Nitro-L-arginine-methyl ester prevented L-arginine from exerting an effect on gastric motility.

CONCLUSIONS

Motility increases obtained after microinjection of L-arginine into the dorsal motor nucleus and prevention of these motility increases with microinjection of a NO synthase inhibitor provide functional evidence for the presence of NO synthase in the dorsal motor nucleus of the vagus in the cat.

AMPA-selective glutamate receptor subtype immunoreactivity in the aged human hippocampal formation

It has been hypothesized that, in Alzheimer's disease, glutamate-mediated excitotoxicity contributes to the degeneration of selected populations of neurons. In the present study, immunocytochemical techniques were used to determine the distribution and anatomical features of GluR1- and GluR2/3-immunolabeled cell bodies and processes within the hippocampal formation of normal (i.e., no pathology) elderly humans. The results of this study provide an essential baseline with which to compare the expression and distribution of glutamate receptor subunits within the brains of patients with Alzheimer's disease. With respect to GluR1 immunoreactivity, the molecular layer of the dentate gyrus displays the most intense immunolabeling of any hippocampal structure. Contributing to this intense labeling are apical dendrites that arise from neurons within the adjacent granule cell layer. Interestingly, GluR1-labeled neurons account for a relatively small percentage of the total number of neurons as revealed by Nissl staining in the granule cell layer. In contrast, GluR2/3-labeled neurons are densely distributed throughout the granule cell layer, yet they provide relatively few processes to the adjacent molecular layer compared to GluR1-positive processes. GluR1 labeling is also prominent within the CA fields of Ammon's horn, with CA2 > CA3 > CA1 > or = CA4. Most prominent within the CA fields are the labeled dendrites of pyramidal neurons. In many instances, apical dendrites can be traced into the adjacent stratum radiatum, where they impart a deep striated appearance to this region of the hippocampus. Robust GluR2/3 labeling is also observed within the pyramidal layer of Ammon's horn, with an order of staining intensity similar to that observed for GluR1. However, unlike GluR1 labeling, which is localized predominantly along dendrites, GluR2/3 labeling is observed primarily in association with cell bodies. Collectively, these data suggest that the molecular composition of the AMPA receptor complex may differ between the dendrite and soma of granule and pyramidal neurons within the hippocampal formation, so functionally we may predict that these two regions of the neuron would respond differently following glutamate receptor stimulation.

Atomic force microscopy of paired helical filaments isolated from the autopsied brains of patients with Alzheimer's disease and immunolabeled against microtubule-associated protein tau

Atomic force microscopy was employed to study the structural features of paired helical filaments isolated from autopsied brains of Alzheimer's disease patients. The identity of paired helical filaments was confirmed following a specific immunogold labeling using antibodies directed against the microtubule-associated protein tau, which is the main constituent of paired helical filaments. Computer-assisted analysis of high resolution, three-dimensional images allowed us to study the longitudinal and cross-sectional profiles of individual filaments. Vertical dimensions of filaments were assessed along these sectional profiles. The smallest vertical diameter (6.66 +/- 0.78 nm) was obtained at the level of the greatest lateral profile (ie, "loop"), while the greatest vertical diameter was two times larger (13.68 +/- 1.46 nm) and was obtained at the level of the smallest lateral profile (ie, "crossover") of the filament. Based on the shapes of these sectional profiles and their vertical dimensions, paired helical filaments appeared to be composed of two identical integral subunits, each of a circular cross-sectional profile of approximately 7 nm in diameter, wound around one another in a left helical manner, with a 7-nm center-to-center separation. Half-period of this helix was estimated at 81.4 +/- 2.1 nm. Serial cross-sectional profiles of paired helical filaments were further utilized to construct a theoretical model of their internal organization. This model suggests that each structural subunit of the paired helical filament incorporates at least four identical protofilaments.

