Somatostatin expression in the cerebellar cortex during postnatal development

Summary The distribution of somatostatin-immunoreactive (SOM-IR) elements in the cerebellar cortex of the rat has been studied at different stages of postnatal development (from birth to day 30) and in adult animals using immunohistochemistry. The results showed that in vermis of new born animals there are three main groups of SOM-IR structures within the cortex which subsequently spread along the Purkinje cell layer. In addition, both in the vermis and in the lateral lobes, numerous more evenly distributed SOM-positive cells and fibers could be seen. SOM-IR Golgi cells, Purkinje cells and climbing fibers could then be recognized during the subsequent developmental stages. In the vermal zone, SOM-IR Purkinje cells formed patches, which seemed to be part of a sagittal columnar or band-like organization. This was most obvious between days 5 and 21 of postnatal development. Subsequently there was a reduction in the number of immunoreactive Purkinje cells but a patchy disposition remained. In addition high numbers of SOM-IR Purkinje and Golgi cells and also climbing fibers were identified in the flocculus and paraflocculus at all stages of development studied, and they were also seen in the adult rats in these regions. In the lateral lobes expression of SOM-like immunoreactivity (LI) decreased and almost completely disappeared in adult animals. The present results demonstrate that a SOM or a SOM-LI peptide can be transiently detected in many Purkinje and Golgi cells in the cerebellar cortex, suggesting a role in events related to developmental processes. However, in some regions and structures SOM-LI can be seen also in adult animals. Dedicated to: Prof. Alf Brodal     

Optokinetic nystagmus in the rabbit and its modulation by bilateral microinjection of carbachol in the cerebellar flocculus

Summary 1. In the alert, pigmented rabbit, eye movements were recorded during optokinetic nystagmus (OKN) and during optokinetic afternystagmus (OKAN). These responses were elicited by steps in surround-velocity ranging from 5–110°/s during binocular as well as monocular viewing. 2. In the baseline condition, OKN showed an approximately linear build-up of eye velocity to a steady-state, followed by a linear decay of eye velocity during OKAN after the lights were turned off. Build-up during binocular viewing was characterized by a constant, maximum eye-acceleration (about 1°/s²) for stimulus velocities up to 60°/s. OKAN, instead, was characterized by a fixed duration (about 10 s) for stimulus velocities up to 20°/s. Steady-state eye velocity saturated at about 50°/s. 3. Monocular stimulation in the preferred (nasal) direction elicited a build-up that was on average twice as slow as during binocular stimulation. Steady-state velocity during monocular stimulation saturated at about 20°/s. OKAN was of equal duration as during binocular stimulation. In the non-preferred direction, a very irregular nystagmus was elicited without velocity build-up. The stronger response to binocular stimulation, compared to the responses under monocular viewing condition in either nasal and temporal direction suggests potentiation of the signals of either eye during binocular viewing. 4. OKN and OKAN were re-assessed after intra-floccular microinjection of the nonselective cholinergic agonist carbachol. In the binocular viewing condition, eye-acceleration during build-up was strongly enhanced from 1°/s² before to 2.5°/s² after injection. The saturation level of steady-state eye velocity was also increased, from 50°/s before to more than 60°/s after carbachol. The duration of OKAN, however, was shortened from 10 s before to 6 s after injection. The response to monocular stimulation in the preferred direction revealed similar changes. 5. The flocculus appears to be involved in the control of the dynamics of OKN in the rabbit. Cholinergic mechanisms affect the floccular control of the rate at which slow-phase velocity can be built up and the rate of decay of eye velocity during OKAN. Cholinergic stimulation of the flocculus enhances the dynamics of OKN, while velocity storage is shortened.     

Optokinetic response of simple spikes of Purkinje cells in the cerebellar flocculus and nodulus of the pigmented rabbit

