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H van der Loos

Publications and source records attributed to H van der Loos.

10 recordsLinked to original sources
PubMed1992

Synapses on motoneuron dendrites in the brachial section of the frog spinal cord: a computer-aided electron microscopic study of cobalt-filled cells.

Cobalt-labelled motoneuron dendrites of the frog spinal cord at the level of the second spinal nerve were photographed in the electron microscope from long series of ultrathin sections. Three-dimensional computer reconstructions of 120 dendrite segments were analysed. The samples were taken from two locations: proximal to cell body and distal, as defined in a transverse plane of the spinal cord. The dendrites showed highly irregular outlines with many 1-2 microns-long 'thorns' (on average 8.5 thorns per 100 microns 2 of dendritic area). Taken together, the reconstructed dendrite segments from the proximal sites had a total length of about 250 microns; those from the distal locations, 180 microns. On all segments together there were 699 synapses. Nine percent of the synapses were on thorns, and many more close to their base on the dendritic shaft. The synapses were classified in four groups. One third of the synapses were asymmetric with spherical vesicles; one half were symmetric with spherical vesicles; and one tenth were symmetric with flattened vesicles. A fourth, small class of asymmetric synapses had dense-core vesicles. The area of the active zones was large for the asymmetric synapses (median value 0.20 microns 2), and small for the symmetric ones (median value 0.10 microns 2), and the difference was significant. On average, the areas of the active zones of the synapses on thin dendrites were larger than those of synapses on large calibre dendrites. About every 4 microns 2 of dendritic area received one contact. There was a significant difference between the areas of the active zones of the synapses at the two locations. Moreover, the number per unit dendritic length was correlated with dendrite calibre. On average, the active zones covered more than 4% of the dendritic area; this value for thin dendrites was about twice as large as that of large calibre dendrites. We suggest that the larger active zones and the larger synaptic coverage of the thin dendrites compensate for the longer electrotonic distance of these synapses from the soma.

Animals↗
PubMed1992

Plasticity in the barrel cortex of the adult mouse: effects of chronic stimulation upon deoxyglucose uptake in the behaving animal.

We investigated experience-dependent regulation of neuronal activity in the whisker-to-barrel pathway of the adult mouse using the autoradiographic deoxyglucose (DG) method. Animals were placed in the Lausanne whisker stimulator, and three of their whisker follicles were passively stimulated for a period of 1, 2, or 4 d. After this period, mice received a dose of DG and were placed in a cage containing a pile of wooden sticks. Mice that underwent the same procedure except the passive stimulation served as controls. Patterns of stimulus-dependent DG uptake were studied in the somatosensory cortex and in the trigeminal sensory brainstem complex. DG uptake in the barrels corresponding to the passively stimulated whiskers was lower than in controls. This decrease was present throughout the radial extent of a barrel column and was observed in all passively stimulated animals. Quantitative analysis confirmed these observations and, furthermore, showed a statistically significant decrease in DG uptake in barrels neighboring the passively stimulated ones. In half of the animals, the brainstem nuclei showed a decreased DG uptake in the representation of the passively stimulated whiskers, whereas in the other animals the pattern of DG uptake was as in controls. We propose that the signs of cortical plasticity are due to a mechanism that operates in layer IV and functions as a gate for peripheral sensory activity to enter cortical circuitry.

Animals↗
PubMed1991

Vibrissa-related behavior in mice: transient effect of ablation of the barrel cortex.

Knowing that the mystacial vibrissae are an important part of the tactile sensory apparatus of rodents, we investigated the role of the barrel cortex - the endstation of the pathway between whiskerpad and cerebral cortex - in mouse behavior. We tested 15 female adult mice 2 and 10 weeks after both unilateral ablation of the barrel cortex and removal of the vibrissae on the same side in order to assess acute as well as transient effects of the cortical lesion. Two kinds of behavioral tests were performed on animals permanently provided with opaque lenses: one involved a passive stimulation of the vibrissae; the other was the 'gap-crossing' test which required the animal's active use of the vibrissae. Lesioned subjects did not show a deficit during passive stimulation of the vibrissae. On the contrary, there was a deficit during the gap-crossing test 2 weeks after the ablation of the barrel cortex. The deficit partly disappeared when the subjects were tested 10 weeks later. The results show that in mice, the barrel cortex is involved in the performance of complex behavioral tasks. The recovery of function could be due to changes in strategies to solve the gap-crossing test and/or to physical changes in neuronal circuitry. In either case, the results are relevant for the interpretation of cortical transplantation models using the whisker-to-barrel pathway.

