Postnatal differentiation of firing properties and morphological characteristics in layer V pyramidal neurons of the sensorimotor cortex

The maturational profile of the firing characteristics of 217 layer V pyramidal neurons of rat sensorimotor cortex, injected with biocytin for morphological reconstruction, was analysed by means of intracellular recordings made between postnatal day (P)3 and 22. Starting from the onset of the second postnatal week, the pyramidal neurons could be differentiated as adapting or non-adapting regular spiking on the basis of the presence or absence of spike frequency adaptation. The percentage of non-adapting regular spiking neurons was very high during the second postnatal week (53%) and progressively decreased with age, concurrently with the appearance of the new class of intrinsically bursting neurons (beginning of the third week) whose percentage progressively increased from 23%, found in P14-P16 rats, to 46% in adult rats. Non-adapting regular spiking neurons were found to share with intrinsically bursting neurons several physiological characteristics comprehending faster action potentials, more prominent effect of anomalous rectification and consistent depolarizing afterpotentials, that differentiated them from the adapting regular spiking neurons. Moreover, intrinsically bursting and non-adapting regular spiking neurons were characterized by a round-shaped distribution of basal dendrites and expanded apical dendritic arborization, that differentiated them from the adapting regular spiking neurons showing a simpler dendritic arborization. These morphological hallmarks were seen in immature intrinsically bursting neurons as soon as they became distinguishable, and in immature non-adapting regular spiking neurons starting from the onset of the second postnatal week. These findings suggest that a significant subpopulation of immature non-adapting regular spiking neurons are committed to becoming bursters, and that they are converted into intrinsically bursting neurons during the second postnatal week, as soon as the ionic current sustaining the burst firing is sufficiently strong. The faster action potentials in both immature non-adapting regular spiking and intrinsically bursting neurons suggest a higher density of Na+ channels in these neuronal classes: the maturational increase in Na+-current, namely of its persistent fraction, may represent the critical event for the conversion of the non-adapting regular spiking neurons into the intrinsically bursting ones.     

Dendritic changes of the pyramidal neurons in layer V of sensory-motor cortex of the rat brain during the postresuscitation period

The present study examined the temporal pattern and cellular localisation of nitric oxide synthase in Endotoxin-Induced Uveitis (EIU). Lewis rats (n=40) received a single footpad injection of 200 microg of bacterial lipopolysaccharide. Animals were killed at 0, 2, 4, 6, 12, 24, 48 and 72 hr after injection and ocular tissues prepared as iris-ciliary body wholemounts or frozen sections of the anterior segment. The expression of constitutive nitric oxide synthase (cNOS) and inducible nitric oxide synthase (iNOS) was investigated at all time points by immunohistochemistry. A further group of animals (n=6) were killed at the peak of the disease (12 hr) and the cellular co-localisation of iNOS on resident and infiltrating immune cells was investigated by double immunohistochemistry utilising the biotinylated monoclonal antibodies ED1, ED2 and Ox6. Expression of cNOS on iris vessels did not alter during the course of EIU. Quantitative analysis of iris-ciliary body wholemounts revealed the first evidence of iNOS+ at 2 hr which increased dramatically at 4 and 6 hr with a peak at 12 hr. The expression of iNOS in the early phase of the disease (2-6 hr) was associated with small round marginating and newly extravasated cells that on morphological criteria were most likely neutrophils and monocytes. At 12 hr, cells of more mixed morphologies began to express iNOS and double labelling revealed 70% of these cells were also ED1(+) (a lysosomal antigen present in monocytes/macrophages and dendritic cells), 52% were Ox6(+) (MHC class II) (dendritic cells, activated macrophages and some T-cells) and 19% were ED2(+) (pan-specific resident tissue macrophages). Expressed in an alternative manner, 10% of the total ED1(+) cell population, 11% of the ED2(+) cells and 44% of Ox6(+) cells co-expressed iNOS. Expression of iNOS decreased significantly by 24 hr to near baseline levels and was absent by 48 and 72 hr. Within the ciliary processes iNOS+ dendriform cells were noted at 6 hr and accumulations of many small round iNOS+ cells were present at 12 hr. The ciliary epithelium did not at any time express iNOS at the protein level detectable by immunohistochemistry. The results of this study suggest that iNOS expression early in EIU is associated with infiltrating or newly recruited neutrophils and monocytes/macrophages in the iris whereas later in the disease resident tissue macrophages and MHC class II+ cells (activated macrophages and putative dendritic cells) in the iris and ciliary body may synthesise nitric oxide. The role of this late phase of nitric oxide synthesis may include lymphocytostasis and immunosuppression as proposed in other tissue sites. The outcome of the present study may help in planning therapeutic strategies using NOS inhibitors.     

