ISSN:
1432-1351
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Biologie
,
Medizin
Notizen:
Summary 1. Five pairs of nonspiking giant interneurons (NGIs) were identified morphologically and functionally in the protocerebrum of the crayfish (Procambarus clarkii) brain: G1, G2, and G3 are contained in one cluster, G4 and G5 are separate. 2. None of the NGIs has a demonstrable axon, but all have thick and long dendritic processes. The dendritic processes extend across the midline of the brain and spread fine branches out over the ipsi- and contralateral halves of the protocerebrum (Figs. 2–6, 11). The dendritic processes of Gl, G2, and G3 are characteristically intertwined to form a cluster just above the protocerebral bridge (Figs. 4–6). 3. The primary neurite of each NGI links its dendritic process through the optic tract to its pear-shaped soma in the distal end of the optic tract (Figs. 2, 4). 4. Selectively stained branches of an NGI and a sustaining fiber (SF) appear to have contact points between them within and around the cluster of G1, G2, and G3 at the light microscope level (Fig-7). 5. Illumination of the contra- and ipsilateral eyes, respectively, elicits depolarizing and hyperpolarizing potentials without action potentials in each of G1, G2, and G3 (Fig. 8). The amplitude of these potentials depends on the intensity of illumination and on the area of the eye that is illuminated. Larger potentials are evoked when the posterior part of either eye is illuminated (Fig. 9). Depolarizing the NGIs (G1, G2, G3) results in an increase of the ipsilateral response and a decrease of the contralateral response. Hyperpolarizing the NGIs has the opposite effect (Fig. 8). 6. Depolarizing potentials in G1, G2, and G3 are preceded by action potentials in the contralateral SFs with receptive fields in the posterior part of the eye. Hyperpolarizing potentials in these cells are preceded by action potentials in homologous ipsilateral SFs (Fig. 10). 7. Illumination of the anterior part of either eye strongly depolarizes G4. Illumination of the posterior part of either eye slightly hyperpolarizes it. G5 is hyperpolarized on illumination of the posterior part of the ipsilateral eye (Fig. 11). Neither cell supports action potentials. 8. The structural and functional implications of the nonspiking giant interneurons are discussed, in relation to the motor neurons which mediate compensatory eye-stalk movements in response to visual and geotactic stimuli.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00610960
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