Summary Under anesthesia with N₂O (70%) and halothane (2–4%), Purkinje cell activities were extracellularly recorded in the flocculus and nodulus of immobilized pigmented rabbits. Large field (60° × 60°) optokinetic stimulation (OKS) was delivered to the central visual field of one eye with a constant velocity (0.1–4.0 °/S) at 0°, 45°, 90° or 135° to the horizontal plane of the eye. Most of the Purkinje cells in the flocculus and the nodulus showed significant simple spike modulations to OKS delivered to either eye. As a whole, the preferred directions of simple spike responses in the flocculus had the same orientation as those of complex spike responses. However, the preferred directions and amplitudes of modulation of simple spike responses did not necessarily correlate with those of complex spike responses in individual flocculus Purkinje cells. On the other hand, the preferred directions of simple and complex spike responses were not necessarily in the same orientation in the nodulus. The optimum velocity for simple spike responses was in the range 0.1–2.0°/s for Purkinje cells in both the flocculus and the nodulus. The amplitude and time to peak of the simple spike responses of nodulus Purkinje cells were significantly smaller and longer, respectively, than those of flocculus Purkinje cells. In both the flocculus and the nodulus, Purkinje cells whose simple spikes preferred the horizontal orientation (H cells) and the vertical orientation (V cells) showed clustering. In particular, zonal organization was noted in the flocculus. H cells were localized in a dorso-ventral zone in the rostral one third of the flocculus, and V cells were in two distinct zones rostral and caudal to the H cell zone. The locations of H and V cells in the flocculus correspond to the H zone and V zones, respectively, determined on the basis of the preferred directions of complex spike responses to OKS. This indicates that the same subdivisions of the flocculus are supplied with optokinetic signals with the same orientation selectivity through both mossy and climbing fibers, and suggest that such subdivisions of the flocculus are functional units which control horizontal and vertical components of optokinetic eye movements. The present results indicate that the flocculus and the nodulus are supplied with distinct optokinetic signals through mossy fibers and play different roles in controlling optokinetic eye movements.     

Studies of muscarinic receptor reserve linked to phosphoinositide hydrolysis in parotid gland and cerebral cortex

Hydrolysis of inositol phospholipids caused by muscarinic agonists was studied in the guinea-pig parotid gland (PG) and cerebral cortex (CX). The present study describes the effect of two muscarinic agonists, carbachol and oxotremorine, on stimulation of phosphoinositide hydrolysis and on binding of [³H]NMS in the presence of the irreversible muscarinic antagonist benzilyl choline mustard (BCM). Carbachol and oxotremorine stimulated the formation of inositol phosphates in PG, pD₂(Carb) = 5.3 ± 0.1, pD₂(Oxo) = 5.9 ± 0.1 and in CX, pD₂(Carb) = 4.3 ± 0.2, pD₂(Oxo) = 5.8 ± 0.2. In the present study slices from both tissues have been exposed to 0.1 μM BCM for 2, 5 and 10 min. Treatment for 10 min caused a 75–85%, reduction in specific [³H]N-methyl scopolamine ([³H]NMS) binding sites in both PG and CX. Following 2 min BCM treatment of PG a marked decrease in pD₂ value of the carbachol-stimulated inositol phosphate formation was found. This effect was not found in CX. The results showed that a 30–40% reduction in binding sites shifted the carbachol concentration response curve to the right by one order of magnitude and reduced the oxotremorine-induced release of inositol phosphates by approximately 20%. In PG, the BCM-induced reduction of the carbachol-stimulated inositol phosphate formation was paralleled by the reduction in receptor binding sites. Similar treatment, but in CX, showed a lower reduction of the carbachol-stimulated inositol phosphate formation as compared to the reduction in receptor-binding sites. The results from the present study indicate that stimulation of phosphoinositide hydrolysis in PG involves a receptor reserve, mainly via stimulation of M₂-muscarinic receptors.     

Muscarinic receptors in basal ganglia in dementia with Lewy bodies,Parkinson's disease and Alzheimer's disease

