Statins decrease dendritic arborization in rat sympathetic neurons by blocking RhoA activation

Clinical and experimental evidence suggest that statins decrease sympathetic activity, but whether peripheral mechanisms involving direct actions on post-ganglionic sympathetic neurons contribute to this effect is not known. Because tonic activity of these neurons is directly correlated with the size of their dendritic arbor, we tested the hypothesis that statins decrease dendritic arborization in sympathetic neurons. Oral administration of atorvastatin (20 mg/kg/day for 7 days) significantly reduced dendritic arborization in vivo in sympathetic ganglia of adult male rats. In cultured sympathetic neurons, statins caused dendrite retraction and reversibly blocked bone morphogenetic protein-induced dendritic growth without altering cell survival or axonal growth. Supplementation with mevalonate or isoprenoids, but not cholesterol, attenuated the inhibitory effects of statins on dendritic growth, whereas specific inhibition of isoprenoid synthesis mimicked these statin effects. Statins blocked RhoA translocation to the membrane, an event that requires isoprenylation, and constitutively active RhoA reversed statin effects on dendrites. These observations that statins decrease dendritic arborization in sympathetic neurons by blocking RhoA activation suggest a novel mechanism by which statins decrease sympathetic activity and protect against cardiovascular and cerebrovascular disease.     

Ultrastructural study of glial gap junctions in the thalamic nuclei of rat

Despite a growing interest in gap junctions (GJs) of mammalian brain, their distribution and role in cell ensembles of thalamus remains unknown. The aim of this work was ultrastructural and immunoelectron study of glial GJs in ventral posteromedial (VPM) and posteromedial (POM) thalamic nuclei and thalamic reticular nucleus (RTN) of rats. GJs were identified by standard techniques of transmission electron microscopy and by pre-embedding immunohistochemistry protocol using anti-connexin-43 antibodies with Dako EnVision System + Peroxidase (DAB) detecting system. It was found that glial cells surround thalamocortical axons and axo-spiny synapses and form numerous elongated gap junction plaques located near chemical synapses. A single axon-spiny chemical synapse can be surrounded by several (up to 4) gap junctions that seem to form peculiar networks of glial cells united by GJs. Closely adjacent gap junctions disposed at an angle from 30° to 140° to each other were revealed. Immunoelectron labeling demonstrated that gap junction plaques located around chemical synapses have an astroglial origin. Despite the accumulation of osmiophilic material in the contact zone, ultrastructural signs of GJs were clearly identified. Due to the formation of intercellular glia-glial GJs astroglia may acquire a function of spatial buffer to regulate extracellular concentration of potassium and other ions, providing intracellular and extracellular ion homeostasis. We believe that astroglial processes joined into a network by GJs play a key role in the circulation of information and can modulate subcortical neuronal ensembles. We suggest that a close spatial location of astroglial GJs and asymmetrical chemical synapses is reflected in the functional organization of specific and nonspecific thalamic nuclei, which are the main centers of the afferent and efferent inputs of the cerebral cortex.     

Unit responses of the thalamic and ventral anterior thalamic nuclei to electrical stimulation of thalamic relay nuclei in cats

Responses of 92 neurons of the reticular (R) and 105 neurons of the ventral anterior (VA) thalamic nuclei to stimulation of the ventrobasal complex (VB) and the lateral (GL) and medial (GM) geniculate bodies were investigated in cats immobilized with D-tobocurarine. Altogether 72.2% of R neurons and 76.2% of VA neurons responded to stimulation of VB whereas only 15.0% of R neurons and 27.1% of VA neurons responded to stimulation of GM and 10.2% of R neurons and 19.6% of VA neurons responded to stimulation of GL. The response of the R and VA neurons to stimulation of the relay nuclei as a rule was expressed as excitation. A primary inhibitory response was observed for only two R and three VA neurons. Two types of excitable neurons were distinguished: The first respond to afferent stimulation by a discharge consisting of 5–15 spikes with a frequency of 250–300/sec; the second respond by single action potentials. Neurons of the first type closely resemble inhibitory interneurons in the character of the response. Antidromic responses were recorded from 2.2% of R neurons and 7.8% of VA neurons during stimulation of the relay nuclei. Among the R and VA neurons there are some which respond to stimulation not only of one, but of two or even three relay nuclei. If stimulation of one relay nucleus is accompanied by a response of a R or VA neuron, preceding stimulation of another nucleus leads to inhibition of the response to the testing stimulus if the interval between conditioning and testing stimuli is less than 30–50 msec.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 8, No. 6, pp. 597–605, November–December, 1976.     

