Cytochrome P-45011 beta in rat brain

The presence of cytochrome P-45011 beta in rat brain was studied by immunohistochemistry using polyclonal rabbit antibodies raised against purified bovine adrenocortical P-45011 beta, which is involved in the steroid 11 beta-hydroxylation and glucocorticoid formation. The results showed that cytochrome P-45011 beta immunoreactivity is selectively localized to the tracts of myelinated fibers throughout the brain. The specificity of immunohistochemical stainings with P-45011 beta antibodies was established by control tests including nonimmune rabbit immunoglobulin Gs and P-45011 beta antibodies absorbed with purified antigen. Western immunoblots of homogenates from different brain areas with P-45011 beta antibodies, together with biochemical enzymatic assays for cytochrome P-45011 beta monooxygenase activity in these homogenates, confirmed the selective localization of this enzyme observed with immunohistochemistry. Cytochrome P-45011 beta and 11 beta-hydroxylase activity were detected in a homogenate from the cortical white matter (brain area rich in myelinated fibers) as in that from the rat adrenal, but were not detectable in a homogenate from the cerebral cortex (brain area poor in myelinated fibers). Furthermore, quantitation of the P-45011 beta bands on the immunoblots by the areal density revealed that the cortical white matter contains approximately 1.4 pmol of cytochrome P-45011 beta/mg of tissue protein, the value of which was about one sixth of the corresponding value estimated in the rat adrenal. This relatively high content of cytochrome P-45011 beta was also reflected in a relatively high level of 11 beta-hydroxylase activity measured in a homogenate of this brain area by biochemical enzymatic assays using [4-14C]-11-deoxycorticosterone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Morphology of corticotectal cells in the primary visual cortex of hooded rats

In primary visual cortex of hooded rats, pyramidal cells in layer V may be classified as long, medium, or short, on the basis of the layer in which the apical dendrite terminates. The present study determines which of these types of pyramidal cells project to the superior colliculus. Two different strategies were used to label corticotectal cells with horseradish peroxidase (HRP). In the first set of experiments, a large number of corticotectal cells were labeled by retrograde transport following injection of HRP into the superior colliculus. In the second set of experiments, single unit recording was used to identify corticotectal cells physiologically by antidromic activation from the superior colliculus. These cells were then impaled and labeled by intracellular iontophoresis of HRP. The results from both techniques suggest that only long pyramidal cells send an axon to the superior colliculus. These cells are distinguished by an apical dendrite that extends into layer I. We conclude that in hooded rats corticotectal cells in primary visual cortex are the long pyramids in layer V.     

Synaptic organization of cortico-cortical connections from the primary visual cortex to the posteromedial lateral suprasylvian visual area in the cat

The synaptic organization of the projection from the cat striate visual cortex to the posteromedial lateral suprasylvian cortical area (PMLS) was examined. The anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) was iontophorectically delivered into area 17, and anterogradely labeled fibers were revealed in PMLS by means of an immunocytochemical detection method. Most axons and presumptive terminal swellings were found in layers III and IV. The neuronal elements (n = 190) that were postsynaptic to anterogradely labeled boutons were quantitatively analyzed. All anterogradely labeled cortico-cortical boutons (n = 182) established type 1 synapses. The results show that 83% of the postsynaptic targets were dendritic spines, probably belonging to pyramidal cells. Dendritic shafts constituted 17% of the targets. The dendritic shafts postsynaptic to cortico-cortical boutons were studied for the presence of gamma-aminobutyric acid (GABA) with a postembedding immunogold method. Most dendritic shafts (85%) that were tested were found to be GABA-positive, demonstrating that they originate from local inhibitory neurons. Taking into account that most postsynaptic targets were spines and extending the results of the immunocytochemical testing to the total population of postsynaptic dendrites, it was calculated that at least 14% of targets originated from GABA-positive cells. Thus cortico-cortical axons establish direct monosynpatic connections mainly with pyramidal and to a lesser extent with GABAergic nonpyramidal neurons in area PMLS, providing both feedforward excitation and feedforward inhibition to a visual associational area known to be involved in the processing of motion information. The results are consistent with previously demonstrated deficits in physiological properties of neurons in PMLS following removal of cortico-cortical afferents.     