Reduction of AMPA-selective glutamate receptor subunits in the entorhinal cortex of patients with Alzheimer's disease pathology: a biochemical study

Using biochemical techniques we determined concentrations of the AMPA-selective glutamate receptor subunits GluR1 and GluR2/3 in the entorhinal cortex of patients with Alzheimer's disease pathology and age-matched controls. Tangle density was also determined in anatomically matched samples and correlated with GluR1 and GluR2/3 receptor concentration. In Alzheimer's disease brain, Western blot analysis revealed average reductions of 43% and 38% for GluR1 and GluR2/3, respectively. Based on previous immunohistochemical studies, we infer that the majority of protein reduction was due to decreases in GluR1 and GluR2/3 immunolabeled elements in the more superficial layers of the entorhinal cortex (layers II and III). These layers of the entorhinal cortex contained numerous neurofibrillary tangles in Alzheimer's disease, but neither GluR1 nor GluR2/3 protein concentration correlated significantly with tangle density. We hypothesize that the decrease in specific glutamate receptor subunits, particularly GluR2/3, may contribute to the vulnerability of neurons in the entorhinal cortex via mechanisms involving calcium conductance through AMPA-selective channels.

Step phase-related excitability changes in spino-olivocerebellar paths to the c1 and c3 zones in cat cerebellum

1. Chronically implanted microwires were used to record extracellular field potentials generated in the c1 and c3 zones in the cortex of lobules V and VI of the cerebellum by non-noxious stimuli delivered to the superficial radial nerve in the ipsilateral forelimb. Responses due to input via climbing fibre afferents were studied; their latency and other characteristics identified them as mediated mainly via the dorsal funiculus spino-olivocerebellar path (DF-SOCP). 2. Responses at individual sites were studied repeatedly with a range of stimulus intensities and during two different behaviours: quiet rest and steady walking on an exercise belt. For responses during walking, step histograms were constructed showing response mean size during different tenths of the step cycle in the ipsilateral forelimb, both in absolute terms and relative to mean size during rest. 3. Step histograms for the same site on different days or different stimulus intensities varied appreciably in form but in both cases the timing of the largest response was usually the same or shifted by only one step tenth. 4. In both zones the largest responses during walking occurred overwhelmingly during the E1 step phase when the limb is extended forwards and down to establish footfall. Least responses were much less uniform in timing but were mostly during stance, particularly its early (E2) part. 5. In many histograms the smallest responses were smaller in mean size than the responses during rest while the largest were larger. These changes were not paralleled by changes in nerve volley size, so presumably reflect step-related central changes in pathway excitability. Facilitations and depressions were differently affected by stimulus intensity and sometimes occurred independently, suggesting generation by separate mechanisms. 6. In both zones there were differences between recording sites which suggests that different DF-SOCP subcomponents innervate different parts of the zones. However, no systematic differences could be firmly established between the medial and lateral subzones of the c1 zone. 7. The results are discussed in relation to the hypothesis that the DF-SOCP constitutes the afferent limb of a transcerebellar mechanism involved in adapting the evolving step.

AMPA-selective glutamate receptor subtype immunoreactivity in the hippocampal formation of patients with Alzheimer's disease

Immunocytochemical techniques were employed in order to examine the distribution and relative intensity of the AMPA receptor subunits GluR1 and GluR2/3 within the hippocampal formation of normal controls and Alzheimer's disease (AD) cases. Throughout our investigation we examined cases exhibiting a wide range of pathologic severity, thus allowing us to correlate our immunohistochemical data with the extent of pathology. Specifically, we investigated the distribution of these receptor subunits in hippocampal sectors that are particularly vulnerable to AD pathology (i.e., CA1 and subiculum) and compared these findings with those obtained following examination of sectors that are generally resistant to pathologic change (i.e., CA2/3, dentate gyrus). Within vulnerable sectors we observed a variable loss of GluR1 and GluR2/3 immunolabeling. The degree to which these proteins were reduced appeared to correlate with the extent of neurofibrillary pathology and cell loss. Despite the loss of labeled cells, the intensity of immunolabeling within the remaining neurons was comparable with, and in many instances even greater than, that observed in control cases. Within resistant sectors, the distribution of immunoreactive elements was comparable in both case groups yet the intensity of immunolabeling was markedly increased in AD cases, particularly in the molecular layer of the dentate gyrus and in the stratum lucidum of CA3 (i.e., the termination zones of perforant pathway and mossy fibers). In addition, within AD cases dramatic increases were observed within the supragranular and polymorphic layer of the dentate gyrus (i.e., the terminal zones of sprouting mossy fiber collaterals). The increase in GluR1 and GluR2/3 immunolabeling is hypothesized to occur in response to the deafferentation of selected glutamatergic pathways. Moreover, our data support that hippocampal plasticity is preserved, even in severe AD cases, and suggest a critical role for AMPA receptor subunits in this plasticity and in maintaining hippocampal functioning.

