[Standardized neurologic study in senile dementia of Alzheimer's type]

Seventy five patients affected by senile dementia of the Alzheimer type (mean age 82) have been submitted to a standardized neurological examination of 88 items. Gait abnormalities were present in 57% of the cases. Extrapyramidal symptoms (akinesia or rigidity or tremor) were noticed in 64% of the cases but they were rarely associated with a typical parkinsonian syndrome. Myoclonus was observed in only 4 patients. The gait abnormalities were significantly associated with the presence of rigidity and grasp reflex but not with other primitive reflexes. The only symptoms to be correlated with dementia severity as assessed by the Mini Mental State were rigidity and optokinetic nystagmus abolition. Tremor and amyotrophy of the hands appeared to be negatively correlated to dementia severity.

[Quantified neuropsychological study in senile dementia of Alzheimer's type]

Forty six patients affected by senile dementia of the Alzheimer type and 20 control subjects of similar age, sex and educational level have been studied, using a quantified neuropsychological battery (Wechsler memory scale, Raven progressive matrices and quantified tests for aphasia, apraxia and agnosia). There was a significant correlation between the scores of all cognitive functions with one another and with the Mini Mental State. The results show a rather global impairment of cognitive functions in these patients and suggest that intellectual impairment progresses as a continuum in senile dementia of the Alzheimer type.

Platelet [3H]-imipramine binding is not modified in Alzheimer's disease

Platelet [3H]-imipramine binding was studied in patients with Alzheimer's disease and control subjects matched to the patients for age and sex. There were no differences in the binding parameters of [3H]-imipramine on platelet membranes from patients with Alzheimer's disease, when compared with the control group. These results suggest that [3H]-imipramine binding could be a useful tool to discriminate between demented and depressive patients in elderly populations.

Galanin blocks the slow cholinergic EPSP in CA1 pyramidal neurons from ventral hippocampus

Using intracellular recordings from slice preparations, we studied the effects of the peptide galanin on the properties of CA1 pyramidal neurons from rat ventral hippocampus. Galanin, applied in the superfusing medium, had a weak and inconsistent effect on the membrane potential or on the afterhyperpolarization which follows a train of spikes. Galanin, which is localized in some cholinergic neurons of the septo-hippocampal pathway, did not affect the action of acetylcholine or carbachol on CA1 pyramidal neurons. However, it did have a presynaptic inhibitory effect on the cholinergic terminals, blocking the slow cholinergic excitatory post-synaptic potential (EPSP) induced by the release of endogenous acetylcholine on the pyramidal neurons. This effect was reversible and mimicked by atropine. These results suggest that the peptide galanin, colocalized with acetylcholine in some septo-hippocampal neurons might play a role in the control of acetylcholine release.

Involvement of a pertussis toxin-sensitive G-protein in the pharmacological properties of septo-hippocampal neurones

1. The physiological and pharmacological properties of identified septo-hippocampal neurones (SHNs) have been studied in rats pretreated with the bacterial toxin, pertussis toxin (PTX). 2. In rats anaesthetized with urethane and pretreated with PTX, the axonal conduction velocity was unchanged while the mean spontaneous activity was significantly increased. 3. PTX pretreatment had no effect on responses of SHNs to the iontophoretic application of gamma-aminobutyric acid (GABA) and cholinoceptor agonists (acetylcholine or carbachol). 4. Baclofen and 5-hydroxytryptamine (5-HT), almost exclusively inhibitory in control rats, had little effect or an excitatory effect in PTX pretreated rats. 5. These results suggest the involvement of a pertussis toxin-sensitive G-protein in responses medicated by 5-HT and GABAB-receptors but not in responses mediated by cholinoceptors and GABAA-receptors in medial septum neurones projecting into the hippocampus.

Age-related changes in dopaminergic and serotonergic indices in the rat forebrain

Age-related changes in the content of dopamine (DA), homovanillic acid (HVA), dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in anterior cerebral cortex, hippocampus and striatum of the rat have been investigated using HPLC with electrochemical detection. A significant decrease in HVA was observed in the striatum and hippocampus of the aged (27 months) animals, as compared to the controls (2.4 to 2.6 months). A significant decrease in DA levels was also observed in the hippocampus but not in the striatum. In contrast, the level of DA in the cerebral cortex was markedly increased in the aged animals. A concomitant increase in 3-MT level was observed. Finally the level of 5-HIAA was significantly increased in striatum and hippocampus.

Septo-hippocampal neurons in the aged rat: relation between their electrophysiological and pharmacological properties and behavioral performances

The performances of aged (24-26 months) rats in two behavioral tasks (passive avoidance and spontaneous alternation) have been studied. Subpopulations of old animals were found to be impaired in these tasks. Most of the impaired animals, however, were not impaired in both tasks. The properties of the septo-hippocampal neurons (SHNs) were subsequently studied in the same group of experimental animals, anesthetized with urethane, using electrophysiological techniques. The spontaneous activity of SHNs displaying a rhythmically bursting activity (RBA) was significantly higher in animals impaired in the spontaneous alternation task. The proportion of SHNs with RBA was significantly lower and the frequency of the RBA was higher in animals impaired in the passive avoidance task. The pharmacological properties of the SHNs were not significantly different in the various groups. The significance of these complex correlations with regard to the age-related alterations of SHNs properties is discussed.

