[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.