Photochemical brain injury in rats triggers DNA fragmentation, p53 and HSP72

The aim of the study was to examine whether apoptosis, apoptosis-related protein p53 and heat-shock protein (HSP) 72 participate in the response of the brain to focal injury. Male Sprague-Dawley rats received intravenously a photosensitive dye rose bengal. Unilateral cortical thrombosis was induced by illuminating the skull of rose bengal-treated rats for 10 min with a focused beam of light. Animals were killed and brains were processed for immunohistochemical detection of DNA fragmentation, p53, and HSP72 kD. DNA fragmentation and p53 were increased only in the perifocal area in the cortex ipsilateral to the thrombotic focus, while HSP72 increased throughout the ipsilateral cortex, except in the immediate perifocal area. The results suggest that in response to focal brain injury, some cells die through an apoptotic process that might involve an accumulation of p53.

The distribution of cholinergic perikarya with respect to enkephalin-rich patches in the caudate nucleus of the adult cat

The distribution of cholinergic interneurons with respect to enkephalin-rich patches in the caudate nucleus of the cat was examined using both computer-assisted 3-D reconstruction and immunocytochemical techniques. Examination of the 3-D distribution of perikarya staining for choline acetyltransferase (ChAT) revealed that these cells were not evenly distributed within the caudate nucleus but exhibited areas of increased and decreased density. Comparison of the 3-D distribution of cholinergic perikarya to that of the enkephalin-rich patches indicated that areas of increased ChAT+ cell density often corresponded to the positions of enkephalin-rich patches within the dorsal-lateral caudate nucleus. At more ventral regions, there was no clear correspondence between areas of increased ChAT+ cell density and enkephalin-rich patches. In agreement with these observations, a quantitative analysis of sections double-labeled for ChAT and enkephalin revealed that the density of cholinergic neurons within enkephalin-rich patches was twice that in the surrounding tissue in the dorsal region of the caudate nucleus. In contrast at more ventral levels, the difference in the density of ChAT+ cells in enkephalin-rich patches did not significantly differ from that in the surrounding striatal tissue. Both the results of the 3-D and the double-labeling analysis suggest that cholinergic neurons are not evenly distributed within the caudate nucleus of the cat but form loose clusters which are associated dorsally with the enkephalin-rich patches. These results also provide further evidence of heterogeneity within the striosomal compartment in the cat.

LIGA20, a lyso derivative of ganglioside GM1, given orally after cortical thrombosis reduces infarct size and associated cognition deficit

A bilateral photochemically induced thrombotic lesion of rat sensorimotor cortex (approximately 3 mm in diameter and 25 mm3 in volume) is associated with a persistent cognition (learning and memory) deficit, which was evaluated with water maze tasks. The N-dichloroacetylsphingosine derivative of lysoGM1 (LIGA20) administered after the lesion either i.v. or per or reduces the infarct size by 30-40% and attenuates the associated cognition deficits, presumably by limiting the extent of damage of neurons at risk located in the surroundings of the infarcted core (i.e., area penumbra). The LIGA20 protection is dose and time dependent. Maximal protection is afforded by a single dose of LIGA20 of 34 mumol/kg i.v. 1 hr after lesion or by a dose of 270 mumol/kg per os when administered 1 hr and 24 hr after the lesion. The protective effect of LIGA20 can be observed when the drug is administered i.v. up to 6 hr after the lesion. The protective efficacy of the oral administration of LIGA20 is related to its physiochemical properties, which, unlike those of GM1, allow absorption from the gastrointestinal tract. LIGA20 given orally reaches the brain promptly and rapidly inserts into the neuronal membranes. Here, by an unknown molecular mechanism, LIGA20 selectively reduces the pathological amplification of Ca2+ signaling elicited by persistent stimulation of ionotropic glutamate receptors in the area penumbra.