The somatotopic localisation of the descending cortical tract in the cerebral peduncle: a study using MRI of changes following Wallerian degeneration in the cerebral peduncle after a supratentorial vascular lesion

We studied the effects of Wallerian degeneration in the cerebral peduncle shown by magnetic resonance imaging (MRI) following a supratentorial vascular lesion, to identify the somatotopic localisation of the descending cortical tracts. Patients with a lesion involving a large area of a cerebral hemisphere had an area of abnormal signal intensity in the whole cerebral peduncle, suggesting Wallerian degeneration of all the whole descending cortical tracts. With a small lesion confined to the precentral gyrus, corona radiata, or posterior limb of the internal capsule there was an abnormal signal at the centre of the peduncle, suggesting degeneration of the precentrospinal tract. Those with a small lesion confined to the paracentral gyrus had an abnormal area slightly lateral to the centre of the peduncle, suggesting degeneration of the parietospinal tract. Patients with a lesion of the parietal or temporal lobes, not including the paracentral or precentral gyri, corona radiata, or the posterior limb of the internal capsule, had an abnormal area laterally in the peduncle, suggesting degeneration of the parietopontine or temporopontine tract.     

Distribution of cytochrome oxidase and parvalbumin in the primary visual cortex of the adult and neonate monkey,Callithrix jacchus

The anatomical distributions of the mitochondrial enzyme cytochrome oxidase (CO) and of the calcium binding protein parvalbumin (PV) were studied in the striate cortex of adult and neonate New World monkeys (Callithrix jacchus). In the adult marmoset, both proteins were found in laminar arrangements similar to those described for the macaque monkey, with prominent bands of PV-like immunoreactive (PV-LI) puncta in layers IV and IIIb, and fairly evenly distributed PV-LI nonpyramidal neurons. Furthermore, the pattern of CO activity in area 17 of the neonate marmoset was almost identical to the CO pattern described in neonate macaque and squirrel monkeys. It came, therefore, as a surprise to find that the adult pattern of PV-like immunoreactivity (PV-LI) in the marmoset striate cortex arises from a neonatal pattern strikingly different from that seen in any developmental stage of the macaque, or in any other mammal studied so far. In the deep layers IV through VI of the neonate marmoset, a large number of PV-LI neurons was stained in bandlike patterns, their number in layers IV and V exceeding the number of PV-LI neurons present in these layers of the adult marmoset area 17. Staining of layers IV and VI was restricted to area 17 and involved nonpyramidal cells and their exceeding the number of PV-LI neurons present in these layers of the adult marmoset area 17. Staining of layers IV and VI was restricted to area 17 and involved nonpyramidal cells and their processes. The stained band of layer V, in contrast, continued throughout most of the neocortex. In area 17, an estimated 10 to 20% of the stained cells in layer V exhibited pyramidal shapes. The findings show that the expression of PV by visual cortical cells occurs before birth and suggest that the comparatively early onset of PV expression is not dependent on the onset of textured vision. The exuberant number of stained cells in some layers, and particularly the staining of pyramidal cells, in the neonate marmoset, suggest that a considerable number of cells possesses the stainability for PV-LI only transiently, i.e., in the marmoset, these cells have a specific demand for parvalbumin during this phase of their development. © 1994 Wiley-Liss, Inc.     

White Matter Fiber Tracking Computation Based on Diffusion Tensor Imaging for Clinical Applications

Fiber tracking allows the in vivo reconstruction of human brain white matter fiber trajectories based on magnetic resonance diffusion tensor imaging (MR-DTI), but its application in the clinical routine is still in its infancy. In this study, we present a new software for fiber tracking, developed on top of a general-purpose DICOM (digital imaging and communications in medicine) framework, which can be easily integrated into existing picture archiving and communication system (PACS) of radiological institutions. Images combining anatomical information and the localization of different fiber tract trajectories can be encoded and exported in DICOM and Analyze formats, which are valuable resources in the clinical applications of this method. Fiber tracking was implemented based on existing line propagation algorithms, but it includes a heuristic for fiber crossings in the case of disk-shaped diffusion tensors. We successfully performed fiber tracking on MR-DTI data sets from 26 patients with different types of brain lesions affecting the corticospinal tracts. In all cases, the trajectories of the central spinal tract (pyramidal tract) were reconstructed and could be applied at the planning phase of the surgery as well as in intraoperative neuronavigation.     

Neural dynamics in cortex-striatum co-cultures-II. Spatiotemporal characteristics of neuronal activity

Neural dynamics in organotypic cortex-striatum co-cultures grown for three to six weeks under conditions of dopamine deficiency are described. Single neuron activities were recorded intra- and extracellularly, and spatiotemporal spreading of population activity was mapped using voltage-sensitive dyes. The temporal properties of spike firing were characterized by interspike interval histograms, autocorrelation and crosscorrelation.

