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.

---

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.

     

Isolation and reconstitution of furosemide-binding proteins from Ehrlich ascites tumor cells

Summary Furosemide-binding proteins were isolated from cholate-solubilized membranes of Ehrlich ascites tumor cells by affinity chromatography, using furosemide as ligand. Solubilized proteins retarded by the affinity material were eluted by furosemide. In reducing and denaturing gels, the major proteins eluted by furosemide were 100 and 45 kDa. In nonreducing, nondenaturing gels, homodimers of both polypeptides were found, whereas no oligomeric proteins containing both polypeptides were seen. It is concluded that the furosemide gel binds two distinct dimeric proteins. The isolated proteins were reconstituted into phospholipid vesicles and the K⁺ transport activity of these vesicles was assayed by measurement of⁸⁶Rb⁺ uptake against a large opposing K⁺ gradient. The reconstituted system was found to contain a K⁺ transporting protein, which is sensitive to Ba²⁺ like the K⁺ channel previously demonstrated to be activated in intact cells after cell swelling.     

Effects of oxymorphazone in frogs: long lasting antinociception in vivo, and apparently irreversible binding in vitro

Oxymorphazone (at doses of 50-200 mg/kg) was found to be a relatively weak antinociceptive drug in intact frog (Rana esculenta) when acetic acid was used as pain stimulus. Frogs remained analgesic for at least 48 hrs following oxymorphazone (200 mg/kg) administration. The ligand increased the latency of wiping reflex in spinal frogs too. These effects were blocked by naloxone. In equilibrium binding studies (3H)oxymorphazone had high affinity to the opioid receptors of frog brain and spinal cord as well (apparent Kd values were 8.9 and 10.6 nM, respectively). Kinetic experiments show that only 25% of the bound (3H)oxymorphazone is readily dissociable. Preincubation of the membranes with labeled oxymorphazone results in a washing resistant inhibition of the opioid binding sites. At least 70% of the (3H)oxymorphazone specific binding is apparently irreversible after reaction at 5 nM ligand concentration, and this can be enhanced by a higher concentration of tritiated ligand.     

Aldosterone regulates paracellular pathway resistance in rabbit distal colon

Summary Regulation of the paracellular pathway in rabbit distal colon by the hormone aldosterone was investigated in vitro in Ussing chambers by means of transepithelial and microelectrode techniques. To evaluate the cellular and paracellular resistances an equivalent circuit analysis was used. For the analysis the apical membrane resistance was altered using the antibiotic nystatin. Under control conditions two groups of epithelia were found, each clearly dependent on the light: dark regime. Low-transporting epithelia (LT) were observed in the morning and high-transporting epithelia (HT) in the afternoon. Na⁺ transport was about 3-fold higher in HT than in LT epithelia. Incubating epithelia of both groups with 0.1 mol·1^-1 aldosterone on the serosal side nearly doubled in LT epithelia the short circuit current and transepithelial voltage but the transepithelial resistance was not influenced. Maximal values were reached after 4–5 h of aldosterone treatment. In HT epithelia due to the effect of aldosterone all three transepithelial parameters remained constant over time. Evaluation of the paracellular resistance revealed a significant increase after aldosterone stimulation in both epithelial groups. This increase suggests that tight junctions might have been regulated by aldosterone. The hormonal effect on electrolyte transport was also dependent on the physiological state of the rabbit colon. Since net Na⁺ absorption in distal colon is, in addition to transcellular absorption capacity, also dependent on the permeability of the paracellular pathway, the regulation of tight junctions by aldosterone may be a potent mechanism for improving Na⁺ absorption during hormone-stimulated ion transport.Abbreviations V _t transepithelial potential difference (mV) - R _t transepithelial resistance (·cm²) - G _t transepithelial conductance (mS·cm^-2) - I_sc calculated short circuit current (A·cm^-2) - V _a apical membrane potential difference (mV) - V _bl basolateral membrane potential difference (mV) - voltage divider ratio - R _a apical membrane resistance (·cm²) - R _bl basolateral membrane resistance (·cm²) - R _c cellular resistance ( of apical and basolateral resistance) (·cm²) - R _p resistance of the paracellular pathway (·cm²) - G _a apical membrane conductance (mS·cm^-2) - G _bl basolateral membrane conductance (mS·cm^-2) - G _p paracellular conductance (mS·cm^-2) - G _t transepithelial conductance (mS·cm^-2) - HT _contr high transporting control epithelia - LT _contr low transporting control epithelia - HT _aldo aldosterone incubated high transporting epithelia - LT _aldo aldosterone incubated low transporting epithelia