AMPA-selective glutamate receptor subtype immunoreactivity in the entorhinal cortex of non-demented elderly and patients with Alzheimer's disease

The present work employed immunocytochemical techniques and examined the distribution and cytological features of the AMPA receptor subunits, GluR2/3 and GluR1 within the entorhinal cortex of non-demented elderly (NC), patients with neuropathological and clinical verification of Alzheimer's disease (AD) and patients without a clinical history of dementia yet exhibiting sufficient quantities of senile plaques to meet neuropathological criteria of Alzheimer's disease (HPND). In NC cases, GluR2/3-immunolabeled neurons were abundantly distributed throughout layers II, III, V and VI of the entorhinal cortex. In contrast, GluR1-positive cells were comparatively sparse in number and largely restricted to layers V and VI. In AD, GluR2/3- and GluR1-labeled neurons were markedly reduced. Similarly, adjacent Nissl-stained tissue sections revealed substantial cell loss in the entorhinal cortex thus providing a reasonable explanation for the loss of these receptor subunits. Importantly, a dramatic loss of GluR2/3- and GluR1-immunolabeled neurons is also observed in the HPND cases, although examination of Nissl-stained tissue sections reveals little if any evidence of cell loss. The latter data suggest that a 'down-regulation' of these receptor subunits occurs prior to the actual loss of these cells. Furthermore, we hypothesize that the decrease of specific AMPA receptor subunits may influence neuronal vulnerability via a mechanism involving increased intracellular calcium and the destabilization of intracellular calcium homeostasis.

Immunocytochemical distribution of peptidergic and cholinergic fibers in the human amygdala: their depletion in Alzheimer's disease and morphologic alteration in non-demented elderly with numerous senile plaques

As part of an ongoing investigation devoted to understanding the pathogenesis of senile plaques, we employed histochemical and immunocytochemical techniques to examine the distribution and cytologic features of acetylcholinesterase (AChE), choline acetyltransferase (ChAT), somatostatin (SOM), neurotensin (NT) and substance P (SP) containing fibers and neurons within the amygdala of: (1) patients with Alzheimer's disease (AD); (2) age-matched non-demented controls (NC); and (3) a group of non-demented cases, who upon postmortem neuropathologic examination exhibited sufficient numbers of senile plaques to be classified as AD. This latter group was referred to as high plaque non-demented (HPND). For every case, the distribution of immunolabeled fibers and neurons were determined for each transmitter throughout the various subnuclei of the amygdala. In addition, in the AD and HPND cases the topographic distribution of senile plaques was determined throughout the amygdala using thioflavine-S and Bielschowsky silver methods. In the amygdala, the distribution and density of senile plaques were not bound by conventional cytoarchitectural groupings but rather were most dense in the ventromedial regions of the amygdala with decreasing density in dorsal and lateral directions. Importantly, the density and distribution of senile plaques failed to correlate with the normal topography and/or density of the various peptidergic or cholinergic fibers within the amygdala. The finding that plaques do not correlate with the topographic distribution of any specific transmitter system suggests that plaques likely do not arise from the degeneration of a single neurotransmitter system (i.e., the cholinergic system). However, the finding that in AD a transmitter is most markedly depleted in regions of greatest plaque density, suggests certain constituents of the plaque (e.g. beta-amyloid) may be contributing to the degeneration of local fibers. The extent to which a transmitter was depleted in AD patients varied considerably among those four investigated with the cholinergic and NT systems displaying the most dramatic reductions, followed by SP and SOM. Despite these differential reductions in fiber density, all four neurotransmitters were found localized within dystrophic neurites and in most instances these dystrophic neurites were associated with thioflavine-positive senile plaques. In contrast to the AD cases, the HPND cases were characterized by no significant reductions in immunolabeled fibers, although immunostained dystrophic neurites were very prevalent in the HPND cases. These data suggest that dystrophic neurites occur very early in the disease process and likely precede the actual loss of fibers when or if it occurs.(ABSTRACT TRUNCATED AT 400 WORDS)