Dopamine decreases the excitability of layer V pyramidal cells in the rat prefrontal cortex

In both primates and rodents, the prefrontal cortex (PFC) is highly innervated by dopaminergic fibers originating from the ventral tegmental area, and activation of this mesocortical dopaminergic system decreases spontaneous and evoked activity in the PFC in vivo. We have examined the effects of dopamine (DA), over a range of concentrations, on the passive and active membrane properties of layer V pyramidal cells from the rat medial PFC (mPFC). Whole-cell and perforated-patch recordings were made from neurons in rat mPFC. As a measure of cell excitability, trains of action potentials were evoked with 1-sec-long depolarizing current steps. Bath application of DA (0.05-30 microM) produced a reversible decrease in the number of action potentials evoked by a given current step. In addition, DA reversibly decreased the input resistance (RN) of these cells. In a subset of experiments, a transient increase in excitability was observed after the washout of DA. Control experiments suggest that these results are not attributable to changes in spontaneous synaptic activity, age-dependent processes, or strain-specific differences in dopaminergic innervation and physiology. Pharmacological analyses, using D1 agonists (SKF 38393 and SKF 81297), a D1 antagonist (SCH 23390), a D2 receptor agonist (quinpirole), and a D2 antagonist (sulpiride) suggest that decreases in spiking and RN are mediated by D2 receptor activation. Together, these results demonstrate that DA, over a range of concentrations, has an inhibitory effect on layer V pyramidal neurons in the rat mPFC, possibly through D2 receptor activation.     

Cytochrome-oxidase blobs and intrinsic horizontal connections of layer 2/3 pyramidal neurons in primate V1

Pyramidal neurons in superficial layers of cerebral cortex have extensive horizontal axons that provide a substrate for lateral interactions across cortical columns. These connections are believed to link functionally similar regions, as suggested by the observation that cytochrome-oxidase blobs in the monkey primary visual cortex (V1) are preferentially connected to blobs and interblobs to interblobs. To better understand the precise relationship between horizontal connections and blobs, we intracellularly labeled 20 layer 2/3 pyramidal neurons in tangential living brain slices from V1 of macaque monkeys. The locations of each cell body and the cell's synaptic boutons relative to blobs were quantitatively analyzed. We found evidence for two cell types located at characteristic distances from blob centers: (1) neurons lacking long-distance, clustered axons (somata 130-200 microm from blob centers) and (2) cells with clustered, long-distance axon collaterals (somata < 130 microm or >200 microm from blob centers). For all cells, synaptic boutons close to the cell body were located at similar distances from blob centers as the cell body. The majority of boutons from cells lacking distal axon clusters were close to their cell bodies. Cells located more than 200 microm from blob centers were in interblobs and had long-distance clustered axon collaterals selectively targeting distant interblob regions. Cells located less than 130 microm from blob centers were found within both blobs and interblobs, but many were close to traditionally defined borders. The distant synaptic boutons from these cells were generally located relatively near to blob centers, but the neurons closest to blob centers had synaptic boutons closer to blob centers than those farther away. There was not a sharp transition that would suggest specificity for blobs and interblobs as discrete, binary entities. Instead they appear to be extremes along a continuum. These observations have important implications for the function of lateral interactions within V1.     

