Lutgarde Arckens

Neurofilament protein: A selective marker for the architectonic parcellation of the visual cortex in adult cat brain

In this immunocytochemical study, we examined the expression profile of neurofilament protein in the cat visual system. We have used SMI‐32, a monoclonal antibody that recognizes a nonphosphorylated epitope on the medium‐ and high‐molecular‐weight subunits of neurofilament proteins. This antibody labels primarily the cell body and dendrites of pyramidal neurons in cortical layers III, V, and VI. Neurofilament protein‐immunoreactive neurons were prominent in 20 visual cortical areas (areas 17, 18, 19, 20a, 20b, 21a, 21b, and 7; posteromedial lateral, posterolateral lateral, anteromedial lateral, anterolateral lateral, dorsal lateral, ventral lateral, and posterior suprasylvian areas; anterior ectosylvian, the splenial, the cingulate, and insular visual areas; and the anterolateral gyrus area). In addition, we have also found strong immunopositive cells in the A laminae of the dorsal part of the lateral geniculate nucleus (dLGN) and in the medial interlaminar nucleus, but no immunoreactive cells were present in the parvocellular C (1–3) laminae of the dLGN, in the ventral part of the LGN and in the perigeniculate nucleus. This SMI‐32 antibody against neurofilament protein revealed a characteristic pattern of immunostaining in each visual area. The size, shape, intensity, and density of neurofilament protein‐immunoreactive neurons and their dendritic arborization differed substantially across all visual areas. Moreover, it was also obvious that several visual areas showed differences in laminar distribution and that such profiles may be used to delineate various cortical areas. Therefore, the expression of neurofilament protein can be used as a specific marker to define areal patterns and topographic boundaries in the cat visual system. J. Comp. Neurol. 441:345–368, 2001.

Functional striatal hypodopaminergic activity in mice lacking adenosine A(2A) receptors.

Adenosine and caffeine modulate locomotor activity and striatal gene expression, partially through the activation and blockade of striatal A2A receptors, respectively. The elucidation of the roles of these receptors benefits from the construction of A2A receptor‐deficient mice (A2A‐R−/−). These mice presented alterations in locomotor behaviour and striatal expression of genes studied so far, which are unexpected regarding the specific expression of A2A receptor by striatopallidal neurones. To clarify the functions of A2A receptors in the striatum and to identify the mechanisms leading to these unexpected modifications, we studied the basal expression of immediate early and constitutive genes as well as dopamine and glutamate neurotransmission in the striatum. Basal zif268 and arc mRNAs expression was reduced in mutant mice by 60–80%, not only in the striatum but also widespread in the cerebral cortex and hippocampus. Striatal expression of substance P and enkephalin mRNAs was reduced by about 50% and 30%, respectively, whereas the expression of GAD67 and GAD65 mRNAs was slightly increased and unaltered, respectively. In vivo microdialysis in the striatum revealed a 45% decrease in the extracellular dopamine concentration and three‐fold increase in extracellular glutamate concentration. This was associated with an up‐regulation of D1 and D2 dopamine receptors expression but not with changes in ionotropic glutamate receptors. The levels of tyrosine hydroxylase and of striatal and cortical glial glutamate transporters as well as adenosine A1 receptors expression were indistinguishable between A2A‐R−/− and wild‐type mice. Altogether these results pointed out that the lack of A2A receptors leads to a functional hypodopaminergic state and demonstrated that A2A receptors are necessary to maintain a basal level in immediate early and constitutive genes expression in the striatum and cerebral cortex, possibly via their control of dopamine pathways.

Cooperative changes in GABA, glutamate and activity levels: the missing link in cortical plasticity