Derivatives of the muscarinic antagonist 3-quinuclidinyl-4-iodobenzilate (QNB), particularly [123I]-(R,R)-I-QNB, are currently being assessed as in vivo ligands to monitor muscarinic receptors in Alzheimer's disease (AD) and dementia with Lewy bodies (DLB), relating changes to disease symptoms and to treatment response with cholinergic medication. To assist in the evaluation of in vivo binding, muscarinic receptor density in post-mortem human brain was measured by autoradiography with [125I]-(R,R)-I-QNB and [125I]-(R,S)-I-QNB and compared to M1 ([3H]pirenzepine) and M2 and M4 ([3H]AF-DX 384) receptor binding. Binding was calculated in tissue containing striatum, globus pallidus (GPe), claustrum, and cingulate and insula cortex, in cases of AD, DLB, Parkinson's disease (PD) and normal elderly controls. Pirenzepine, AF-DX 384 and (R,S)-I-QNB binding in the striatum correlated positively with increased Alzheimer-type pathology, and AF-DX 384 and (R,R)-I-QNB cortical binding correlated positively with increased Lewy body (LB) pathology; however, striatal pirenzepine binding correlated negatively with cortical LB pathology. M1 receptors were significantly reduced in striatum in DLB compared to AD, PD, and controls and there was a significant correlation between M1 and dopamine D2 receptor densities. [3H]AF-DX 384 binding was higher in the striatum and GPe in AD. Binding of [125I]-(R,R)-I-QNB, which may reflect increased muscarinic M4 receptors, was higher in cortex and claustrum in DLB and AD. [125I]-(R,S)-I-QNB binding was higher in the GPe in AD. Low M1 and D2 receptors in DLB imply altered regulation of the striatal projection neurons which express these receptors. Low density of striatal M1 receptors may relate to the extent of movement disorder in DLB, and to a reduced risk of parkinsonism with acetylcholinesterase inhibition.     

Co-localization of glycine and gaba immunoreactivity in interneurons in Macaca monkey cerebellar cortex

Previous work demonstrates that the cerebellum uses glycine as a fast inhibitory neurotransmitter [Ottersen OP, Davanger S, Storm-Mathisen J (1987) Glycine-like immunoreactivity in the cerebellum of rat and Senegalese baboon, Papio papio: a comparison with the distribution of GABA-like immunoreactivity and with [3H]glycine and [3H]GABA uptake. Exp Brain Res 66(1):211-221; Ottersen OP, Storm-Mathisen J, Somogyi P (1988) Colocalization of glycine-like and GABA-like immunoreactivities in Golgi cell terminals in the rat cerebellum: a postembedding light and electron microscopic study. Brain Res 450(1-2):342-353; Dieudonne S (1995) Glycinergic synaptic currents in Golgi cells of the rat cerebellum. Proc Natl Acad Sci U S A 92:1441-1445; Dumoulin A, Triller A, Dieudonne S (2001) IPSC kinetics at identified GABAergic and mixed GABAergic and glycinergic synapses onto cerebellar Golgi cells. J Neurosci 21(16):6045-6057; Dugue GP, Dumoulin A, Triller A, Dieudonne S (2005) Target-dependent use of coreleased inhibitory transmitters at central synapses. J Neurosci 25(28):6490-6498; Zeilhofer HU, Studler B, Arabadzisz D, Schweizer C, Ahmadi S, Layh B, Bosl MR, Fritschy JM (2005) Glycinergic neurons expressing enhanced green fluorescent protein in bacterial artificial chromosome transgenic mice. J Comp Neurol 482(2):123-141]. In the rat cerebellum glycine is not released by itself but is released together with GABA by Lugaro cells onto Golgi cells [Dumoulin A, Triller A, Dieudonne S (2001) IPSC kinetics at identified GABAergic and mixed GABAergic and glycinergic synapses onto cerebellar Golgi cells. J Neurosci 21(16):6045-6057] and by Golgi cells onto unipolar brush and granule cells [Dugue GP, Dumoulin A, Triller A, Dieudonne S (2005) Target-dependent use of coreleased inhibitory transmitters at central synapses. J Neurosci 25(28):6490-6498]. Here we report, from immunolabeling evidence in Macaca cerebellum, that interneurons in the granular cell layer are glycine+ at a density of 120 cells/linear mm. Their morphology indicates that they include Golgi and Lugaro cell types with the majority containing both glycine and GABA or glutamic acid decarboxylase. These data are consistent with the proposal that, as in the rat cerebellum, these granular cell layer interneurons corelease glycine and GABA in the primate cerebellum. The patterns of labeling for glycine and GABA within Golgi and Lugaro cells also indicate that there are biochemical sub-types which are morphologically similar. Further, we find that glycine, GABA and glutamic acid decarboxylase identified candelabrum cells adjacent to the Purkinje cells which is the first time that this interneuron has been reported in primate cerebellar cortex. We propose that candelabrum cells, like the majority of Golgi and Lugaro cells, release both glycine and GABA.     

