Biomedical subjects

H. J. Luhmann

Publications and source records attributed to H. J. Luhmann.

3 recordsLinked to original sources

PubMed1990

Horizontal Interactions in Cat Striate Cortex: I. Anatomical Substrate and Postnatal Development.

The system of tangential connections was studied in area 17 of normally reared (NR), binocularly deprived (BD) and dark-reared (DR) kittens and adult cats. Connections were labelled antero- and retrogradely by intracortical micro-injections of several fluorescent markers and horseradish peroxidase conjugated with wheat-germ agglutinin (WGA-HRP). In 5-day-old kittens tangential connections consist of homogeneously distributed fibres extending maximally over 2.7 mm. Around postnatal day (pnd) ten these connections start to express the patchy pattern characteristic of the adult. Retrogradely stained somata and anterogradely labelled terminals become organized in individual 300 to 350 microm wide clusters with a centre-to-centre spacing of about 500 microm. During the first three postnatal weeks the horizontal connections increase their span to up to 10.5 mm and the spacing between individual patches increases to about 700 microm. Over the following 4 weeks these projections become reduced in length and number. In adult NR cats, tangential connections span a distance of up to 3 mm and form a lattice of 200 - 500 microm wide clusters, which have an average centre-to-centre spacing of 1050 microm. Tangential connections originate and terminate in all cortical laminae except layer I and they are organized in register. The distances spanned are largest in supragranular, intermediate in infragranular and shortest in granular layers. In BD and DR cats older than 10 weeks, the length of intracortical tangential fibres becomes reduced to the same extent as in NR animals, but individual clusters are less numerous. The authors conclude that the lattice-like structure of lateral connections evolves independently of visual experience, and that the selectivity of interactions results from pruning of initially exuberant connections. It is suggested that this pruning process is dependent on activity and influenced by visual experience.

Journal Article↗

PubMed1990

Horizontal Interactions in Cat Striate Cortex: II. A Current Source-Density Analysis.

The current source-density (CSD) analysis was used to investigate the organization of tangential synaptic connections in primary visual cortex of normally reared (NR) kittens and of NR, binocularly deprived (BD) and dark-reared (DR) adult cats. Laminar profiles of field potentials, elicited by intracortical microstimulation were measured at various distances from the stimulating electrodes. To exclude contamination by axon collaterals of antidromically stimulated thalamo-cortical fibres, these were destroyed by injecting the cytotoxin N-methyl-D-aspartate (NMDA) into the lateral geniculate nucleus 13 - 27 days before recording. The CSD profiles revealed distinct layer-specific patterns of lateral spread of activity. Invariably, the most prominent, long-lasting and far reaching responses were recorded in supragranular layers. Responses in layer IV were brief and confined to the vicinity of the stimulation site. Responses in infragranular layers spread as far as those in supragranular layers, but were of smaller amplitude. Latency considerations, the results of double shock stimulation, and the effects of translaminar cuts, suggest that these responses were monosynaptic and mediated by intracortical pathways with a conduction velocity of 0.3-5 m/s. The spatial spread of these responses changed substantially with age but was not influenced by visual deprivation. In NR adults, supra- and infragranular responses were recordable up to 2.5 mm from the stimulation site and layer IV responses up to 1 mm from the stimulation site. In kittens, the former responses spread up to 5 mm and the latter up to 2 mm from the site of stimulation. The amplitude of the responses decreased with distance from the stimulation site. This decrease was not always monotonic suggesting inhomogeneities in the tangential projections. The laminar distribution of current sinks and sources indicates that the pathways mediating tangential interactions form excitatory synapses on apical dendrites of pyramidal cells. It is concluded that the spatial spread of tangential excitatory interactions decreases with age, but that neither the laminar pattern nor the age-dependent reduction in the strength of tangential interactions are influenced by visual deprivation.

Journal Article↗

PubMed1990

Horizontal Interactions in Cat Striate Cortex: III. Ectopic Receptive Fields and Transient Exuberance of Tangential Interactions.

In this study the developmental changes of intracortical connectivity are related to changes of cortical receptor fields (RFs). The RFs of striate cortex neurons of 4- to 8.5-week-old kittens, reared under normal conditions (NR) or in a selective visual environment (SE), were analysed quantitatively and compared with adult cats. To unmask weak inputs from outside the conventional RF (CRF), cell excitability was raised by iontophoretic application of glutamate (GLU) and/or bicuculline methiodide (BIC) or by light stimulation of the CRF. Both the dominant discharge region (DDR) and the total RF (TRF) area were significantly larger in NR and SE kittens than in adult cats. Moreover, in kittens 18% of the cells had additional ectopic fields that were excitatory, had similar orientation preferences as the CRF, and ranged 4 degrees to 23 degrees from the centre of the CRF. In 74% of the cases the ectopic fields were direction-selective and 70% of them preferred stimuli moving toward the CRF. Ectopic fields occurred mainly in supragranular cells, were similarly frequent in simple and complex cells and slightly more frequent in SE (20.7%) than in NR (13.3%) kittens. In adult cats only one of 83 cells tested had an ectopic field. It is concluded that the age-dependent decrease in the RF size, the laminar distribution of cells having an ectopic RF, and the numerical reduction of these cells with age correlate well with the organization and postnatal pruning of tangential projections, suggesting that these contribute to the elaboration of specific response properties. Moreover, the authors infer from the early presence and from the selectivity of ectopic fields that the system of horizontal intrinsic connections mediates far-reaching, excitatory interactions between cortical neurons with similar functional properties and serves as a substrate for the processing of global aspects of visual patterns.

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