Cholinergic neurons are distributed preferentially in areas rich in substance P-like immunoreactivity in the caudate nucleus of the adult cat

The distribution of cells stained immunocytochemically for the cholinergic marker choline acetyltransferase was compared to the pattern of substance P immunoreactivity in the caudate nucleus of adult cats using a double-label immunocytochemical protocol and three-dimensional reconstructions of adjacent sections single-labeled for either substance P or choline acetyltransferase. Substance P immunoreactivity was distributed in a highly complex mosaic within the caudate nucleus of the cat. In the dorsal caudate nucleus, substance P-rich zones consisting of either clusters of substance P-positive cell bodies or fibers were seen against a lighter staining background. The density of cholinergic neurons was found to be significantly greater within these substance P-rich patches in comparison to surrounding regions. The pattern of substance P immunoreactivity within the ventral caudate nucleus differed from that in more dorsal regions. Clear substance P-rich patches were not seen in this region, but a large substance P-rich area consisting of a dense plexus of substance P-containing fibers was visible. Embedded within this substance P-rich area were fairly discrete patches of light substance P staining. As in the dorsal caudate nucleus, increased numbers of cholinergic neurons and processes were associated with substance P-rich regions in the ventral caudate nucleus. Choline acetyltransferase-positive perikarya also appeared to be concentrated in substance P-rich areas in the nucleus accumbens and olfactory tubercle. The results of this study suggest that a close relationship exists between the distribution of substance P fibers and cholinergic perikarya in the striatum of the cat.

Morphologic alterations of choline acetyltransferase-positive neurons in the basal forebrain of aged behaviorally characterized Fisher 344 rats

We examined Fisher 344 female rats aged 6, 27, and 33 months old. Prior to sacrifice and morphometric analyses of forebrain cholinergic neurons all rats underwent behavioral characterization in a spatial learning task using the Morris water maze. Performance on the spatial task permitted subsequent grouping of the 27- and 33-month-old animals into impaired or nonimpaired groups. Importantly, the percentage of animals that displayed spatial impairments increased sharply with advancing age. Quantitative assessment of the size and density of choline acetyltransferase (ChAT)-positive neurons throughout the basal forebrain revealed a significant enlargement of forebrain cholinergic neurons within 27-month-old nonimpaired rats compared to 6-month-old rats and 27- and 33-month-old impaired animals. This increase in size was most noted in the medial septum and nucleus of the diagonal band. Significant decreases in the density of ChAT-positive neurons was observed only in the nucleus of the diagonal band of 27-month-old impaired rats compared to 6-month-old controls. Although the significance of enlarged forebrain cholinergic neurons is unclear, we discuss the possibility that within aged rodents neuronal swelling is an active event and represents an early manifestation of the aging process and may constitute a restorative and/or compensatory event in that these rats are relatively asymptomatic with respect to their behavioral deficits. In addition, we discuss in some detail various technical and life effect issues which may vary the outcome of investigations of aged rodents.

Evidence that transmitter-containing dystrophic neurites precede those containing paired helical filaments within senile plaques in the entorhinal cortex of nondemented elderly and Alzheimer's disease patients