Animals↗
PubMed1986

Distal dendrites of frog motor neurons: a computer-aided electron microscopic study of cobalt-filled cells.

With the aid of the cobalt labelling technique, frog spinal cord motor neuron dendrites of the subpial dendritic plexus have been identified in serial electron micrographs. Computer reconstructions of various lengths (2.5-9.8 micron) of dendritic segments showed the contours of these dendrites to be highly irregular, and to present many thorn-like projections 0.4-1.8 micron long. Number, size and distribution of synaptic contacts were also determined. Almost half of the synapses occurred at the origins of the thorns and these synapses had the largest contact areas. Only 8 out of 54 synapses analysed were found on thorns and these were the smallest. For the total length of reconstructed dendrites there was, on average, one synapse per 1.2 micron, while 4.4% of the total dendritic surface was covered with synaptic contacts. The functional significance of these distal dendrites and their capacity to influence the soma membrane potential is discussed.

Animals↗
PubMed1986

The time course of the changes in axon number of both oculomotor nerves in normal and unilaterally enucleated Xenopus laevis.

UNLABELLED: In this paper we analyze long-term changes, extending into adulthood, of the number of axons in the oculomotor nerve of Xenopus laevis. We counted the number of axons in that nerve in normal control (nor) animals, and on the operated (ipsilateral, ip) and contralateral (co) sides of enucleated animals at premetamorphosis, metamorphic climax, juvenile (3 and 7 months) and adult (16.5 months) stages. The experimental animals had had one of their ocular primordia removed at hatching. In the nor-nerves there is a loss of 23% of the axons between premetamorphosis and climax, then a further drop of 35% by the 3-month stage, followed by a gain of 39% on reaching adulthood. At premetamorphosis the ip-nerves already contain less than the normal number of axons, which is reduced a further 73% by 3 months; there is no subsequent increase in adulthood. The co-nerves lose no axons from premetamorphosis to climax; they therefore have 30% more axons than normals; this excess is kept until 7 months; from then to sexual maturity the increase is only 11%. CONCLUSIONS: (1) unilateral target removal affects also the nerve innervating the contralateral target: the increased loss of axons on the operated side is accompanied by reduced loss on the other; (2) the contralateral side displays for some time an excess of axons compared to normal, but this is finally cancelled out by the addition of many axons in the adult nor animals; (3) adjustment of axon number is not restrained to embryonic stages but continues at least until sexual maturation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Removal and reimplantation of the parietal cortex of the neonatal mouse: consequences for the barrelfield.

The barrelfield, i.e., the cortical representation of the contralateral whiskerpad, develops in the mouse between postnatal days 4 and 6 (P4 and P6). The pattern of barrels in the barrelfield is dependent on that of the whiskers on the whiskerpad. We removed (unilaterally) and reimplanted, with normal orientation (n = 23) or after 180 degrees rotation (n = 23), that part of the pallium where the barrelfield is to develop. These operations were made at birth (PO), at P1 or at P3. Our aim was to know whether a homeomorphic representation of the periphery would be established, by regeneration or by retarded growth of surviving thalamic fibers into the cortex, and if so, whether it could be modified in its orientation. Of group (i) 16 animals survived of which 14 killed between P26 and P29 could be analyzed. We operated 11 at PO and 4 of these had a normal barrelfield, two a rotated one (by about 30 degrees) with some barrels in odd positions, one a wildly disorganized one and 4 no barrels at all. Three mice operated at P3 presented a normal barrelfield. In group (ii) operated at PO, the 17 survivors, killed between P13 and P68, had no barrels. The results indicate that a homeomorphic representation of the periphery may be established in the somatosensory cortex after an early, complete and massive interruption not only of all its afferent and efferent fibers, but also of its vascularization. With respect to animals of group (ii) we cannot rule out the ingrowth of thalamic afferents into the implant.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1983

Detergent-soaked HRP-chips: a new method for precise and effective delivery of small quantities of the tracer to nervous tissue.

We dissolved horseradish peroxidase (HRP) in a 5% aqueous detergent solution (Nonidet P-40) and dried it to a solid mass which was then fragmented into small chips of convenient size. These were applied to the cut or crushed oculomotor nerves of Xenopus laevis tadpoles. This method combines the advantages of solid HRP (high concentration) and the presence of a detergent (enhanced uptake). Moreover, as compared to chips of HRP alone, addition of the detergent facilitated the manipulation of the chips.

Animals↗