Hemicholinium-3 selectively alters the rhythmically bursting activity of septo-hippocampal neurons in the rat

The medial septal area contains neurons which project to the hippocampal formation. A sizeable proportion of these septo-hippocampal neurons (SHNs) are cholinergic. About 40% of them also display a characteristic discharge pattern in rhythmic bursts. We hypothesized that SHNs with a rhythmically bursting activity (RBA) are the cholinergic ones. To test this hypothesis we studied the effects of acetylcholine synthesis blockade by hemicholinium-3 (HC-3) on the properties of the SHNs. HC-3 (16, 32 or 64 micrograms total dose) or saline were injected in the lateral ventricles of adult male Sprague-Dawley rats anesthetized with urethane. Extracellular recordings from SHNs in the medial septal area were obtained within hours after HC-3 injections (n = 24 animals). SHNs were identified by their antidromic response following electrical stimulation of the fimbria-fornix. The pharmacological properties of SHNs were studied in some animals using microiontophoretic applications from multibarreled electrodes filled with various neurotransmitters. The hippocampal rhythmic slow activity (RSA or theta) was abolished even after the lowest dose of HC-3 tested (16 micrograms). No significant change in SHNs conduction velocity or spontaneous activity was observed at any dose of HC-3. The percentage of SHNs with RBA was unchanged. In contrast the mean frequency of the RBA was decreased by HC-3 in a dose-dependent fashion. The mean frequency was lowest within the first 3 h after injection. Although the mean spontaneous activity was unchanged SHNs tended to have more spikes per burst. The effects of various neurotransmitters on SHNs were qualitatively unchanged after HC-3 injection. These results suggest that acetylcholine synthesis blockade by HC-3 leads not only to the disappearance of the hippocampal RSA in urethane-anesthetized animals, but also to a decrease in the frequency of the rhythmically bursting activity of the SHNs. Since the 4-Hz hippocampal theta is atropine-sensitive, the results provide indirect evidence that the SHNs with rhythmically bursting activity are the cholinergic SHNs.

Cholinergic and peptidergic projections from the medial septum and the nucleus of the diagonal band of Broca to dorsal hippocampus, cingulate cortex and olfactory bulb: a combined wheatgerm agglutinin-apohorseradish peroxidase-gold immunohistochemical study

We have examined the distribution pattern and the density of various neuropeptide, neurotransmitter and enzyme containing neurons in the rat medial septum and the nucleus of the diagonal band of Broca to assess their possible involvement in the septohippocampal, septocortical and septobulbar pathways. Immunohistochemical methods were combined with the retrograde transport of a protein-gold complex injected in the hippocampus, the cingulate cortex or the olfactory bulb. Cholinergic neurons were the most numerous. Galanin-positive neurons were about two or three times less numerous than cholinergic cells. Both these cell types had a similar location though the choline acetyl transferase-like immunoreactive cells extended more caudally in the horizontal limb of the nucleus of the diagonal band of Broca. Immunoreactive cells for other neuroactive substances were few (calcitonin gene-related peptide, luteinizing hormone releasing hormone. [Met]enkephalin-arg-gly-leu) or occasional (dynorphin B, vasoactive intestinal polypeptide, somatostatin, neurotensin, cholecystokinin, neuropeptide Y and substance P). No immunoreactive cells for bombesin, alpha atrial natriuretic factor, corticotropin releasing factor, 5-hydroxytryptamine, melanocyte stimulating hormone, oxytocin, prolactin, tyrosine hydroxylase or arg-vasopressin were present. Choline acetyltransferase- and galanin-like immunoreactive cells densely participate to septal efferents. Cholinergic neurons constituted the bulk of septal efferent neurons. Galanin-positive cells were 22% of septohippocampal, 8% of septocortical, and 9% of septobulbar neurons. Galanin containing septohippocampal neurons were found in the medial septum and the nucleus of the diagonal band of Broca; galanin-positive septobulbar and septocortical cells were limited to the nucleus of the diagonal band of Broca. Occasional double-labellings were noticed with some peptides other than galanin. Luteinizing hormone-releasing hormone, calcitonin gene-related peptide and enkephalin were the most often observed; some other projecting cells stained for vasoactive intestinal polypeptide or dynorphin B. Luteinizing hormone-releasing hormone, calcitonin gene-related peptide and enkephalin were observed in septohippocampal neurons; luteinizing hormone-releasing hormone and vasoactive intestinal peptide were observed in septocortical neurons and calcitonin gene-related peptide, luteinizing hormone-releasing hormone and dynorphin B were observed in septo-bulbar cells. These results show that, in addition to acetylcholine, galanin is a major cellular neuroactive substance in septal projections to the hippocampus, the cingulate cortex and the olfactory bulb. The presence of septal projecting neurons immunoreactive for other peptides shows that a variety of distinct peptides may also participate, but in a smaller number, to septal efferent pathways.

Effect of psychotropic drugs on identified septohippocampal neurons

The effects of various psychotropic drugs (benzodiazepines, antidepressants, neuroleptics and nootropic drugs, a family of cognition activator agents) on firing rates of septohippocampal neurons, identified by electrical antidromic stimulation, were studied in the medial septum-nucleus of the diagonal band of Broca of rats anaesthetized with urethan. Extracellular potentials from single septohippocampal neurons were recorded using glass pipettes. Drugs were applied by either microiontophoresis or intravenous injections (i.v.). Benzodiazepines produced a marked depression of spontaneous firing rates of septohippocampal neurons whether applied i.v. (diazepam) or iontophoretically (flurazepam, midazolam). In addition, diazepam had a potent depressant effect on the rhythmically bursting activity of the septohippocampal neurons. Baclofen also had an inhibitory effect. Antidepressant drugs (applied by iontophoresis) as well as amphetamine, had a depressant effect on spontaneous firing rates. Neuroleptics (i.v.) had less significant or consistent effects on septohippocampal neurons, although the effects of haloperidol were usually inhibitory. Nootropic drugs were generally ineffective. These data indicate that most psychotropic drugs tested (with the exception of nootropic drugs) have an inhibitory effect on the spontaneous activity of septohippocampal neurons. However, benzodiazepines seem to be more active than antidepressants or neuroleptics. Oxotremorine (i.v.) had a potent excitatory effect on septohippocampal neurons. Atropine (i.v.) increased the septohippocampal neurons' firing rate in some cases. These results are discussed in view of the possible implication of the involvement of septohippocampal neurons in the mediation of the effects of psychotropic drugs on the central nervous system and, more specifically, on the cholinergic systems.