Functional synergism between putative gamma-aminobutyrate-containing neurons and pyramidal neurons in prefrontal cortex

The responses of putative gamma-aminobutyratergic interneurons (fast-spiking) and pyramidal (regular-spiking) cell pairs were compared in monkeys performing visual and memory-guided oculomotor tasks. Both fast- and regular-spiking neurons had similar receptive fields, indicating that gamma-aminobutyratergic interneurons carry a specific informational signal, as opposed to providing nonspecific modulation. However, the responses of the pairs were inverted and the timing of excitatory and inhibitory responses appeared to be phased, a property consistent with gamma-aminobutyrate-mediated shaping of receptive fields. These observations (i) provide evidence that interneurons and pyramidal cells can be differentiated in vivo and (ii) begin to elucidate the role of gamma-aminobutyratergic mechanisms in cognition.     

Postnatal maturation of the layer III pyramidal neurons in the human prefrontal cortex: a quantitative Golgi analysis

In this study we examined the morphological maturation of the basal dendritic field of layer III pyramidal neurons located in the human dorsolateral prefrontal cortex in subjects ranging from 7.5 months after birth up to 27 years. The sections were stained with the Golgi-Cox method and the three-dimensional branching pattern was measured with a semi-automatic dendrite measuring system. Results show a rapid growth phase of the dendritic field from 7.5 months after birth up to one year. A marked increase in total dendritic length is observed, for which elongation of the terminal segments, longer intermediate segments and an increase in number of segments is an explanation. The dendritic length appears to have stabilized after one year, leading us to conclude that the postnatal morphological maturation of the layer III pyramidals does not continue well into childhood, but is completed at a much younger age. Additionally we analyzed the effect of varying section thickness on dendritic parameters and found no tendency for higher dendritic values with increasing section thickness for the range of thickness values of the histological sections used.     

Molecular heterogeneity of Vicia villosa-recognized perineuronal nets surrounding pyramidal and nonpyramidal neurons in the guinea pig cerebral cortex

This study examined the influence of trunk recruitment on the kinematic characteristics of pointing movements. The distribution of final positions of the hand, the extent and direction of the hand trajectory was basically preserved when trunk movement was combined with arm pointing. These effects were observed during pointing not only with but also without vision. The results imply that two functionally independent units of coordination are used in pointing regardless of visual feedback-one producing arm movement to the target (the reaching synergy) and the other coordinating trunk and arm movements diminishing the influence of the trunk on the arm endpoint trajectory (the compensatory synergy).     

Hemispheric differences in layer III pyramidal neurons of the anterior language area

OBJECTIVE: The major objective of this study was to determine if the lateralization of motor speech functions may be associated with hemispheric differences in the size of layer III pyramidal neurons in Brodmann's area 45. DESIGN: A case series design involving postmortem human specimens was used to compare the cross-sectional area of NissI-stained layer III pyramidal neurons of Brodmann's area 45 from the left and right hemispheres. SUBJECTS: A convenience sample consisting of seven cases with no known neurological or psychiatric disorders was obtained at autopsy. MAIN OUTCOME MEASURES: The cross-sectional area of layer III pyramidal neurons in both left and right hemispheres was measured in four fields per hemisphere per brain using a computerized image analysis system. Measurements of both the largest layer III pyramids and of all layer III pyramids were done. RESULTS: The largest layer III pyramidal neurons of area 45 were significantly larger in the left than in the right hemisphere in both an unblinded and a blinded series of measurements. However, this hemispheric difference appeared to be restricted to the largest neurons, since the mean size of all layer III pyramids in this area was not significantly different in the left and right hemispheres. CONCLUSIONS: The presence of a unique population of large pyramidal neurons in left Brodmann's area 45 may be related to the involvement of this region in the circuitry that mediates motor speech functions.     

