Simultaneous Recording of Input and Output of Lateral Geniculate Neurones

TO understand the way in which the cat dorsal lateral geniculate nucleus (LGN) processes visual information it would be useful to know the number and type of retinal inputs to individual LGN neurones. Using electrical stimulation of the optic nerve Bishop et al.¹concluded that an impulse in a single optic nerve fibre is sufficient to excite a single LGN neurone. From the appearance of excitatory postsynaptic potentials (EPSPs) recorded essentially intracellularly, Creutzfeldt suggested that LGN neurones are driven by perhaps one² or a few³ retinal ganglion cells. Hubel and Wiesel⁴ proposed models of convergence of several retinal inputs on single LGN neurones based on analyses of receptive fields. Guillery⁵ produced anatomical evidence that some types of LGN neurones receive inputs from several different retinal fibres. Now we report direct observations which were made by recording simultaneously from single LGN neurones and from individual retinal ganglion cells which provided excitatory input to them. We shall not consider inhibitory influences, which are currently under study.     

Wall extensibility and gravitropic curvature of sunflower hypocotyls: correlation between timing of curvature and changes in extensibility

Abstract. Gravitropic curvature results from unequal growth rates on the upper and lower sides of horizontal stems. These unequal growth rates cold be due to differences in wall extensibility between the two sides. To test this, the time course of curvature of horizontal sunflower ( Helianthus anmus L.) hypocotyls was determined and compared with the time courses of changes in Instron-measured wall extensibility (PEx) of the upper and lower epidermal layers. As gravicurvature developed, so did the difference in PEx between the upper and lower epidermis. The enhanced growth rate on the lower side during the period of maximum increase in curvature was matched by PEx values greater than those of the vertical control, while the inhibited growth rate on the upper side was accompanied by PEx values below that of the control. The close correlation between changes in growth rates and alterations in PEx demonstrates that changes in wall extensibility play a major role in controlling gravicurvature.     

EVIDENCE ON THE SITE OF ACTION OF GROWTH RETARDANTS

1. The ability of five growth retardants to inhibit the GA-inducedand endogenous growth of Avena leaf sections has been investigated.The retardants vary in effectiveness. The order, from most effectiveto least, is Phosfon D, Amo-1618, C011, CCC and B995. 2. The inhibition of growth caused by Phosfon D and Amo-1618is not reversed by GA. It is apparent that the retardants donot compete with GA at the site of GA-action. 3. Addition of IAA will partially reverse the inhibition inducedby Phosfon D or Amo-1618. It is concluded that the retardantsact in part in Avena leaf sections by interfering with the auxinmetabolism of the tisssue. ¹ Supported in part by grants G-14578 and GB-1950 from the NationalScience Foundation ² Present address: Department of Botany, University of Washington,Seattle, Washington     

The Effect of High Concentrations of Auxin on the Extension of Avena Coleoptile Sections

The response of Avena coleoptile sections to high concentrationsof auxin has been determined in the absence of all additivesexcept sucrose. In most experiments the growth-time curves with75 p.p.m. IAA showed two linear phases. In the first phase,which lasted for only 2–4 hours, extension was as rapidwith 75 p.p.m. IAA as with 5 p.p.m. IAA. This rapid initialexpansion phase was then succeeded by a second phase which persistedfor at least 20 hours. During this second linear phase the growth-ratewith 75 p.p.m. IAA was lower than with an auxin concentrationof 5 p.p.m. In some experiments the first phase was absent andonly the second phase was present. The response of sections to high concentrations of auxin wasnot influenced by the presence of buffers or absorbable cations.Omission of sucrose or the presence of moderate amounts of ethanolcaused the resulting growth curves to be non-linear. The rate of uptake of auxin into the tissues was dependent onthe auxin concentration and was constant for at least 24 hours.     

Is wall-bound calcium redistributed during the gravireaction of stems and coleoptiles?

We have tested the hypothesis that wall-bound calcium is redistributed from the lower to the upper sides of horizontal stems and coleoptiles during the reaction phase of gravicurvature. We used atomic absorption spectrometry to measure wall-bound calcium in the epidermal and internal layers of sunflower (Helianthus annum L.) hypocotyls and pea (Pisum sativum L.) epicotyls, and total calcium in maize (Zea mays L.) coleoptiles at the time of maximal gravireaction. In every case, we found that there was no measurable redistribution of wall-bound calcium either from the lower to the upper sides, or between epidermal and inner tissues in response to the gravistimulus. These results indicate that a redistribution of wall-bound calcium does not play a role during the gravireaction of stems and coleoptiles.