Different intracortical mechanisms have been reported to contribute to the substantial topographic reorganization of the mammalian primary visual cortex in response to matching lesions in the two retinas: an immediate expansion of receptive fields followed by a gradual shift of excitability into the deprived area and finally axonal sprouting of laterally projecting neurons months after the lesion. To gain insight into the molecular mechanisms of this adult plasticity, we used immunocytochemical and bioanalytical methods to measure the glutamate and GABA neurotransmitter levels in the visual cortex of adult cats with binocular central retinal lesions. Two to four weeks after the lesions, glutamate immunoreactivity was decreased in sensory‐deprived cortex as confirmed by HPLC analysis of the glutamate concentration. Within three months normal glutamate immunoreactivity was restored. In addition, the edge of the unresponsive cortex was characterized by markedly increased glutamate immunoreactivity 2–12 weeks postlesion. This glutamate immunoreactivity peak moved into the deprived area over time. These glutamate changes corresponded to decreased spontaneous and visually driven activity in unresponsive cortex and to strikingly increased neuronal activity at the border of this cortical zone. Furthermore, the previously reported decrease in glutamic acid decarboxylase immunoreactivity was found to reflect decreased GABA levels in sensory‐deprived cortex. Increased glutamate concentrations and neuronal activity, and decreased GABA concentrations, may be related to changes in synaptic efficiency and could represent a mechanism underlying the retinotopic reorganization that occurs well after the immediate receptive field expansion but long before the late axonal sprouting.

Fluorescent two-dimensional difference gel electrophoresis and mass spectrometry identify age-related protein expression differences for the primary visual cortex of kitten and adult cat

The recent introduction of fluorescent two‐dimensional difference gel electrophoresis, combined with mass spectrometry, has greatly simplified the analysis and identification of differentially expressed proteins by eliminating intergel variability. In this report, we describe the successful application of this functional proteomics approach to compare protein expression levels in visual cortical area 17 of adult cats and 30‐day‐old kittens, in order to identify proteins expressed in an age‐related fashion. We identified 16 proteins that were more abundantly expressed in kitten striate cortex and 12 proteins with a pronounced expression in adult cat area 17. Among those isolated from kitten area 17 were proteins related to axon growth and growth cone guidance and to the formation of cytoskeletal filaments. Glial fibrillary acidic protein, as identified in adult cat area 17, has been implicated previously in the termination of the critical period for cortical plasticity in kittens. In situ hybridization experiments for two of the identified proteins, glial fibrillary acidic protein and collapsin response mediator protein 5, confirmed and extended their differential expression to the mRNA level. Our findings show that two‐dimensional difference gel electrophoresis combined with mass spectrometry is a powerful approach that permits the identification of small protein expression differences correlated to different physiological conditions.

Recent advances in 2D electrophoresis: an array of possibilities

2D electrophoresis is currently the most widespread technique used for performing functional proteomics (i.e., the large-scale analysis of alterations in protein expression levels). Nevertheless, several limitations inherent to this technology have restricted the full potential of this protein differential display methodology for years. This has even led to the abandonment of 2D electrophoresis by several groups that switched to performing gel-free functional proteomics analyses based on liquid chromatography and mass spectrometry. Meanwhile, important recent advances in 2D electrophoresis, such as the introduction of fluorescent 2D difference gel electrophoresis and numerous protein prefractionation techniques, have thoroughly modernized 2D electrophoresis, making it again one of the preferred methods for the analysis of protein expression differences in many laboratories.

Investigation of cortical reorganization in area 17 and nine extrastriate visual areas through the detection of changes in immediate early gene expression as induced by retinal lesions

The effect of binocular central retinal lesions on the expression of the immediate early genes c‐fos and zif268 in the dorsal lateral geniculate nucleus ( dLGN ) and the visual cortex of adult cats was investigated by in situ hybridization and immunocytochemistry. In the deafferented region of the dLGN , the c‐fos mRNA level was decreased within 3 days. The dimensions of the geniculate region showing decreased amounts of c‐fos mRNA matched the predictions based on the lesion size and the retinotopic maps of Sanderson ([1971] J. Comp. Neurol. 143:101–118). We did not detect zif268 mRNA in the dLGN . At the cortical level, both c‐fos and zif268 mRNA expression decreased in the sensory‐deprived region of area 17. In addition, the portions of areas 18, 19, 21a, 21b, and 7, as well as the posterior medial lateral suprasylvian area, the posterior lateral lateral suprasylvian area, the ventral lateral suprasylvian area, and the dorsal lateral suprasylvian area corresponding to the retinal lesions also displayed decreased c‐fos and zif268 mRNA levels. Immunocytochemistry revealed similar changes for Zif268 and Fos protein. Three days post lesion, the dimensions of the lesion‐affected cortical loci exceeded the predictions in relation to the size of the retinal lesions and the available retinotopic maps. Longer postlesion survival times clearly resulted in a time‐dependent restoration of immediate early gene expression from the border to the center of the lesion‐affected cortical portions. Our findings represent a new approach for investigating the capacity of adult sensory systems to undergo plastic changes following sensory deprivation and for defining the topographic nature of sensory subcortical and cortical structures. J. Comp. Neurol. 425:531–544, 2000.