Neuropeptides and septo-hippocampal neurons: electrophysiological effects and distributions of immunoreactivity

The septo-hippocampal neurons (SHNs), located in the medial septum, project to the hippocampal formation. The population of SHNs, as shown by single unit recordings in urethane-anesthetized rats, is heterogeneous, both in terms of patterns of spontaneous activity (a significant proportion of the SHNs display a characteristic rhythmically bursting activity at about 4 Hz) and of conduction velocity. Their average rate of spontaneous discharge is quite high (20 impulses per second). They are excited by the iontophoretic application of acetylcholine and various cholinergic agonists. They are also excited by some peptides such as substance P and TRH. Parallel studies in aged animals show that the physiological properties of the SHNs are altered, while their pharmacological properties seem to be unchanged. Immunohistochemical investigations using antibodies against various peptides and a monoclonal antibody against choline acetyltransferase (ChAT) show that SHNs retrogradely-labeled from the hippocampus often contain ChAT, less frequently galanin-like immunoreactivity and in a few cases enkephalin, luteinizing hormone-releasing hormone, or calcitonin gene-related peptide. In contrast, cholecystokinin, vasoactive intestinal peptide, substance P, somatostatin, dynorphin-B and neurotensin, although present in some medial septal neurons, were never observed in neurons projecting to the hippocampus.

Electrophysiological and pharmacological properties of neurons within solid basal forebrain transplants in the rat brain

Electrophysiological and pharmacological properties of neurons within solid basal forebrain transplants were studied in adult rats anesthetized with urethane. No specific topography of the neurons recorded was observed within the graft. The mean spontaneous activity of the grafted neurons (GNs) was relatively low (4.9 impulses/s) but not unlike that of other central neurons in situ. A large proportion of GNs fired with regular discharges, but other modes of discharge were also observed. A few rhythmically bursting GNs were recorded having a discharge pattern very much like that of the rhythmically bursting medial septal neurons. The responses of GNs to glutamate, gamma-aminobutyric acid, acetylcholine, serotonin and norepinephrine was fairly similar to those described in other central structures.

An iontophoretic study of single somatosensory neurons in rat granular cortex serving the limbs: a laminar analysis of glutamate and acetylcholine effects on receptive-field properties

1. Glutamate, acetylcholine (ACh), and bicuculline were delivered by iontophoretic pipettes to the 545 neurons described in the preceding paper. Their response properties were examined to determine the effect of these compounds on the behavior of neurons in rat somatosensory cortex. 2. The responses to glutamate covered a broad range. Some cells were completely depolarized by small amounts of this excitatory amino acid, whereas others were extremely insensitive requiring in excess of 100 nA to be excited. This range of sensitivities was seen throughout all cortical layers. 3. Glutamate was most effective in uncovering new receptive fields or in enhancing preexisting somatic responses in the bottom of layer II/III and in layer IV. Receptive fields uncovered by glutamate had properties comparable to receptive fields observed without drugs. Overall, glutamate enhanced the ability of afferent inputs to drive 39% of the neurons tested. 4. In 61% of the cells tested with glutamate there was no evidence of somatic input even during excitation with glutamate. Of 50 cells displaying receptive fields, only two were enlarged by treatment with glutamate. For 36 other cells receptive fields of normal dimensions were uncovered during glutamate administration. 5. Bicuculline uncovered more somatic inputs than either glutamate or ACh, leaving only 37% of 86 cells tested without evidence of excitatory inputs from the skin. Bicuculline produced an average receptive-field enlargement of 8.7 times in 11 of 56 cells tested. This drug acted uniformly throughout the cortical layers. 6. ACh excited 36.9% of the 360 cells tested. Those excited tended to be located in laminae Vb and VIb. The effects of ACh on afferent response properties could not be predicted from its ability to excite a cell. The magnitude of the response to 100 nA of ACh varied with the laminar position of the cell being tested, being weakest in layer II/III and greatest in layer Vb. 7. Overall, 34.2% of 263 cells showed changes in afferent drive during ACh treatment. ACh enhanced the responses to somatic stimulation most frequently in laminae IV and V. 8. Of the 90 neurons tested for long-term effects, 27% displayed effects of ACh that significantly outlasted the duration of the ACh administration. In 18% of these, changes lasted for greater than 5 min, sometimes remaining altered for the duration of the time that the cell was studied. These long-term changes in excitability were generally produced by administration of ACh during the time that the cell was excited by glutamate or by somatic stimulation.

An electrophysiological study of single somatosensory neurons in rat granular cortex serving the limbs: a laminar analysis

1. Recordings were made from 545 neurons in somatosensory granular cortex of anesthetized Sprague-Dawley rats. Of this sample, 32% were active spontaneously. Active neurons were not distributed uniformly throughout cortex but were most common in layer V. The highest mean spontaneous discharge frequency also was found in this layer. Cells with the lowest rates of spontaneous activity were located immediately above and below. One subset of spontaneously active neurons was characterized by an unusually high discharge frequency modulated by somatic stimulation. 2. Only 25.8% of the 534 neurons tested in granular cortex could be activated by somatic stimuli. Only 9.4% had cutaneous receptive fields, and 2.4% received deep inputs. The remainder (14.0%) were driven by higher intensity stimuli and could not be classified unequivocally as either cutaneous or deep. The 50 neurons with cutaneous receptive fields were located in the middle third of the cortex, and those with the largest receptive fields were found most superficially. Neurons driven by somatic stimuli were found most frequently in layer Vb, where 44.5% of the sample confirmed histologically to be in layer Vb could be excited. 3. The large proportion of neurons lacking demonstrable somatic inputs was attributed to the use of iontophoretically administered glutamate, which allowed the detection of many unresponsive neurons. This proportion was not reduced by the use of nitrous oxide and halothane as an anesthetic. 4. Neurons activated only by deep inputs were found on the medial and rostral edge of the hindlimb granular cortex, suggesting that deep and cutaneous inputs may be segregated in this species. 5. Electrical stimuli applied to the foot pads activated a sample of neurons differing from those driven by natural somatic stimuli in terms of depth, spontaneous activity, probability of somatic input, and probability of activation by the pyramidal tract. 6. Pyramidal tract neurons tended to be located in layer Vb, were active spontaneously, and had evidence of somatic inputs, although most required relatively intense stimuli to be excited. Other neurons activated synaptically from the pyramidal tract were located in the layers immediately above and below the pyramidal tract neurons. These cells were divided into two groups on the basis of action-potential latency, action-potential shape, and sensitivity to acetylcholine.