The distribution of muscarinic M1 receptors in the human hippocampus

The muscarinic M1 receptor plays a significant role in cognition, probably by modulating information processing in key regions such as the hippocampus. To understand how the muscarinic M1 receptor achieves these functions in the hippocampus, it is critical to know the distribution of the receptor within this complex brain region. To date, there are limited data on the distribution of muscarinic M1 receptors in the human hippocampus which may also be confounded because some anti-muscarinic receptor antibodies have been shown to lack specificity.Initially, using Western blotting and immunohistochemistry, we showed the anti-muscarinic M1 receptor antibody to be used in our study bound to a single 62 kDa protein that was absent in mice lacking the muscarinic M1 receptor gene. Then, using immunohistochemistry, we determined the distribution of muscarinic M1 receptors in human hippocampus from 10 subjects with no discernible history of a neurological or psychiatric disorder.Our data shows the muscarinic M1 receptor to be predominantly on pyramidal cells in the hippocampus. Muscarinic M1 receptor positive cells were most apparent in the deep polymorphic layer of the dentate gyrus, the pyramidal cell layer of cornu ammonis region 3, the cellular layers of the subiculum, layer II of the presubiculum and layer III and V of the parahippocampal gyrus. Positive cells were less numerous and less intensely stained in the pyramidal layer of cornu ammonis region 2 and were sparse in the molecular layer of the dentate gyrus as well as cornu ammonis region 1. Although immunoreactivity was present in the granular layer of the dentate gyrus, it was difficult to identity individual immunopositive cells, possibly due to the density of cells.This distribution of the muscarinic M1 receptors in human hippocampus, and its localisation on glutamatergic cells, would suggest the receptor has a significant role in modulating excitatory hippocampal neurotransmission.     

Quantitative analysis of granule cell axons and climbing fiber afferents in the turtle cerebellar cortex

The turtle cerebellar cortex is a single flat sheet of gray matter that greatly facilitates quantitative analysis of biotylinated dextran amine labeled granule cell and olivocerebellar axons and Nissl-stained granule and Purkinje neurons. On average, ascending granule cell axons are relatively thicker than their parallel fiber branches (mean±SD: 0.84±0.17 vs 0.64±0.12 µm, respectively). Numerous en passant swellings, the site of presynaptic contact, were present on both ascending and parallel fiber granule cell axons. The swellings on ascending axons (1.82±0.34 µm, n=52) were slightly larger than on parallel fibers (1.43±0.24 µm, n=430). In addition, per unit length (100 µm) there were more swellings on ascending axons (11.2±4.2) than on parallel fibers (9.7±4.2). Each parallel fiber branch from an ascending axon is approximately 1.5 mm long. Olivocerebellar climbing fiber axons followed the highly tortuous dendrites of Purkinje cells in the inner most 15–20% of the molecular layer. Climbing fibers displayed relatively fewer en passant swellings. The spatial perimeter of climbing fiber arbors (area) increased 72% from anteriorly (1797 µm²) to posteriorly (3090 µm²) and 104% from medially (1690 µm²) to laterally (3450 µm²). Differences in the size and spacing of en passant swellings on granule cell axons suggest that ascending axons may have a functionally more significant impact on the excitability of a limited number of radially overlying Purkinje cells than the single contacts by parallel fiber with multiple orthogonally aligned Purkinje cell dendrites. The spatially restricted distribution of climbing fibers to the inner most molecular layer, the paucity of en passant swellings, and different terminal arbor areas are enigmatic. Nevertheless, these finding provide important anatomical information for future optical imaging and electrophysiological experiments.     

Heterogeneity of calretinin expression in the avian cerebellar cortex of pigeons and relationship with zebrin II