Cortical pyramidal neurons (n = 40) showed irregular firing with a weak tendency to burst or to oscillate. Crosscorrelations revealed strong near-coincident firing and synaptic interactions. Disinhibition was a notable feature in a strongly firing cortical interneuron. Cortical activity spread in the co-culture, thus inducing an overall, homogeneous depolarization in the striatal part. Striatal cells were divided into principal cells and type I and II secondary cells. Principal cells (n = 40) were similar to those reported previously in vivo. Spiking activity ranged from irregular spiking at very low rates to episodic bursting, with an average burst duration of 1 s. Interspike intervals were single-peaked. Intracellular recordings revealed characteristic, long-lasting subthreshold depolarizations (“enabled state”) that were shortened by local muscarinic receptor blockade. During prolonged time periods in the “enabled state”, locally applied bicuculline induced strong firing in most principal neurons. Striatal secondary type I neurons (n = 25) showed high spiking rates, single- and double-peaked interval histograms and low-threshold, short-lasting stereotyped bursting activity and occasional rhythmic bursting. The firing of these neurons was increased by bicuculline. Crosscorrelations showed synchronization of these cells with principal cell activity. Secondary type II neurons (n = 15) revealed tonic, irregular firing patterns similar to cortical neurons, except with occasional firing in doublet spikes.

We conclude that under conditions of dopamine deficiency in corticostriatal co-cultures (i) the cortex induces the “enabled” state and typical bursting mode in striatal principal neurons; (ii) principal neurons are strongly inhibited during the “enabled” state; (iii) muscarinic activity, presumably from tonically active striatal cholinergic interneurons, stabilizes the “enabled” state; (iv) striatal GABAergic interneurons receive synaptic inhibition and take part in synchronized activity among striatal principal cells. Our results favor the view of the striatum as a lateral inhibition network.     

Frequency-to-voltage conversion in the pyramidal tract neuron: an important role of the inhibitory postsynaptic potential

Frequency-coded impulses are known to be converted into postsynaptic potentials (PSPs) at the synapse of a target neuron. This can be termed frequency-voltage (F-V) conversion. Studies on this problem in pyramidal tract neurons (PTNs) showed that not only the amplitude but also the duration of depolarizing PSPs was determined as a function of the input impulse frequency. Two opposite patterns of F-V conversion were observed following activation of two input systems to PTNs. Inhibitory postsynaptic potentials were found to play an important role in the regulation of the duration of PSPs by curtailing excitatory post-synaptic potentials.     

锥体束神经元在大鼠、树皮层的分布及其与GABA能神经元的关系

以大鼠和树作为研究材料，在脑桥下缘切断一侧锥体束，用HRP逆行标记和计算机三维重构观察锥体束神经元在皮层的分布，以及在光镜和电镜下观察锥体束神经元和GABA能神经元的关系。逆行标记的锥体来神经元主要分布于皮层的运动区和体感区，在枕区、扣带区、颞区和屏状皮层中都有少量分布。树锥体束神经元的总数是大鼠的1．5倍，用计算机重构显示HRP标记的锥体束神经元在脑内吻尾方向上的分布跨度比大鼠小，故其分布范围较大鼠集中，密度较高，且其中大细胞也较多．树的锥体来神经元长径在15μm以上者占74．0％；大鼠则占62．9％。在电镜下观察这些锥体束神经元的胞体上全分布着对称型的突触，其中既有GABA能，也有非GA-BA能者。不同胞体上接受GABA能和非GABA能突触的比例不同，一种较大的胞体上GABA与non－GABA阳性终末相比，前者数量大（13：3）而较小的胞体上则相反，两者的数量相比，为7：18。大鼠和树的锥体束神经元胞体的单位周长上接受的突触数目也不同，树锥体束神经元胞体的10μm单位周长上分布有4．4个突触。大鼠则为3．4个。随着动物进化锥体束神经元接受突触的数目有增加的趋势．     

Neural Correlates of the Results-of-Action Acceptor in a Functional Biotechnical Complex

This report presents data illustrating the neurophysiological features of efferent-afferent convergence on cortical neurons. During combination of stimulus of pyramidal tract axons with electrocutaneous reinforcement, some of the study neurons were found to change the parameters of their activity evoked by stimulation of this tract: evoked responses started to reproduce the structure of responses to the reinforcement. The most dynamic rearrangements of pyramidal tract responses were obtained in experiments in which the study neurons were included in a biotechnical complex with feedback, the complex consisting of neuron-computer-stimulator-animal and actually being an analog of a natural functional system. The role of efferent-afferent convergence on CNS neurons in the development of the results-of-action acceptor of a functional system for a voluntary behavioral act is discussed.