An electrophysiological laminar analysis of single somatosensory neurons in partially deafferented rat hindlimb granular cortex subsequent to transection of the sciatic nerve

A sample of 302 neurons in rat hindlimb granular cortex was studied between 2 and 3 weeks after transection and ligation of the sciatic nerve. These neurons were compared to a control sample obtained from normal rats under similar experimental conditions. After sciatic nerve transection the proportion of neurons driven by somatic stimuli applied to the hindlimb (29.1%) was not significantly different from the proportion observed in the control sample (25.8%). The proportion of neurons with cutaneous receptive fields was also the same before and after nerve transection although the proportion of neurons responding to higher threshold taps was reduced. Spontaneously active neurons were encountered more frequently after sciatic nerve transection than in the control (45% vs 32%) and their mean discharge frequency was higher (8.6 vs 6.4 imp/s). Twice as many (10.2% vs 5.2%) spontaneously active neurons whose discharge was modulated by afferent stimuli were found after sciatic nerve transection. This and several other lines of evidence suggest that the cortical neurons were released from inhibition by the sciatic nerve transection. The number of spontaneously active neurons and the mean discharge rate were increased in each cortical lamina suggesting that the increased excitability seen after deafferentation occurred in all cortical layers. Neurons throughout the portion of the hindlimb representation studied could be driven from the remaining innervated region of the hindlimb, including one and sometimes two digits, part of the palm and most of the dorsum of the foot. More neurons were driven by receptive fields on the ankle than was the case for normal rats. Most neurons with cutaneous receptive fields were distributed in the same layers as those in the control group and had normal shapes and appearances. However, there were few of small size. Most were of moderate dimensions well within the normal range. Seven examples were found with unusually large proportions of their field extending from the foot onto the ankle and covering most of the posterior quadrant of the animal. In normal cortex the largest receptive fields were found in the middle layers. This distribution was not as clear after sciatic nerve section and a mixture of large and medium-sized receptive fields occurred at each depth. Further, some neurons with cutaneous receptive fields were found above 300 micron and below 1000 micron, depths where receptive fields were uncommon in the normal sample.

Somatosensory neurons in partially deafferented rat hindlimb granular cortex subsequent to transection of the sciatic nerve: effects of glutamate and acetylcholine

The effects of drugs administered iontophoretically were studied on 302 neurons isolated from partially deafferented hindlimb granular cortex of the rat and were compared to a previously studied sample from normal granular cortex. The proportions of cells affected by glutamate and acetylcholine (ACh) were not markedly different after partial deafferentation, but the cells were more readily depolarized by glutamate and their responses to a fixed dose of glutamate were larger. Fewer cells were excited strongly by ACh (up to the point of depolarization block) and the amplitudes of responses to test pulses of ACh were reduced in infragranular layers after partial deafferentation. Fifteen cells (5.9%) were inhibited by ACh administration, whereas in normal cortex this value was less than 1%. Fewer receptive fields were uncovered by glutamate after partial deafferentation, but more receptive fields were enlarged by this substance after nerve transection. These data were interpreted to mean that the cells from deafferented cortex had fewer excitatory inputs and as well, were apparently under a comparatively weaker degree of inhibitory control after deafferentation. The administration of ACh uncovered fewer somatic inputs than in normal animals. Responses were enhanced by ACh less frequently, and repeated treatments with ACh often led to a reduction in the effectiveness of the afferent stimulus. Increases in neuronal thresholds for somatic stimuli also were observed. The laminar distribution of the effects of ACh was similar to the distribution observed in normal animals. The responses to iontophoretically administered ACh and its agonists appeared to be mediated through both nicotinic and muscarinic receptor processes after partial deafferentation. Often the time course of the effects of ACh was abnormal, being characterized by oscillations between silence and very high rates of discharge with a period of 6-12 s. These observations are consistent with the hypothesis that after a major deafferentation (i) there is a reduction of the inhibitory controls normally present in the somatosensory cortex, and (ii) neuronal responses to ACh are modified in partially deafferented cortex. The magnitude of the responses of cells to ACh in the supragranular layers are larger after deafferentation whereas the magnitude of responses in the infragranular layers are reduced by this procedure. These changes may be related to changes induced by deafferentation in the distribution of receptors and/or in their pharmacological properties.

Differential effects of M1 and M2 muscarinic drugs on septohippocampal, hippocampal and cortical neurons in the rat

The effects of muscarinic agonists (McN-A-343, pilocarpine, oxotremorine-M, carbachol) and antagonists (pirenzepine, gallamine) applied by iontophoresis were studied on several neuronal populations in the central nervous system of rats anesthetized with urethane. Septohippocampal neurons and neurons from hippocampus, subiculum and somatic sensory cortex were studied. Oxotremorine-M and carbachol had (almost exclusively) potent excitatory effects whereas pilocarpine had some and McN-A-343 had almost exclusively inhibitory effects on the 4 populations of neurons studied. Pirenzepine blocked more easily the effects of pilocarpine and McN-A-343 than those of oxotremorine-M or carbachol. These results suggest (i) that many central neurons may bear different functional muscarinic receptors and (ii) that the various agonists studied might act through (at least partially) different mechanisms.

Contrasting properties of medial septal neurons projecting to hippocampus or interpeduncular nucleus in the rat

The properties of neurons of the medial septal nucleus and of the nucleus of the diagonal band of Broca which project to hippocampus or to interpeduncular nucleus were compared in rats anesthetized with urethane. Neurons projecting to the interpeduncular nucleus had a slower conduction velocity and a lower spontaneous discharge rate. In contrast, their responses to various putative neurotransmitters (glutamate, GABA, acetylcholine) were similar. In a few cases, neurons projecting to both structures (i.e., with branched axons) were observed. Both septohippocampal and septointerpeduncular pathways are known to be partly cholinergic. Our results show that they originate from two independent populations of medial septal-nucleus of the diagonal band of Broca neurons with different physiologic properties.

Serum neuron-specific enolase in senile dementia of the Alzheimer type

The level of neuron-specific enolase (NSE), a glycolytic enzyme localized in neurons, was measured in the serum of patients with senile dementia of the Alzheimer type (SDAT). No difference was observed between NSE levels in SDAT and in healthy elderly controls of the same age range. No correlation was found between NSE levels and severity of the cognitive deficits. There was a marginally significant negative correlation between age and NSE, younger patients having higher NSE levels. The present results suggest that serum NSE is not a useful biological marker in the senile form of the dementia of the Alzheimer type.