The cerebellar cortex has a fundamental parasagittal organization that is reflected in the physiological responses of Purkinje cells, projections of Purkinje cells, afferent inputs from climbing and mossy fibres and the expression of several molecular markers. The most thoroughly studied of these molecular markers is zebrin II (ZII; a.k.a. aldolase C). ZII is differentially expressed in Purkinje cells, resulting in a pattern of sagittal stripes of high expression (ZII+ve) interdigitated with stripes of little or no expression (ZII−ve). The calcium binding protein calretinin (CR) is expressed heavily in mossy fibres terminating throughout the cerebellar cortex, but whether CR is heterogeneously expressed in parasagittal stripes, like ZII, is unknown. In this study, we examined CR expression in the cerebellum of pigeons and compared it to that of ZII. CR was expressed heavily in the granule layer in mossy fibres and their terminal rosettes. Moreover, CR is expressed heterogeneously in the granule layer such that there are sagittal stripes of heavy CR labelling (CR+ve) alternating with stripes of weaker labelling (CR−ve). The CR heterogeneity is most notable in folium IXcd and folia II–IV in the anterior lobe. In the anterior lobe, the central CR+ve stripe spanning the midline is aligned with the central ZII+ve stripe, whereas the other CR+ve stripes are aligned with the ZII−ve stripes. In IXcd, the CR+ve stripes are aligned with the ZII+ve stripes. This combination of aligned and unaligned CR+ve stripes, relative to ZII+ve stripes, differs from that of parvalbumin and other neurochemical markers, but the functional consequences of this is unclear. With respect to the posterior lobe, we suggest that the CR+ve mossy fibres to IXcd originate in two retinal recipient nuclei that are involved in the processing of optic flow.     

Eye velocity responsiveness and its proprioceptive component in the floccular Purkinje cells of the alert pigmented rabbit

Summary Eye velocity responsiveness of floccular Purkinje cells was studied in alert, pigmented rabbits. Conjugate horizontal eye nystagmus was elicited by application of electric pulse trains (10–50 A, 30 c/s) to the optic tract through chronically implanted electrodes. Purkinje cells were sampled with an extracellular microelectrode from the flocculus, and their involvement in different oculomotor functions was specified by electrical stimulation at their recording sites. At those sites where abduction of the ipsilateral eye was elicited, the discharge frequency of simple spikes usually increased during slow eye movement to the ipsilateral side and decreased during eye movement to the contralateral side in nystagmus and after-nystagmus. Within a limited range, the discharge frequency increased linearly with eye velocity, at an average rate of 1.6 impulse s^–1/degree s^–1. An opposite directional specificity (decrease in ipsilateral and increase in contralateral eye movement) and directional nonspecificity were common at other floccular sites where local stimulation elicited downward or no eye movement. Retrobulbar anesthesia of proprioceptive afferents from one eye reduced the eye velocity responsiveness of Purkinje cells in the ipsilateral flocculus by 31%, but did not affect their responsiveness in the contralateral flocculus. These observations indicate that eye velocity input to the rabbit flocculus arises partly from peripheral receptors but mainly from the central oculomotor system, and that responsiveness of Purkinje cells to the input is organized specifically according to their functional involvement.This work was supported by a grant from the Japanese Ministry of Education, Science and Culture (57770092)     

Interrelations of basket cell axons and climbing fibers in the cerebellar cortex of the rat

Summary An analytical study was undertaken with both electron microscopy and the rapid Golgi method in order to clarify the interrelations of climbing fibers, basket cell axons, and Purkinje cell dendrites. The two fibers are readily distinguished in electron micrographs by means of their differing content of microtubules and neurofilaments, the packing density of synaptic vesicles, and the disposition of their synaptic junctions on the Purkinje cell dendrite. Climbing fibers are generally thin and contain many microtubules. They give off attenuated collaterals, whose rounded varicosities are densely packed with vesicles and which form en passant synapses with clusters of thorns projecting from the major Purkinje dendrites. In contrast, basket axons are relatively thick and contain many neurofilaments. By means of slight dilatations containing loosely aggregated vesicles, the axon and its collaterals form numerous synapses en passant with the smooth dendritic shafts and the perikaryon of the Purkinje cell. Climbing fibers and basket cell axons run along parallel with each other but without forming axo-axonic synapses as they ascend over the surface of the Purkinje dendrites. Both fibers form especially elaborate intertwined festoons at the branching points of the major dendrites. The kinds of synapses found are described in detail, and the functional implications are discussed.The hypothesis is developed that the dendritic thorn is a device for isolating the subsynaptic membrane from electrical events in the rest of the dendrite at the cost of reducing the effectiveness of the synapse. This principle is incorporated in the Purkinje dendrite—parallel fiber synapses, in which an individual fiber can be expected to have little importance. The disadvantage of using thorns as postsynaptic surfaces can be mitigated by clustering them and increasing the number of thorns contacted by each presynaptic terminal. This method is utilized at the junctions between the climbing fiber and the Purkinje dendrite to produce one of the most powerful excitatory synapses known. It is furthermore suggested that the elaborate plexus of climbing fibers and basket cell axons synapsing in the crotches of branching dendrites is strategically located to control the flow of information in the Purkinje cell dendritic tree.Supported by U.S. Public Health Service Research Grant NS03659 and Training Grant NS05591 from the National Institute of Neurological Diseases and Stroke.Postdoctoral trainee in Anatomy under Training Grant GM906 from the National Institute of General Medical Sciences.     

