Hendrik Van der Loos

Synaptogenesis in human visual cortex — evidence for synapse elimination during normal development ☆

Age-related changes in synaptic density in human visual cortical area 17 (striate cortex) were determined, based on counts in material prepared for electron microscopy with the phosphotungstic acid method. The results were correlated with measurements of the volume of striate cortex from celloidin sections. Two periods were defined, one of rapid synapse production which ends at about postnatal age 8 months, and a subsequent longer period of synapse elimination which extends past age 3 years. Exuberant synaptic connections during early childhood may impart to the immature cerebral cortex plasticity which is lost in the adult.

Barreloids in mouse somatosensory thalamus.

Abstract In the mouse, in the medial part of the ventrobasal complex of the thalamus (VBm), an array of rod-shaped domains, poor in perikarya and with a diameter of about 70 μm, is embedded in a lattice of high cell packing-density. Each domain forms the core of a ‘barreloid’. The arrangement of barreloids is topologically equivalent to that of the large barrels in the cortical somatosensory area (SI).

Does the skin tell the somatosensory cortex how to construct a map of the periphery

When the muzzle of a mouse bears an occasional extra whisker, the corresponding barrelfield (in the contralateral somatosensory cortex) contains an extra barrel in a topologically equivalent place and vice versa. Since the pattern of vibrissal follicles is laid down 7 days before birth and that of the barrels 3 days after birth, the former pattern appears to be responsible for the establishment of the latter. We propose that the answer to the titles question is yes.

A magnetic device to stimulate selected whiskers of freely moving or restrained small rodents: its application in a deoxyglucose study

After receiving an intraperitoneal injection of [14C]2-deoxy-D-glucose (2-DG), a total of 28 mice which had pieces of metal wire glued to certain whiskers (all others were clipped) were exposed to magnetic field bursts. The stimulated whiskers were B1 (freely moving mice, set I) or whiskers C1-3 and E1 (restrained mice, set II) on the left side. In set I, stimulated mice were compared with animals of various control groups. Autoradiography demonstrated an activation of columnar shape overlying the presumed corresponding barrel contralateral to stimulation; in a part of the ipsilateral barrelfield, 2-DG uptake was depressed significantly. In the subnuclei caudalis and interpolaris of the trigeminal brainstem complex a spot of activation was observed ipsilaterally but there was no depression contralaterally. Whereas several animals of the control groups showed some aspects of these responses, they were consistent only in stimulated mice. In set II, animals received stimulation with different intensities. 2-DG uptake was higher in barrels C1-3 than in E1. It increased with increasing intensity. The same observations were made in two nuclei of termination. The device we describe here can be used to study stimulus-specific responses at various levels of the somatosensory pathway.

The mode of activation of a barrel column : response properties of single units in the somatosensory cortex of the mouse upon whisker deflection

Response properties of single units in the mouse barrel cortex were studied to determine the sequence in which the neurons that form a cortical column become activated by a single‘natural’stimulus. Mice (n= 11) were anaesthetized with urethane. For a total of 153 cells, grouped by cortical layer, responses to a standardized deflection of a single whisker were characterized using poststimulus time and latency histograms. Usually, for each unit, data were collected for stimulation of its principal whisker (PW; the whiskers corresponding to the barrel column in which the cell was located) and of the four whiskers surrounding the PW. In all layers, PW stimulation evoked responses at shorter latency than surround whisker stimulation. In layers II – III and IV a bimodal distribution of cells according to latency to PW stimulation was found. Statistical analysis indicated the presence of two classes of cells in each of these layers:‘fast’units (latency < 15 ms) and slow’units (latency >15 ms). The great majority of cells in layers I, V and VI fired at latencies of >20 ms to PW stimulation. In general, stimulation of surround whiskers evoked a smaller response than PW stimulation. The fast cells of layer IV showed the greatest response to PW stimulation (mean = 1.78 spikes/100 ms poststimulus). Their firing was maximal during the 10–20 ms poststimulus epoch, while the slow layer IV cells fired maximally during the 20 – 30 ms poststimulus epoch. Surround inhibition occurred in all layers within the first 10 ms after stimulus onset, during which period the fast cells are the most active ones, and are thus likely to be responsible for the surround inhibition. This notion is supported by an analysis of spike duration that showed that eight of the ten cells with a thin spike (supposed to be GABAergic; McCormick et al., J. Neurophysiol., 54, 782 – 806, 1985), had PW latencies of <15 ms. We conclude that the activation of a barrel column is initially inhibitory in nature.

Barrelfield expansion after neonatal eye removal in mice.

We investigated the effect of neonatal eye removal on the tangential extent of the barrelfield in mice. Areas were measured in drawings made from tangentially cut Nisslstained sections of somatosensory cortex. We compared areas of 29 barrels, corresponding to 29 mystacial vibrissae, between adult mice enucleated at birth (n = 13) and their intact littermates (n = 13). Multivariate analysis of variance showed that the barrelfield was larger in enucleated mice. This expansion was mainly due to the increase in areal extent of the barrels corresponding to the dorsalmost row of vibrissae, and of a set of barrels corresponding to rostral vibrissae near the nose and mouth. Evidently, early enucleation has a significant cross-modal effect on the somatosensory cortex.