[Elementary test of concentration, orientation and memory. Application to the detection of dementia states in daily practice]

The authors present a french version of the Katzman short orientation memory concentration test. The 6 items of the test include 3 orientation questions, 2 mental control items and an address memory phrase. Time for administration is less than 5 minutes. This french version of the test has been validated as a measure of cognitive impairment in a population of 200 subjects including 140 patients without cognitive impairment and 60 demented subjects. As defined by a 10/11 cut-off score, sensibility and specificity for the diagnosis of dementia were 91 p. 100 and 95 p. 100 respectively. Correlation of the scores with those obtained by the Mini mental state was highly significant. This fast, easy and reliable test seems particularly suitable for the detection of cognitive impairment in clinical practice.

Somatosensory cortical neurons with an identifiable electrophysiological signature

In both cats and rats, neurons with a distinctively narrow action potential were recognized as a small subset of all neurons isolated in the somatosensory cortex. These cells were characterized by generally having a spontaneous activity, some evidence of an afferent input, a sensitivity to glutamate but a relative resistance to depolarization block induced by glutamate and a marked insensitivity to acetylcholine. Two were filled with horseradish peroxidase (HRP) and recovered. Although others have suggested that such neurons are interneurons, following reconstruction it was apparent that the two cells filled with HRP were pyramidal cells. These observations suggest that there may be more than one class of cortical neurons with thin spikes.

Neurons without demonstrable receptive fields outnumber neurons having receptive fields in samples from the somatosensory cortex of anesthetized or paralyzed cats and rats

In many common experimental conditions the majority of the neurons isolated in cat and rat somatosensory cortex using extracellular recording techniques are unresponsive to somatic stimuli. This population of cells becomes amenable to experimental manipulation with iontophoretic administration of glutamate, other putative neurotransmitters, and their agonists and antagonists. During administration of glutamate or bicuculline methiodide as many as half of the unresponsive cells could be shown to receive somatic inputs that did not drive the cells without drug treatments. Several hypotheses are discussed concerning the possible origin and function of the unresponsive neurons and the conditions under which they might play an active role in cortical function such as during altered patterns of afferent input, enhanced release of acetylcholine, reduction of GABAergic inhibition and situations involving learning or directed attention. The unresponsive neurons may be a characteristic that differentiates somatosensory cortex from subcortical sensory pathways.

Pharmacological modulation of cortisol secretion and dexamethasone suppression in Alzheimer's disease

We have investigated the dexamethasone suppression of cortisol release in a group of 28 patients with senile dementia of the Alzheimer type (SDAT) after stimulation by physostigmine and clonidine, as compared with basal conditions. All patients but one had previously been evaluated with a depression symptom checklist and had submitted to a standard Dexamethasone Suppression Test (DST). SDAT patients showed normal baseline cortisol values measured at 4:00 PM. DST was reproducible, but nonsuppression did not appear to be a feature of the disease, nor of the dementia syndrome, although a majority of the most demented patients were found to be nonsuppressors. Physostigmine stimulated cortisol secretion in 20 of 24 cases, irrespective of the severity of dementia. Clonidine induced a secretion in 12 of 15 cases, but this was less than that observed after cholinergic stimulation. Physostigmine made cortisol release significantly less sensitive to the suppressive effect of dexamethasone than clonidine in SDAT. This double response should be tested as a possible predictor of a cholinergic therapeutic effect.

A comparative evaluation of the short orientation memory concentration test of cognitive impairment

In order to assess the relative sensitivity and specificity of Katzman's short orientation memory concentration test (OMCT), 89 non demented patients and 44 patients affected by vascular or degenerative dementia were consecutively evaluated by three different mental status tests. The OMCT appeared equivalent to the Mini Mental State Examination in identifying dementia. Optimum sensitivity and specificity, respectively 88% and 94%, were achieved by a 10/11 cut-off score, giving a 11% false positive rate. Among patients with Alzheimer's disease, the OMCT score was correlated with mean values of a simple reaction time. It was also correlated with the Wechsler global MQ and the orientation, logical memory and paired associates items of the scale. There was no relationship between the OMCT score and the coloured Progressive Matrices IQ. The OMCT was reliable when given at 1 month interval. Serial evaluations did not show any significant practice effect.

Modulation of the excitability of septohippocampal terminals in the rat: relation to neuronal discharge rate

The excitability of the axonal terminals of medial septal neurons projecting to the dentate gyrus has been studied in the anesthetized rat under various experimental conditions: spontaneous or drug-induced variations in neuronal soma discharge rate, conditioning stimulation of afferent pathways (perforant path, commissural pathway, fimbria-fornix). It has been observed that terminals excitability is inversely correlated to the level of neuronal ongoing activity. These effects were observed on virtually all septal neurons projecting to the dentate gyrus. Since about one half of the septohippocampal neurons are likely to be cholinergic, it follows that such a phenomenon is not transmitter specific.

Septo-hippocampal neurons: altered properties in the aged rat

The septo-hippocampal pathway is one of the best characterized cholinergic pathways of the mammalian central nervous system. It is very likely that this pathway is involved in the pathophysiology of dementia of the Alzheimer's type and perhaps of normal aging also. The properties of the septo-hippocampal neurons identified by their antidromic response to the electrical stimulation of the fimbria-fornix were altered in aged (27 months) rats as compared to young (2-3 months) controls: their pattern of spontaneous activity (including the frequency of occurrence of a rhythmically bursting activity) and their axonal conduction velocity were altered. The intensity of these changes was dependent on the presence of pituitary tumor which developed spontaneously in about 1/3 of the animals. These results provide direct evidence of the involvement of septo-hippocampal neurons in the aging process.

The Hoffmann reflex (H-reflex) in senile dementia of the Alzheimer's type--preliminary results

The Hoffmann reflex (H-reflex) and direct motor response (M) were investigated (latency, amplitude and excitability curves were analyzed) in patients with senile dementia of the Alzheimer's type (SDAT). M responses had similar latencies in SDAT patients and old control subjects. H reflex latencies were similar in SDAT patients and old control subjects but longer than in younger controls. The H max/M max ratio was also lower in SDAT patients and old control subjects than in younger controls. The excitability curve of the H-reflex (using a double shock procedure) in SDAT patients was lower than in non-demented old controls for all values of the interstimulus intervals.