Directional organization of eye movement and visual signals in the floccular lobe of the monkey cerebellum

The floccular lobe of the monkey is critical for the generation of visually-guided smooth eye movements. The present experiments reveal physiological correlates of the directional organization in the primate floccular lobe by examining the selectivity for direction of eye motion and visual stimulation in the firing of individual Purkinje cells (PCs) and mossy fibers. During tracking of sinusoidal target motion along different axes in the frontoparallel plane, PCs fell into two classes based on the axis that caused the largest modulation of simple-spike firing rate. For horizontal PCs, the response was maximal during horizontal eye movements, with increases in firing rate during pursuit toward the side of recording (ipsiversive). For vertical PCs, the response was maximal during eye movement along an axis just off pure vertical, with increases in firing rate during pursuit directed downward and slightly contraversive. During pursuit of target motion at constant velocity, PCs again fell into horizontal and vertical classes that matched the results from sinusoidal tracking. In addition, the directional tuning of the sustained eye velocity and transient visual components of the neural responses obtained during constant velocity tracking were very similar. PCs displayed very broad tuning approximating a cosine tuning curve; the mean half-maximum bandwidth of their tuning curves was 170–180 °. Other cerebellar elements, related purely to eye movement and presumed to be mossy fibers, exhibited tuning approximately 40 ° narrower than PCs and had best directions that clustered around the four cardinal directions. Our data indicate that the motion signals encoded by PCs in the monkey floccular lobe are segregated into channels that are consistent with a coordinate system defined by the vestibular apparatus and eye muscles. The differences between the tuning properties exhibited by PCs compared with mossy fibers indicate that a spatial transformation occurs within the floccular lobe.     

Role of cerebellar flocculus in adaptive interaction between optokinetic eye movement response and vestibulo-ocular reflex in pigmented rabbits

Summary Sustained sinusoidal oscillation of a striped cylindrical screen around a stationary, alert pigmented rabbit with certain parameters (for 4h, 5°, 7.5°, or 10° peak-to-peak, 0.1 or 0.2 Hz) adaptively modified not only the horizontal optokinetic response (HOKR) but also the horizontal vestibulo-ocular reflex (HVOR). The major effects thus obtained during 4 h were an increase in the HOKR gain by 0.23, and that of the HVOR gain by 0.18. Bilateral destruction of floccular Purkinje cells with microinjection of kainic acid abolished these effects on both HOKR and HVOR. Single unit activities of floccular Purkinje cells were recorded from the floccular areas related to horizontal eye movements (H-zone) with local stimulus effects. Most H-zone Purkinje cells normally exhibited modulation of simple spike discharge in phase with screen velocity and out of phase with turntable velocity. Sustained screen oscillation (7.5°, 0.1 Hz) for 1 h increased the simple spike responses not only to screen but also to turntable oscillation. No such changes were observed in other floccular areas. These observations suggest that sustained optokinetic stimulations induce adaptation of HVOR through an interaction of retinal slip and head velocity signals within the flocculus or its related neuronal tissues.     

Effects of subacute treatment with toluene on cerebrocortical α- and β-adrenergic receptors in the rat. Evidence for an increased number and a reduced affinity of β-adrenergic receptors

Subacute treatment with toluene (80–1500 p.p.m.) produces a dose-dependent reduction of affinity and increase in density of the β-adrenergic antagonist [³H]dihydroalprenolol binding sites in the frontoparietal cortex of the male rat, while the binding characteristics of a,-adrenergic ([³H]WB 4101) and α₂^-adrenergic ([³H]p-aminoclonidine) binding sites in the same region is unaffected by this treatment as evaluated in vitro. Therefore, it is suggested that the cortical β-adrenergic receptors are particularly vulnerable to the action of toluene in vivo. It is speculated that as a result cortical β-adrenergic neurotransmission may be altered following exposure to low concentrations of toluene, possibly related to the physico-chemical properties of toluene, leading to changes in membrane fluidity.     