GABAergic neurons in the barrel cortex of the mouse: An analysis using neuronal archetypes

SummaryWe describe the morphological types of glutamic acid decarboxylase (GAD) immunoreactive cells in the barrel cortex of the mouse. A method is introduced and applied, which combines qualitative and quantitative criteria to classify these cells through the use of multivariate statistics. With the aid of an interactive computer microscope, 2010 GAD-positive neurons were harvested. Each cell was assigned to one of a set of qualitatively defined classes (archetypes) and further characterized by various morphometric parameters. Through the statistical analysis, new sets of hierarchically ordered archetypes were inferred; these served to classify cells which, due to lack of morphological detail, were unclassifiable using qualitative criteria only. We here report on the characteristics of eight archetypes of GAD-positive neurons, distinguished by means of their size, shape, and orientation and the distribution of their cell bodies over the cortical layers. Some archetypes were observed mostly in the upper layers of the cortex (group I triangular and group I horizontal fusiform cells), others mostly in the lower layers (group II triangular and group II horizontal fusiform cells). Bulb and vertical fusiform, as well as vertical star and horizontal star cells, were present throughout the entire cortical thickness. The star cells formed the two most frequent archetypes. This classification constitutes a baseline which we currently use to elucidate whether differences exist in the birthdates among the GABAergic archetypes within each layer of the mouse barrel cortex.

The Long Distance Effects of Brain Lesions: Visualization of Axonal Pathways and Their Terminations in the Human Brain by the Nauta Method

This study aims at determining the reliability and the optimal post-injury survival time for the application of the Nauta technique to the analysis of the human brain. The Nauta method reveals the degeneration not only of nerve fibers, myelinated and unmyelinated, but also of their terminations. Immunohistochemical and ultra-structural observations appear to prove that the Nauta technique indeed stains axons in human autopsy material. The optimal survival time for the use of the Nauta method was found to be between nine days and five months. In cases with longer survival times—up to 20 months—the Nauta technique and a previously proposed polarizing technique (showing birefringent breakdown products of myelin) can be used as complementary methods. Applying these techniques to the human brain may help define the anatomical basis of neurological and neuropsychological symptoms important for man.

Maturation of the neuronal metabolic response to vibrissa stimulation in the developing whisker-to-barrel pathway of the mouse.

We examined functional maturation in the mouse whisker-to-barrel pathway from P2 (P0 is the day of birth) to adulthood using the autoradiographic deoxyglucose (DG) method. After intraperitoneal DG injection, left whiskers C1-3 and E1 were stimulated. Sections were cut transversely through the brainstem, and coronally or tangentially through the parietal cortex. After autoradiography, the sections were stained for Nissl or for cytochrome oxidase (CO) activity. In subnuclei caudalis and interpolaris of the spinal trigeminal nucleus ipsilateral to stimulation, DG uptake evoked by the deflection of whiskers C1-3 was present at P2; in subnucleus oralis, nucleus principalis and the contralateral nucleus ventrobasalis of the thalamus, at P4; and in the contralateral barrel cortex, at P7. The first stimulus-dependent DG uptake appeared a few days after the appearance of whisker-related patterns seen in the CO- or Nissl-stained sections. In subnuclei caudalis and interpolaris, areas of stimulus-dependent DG uptake were initially larger than the CO segments representing the stimulated whiskers. Later, areas of stimulus-dependent DG uptake and CO segments matched well. DG uptake evoked by the stimulation of whisker E1 appeared 2-3 days later than that evoked by stimulation of whiskers C1-3. In nucleus principalis, one large area of stimulus-dependent DG uptake covered the representations of the caudal whiskers of all five rows--an observation made at all ages studied. In thalamus, stimulus-dependent DG uptake was found laterally in nucleus ventrobasalis. In barrel cortex, at P7, stimulus-dependent DG uptake was restricted to layers III and IV, but covered more barrels than whiskers stimulated. At P9, a second spot of high DG uptake was seen in deep layer V in register with that in layers III and IV. From P10 onwards, stimulus-dependent DG uptake stretched from layer II to layer VI, and in layer IV, in which it was highest, it was restricted to the barrels C1-3 and E1. In all stations, stimulus-dependent DG uptake decreased in magnitude after P10. While the onset of stimulus-dependent DG uptake is the result of the establishment of functional projections up to that station, the subsequent changes in size of the responding areas may well be due to the partial elimination of terminals, the maturation of local inhibitory circuits, and/or the development of cortical projections to the nuclei of termination and to the thalamic relay.

Cultured embryonic non-innervated mouse muzzle is capable of generating a whisker pattern.

The whisker pattern on the muzzle of the mouse is mapped in the contralateral parietal neocortex, each whisker follicle projecting to its own multineuronal unit (‘barrel’). To determine the role, if any, of the peripheral innervation in the establishment of the vibrissal array, we cultured non‐innervated prospective whiskerpads from 9‐ and 10‐day‐old embryos, mostly on chorioallantoic membrane. The results show that skin, alone, is capable of generating the whisker pattern, thus adducing a strong argument for the hypothesis that the central brain maps have their origin in the periphery.