Calcium currents in acutely isolated stellate and pyramidal neurons of rat entorhinal cortex

Calcium currents were studied in morphologically identified pyramidal and stellate neurons acutely isolated from layer II/III of rat entorhinal cortex, using the whole-cell patch-clamp configuration. The peak amplitude of high-voltage activated current (HVA) measured at +10 mV was not different in both neuron populations with 0.94+/-0.08 nA for pyramidal and 1.03+/-0.08 nA for stellate cells. Stellate neurons had a larger capacitance (14.4+/-1. 1 pF) than pyramidal neurons (9.6+/-0.8 pF), indicating a 50% larger cell surface. Most striking was the difference between the current density in stellate (79+/-8 pA/pF) versus pyramidal neurons (113+/-13 pA/pF). The potential of half maximal inactivation was not different: -37+/-2 mV (pyramidals) and -37+/-3 mV (stellates). Half of the cells contained a low-voltage activated calcium current (LVA) with a peak amplitude that was twice as large in stellate as in pyramidal neurons (0.21+/-0.04 nA resp. 0.11+/-0.03 nA; at -50 mV). In contrast to the HVA component, the current density of the LVA component was not different between cell types (13+/-3 pA/pF vs. 13+/-2 pA/pF). This implies that the relative abundance of LVA and HVA currents in stellate and pyramidal neurons is different which could result in different firing characteristics. The potential of half maximal LVA inactivation was -88+/-4 mV (pyramidals) and -85+/-3 mV (stellates). The slope of the voltage dependent steady state inactivation was steeper in stellate (7+/-1 mV) than in pyramidal cells (10+/-2 mV).     

Distribution of inhibitory synapses on the somata of pyramidal neurons in cat motor cortex

The mechanisms by which cortical neurons perform spatial and temporal integration of synaptic inputs are dependent, in large part, on the numbers, types, and distributions of their synapses. To further our understanding of these integrative mechanisms, we examined the distribution of synapses on identified classes of cortical neurons. Pyramidal cells in the cat motor cortex projecting either to the ipsilateral somatosensory cortex or to the spinal cord were labeled by the retrograde transport of horseradish peroxidase. Entire soma of selected corticocortical and corticospinal cells were examined using serial-section electron microscopy. The profiles of these somata and the synapses formed with each of these profiles were reconstructed from each thin section with a computer-aided morphometry system. All somatic synapses were of the symmetrical, presumably inhibitory type. For both cell types, these synapses were not homogeneously distributed over the somatic membrane, but were clustered at several discrete zones. The number and density of synapses on the somata of different corticocortical and corticospinal neurons were not significantly different. However, the density of these synapses was inversely correlated with the size of their postsynaptic somata. We discuss the significance of these findings to the integrative properties of cortical neurons.     

Development of the dendritic fields of layer 3 pyramidal cells in the kitten's visual cortex

The cat's visual cortex is immature at birth and undergoes extensive postnatal development. For example, cells of layers 2 and 3 do not complete migration until about 3 weeks after birth. Despite the importance of dendritic growth for synaptic and functional development, there have been few studies of dendritic development in the cat's visual cortex to correlate with numerous studies of functional and synaptic development. Accordingly, we used the Golgi method to study the development of the dendrites of layer 3 pyramidal cells in the visual cortex of a series of cats ranging in age from 2 days to 3 years. Blocks of visual cortex were impregnated by the Golgi-Kopsch method and sectioned in the tangential plane. Layer 3 pyramidal cells were drawn with a camera lucida and analyzed by Sholl diagrams and vector addition. In kittens < 1 week old, these cells were very immature, with only an apical dendrite and no basal dendrites. Basal dendrites appeared during the second week. By 2 weeks, all of the basal dendrites had emerged from the soma, but they had few branches and were tipped with growth cones. By 4 weeks, they had finished branching but continued to grow in length until, by 5 weeks, they reached their adult size. Examination of the basal dendritic fields in the tangential plane revealed that their dendritic fields were more elongated at 2 weeks than at later ages, perhaps because of their smaller size. The distribution of dendritic field orientations was uniform at all ages except 3 and 4 weeks, when there was a preponderance of fields oriented in the rostrocaudal direction. Because dendritic growth and branching occurred very rapidly over a period that precedes and overlaps with the peak periods of synaptogenesis and of sensitivity to the effects of early visual experience, they may depend on afferent visual activity. The early emergence of primary dendrites, however, suggests that this process is independent of afferent activity. The coincident timing of dendritic branching with the presence of dendritic growth cones suggests that branching may occur at growth cones.     