Receptive-field properties of V1 and V2 neurons in mice and macaque monkeys.

We report the results of extracellular single‐unit recording experiments where we quantitatively analyzed the receptive‐field (RF) properties of neurons in V1 and an adjacent extrastriate visual area (V2L) of anesthetized mice with emphasis on the RF center‐surround organization. We compared the results with the RF center‐surround organization of V1 and V2 neurons in macaque monkeys. If species differences in spatial scale are taken into consideration, mouse V1 and V2L neurons had remarkably fine stimulus selectivity, and the majority of response properties in V2L were not different from those in V1. The RF center‐surround organization of mouse V1 neurons was qualitatively similar to that for macaque monkeys (i.e., the RF center is surrounded by extended suppressive regions). However, unlike in monkey V2, a significant proportion of cortical neurons, largely complex cells in V2L, did not exhibit quantifiable RF surround suppression. Simple cells had smaller RF centers than complex cells, and the prevalence and strength of surround suppression were greater in simple cells than in complex cells. These findings, particularly on the RF center‐surround organization of visual cortical neurons, give new insights into the principles governing cortical circuits in the mouse visual cortex and should provide further impetus for the use of mice in studies on the genetic and molecular basis of RF development and synaptic plasticity. J. Comp. Neurol. 518:2051–2070, 2010.

Behavioural and physiological effects of electrical stimulation in the nucleus accumbens: a review

Electrical stimulation (ES) in the brain is becoming a new treatment option in patients with treatment-resistant obsessive-compulsive disorder (OCD). A possible brain target might be the nucleus accumbens (NACC). This review aims to summarise the behavioural and physiological effects of ES in the NACC in humans and in animals and to discuss these findings with regard to neuroanatomical, electrophysiological and behavioural insights. The results clearly demonstrate that ES in the NACC has an effect on reward, activity, fight-or-flight, exploratory behaviour and food intake, with evidence for only moderate physiological effects. Seizures were rarely observed. Finally, the results of ES studies in patients with treatment-resistant OCD and in animal models for OCD are promising.

Homologous involvement of striatum and prefrontal cortex in rodent and human water maze learning

The multiple memory systems hypothesis posits that dorsal striatum and hippocampus are central nodes in independent memory systems, supporting response-based and place-based learning, respectively. Although our understanding of the function of hippocampus within this framework is relatively well established, the contribution of dorsal striatum is less clear. This in part seems to be due to the heterogeneous nature of dorsal striatum, which receives extensive topographically organized projections from higher cortical areas. Here we quantified neural activity in the intact brain while mice and humans acquired analogous versions of the Morris water maze. We found that dorsomedial striatum and medial prefrontal cortex support the initial acquisition of what is typically considered a hippocampus-dependent spatial learning task. We suggest that the circuit involving dorsomedial striatum and medial prefrontal cortex identified here plays a more task-independent role in early learning than currently thought. Furthermore, our results demonstrate that dorsomedial and dorsolateral striatum serve fundamentally different roles during place learning. The remarkably high degree of anatomical overlap in brain function between mouse and human observed in our study emphasizes the extent of convergence achievable with a well-matched multilevel approach.

Evidence for Cross-Modal Plasticity in Adult Mouse Visual Cortex Following Monocular Enucleation

The goal of this study was to assess cortical reorganization in the visual system of adult mice in detail. A combination of deprivation of one eye and stimulation of the remaining eye previously led to the identification of input-specific subdivisions in mouse visual cortex. Using this information as a reference map, we established to what extent each of these functional subdivisions take part in cortical reactivation and reorganization upon unilateral enucleation. A recovery experiment revealed a differential laminar and temporal reactivation profile. Initiation of infragranular recovery of molecular activity near the border with nonvisual cortex and simultaneous hyperactivation of this adjacent cortex implied a partial nonvisual contribution to this plasticity. The strong effect of somatosensory deprivation as well as stimulation on infragranular visual cortex activation in long-term enucleated animals support this view. Furthermore, targeted tracer injections in visual cortex of control and enucleated animals revealed preexisting connections between the visual and somatosensory cortices of adult mice as possible mediators. In conclusion, this study supports an important cross-modal component in reorganization of adult mouse visual cortex upon monocular enucleation.