Aminergic control of neuronal firing rate in thalamic motor nuclei of the rat

The effects induced on neuronal firing by microiontophoretic application of the biological amines noradrenaline (NA) and 5-hydroxytryptamine (5-HT) were studied "in vivo" in ventral-anterior (VA) and ventrolateral (VL) thalamic motor nuclei of anaesthetized rats. In both nuclei the amines had a mostly depressive action on neuronal firing rate, the percentage of units responsive to NA application (88%) being higher than to 5-HT (72%). Short-lasting (less than 2 min) and long lasting (up to 20 min) inhibitory responses were recorded, the former mostly evoked by NA and the latter by 5-HT ejection. In some cases 5-HT application had no effect on the firing rate but modified the firing pattern. NA-evoked responses were significantly more intense in VL than in VA neurons. Short-lasting inhibitory responses similar to NA-induced effects were evoked by the alpha2 adrenergic receptor agonist clonidine and to a lesser extent by the beta adrenergic receptor agonist isoproterenol. Inhibitory responses to 5-HT were partially mimicked by application of the 5-HT(1A) receptor agonist 8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT) and of the 5-HT2 receptor agonist alpha-methyl-5-hydroxytryptamine (ALPHA-MET-5-HT). The latter evoked excitatory responses in some cases. Both 5-HT agonists were more effective on VA than on VL neurons. The effects evoked by agonists were at least partially blocked by respective antagonists. These results suggest that although both 5-HT and NA depress neuronal firing rate, their effects differ in time course and in the amount of inhibition; besides aminergic modulation is differently exerted on VA and VL.     

Quantitative aspects in the analysis of the synaptic architecture of thalamic sensory relay nuclei

Special orientations of dendritic trees of projective (relay) neurons were observed in the thalamic nuclei; and it was found to be different in the various nuclei. It can be explained by the size, course, site of the fibre bundles which enter and/or transgress the nuclei. The orientation of dendritic tree and the size of the branching area of dendrites (specific active dendritic space) were analysed by computer. The quantitative data of neuronal elements in some thalamic nuclei gave the opportunity to consider the possible degree of divergence and convergence of sensory fibres regarding their connections with the projective neurons.     

Fractal and nonfractal analysis of cell images: comparison and application to neuronal dendritic arborization

 Neurons of the rat spinal cord were stained using the Golgi impregnation method. Successfully impregnated neurons from laminae II, III, and VI were subjected to fractal and nonfractal analyses. Fractal analysis was performed using length-related techniques. Since an application of fractal methods to the analysis of dendrite arbor structures requires caution, we adopted as appropriate a nonfractal method proposing a generalized power-law model with two main nonfractal parameters: (i) the anfractuosity, characterizing the degree of dendritic deviation from straight lines; and (ii) an estimate of the total length of arbor dendrites. The anfractuosity can distinguish between two sets of drawings where the fractal methods failed. We also redefine some basic concepts of fractal geometry, present the ruler-counting method, and propose a new definition of fractal dimension. Received: 5 February 2002 / Accepted: 25 June 2002 Acknowledgement. We thank Ing. Dejan Ristanović for preparing the computer program used in this study. Correspondence to: D. Ristanović (e-mail: dusan@ristanovic.com, Tel.: +381-11-3615767)     

Distribution of directionally selective neurons within the thalamic nuclei and striopallidal complex of the human brain

Spike activity was analyzed in the course of visual testing for directional sensitivity in 177 neuronal populations in different thalamic nuclei and the striopallidal complex in the brain of nine parkinsonian patients, diagnosed and treated using implanted intracerebral electrodes. Directionally selective neurons were discovered in the centrum medianum, the thalamic zona incerta and reticular nucleus, the caudate nucleus, and the central area of the globus pallidus. Proportions and distribution of neurons with different properties were investigated in the thalamic nuclei and striopallidal complex.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 21, No. 5, pp. 652–660, September–October, 1989.     