Preserved number of entorhinal cortex layer II neurons in aged macaque monkeys

The perforant path, which consists of the projection from the layer II neurons of the entorhinal cortex to the outer molecular layer of the dentate gyrus, is a critical circuit involved in learning and memory formation. Accordingly, disturbances in this circuit may contribute to age-related cognitive deficits. In a previous study, we demonstrated a decrease in N-methyl-D-aspartate receptor subunit 1 immunofluorescence intensity in the outer molecular layer of aged macaque monkeys. In this study, we used the optical fractionator, a stereological method, to determine if a loss of layer II neurons occurred in the same animals in which the N-methyl-D-aspartate receptor subunit 1 alteration was observed. Our results revealed no significant differences in the number of layer II neurons between juvenile, young adult, and aged macaque monkeys. These results suggest that the circuit-specific decrease in N-methyl-D-aspartate receptor subunit 1 reported previously occurs in the absence of structural compromise of the perforant path, and thus may be linked to an age-related change in the physiological properties of this circuit.     

Morphological variation of layer III pyramidal neurones in the occipitotemporal pathway of the macaque monkey visual cortex

We compared the morphological characteristics of layer III pyramidal neurones in different visual areas of the occipitotemporal cortical 'stream', which processes information related to object recognition in the visual field (including shape, colour and texture). Pyramidal cells were intracellularly injected with Lucifer Yellow in cortical slices cut tangential to the cortical layers, allowing quantitative comparisons of dendritic field morphology, spine density and cell body size between the blobs and interblobs of the primary visual area (V1), the interstripe compartments of the second visual area (V2), the fourth visual area (V4) and cytoarchitectonic area TEO. We found that the tangential dimension of basal dendritic fields of layer III pyramidal neurones increases from caudal to rostral visual areas in the occipitotemporal pathway, such that TEO cells have, on average, dendritic fields spanning an area 5-6 times larger than V1 cells. In addition, the data indicate that V1 cells located within blobs have significantly larger dendritic fields than those of interblob cells. Sholl analysis of dendritic fields demonstrated that pyramidal cells in V4 and TEO are more complex (i.e. exhibit a larger number of branches at comparable distances from the cell body) than cells in V1 or V2. Moreover, this analysis demonstrated that the dendrites of many cells in V1 cluster along specific axes, while this tendency is less marked in extrastriate areas. Most notably, there is a relatively large proportion of neurones with 'morphologically orientation-biased' dendritic fields (i.e. branches tend to cluster along two diametrically opposed directions from the cell body) in the interblobs in V1, as compared with the blobs in V1 and extrastriate areas. Finally, counts of dendritic spines along the length of basal dendrites revealed similar peak spine densities in the blobs and the interblobs of V1 and in the V2 interstripes, but markedly higher spine densities in V4 and TEO. Estimates of the number of dendritic spines on the basal dendritic fields of layer III pyramidal cells indicate that cells in V2 have on average twice as many spines as V1 cells, that V4 cells have 3.8 times as many spines as V1 cells, and that TEO cells have 7.5 times as many spines as V1 cells. These findings suggest the possibility that the complex response properties of neurones in rostral stations in the occipitotemporal pathway may, in part, be attributed to their larger and more complex basal dendritic fields, and to the increase in both number and density of spines on their basal dendrites.     