Beta amyloid gene duplication in Alzheimer's disease and karyotypically normal Down syndrome

With the recently cloned complementary DNA probe, lambda Am4 for the chromosome 21 gene encoding brain amyloid polypeptide (beta amyloid protein) of Alzheimer's disease, leukocyte DNA from three patients with sporadic Alzheimer's disease and two patients with karyotypically normal Down syndrome was found to contain three copies of this gene. Because a small region of chromosome 21 containing the ets-2 gene is duplicated in patients with Alzheimer's disease, as well as in karyotypically normal Down syndrome, duplication of a subsection of the critical segment of chromosome 21 that is duplicated in Down syndrome may be the genetic defect in Alzheimer's disease.

Septohippocampal neurons after intraventricular AF64A administration in rats: an electrophysiological study

The putative cholinergic neurotoxin, ethylcholine aziridinium ion (AF64A), was injected bilaterally into the cerebral ventricles of male rats. The properties of the medial septum-nucleus of the diagonal band of Broca's area (MS-nDBB) neurons were studied 4 to 6 or 19 to 23 days following injections. The spontaneous activity of those neurons was higher in the injected animals, but their responses to glutamate and cholinergic agonists were not modified. The proportion of orthodromic responses elicited by fimbria-fornix stimulation in MS-nDBB neurons was unchanged. In contrast, the proportion of septohippocampal neurons (SHNs) identified by the antidromic stimulation of the fimbria-fornix was smaller in pretreated animals and their mean antidromic latency was shorter. These results suggest that intracerebroventricular administration of the neurotoxin AF64A is followed by changes in the properties of MS-nDBB neurons and specifically by the disappearance of a subpopulation of SHNs.

Modifications in the cortical regional distribution of choline acetyltransferase, somatostatin and somatostatin binding sites in the normal rat and following lesion of the nucleus basalis

The regional distribution of choline acetyltransferase activity, somatostatin levels and 125I-CGP 23996 (a somatostatin agonist analog) specific binding sites in 10 separate zones of the cerebral cortex was analyzed. The study was performed in normal rats as well as 15 days after unilateral excitotoxic lesion of the nucleus basalis. A significant correlation was found in the controls between the regional distribution of choline acetyltransferase activity and somatostatin concentrations, both most highly concentrated in the piriform and entorhinal cortex. In contrast, the regional density of 125I-CGP 23996 binding sites correlated neither with choline acetyltransferase activity nor with somatostatin levels. Unilateral lesions of the basal forebrain decreased choline acetyltransferase activity in the frontal and parietal cortex, while 125I-CGP 23996 binding decreased in frontal and occipital regions. No decrease in somatostatin content was observed. The results suggest that, in rats, cortical somatostatin receptors could be associated with cholinergic afferents from the nucleus basalis in the frontal cortex only.

Septo-hippocampal neurons in the rat: further study of their physiological and pharmacological properties

Medial septal-nucleus of the diagonal band of Broca area (MS-nDBB) neurons, identified by their antidromic response to the electrical stimulation of the fimbria and/or hippocampus, were studied in the rat under various conditions of anesthesia. These septo-hippocampal neurons (SHNs) were classified into 4 groups on the basis of: (i) their antidromic latency; and (ii) the presence or absence of a rhythmically bursting pattern of spontaneous discharge. The rhythmically bursting activity (43.5% of the SHNs) was highly dependent on the anesthetic conditions. The groups of SHNs differed in their mean conduction velocity and rate of spontaneous activity. In contrast, irrespective of their classification in a particular group, the large majority of the SHNs could be excited by the iontophoretic application of cholinergic agonists. Beside the SHNs, two other populations of MS-nDBB neurons could be identified by electrical antidromic stimulation: neurons projecting to the amygdala (Am) and neurons projecting through the medial forebrain bundle (MFB). Half of the MS-nDBB neurons projecting to Am were also antidromically driven from the fimbria. The axonal branch projecting to Am had a slower conduction velocity than that projecting to hippocampus. In contrast MS-nDBB neurons projecting through the MFB were never antidromically driven from the fimbria, although they received orthodromic inputs. They had a slower conduction velocity than the other groups of MS-nDBB neurons.

Comparison of septo-hippocampal with basalo-cortical projection neurons in the rat: an electrophysiological approach

The electrophysiological properties of septo-hippocampal (SHNs) and basalo-cortical neurons (BCNs) identified by antidromic stimulation were compared in rats anesthetized with urethane. SHNs and BCNs had comparable conduction velocities (about 2-3 m/s) and relatively high spontaneous firing rates (about 20 impulses/s). In contrast, they differed in their pattern of spontaneous discharge as studied by generating inter-spike interval histograms. Many BCNs had a regular pattern of discharge. Among SHNs, about 40% had a spontaneous rhythmically bursting pattern of discharge, whereas the remaining 60% had a more or less irregular pattern. These results suggest that SHNs represent a more heterogeneous neuronal population than BCNs, and that central cholinergic neurons involved in different systems might also have different properties.

Basal forebrain neurons projecting to the rat frontoparietal cortex: electrophysiological and pharmacological properties

Neurons located in the ventromedial globus pallidus (nucleus basalis) and substantia innominata, that were antidromically driven by electrical stimulation of the frontoparietal cortex, were recorded in the urethane anesthetized rat. The basalocortical neurons (BCNs) were antidromically driven with latencies of 1.1-13.5 ms, giving conduction velocities of 0.6-6.8 m/s. Many BCNs had regular patterns of spontaneous discharge (mean spontaneous activity: 20 impulses/s). Most BCNs were not responsive to non-noxious peripheral somatic stimulation. BCNs were readily excited by the iontophoretic application of glutamate and strongly inhibited by GABA. Eighty-five percent of the BCNs could be excited by acetylcholine. They could also be excited by cholinergic agonists. Muscarinic agonists excited a higher proportion of BCNs than nicotinic agonists. Excitatory responses to acetylcholine, carbachol and muscarinic agonists were abolished by atropine.

