Retinotopische Beziehungen und Struktur rezeptiver Felder im Tectum opticum und Praetectum der Katze

Zusammenfassung 1.Von 600 Neuronen des Colliculus superior und Praetectums der Katze wurde mit Stahlmikroelektroden abgeleitet und der Ableitort markiert. Die Lage der rezeptiven Felder wurde mit bewegten und stationären Lichtreizen bestimmt und dem Ableitort zugeordnet.2.Im Colliculus superior und Praetectum fanden sich richtungsspezifische und richtungsunspezifische Bewegungsneurone. Ein Teil der praetectalen Neurone reagierte richtungsspezifisch auf Bewegungen vom Tier weg und auf das Tier zu (S-Neurone).3.Innerhalb einer senkrecht zur Oberfläche des Colliculus verlaufenden Penetrationssäule nahm die Feldgröße bei gleichbleibender Feldposition mit zunehmender Tiefe zu. Zwischen Ableitort und Feldposition bestand eine systematische retinotopische Beziehung. Die Projektion des vertikalen O-Meridians des Gesichtsfeldes verlief im rostralen Drittel des Colliculus von medial nach lateral, die des horizontalen O-Meridians in der Mitte des Colliculus von rostral nach caudal. Das Projektionsschema eines Colliculus enthält einen nasalen Teil der ipsilateralen Gesichtsfeldhälfte.4.Im Praetectum verlief die Projektion vertikaler Meridiane am caudalen Ende von medial nach lateral und überlappte sich teilweise mit dem Projektionsgebiet des vertikalen O-Meridians im Colliculus. Die horizontalen Meridiane verliefen so von caudal nach rostral, daß das Projektionsschema des Praetectums spiegelbildlich zu dem des Colliculus superior angeordnet war. Dieses Projektionsschema galt nur für den Nucleus tractus optici und die Area praetectalis. Die übrigen praetectalen Kerne mit zum Teil sehr großen rezeptiven Feldern und spezifischen Reaktionsweisen erhielten keine retinotopische Projektion.5.Rezeptive Felder der oberflächennahen Schichten waren uniform on-, off-oder on-off strukturiert, Felder tiefergelegener Einheiten waren ungeordnet aus on-, off- und on-off Bezirken zusammengesetzt. Binocular erregbare Neurone zeigten für beide Augen gleiche Position und Struktur der rezeptiven Felder.6.Die Ergebnisse wurden mit den an anderen Tierarten erhobenen Befunden verglichen. Ihre mögliche funktionelle Bedeutung wurde diskutiert.

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Retinotopic relationship and structure of receptive fields in the optic tectum and pretectum of the cat

Summary 1.600 neurons of the cat's superior colliculus and pretectum were recorded and marked with stainless-steel microelectrodes. The position and structure of receptive fields were tested with stationary flickering and moving stimuli. The position of the stimuli in the visual field was determined by the direction of the lamp projecting the light-points because animal and lamp were arranged in a fixed relationship to the screen. The positions of the stimuli were described in a coordinate system based on the horizontal-and vertical zeromeridean of the retina.2.About 55% of tectal neurons are directionally selective and signal mainly movements directed to the periphery of the visual field. Neurons of the pretectum have the same response characteristics as neurons of the superior colliculus but in addition some are selectively responsive to movements towards the animal or away from it (S-neurons).3.Neurons in one functional column (diameter 0.5 mm, length 3.6 mm) perpendicular to the surface of the superior colliculus react to the same position and preferred direction of a moving stimulus. The size, complexity and directional selectivity of the receptive fields increase with the depth of the recorded neurons. The projection of the vertical zero-meridean passes across the rostral part of the colliculus but does not form the rostral border of the superior colliculus. The nasal part of the ipsilateral visual field projects to the most rostral part of the superior colliculus. The projection of the horizontal zeromeridean passes rostro-caudally in a nearly sagittal plane down the middle of the colliculus. Along this projection-line the resolving power is 13°/column in the caudal part and 6°/column in the rostral part of the superior colliculus. The size of the receptive fields increase with their excentricity in the visual field. (Average of field diameters: 26±13°).4.The diameter of receptive fields in the pretectum was 21±11°, except for a few very large fields (70° and larger). Along the medio-lateral axis of the pretectum there was a retinotopic organization identical to that in the colliculus. Along the caudo-rostral axis, the retinotopic organization was the mirror image of that in the colliculus. No retinotopic organization was observed in the so-called deep pretectal nucleus or in the nucleus of the posterior commissure. Neurons of these nuclei may represent more complex levels in the visual pathway.5.The more superficial neurons of the colliculus (0.1–1.8 mm deep) react mainly with uniform on-, off- or on-off responses to stationary flickered stimuli, i.e. their receptive fields (7–20° in diameter) are uniformly on-, off- or on-off. The deeper neurons (2 mm and deeper) have receptive fields (20–40° in diameter) with compound but not antagonistic structure. No receptive fields showed on- or off-inhibition. Binocularly driven neurons have the same position and structure of their receptive fields for both eyes.6.A survey of the literature reveals that all vertebrates so far investigated show small differences in the destination and retinotopic organization of their retinofugal fibre projections and in the types of tectal receptive fields. These differences seem to indicate an adaption to the development of binocular representation of the center of the visual field, of a specialized area of the retina and of a retino-cortical system.

     

Comparative cytological study of Phasianus colchicus,Meleagris gallopavo,and Gallus domesticus

Summary Since viable intergeneric hybrids between the chicken (Gallus domesticus) and the pheasant (Phasianus colchicus) have been reported, as well as interfamilial hybrids between the chicken and the turkey (Meleagris gallopavo), the chromosome complements of the pheasant and the turkey were compared with that of the chicken. In these three species belonging to the order Galli, the Z-chromosomes appeared to be identical, while the autosomal complements of the pheasant and the turkey differed radically from that of the chicken. It was noted with some surprise that the pheasant of the family Phasianidae and the turkey of the family Meleagridae have very similar chromosome complements, at least so far as gross morphology of somatic metaphase chromosomes is concerned.This work was supported in part by grant C-5138 from the National Cancer Institute, U.S. Public Health Service, and grant C-17601 from the National Science Foundation.The authors gratefully acknowledge the generosity of Rea's Game Birds, Paramount, California, who supplied the pheasant chicks, and the McPherin Hatcheries, Sunnymead, California, who furnished the turkey chicks. The authors also appreciate the editorial assistance of'Patricia A. Ray.     

Purinergic Modulation of Hippocampal Acetylcholine Release Involves α-Dendrotoxin-Sensitive Potassium Channels

Modulation of acetylcholine (ACh) release from superfused hippocampal slices was examined when the release of ACh was stimulated by exposure of slices to elevated K+ concentration. Evoked release was not sensitive to inhibition by 0.1 microM tetrodotoxin, but it could be inhibited in a dose-dependent manner by a muscarinic agonist (10-100 nM oxotremorine) and a purinergic agonist (10-100 nM 2-chloroadenosine). The alpha-dendrotoxin (100 nM), which selectively blocks voltage-gated inactivating K+ channels in nerve endings, did not affect the release of ACh under resting or depolarized conditions. However, alpha-dendrotoxin reduced the 2-chloroadenosine-induced inhibition of release, but did not alter the oxotremorine-induced inhibition. These results suggest that an alpha-dendrotoxin-sensitive K+ channel may be activated as an obligatory step in the modulation of ACh release by presynaptic purinergic receptor activation, but not in the modulation by presynaptic muscarinic receptors.