Morphological characteristics of layer II projection neurons in the rat medial entorhinal cortex

Idiopathic left ventricular tachycardia (ILVT) differs from idiopathic right ventricular outflow tract (RVOT) tachycardia with respect to mechanism and pharmacologic sensitivity. ILVT can be categorized into three subgroups. The most prevalent form, verapamil-sensitive intrafascicular tachycardia, originates in the region of left posterior fascicle of the left bundle. This tachycardia is adenosine insensitive, demonstrates entrainment, and is thought to be due to reentry. The tachycardia is most often ablated in the region of the posteroinferior interventricular septum. A second type of ILVT is a form analogous to adenosine-sensitive RVOT tachycardia. This tachycardia appears to originate from deep within the interventricular septum and exits from the left side of the septum. This form of VT also responds to verapamil and is thought to be due to cAMP-mediated triggered activity. A third form of ILVT is propranolol sensitive. It is neither or initiated or terminated by programmed stimulation, does not terminate with verapamil, and is transiently suppressed by adenosine, responses consistent with an automatic mechanism. Recognition of the heterogeneity of ILVT and its unique characteristics should facilitate appropriate diagnosis and therapy in this group of patients.     

Lesion-induced plasticity of central neurons: sprouting of single fibres in the rat hippocampus after unilateral entorhinal cortex lesion

In response to a central nervous system trauma surviving neurons reorganize their connections and form new synapses that replace those lost by the lesion. A well established in vivo system for the analysis of this lesion-induced plasticity is the reorganization of the fascia dentata following unilateral entorhinal cortex lesions in rats. After general considerations of neuronal reorganization following a central nervous system trauma, this review focuses on the sprouting of single fibres in the rat hippocampus after entorhinal lesion and the molecular factors which may regulate this process. First, the connectivity of the fascia dentata in control animals is reviewed and previously unknown commissural fibers to the outer molecular layer and entorhinal fibres to the inner molecular layer are characterized. Second, sprouting of commissural and crossed entorhinal fibres after entorhinal cortex lesion is described. Single fibres sprout by forming additional collaterals, axonal extensions, boutons, and tangle-like axon formations. It is pointed out that the sprouting after entorhinal lesion mainly involves unlesioned fibre systems terminating within the layer of fibre degeneration and is therefore layer-specific. Third, molecular changes associated with axonal growth and synapse formation are considered. In this context, the role of adhesion molecules, glial cells, and neurotrophic factors for the sprouting process are discussed. Finally, an involvement of sprouting processes in the formation of neuritic plaques in Alzheimer's disease is reviewed and discussed with regard to the axonal tangle-like formations observed after entorhinal cortex lesion.     

Differential assembly of coexpressed glutamate receptor subunits in neurons of rat cerebral cortex

In the rat, subunits of the glutamate receptor family fall into three pharmacologically distinct groups: alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid preferring receptors (Glu R1-4), kainate preferring receptors (Glu R5-7, KA 1, KA 2), and N-methyl-D-aspartate preferring receptors (NMDA R1, NMDA R2A-2D). In the present study, we demonstrate immunocytochemically that the majority of neurons in rat cerebral cortex coexpress members of all three groups of glutamate receptor subunits, Glu R2/3, Glu R5/6/7, and NMDA R1. Using immunoaffinity purified or immunoprecipitated alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid, kainate and N-methyl-D-aspartate receptors, we show that alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors containing Glu R1-4, kainate receptors containing Glu R6, Glu R7, and KA 2 and N-methyl-D-aspartate receptors containing NMDA R1 each form distinct protein complexes that do not share subunits. Our data indicate that a mechanism exists which allows for the specific assembly of selected glutamate receptor subunits into functionally and structurally distinct heteromeric receptors.     

Effects of early environments on monkey cortex neuroanatomical changes following somatomotor experience: Effects on layer III pyramidal cells in monkey cortex.

Sixteen infant stumptail monkeys were reared to 6 months under four conditions. Behaviors and cortical neuroanatomy were compared. Earlier studies showed effects on stellate cell dendrites. Here are reported the results in six cortical areas on basilar dendrites of layer III pyramidal cells. Basilar dendrites show significantly larger numbers (p?     