Within the amygdala of elderly subjects and patients with Alzheimer's disease (AD), we recently found evidence suggesting amyloid beta-protein (A beta P) deposition occurs before the appearance of dystrophic neurites. Moreover, these data suggested dystrophic neurites initially lack evidence of cytoskeletal pathology although with time and further maturation, the dystrophic neurites display an altered cytoskeleton as evidenced by their immunoreactivity to Alz-50 and paired-helical filaments (PHF). These findings are of particular relevance to our understanding of the sequence of pathologic events in AD and thus it has become important to determine whether these events are unique to the amygdala or are representative of a more general pattern which can be found throughout the brain. Using a battery of antibodies to markers that are characteristic of AD pathology (i.e., A beta P, PHF, and Alz-50), three peptidergic neurotransmitters (neurotensin, somatostatin, and substance P), and one neurotransmitter biosynthetic enzyme (choline acetyltransferase), we examined the entorhinal cortex (EC) of three groups of subjects (AD, normal elderly, and a group of nondemented elderly with numerous senile plaques). The EC was studied, in part, because it is well recognized as a brain region displaying severe and, most importantly, early pathologic changes. Like the amygdala, we found evidence that amyloid beta-protein immunoreactive (A beta P-IR) and thioflavine-S-positive senile plaques occur within the EC prior to the appearance of transmitter-, Alz-50-, or PHF-immunoreactive dystrophic neurites. We also observed transmitter-immunoreactive dystrophic neurites in the absence of Alz-50 or PHF-immunolabeled dystrophic neurites and transmitter- and Alz-50-IR dystrophic neurites in the absence of those containing PHF. Collectively, these findings were similar to those seen within the amygdala and thus reinforced the concept that A beta P deposition is the primary event in plaque pathology, and this deposition is subsequently followed by the appearance of dystrophic neurites which retain their transmitter phenotype yet lack an altered cytoskeleton. With time, these dystrophic neurites develop cytoskeletal alterations and become immunoreactive to Alz-50 and PHF.

Evidence that transmitter-containing dystrophic neurites precede paired helical filament and Alz-50 formation within senile plaques in the amygdala of nondemented elderly and patients with Alzheimer's disease

Immunocytochemical techniques were employed to examine the temporal ordering whereby amyloid beta-protein (A beta P) and neuronal elements collectively come together to form senile plaques in Alzheimer's disease (AD). Specifically, we addressed three questions: (1) whether A beta P deposition precedes or follows neuritic changes; (2) whether paired helical filament (PHF) formation is an early or late event in the genesis of the dystrophic neurites which participate in plaque formation; and (3) whether the density of senile plaques displays any relationship with the prevalence of PHF or Alz-50 containing neurons. To address these questions we studied the amygdala from a group of patients with AD, a group of nondemented age-matched individuals exhibiting a sufficient number of senile plaques to be classified by neuropathological criteria as AD, and a group of age-matched controls without AD pathology. Amyloid-bearing plaques were demonstrated by A beta P immunolabeling and thioflavine-S staining. Neuritic changes in the form of dystrophic neurites were observed with the aid of antibodies against PHF, Alz-50, as well as antibodies against several neuropeptides (i.e., substance P, somatostatin, and neurotensin) and the acetylcholine biosynthetic enzyme, choline acetyltransferase. By using a graded range of pathologic changes both within and across the patient population to provide us with a means of evaluating plaque deposition from its earliest to most advanced stages of development, we observed in patients and/or regions of the amygdala displaying a mild degree of pathologic change A beta P deposition in the absence of any neuritic changes. With increasing density of A beta P, however, we began to observe dystrophic neurites within plaques. In regions of relatively few plaques, the dystrophic neurites were immunolabeled only with antibodies against the various neurotransmitters and they lacked evidence of cytoskeletal pathology (i.e., Alz-50 or PHF). Only as the density of A beta P increased further within a region, were dystrophic neurites observed that exhibited Alz-50 or PHF. In no instance did we observe a relationship between the density of A beta P deposition and the density of Alz-50 or PHF-immunoreactive neurons. Collectively, our data suggest that the deposition of A beta P is an early pathologic event in senile plaque formation. Thereafter, swollen neurites can be seen in the vicinity of A beta P. This early neuritic response, which can first be visualized by immunolabeling for one or another transmitter substance, is followed by alterations in the cytoskeleton as recognized initially by antibodies to Alz-50 and subsequently by the presence of PHF.