Cerebral neocortical neurons in the aged rat: spontaneous activity, properties of pyramidal tract neurons and effect of acetylcholine and cholinergic drugs

The properties of cortical cerebral neurons have been studied and compared in 2, 22 and 26 month-old Sprague-Dawley rats, using electrophysiological techniques. The mean spontaneous activity of the neurons in old animals (unidentified as well as pyramidal tract neurons) was not different from that of young adult rats. In contrast the mean latency of the antidromic response of pyramidal tract neurons to pyramidal tract stimulation was significantly longer in 26 month-old animals. No difference was observed in the effects of the excitatory amino acid glutamate applied by iontophoresis. The percentage of cortical neurons excited by the iontophoretic application of acetylcholine was similar in young and old animals. Neither the laminar distribution, nor the individual sensitivity of these neurons to acetylcholine were found to be modified. The pharmacological properties of the acetylcholine-induced excitations were unchanged, exhibiting muscarinic as well as nicotinic properties. These results are consistent with the suggestion that the impairment of the cholinergic system with aging is for a large part presynaptic. They also emphasize the fact that several physiological and pharmacological properties of the cerebral cortical neurons show little change with age in Sprague-Dawley rats.

Bethanechol decreases reaction time in senile dementia of the Alzheimer type

Bethanechol, a muscarinic cholinergic agonist, was injected subcutaneously in eight cases of senile dementia of the Alzheimer type. Simple reaction time was measured before, 15 min and 30 min following the injection. Before injection, the patients had significantly longer reaction time than non-demented controls. A significant shortening of the reaction time was observed 15 min but not 30 min after injection. A second group of eight patients with senile dementia of the Alzheimer type, matched for age and mental impairment were injected with saline. No significant shortening of the reaction time was observed. These results suggest that the reaction time can be shortened by a muscarinic agonist in dementia of the Alzheimer type.

Septohippocampal neurons in the rat: an in vivo intracellular study

In vivo intracellular recordings were obtained from septohippocampal neurons identified by their antidromic response to electrical stimulation of the fimbria in rats anesthetized with pentobarbital or urethane. Beside the antidromic response, fimbria stimulation evoked a short-latency depolarizing potential (EPSP) followed by an hyperpolarizing potential which reversed polarity when recorded with KCl-filled electrodes. This IPSP is therefore likely to be chloride-dependent. It was followed by a long-lasting (80-250 ms) depolarizing potential often associated with a burst of spikes. Septohippocampal neurons therefore receive an inhibitory, chloride-mediated, input which itself triggers a long-lasting excitatory event. These results are consistent with extracellular observations. Their significance in the septohippocampal circuitry is discussed.

Effects of TRH, cyclo-(His-Pro) and (3-Me-His2)TRH on identified septohippocampal neurons in the rat

Neurons located in the medial septum-nucleus of the diagonal band of Broca (vertical limb) and antidromically activated by electrical stimulation of the fimbria were recorded in urethane anesthetized rats. Forty-three percent of these septohippocampal neurons (SHNs) were excited by the iontophoretic application of thyrotropin-releasing hormone (TRH). Rhythmically bursting SHNs were more often excited (63%) by TRH than the non-bursting SHNs (35%). The majority of the TRH-sensitive SHNs could also be excited by cholinergic agonists. TRH-induced excitations were not abolished by the simultaneous application of atropine. Potentiation by TRH of acetylcholine, carbachol or glutamate-induced excitations of SHNs were rarely observed. Cyclo (His-Pro) and (3-Me-His2)-TRH were observed to have similar, although less dramatic, effects. These results demonstrate that the SHNs, which are the neurons of origin of the septohippocampal pathway, are readily excited by TRH.

Activation of identified septo-hippocampal neurons by noxious peripheral stimulation

Septo-hippocampal neurons (SHNs) were recorded from the medial septum-diagonal band area of rats anaesthetized with either urethane or fluothane. They were identified by their antidromic response to the electrical stimulation of the fimbria. Their responses to peripheral somatic noxious and non-noxious stimulation were studied. Non-noxious natural stimulations were relatively ineffective. In contrast, 68% of the SHNs were driven by noxious stimulation. The SHNs could be driven either by mechanical or thermal stimulation. Intraperitoneal injection of bradykinin excited about half of the SHNs. Some neurons were able to encode stimulus intensity (strength of the mechanical stimulation and/or temperature of the thermal stimulation). The receptive fields of the SHNs were large, usually involving half of the body or the whole body surface. These results suggest that SHNs, which are at the origin of the cholinergic septo-hippocampal pathway, might be involved in cerebral mechanisms related to nociception.

Septo-hippocampal and other medial septum-diagonal band neurons: electrophysiological and pharmacological properties

Neurons located in the medial septum-nucleus of the diagonal band (vertical limb) area and antidromically activated by electrical stimulation of the fimbria were recorded in urethane anesthetized rats. Forty-five percent of these septo-hippocampal neurons (SHNs) discharged rhythmically in short bursts (mean burst frequency, 4 Hz). They were antidromically driven at short latencies from the fimbria. SHNs driven at long latencies (above 5 ms) were never bursting neurons. Fimbria stimulation also had a powerful inhibitory effect on the spontaneous activity of SHNs. The vast majority of the septo-hippocampal neurons were excited by the iontophoretic application of acetylcholine or cholinergic agonists, carbachol being the most effective. The acetylcholine-induced excitations were readily abolished by atropine. In contrast hexamethonium and mecamylamine were less effective. The rhythmic bursting activity could not be consistently altered by the iontophoretic application of cholinergic agonists or antagonists or of divalent cations. SHNs were also sensitive to various other putative neurotransmitters (substance P, GABA) known to play a role in the medial septal area. Bursting neurons and ACh-sensitive neurons were less frequent among unidentified medial septal neurons. The regulation of the septo-hippocampal cholinergic pathway is therefore not likely to be due to a direct feedback inhibition by locally released acetylcholine. However a strong inhibitory feedback could be exerted by the hippocampo-septal pathway impinging directly or indirectly on septo-hippocampal neurons.