Convergence between projections from different thalamic nuclei to columns of the rat somatosensory cortex

Primuline fluorochrome retrograde transport technique was used to investigate sources of thalamocortical projections to a single rat somatosensory cortex column connected with the projection of the C₃ vibrissa. Labeled cells were identified in eight different thalamic nuclei: two specific, five nonspecific, and one association nucleus. Labeled neurons differed in the degree of stain accumulated as well as cell numbers and density of distribution from one nucleus to another, indicative of the different arborization patterns of their axons within the cortex. Highest numbers of heavily stained cells as well as highest density of distribution were observed in the ventral thalamic nucleus. The convergence seen between different thalamocortical inputs on to a single somatosensory cortex column explains the functional differences observed between neurons belonging to the same column and makes the formation of functionally distinct neuronal groupings appear possible on this structural basis.Neurocybernetics Research Institute, Rostov-on-Don. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 168–174, March–April, 1989.     

The effect of corticosteroids on dendritic development in the rat brain

Sprague-Dawley rats were given 0.02 ml of methylprednisolone (0.06 g/g body wt) 6, 9, or 12 days postnatally. When compared with saline-treated controls, the following effects on dendritic development in layers 3 and 5 of the parietal cortex were observed: (1) no significant alteration in number of basal dendrites; (2) initial increase (at 3 wk of age) in branchings near the perikaryon in the group treated at 12 days; (3) decrease in number of branches at distances ≥270 μm from the perikaryon in layers 3 and 5 in all steroid-treated groups when sacrificed at 6 wk; (4) decrease in number of intersections in layer 5 in all steroid-treated groups when sacrificed at 6 wk; and (5) decrease in number of terminations in layers 3 and 5 in all steroid-treated groups when sacrificed at 6 wk.     

Glycosaminoglycans and glycoproteins associated with rat brain nuclei

The concentration, composition and sulfate labeling of glycosaminoglycans and glycoproteins have been studied in purified nuclei isolated in bulk from rat brain. The concentration of total glycosaminoglycans is 0.142 μmol hexosamine/100 mg protein, comprising 57% chrondroitin 4-sulfate, 7% chondroitin 6-sulfate, 29% hyaluronic acid and 7% heparan sulfate. Control experiments demonstrated that less than 5% of the sulfated glycosaminoglycans associated with nuclei could be accounted for by the nonspecific adsorption of soluble acidic proteoglycans to basic nuclear proteins. Glycoprotein carbohydrate is present at a level of 206 μg/100 mg protein, and has an average composition of 30% N-acetylglucosamine, 29% mannose, 19% N-acetylneuraminic acid, 15% galactose, 4% N-acetylgalactosamine, and 3% fucose. Labeling studies also indicated the presence of ester sulfate residues on the glycoprotein oligosaccharides.     

Amyloid precursor protein promotes post-developmental neurite arborization in the Drosophila brain

The mechanisms regulating the outgrowth of neurites during development, as well as after injury, are key to the understanding of the wiring and functioning of the brain under normal and pathological conditions. The amyloid precursor protein (APP) is involved in the pathogenesis of Alzheimer's disease (AD). However, its physiological role in the central nervous system is not known. Many physical interactions between APP and intracellular signalling molecules have been described, but their functional relevance remains unclear. We show here that human APP and Drosophila APP-Like (APPL) can induce postdevelopmental axonal arborization, which depends critically on a conserved motif in the C-terminus and requires interaction with the Abelson (Abl) tyrosine kinase. Brain injury induces APPL upregulation in Drosophila neurons, correlating with increased post-traumatic mortality in appl(d) mutant flies. Finally, we also found interactions between APP and the JNK stress kinase cascade. Our findings suggest a role for APP in axonal outgrowth after traumatic brain injury.     

Diverse functions of N-cadherin in dendritic and axonal terminal arborization of olfactory projection neurons

The cadherin superfamily of cell adhesion molecules have been proposed to play important roles in determining synaptic specificity in developing nervous systems. We examine the function of N-cadherin in Drosophila second order olfactory projection neurons (PNs), each of which must selectively target their dendrites to one of approximately 50 glomeruli. Our results do not support an instructive role for N-cadherin in selecting dendritic targets; rather, N-cadherin is essential for PNs to restrict their dendrites to single glomeruli. Mosaic analyses suggest that N-cadherin mediates dendro-dendritic interactions between PNs and thus contributes to refinement of PN dendrites to single glomeruli. N-cadherin is also essential for the development of PN axon terminal arbors in two distinct central targets: regulating branch stability in the lateral horn and restricting high-order branching in the mushroom body. Although the N-cadherin locus potentially encodes eight alternatively spliced isoforms, transgenic expression of one isoform is sufficient to rescue all phenotypes.