Calcium electrogenesis in neocortical pyramidal neurons in vivo

Much of what is known about Ca2+ electrogenesis in neocortical cells has been derived from in vitro studies. Since Ca2+ currents are controlled by various modulators, comparing these findings to in vivo data is essential. Here, we analysed tetrodotoxin (TTX)-resistant, presumably Ca2+-mediated potentials in intracellularly recorded neocortical neurons in vivo. TTX was applied locally to block Na+ channels. Its effectiveness was demonstrated by the elimination of fast spikes and orthodromic responses. In response to depolarizing current pulses bringing the membrane potential beyond approximately -33 mV, 71% of neurons generated high-threshold Ca2+ spikes averaging 17 mV. This is in contrast with in vitro findings, where high-threshold spikes could only be elicited following the blockade of K+ conductances. Consistent with this, neurons dialysed with K+ channel blockers in vivo generated high-threshold spikes that had a lower threshold (approximately -40 mV) and, with intracellular Cs+, a larger amplitude, indicating the presence of K+ currents opposing the activation of Ca2+ channels. Only 15% of cortical cells displayed low-threshold Ca2+ spikes. To compare high-threshold Ca2+ spikes evoked by synaptic stimuli or current injection, another group of cortical neurons was dialysed with QX-314 and Cs+, in the absence of extracellular TTX. Synaptic stimuli applied on a background of membrane depolarization elicited presumed Ca2+ spikes whose amplitude varied in a stepwise fashion. Thus, although there are numerous similarities between in vivo and in vitro data, some significant differences were found, which suggest that the high-voltage activated Ca2+ currents and/or the K+ conductances that oppose them are subjected to different modulatory influences in vivo than in vitro.     

Firing characteristics of deep layer neurons in prefrontal cortex in rats performing spatial working memory tasks

Single cells were recorded with 'tetrodes' in regions of the rat medial prefrontal cortex, including those which are targets of hippocampal afferents, while rats were performing three different behavioral tasks: (i) an eight-arm radial maze, spatial working memory task, (ii) a figure-eight track, delayed spatial alternation task, and (iii) a random food search task in a square chamber. Among 187 recorded units, very few exhibited any evidence of place-specific firing on any of the behavioral tasks, except to the extent that different spatial locations were related to distinct phases of the task. Furthermore, no prefrontal unit showed unambiguous spatially dependent delay activity that might mediate working memory for spatial locations. Rather, the cells exhibited diverse correlates that were generally associated with the behavioral requirements of performing the task. This included firing related to intertrial intervals, onset or end of trials, selection of specific arms on the eight-arm radial maze, delay periods, approach to or departure from goals, and selection of paths on the figure-eight track. Although a small number of cells showed similar behavioral correlates across tasks, the majority of cells showed no consistent correlate when recorded across multiple tasks. Furthermore, some units did not exhibit altered firing patterns in any of the three tasks, while others showed changes in firing that were not consistently related to specific behaviors or task components. These results are in agreement with previous lesion and behavioral studies in rats that suggest a prefrontal cortical role in encoding 'rules' (i.e. structural features) or behavioral sequences within a task but not in encoding allocentric spatial information. Given that the hippocampal projection to this cortical region is capable of undergoing LTP, our data lead to the hypothesis that the role of this projection is not to impose spatial representations upon prefrontal activity, but to provide a mechanism for learning the spatial context in which particular behaviors are appropriate.     

Duration of neurofibrillary changes in the hippocampal pyramidal neurons

The clinical course of grave forms of leptospirosis presents with disorders in the fluid and electrolyte balance and acid-base condition (ABC) which fact necessitates taking prompt action for the condition to be corrected. Correction of disorders in the fluid and electrolyte balance involves employment of glucose and salt solutions, dextrans, and in most severe cases albumin drugs under control of hematocrit values, plasma osmolarity, and 24-h diuresis monitoring. Correction of disorders in the ABC is primarily aimed at alleviating the metabolic acidosis through detoxication by applying specific therapy together with oral and parenteral administration of sodium hydrogen carbonate.