In vivo electrochemical detection of 5-hydroxyindoles in rat cerebral cortex and spinal cord: differential effects of p-chloroamphetamine, probenecid and clorgyline

Differential pulse voltammetry associated with carbon fiber microelectrodes was used to detect the 300 mV signal which is known to reflect the concentration of 5-hydroxyindoles in the spinal cord and cerebral neocortex of rats anesthetized with urethane or chloral hydrate. The intraperitoneal injection of p-chloroamphetamine resulted in an increase in the amplitude of the signal in the neocortex but not in the spinal cord. Administration of clorgyline did not consistently modify the signal monitored in the neocortex whereas it decreased in the spinal cord. Probenecid induced a larger increase in 5-hydroxyindoles in the neocortex than in the spinal cord. These results demonstrate that different parts of the serotonergic system might be differentially sensitive to drugs affecting serotonin metabolism.

Cortical projections of the nucleus of the diagonal band of Broca and of the substantia innominata in the rat: an anatomical study using the anterograde transport of a conjugate of wheat germ agglutinin and horseradish peroxidase

The projections of the nucleus of the diagonal band of Broca and of the substantia innominata to the cerebral cortex were studied in the rat, using the anterograde transport of wheat germ agglutinin conjugated with horseradish peroxidase. Following diagonal band injections, fibers were observed ascending in the septum and reaching the cingulate cortex. They had a rostrocaudal, horizontal direction, mostly in layer VI and could be followed over long distances on sagittal sections. The fibers gave off collaterals which were seen ascending in the cerebral cortex and reaching more superficial layers. Following substantia innominata injections, fibers were observed to take two routes: the first one identical to the one described above and a second through the caudate-putamen reaching the temporo-insular cortex. Terminal fields had a more diffuse distribution following substantia innominata than following diagonal band injections. No clear laminar pattern of termination was observed. However the density of terminals was higher in layers IV, V and VI than in layers I, II and III. Since the conjugate used is not taken up by fibers of passage, this pattern of connection is believed to reflect the organization of the projection of the nucleus of the diagonal band and of the substantia innominata to the cerebral cortex.

Acetylcholine excites identified septo-hippocampal neurons in the rat

Neurons of the medial septum-nucleus of the diagonal band of Broca (vertical limb) area were identified as septo-hippocampal neurons by antidromic electrical activation in anesthetized rats. A large majority of these presumably cholinergic neurons could be excited by the iontophoretic application of acetylcholine or cholinergic agonists such as carbachol. The acetylcholine-induced excitations were readily antagonized by atropine. These results suggest that cholinergic neurons can be excited by their own transmitter, i.e. acetylcholine.

A comparative study of two populations of acetylcholine-sensitive neurons in rat somatosensory cortex

The properties of two populations of acetylcholine-sensitive neurons, defined by their different laminar distribution (group A, layers V and upper VIa; group B, layer VIb and underlying white matter) were studied in the SmI cortex of urethane-anesthetized rats. The spontaneous activity of group B neurons was significantly lower than in group A. The proportion of neurons excited by iontophoretic acetylcholine, the duration and the pharmacological properties of the excitations were the same in both groups. The dose-response curves obtained for sets of neurons of both groups, recorded with the same electrode, had comparable slopes. Carbachol had a greater potency than acetylcholine in both groups. In contrast, the latency of the response to acetylcholine was significantly shorter in group B. The amount of current required to increase the spontaneous discharge rate of a given neuron by 200% was lower in group B than in group A. These data suggest that the relative change in firing frequency induced by a given cholinergic input is likely to be larger in group B than in group A. Finally, neuronal excitations could still be obtained in both groups when acetylcholine was applied 300 micron, but not 600 micron, from the cell body, suggesting that the spatial distribution of acetylcholine receptors is similar in groups A and B.

In vivo electrochemical detection of 5-hydroxyindoles in rat somatosensory cortex: effect of the stimulation of the serotonergic pathways in normal and pCPA-pretreated animals

Differential pulse voltammetry was used for the detection of 5-hydroxyindoles in the cerebral cortex of rats anaesthetized with urethane. The stimulation of the lateral hypothalamus or of the dorsal raphe nucleus induced a 10-40% increase in the amplitude of the signal. The signal recorded from p-chlorophenylalanine (pCPA)-pretreated animals was much smaller than in normal animals and could be increased by 5-HTP administration. The stimulation of the serotonergic pathways was ineffective in the pCPA-pretreated animals.

Effects of neuropeptides on rat cortical neurons: laminar distribution and interaction with the effect of acetylcholine

The effects of the microiontophoretic application of five different peptides (cholecystokinin octapeptide sulfated form, cholecystokinin octapeptide non-sulfated form, vasoactive intestinal polypeptide, angiotensin-II and substance P) on cortical neurons were studied in rats anaesthetized with urethane. Vertical electrode penetrations were made in the first somatic sensory cortex and the laminar position of the neurons determined by the reconstruction of the tracks based on extracellular dye deposits. The first type of effect observed was an excitation of some cortical neurons. These neurons were mostly found in infragranular layers, specially in layer Vb. Pyramidal tract neurons were more often excited by peptides than the cortical population taken as a whole. Substance P excited the largest percentage of neurons, followed by vasoactive intestinal polypeptide and cholecystokinin octapeptide sulfated form, whereas angiotensin II and cholecystokinin octapeptide non-sulfated form were the least potent in terms of frequency of neurons excited as well as of amplitude of the responses. The vast majority of the neurons excited by a peptide could also be excited by acetylcholine. A second and independent effect of peptides was observed: the neuronal excitation induced by acetylcholine could be depressed by the simultaneous application of peptide. This depressing effect was also the most frequently observed with substance P, followed by cholecystokinin and vasoactive intestinal polypeptide.

Altered properties and laminar distribution of neuronal responses to peripheral stimulation in the SmI cortex of the arthritic rat

The properties of the neuronal responses to different types of mechanical peripheral stimulation were studied during electrode penetrations in the first somatosensory cortex of anaesthetized rats with polyarthritis. Very few neurons were driven by light cutaneous stimulation (such as brushing) or by intense mechanical stimulation. Most of the neurons were driven by joint movement and/or moderate pressure on the skin. These neurons could be found in all cortical layers, the majority being located in layer V. These results contrast sharply with the properties and laminar distribution of the different functional categories of cortical neurons, as observed in normal animals.