Alzheimer's disease-like dystrophic neurites characteristically associated with senile plaques are not found within other neurodegenerative diseases unless amyloid beta-protein deposition is present

Swollen, bulbous-shaped (dystrophic) neurites are a common pathologic feature of Alzheimer's disease (AD) and represent one of the most abundant neuritic abnormalities within the brains of patients with this disease. In the present study, we sought to determine whether the dystrophic neurites which are observed in association with senile plaques are unique to AD or whether they are characteristic of a more generalized process of neuritic and/or neuronal degeneration which can be observed in other neurodegenerative diseases. To accomplish this, we examined post-mortem brain material from patients with AD, Parkinson's disease (PD), Parkinson's disease with associated AD, Parkinson's disease with dementia yet without AD pathology, Huntington's disease (HD), Pick's disease and normal age-matched controls (NC). Using a battery of antibodies to amyloid beta-protein (A beta P), paired-helical filaments (PHF), tyrosine hydroxylase, substance P, neurotensin, and somatostatin we found that immunolabeled dystrophic neurites of the type characteristically observed in AD, were seen only in cases and in brain regions where A beta P deposition was present. More specifically, brain areas known to display severe afferent and/or local degenerative changes such as the caudate and putamen in all three PD groups, the caudate in the HD cases, and the temporal cortex in the HD and Pick's cases were conspicuously free of these swollen neurites unless A beta P deposition was also present.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the discharge patterns of cat motor cortex neurones during unexpected perturbations of on-going locomotion

1. The impulse activity of single neurones in the forelimb part of the motor cortex was recorded extracellularly in unrestrained cats during self-paced locomotion on a horizontal circular ladder. 2. Fifty-one cells (forty-nine of which discharged rhythmically in time with the step cycle) were recorded during encounters with a number of rungs that could be locked firmly in position or, alternatively, held in position by weak springs so that when stepped on they unexpectedly descended (under the weight of the animal) from 1 to 5 cm before contacting a mechanical stop. 3. In eleven cells (22%) including four fast-axon pyramidal tract neurones (PTNs), an increase in discharge occurred when the contralateral forelimb descended unexpectedly. Onset latency relative to the start of rung movement ranged from ca 20 to ca 100 ms. In eight cells latency was such that most of the response preceded contact of the rung with the stop; averaged over a number of trials the altered discharge in five of these cells (including two PTNs) represented an accurate profile of the averaged velocity of rung (and foot) descent. The three remaining cells appeared to be responding largely to the cessation of rung movement. 4. Thirty-six of the cells were also studied during unexpected descent of the ipsilateral forelimb and six (17%) displayed an increase in discharge (onset latency ca 35 to ca 80 ms); three of these were among those that also responded to contralateral descents. 5. These findings for skilled locomotion requiring a high degree of visuomotor coordination are discussed and it is concluded that the motor cortex is rapidly informed regarding unexpected perturbations delivered to the contralateral forelimb at the onset of stance and that changes are evoked in the pattern of impulse traffic descending via the pyramidal tract.

Ultrastructural examination of enkephalin and substance P input to cholinergic neurons within the rat neostriatum

Enkephalin and substance P-containing inputs to cholinergic perikarya were examined in the rat neostriatum using an ultrastructural immunocytochemical double-labeling protocol. Sections of rat neostriatum were double-labeled for either choline acetyltransferase (ChAT) and substance P or ChAT and enkephalin using silver intensified colloidal gold and peroxidase as labels. Regions containing both ChAT-positive neurons and peroxidase reaction product were identified in the light microscope prior to sectioning for electron microscopy. Substance P-containing terminals which contained round synaptic vesicles and made symmetrical synaptic contacts were commonly observed in the neostriatum. Substance P synapses onto ChAT-positive perikarya and dendrites were frequently observed: up to 5 synaptic contacts were observed onto a ChAT-positive dendrite. Enkephalin labeling was also seen in a population of axon terminals containing round synaptic vesicles and exhibiting symmetrical synaptic specializations. In contrast to substance P-containing terminals, relatively few synaptic contacts were observed onto ChAT-positive labeled perikarya and dendrites although enkephalin-labeled terminals were seen in frequent contact with perikarya and dendrites of unlabeled spiny neurons. Since enkephalin and substance P are contained within different populations of striatal spiny neurons, the results of the present study suggest that these two types of neurons differ in their intrinsic striatal connections.