Formaldehyde-induced neurotoxicity in rat cerebellar cortex and possible protective effects of fatty acids from omega 3 and wheat germ oil supplement: a histopathological and biochemical study

Formaldehyde is a common environmental pollutant with toxic effects and coming mainly from occupational exposure. This study was done to simulate occupational exposure to formaldehyde vapor and study its cerebellar neurotoxicity and the protective role of fatty acids from omega-3 and wheat germ oil. Thirty adult albino rats were divided into three groups were used in the study. Group I (control) was not exposed to any treatment, Group II (experimental) was exposed to formaldehyde vapor and Group III (recovery) was exposed to formaldehyde vapor and given omega-3 and wheat germ oil supplement during exposure. Biochemical and histopathological examinations were done. Biochemical results revealed cerebellar levels were reduced for superoxide dismutase and glutathione peroxidase and elevated for malondialdehyde. Histopathological examination revealed the three layers of the cerebellar cortex especially Purkinje layer were affected by formaldehyde inhalation. The following proteins all showed increased expression, i.e. Glial fibrillary acidic protein, inducible nitric oxide synthetase and BCl-2-associated X protein using immunohistochemical staining. Administration of an omega-3 and wheat germ oil fatty acid supplement during formaldehyde exposure produced partial improvement of the biochemical and histopathological results. Our findings indicated that formaldehyde vapor inhalation induced cerebellar neurotoxicity mainly caused by oxidative stress which could be improved by administration omega 3 and wheat germ fatty acids.     

Conformational changes in muscarinic receptors may produce diminished cholinergic neurotransmission and memory deficits in aged rats

Both clinical and laboratory studies suggest that age-related memory deficits may be due, at least in part, to disturbances in muscarinic acetylcholine (mAChR) receptors. In order to further evaluate this premise, the present studies examined the electrophysiological responses rates of hippocampal pyramidal cells to iontophoretically applied ACh in young, middle-age and aged animals. The relationship between age and muscarinic agonist and antagonist binding in the hippocampus was also examined. In addition, possible age-related changes in receptor-effector coupling were assessed by determining calmodulin levels and the activities of phospholipid methyltransferase I and II. Analysis of electrophysiological data showed selective age-related decrements in the ability of ACh to alter burst rate but not simple spike rate. These age-related decreases in the efficacy of ACh to increase burst rate were not paralleled by decreases in mAChR density as assessed by ³H-QNB binding, but they were temporally paralleled by age-related changes in the ability of oxotremorine to inhibit ³H-QNB binding. In the young animals, the resultant Hill coefficients derived from these analyses approached 1, while in the middle and old aged animals, the Hill coefficients deviated significantly from 1, indicating the possible existence of 2 or more receptor states with differential affinity for oxotremorine in the 2 older age groups. When carbamylcholine was used to inhibit ³H-QNB, these complex binding patterns were seen even in the young, since carbamylcholine induces conformational/orientational changes in the mAChR while oxotremorine does not. It is suggested that declines in mnemonic ability that have been reported previously, parallel the age-related conformation/orientational changes observed in the mAChR since these changes result in a receptor that is “neurophysiologically desensitized.”     

The form of velate astrocytes in the cerebellar cortex of monkey and rat: High voltage electron microscopy of rapid Golgi preparations

Summary High voltage electron microscopy of Golgi preparations vividly displays the veil-like appendages on certain protoplasmic astrocytes. These appendages are extremely thin sheets of cytoplasm or plasmalemmal films expanding from the larger processes of the cells. Because of the prominence of this structural feature, reminiscent of the appearance of astrocytes in tissue culture, we designate these cells as velate astrocytes, in order to distinguish them from those protoplasmic astrocytes that lack such appendages. In the cerebellar cortex, velate astrocytes are represented by two types of neuroglial cell: (1) the Golgi epithelial cell and (2) the common astrocyte of the granular layer. The first type not only gives rise to the Bergmann fibers, but also envelops the Purkinje cell and all of its processes. The second type divides up the granular layer into gross compartments containing individual glomeruli and single or clustered granule cells. The probable significance of this compartmentation is discussed.Supported in part by USPHS research grant NS03659 and training grant NS05591 from the National Institute of Neurological Diseases and Stroke, and by NIH contract 70-4136.