The Royal Society

Computer-controlled operant-conditioning training procedures were used to raise (up-learning) or lower (down-learning) the mean frequency of discharge of the anterior adductor coxa motoneurone of the locust Schistocerca gregaria . Intracellular recordings were made from the soma of the motoneurone during training. The neurone appeared capable of spontaneous discharge in the absence of synaptic input since its mean pacemaker rate was measured after blocking synaptic inputs by infusing high Mg ²⁺ /zero Ca ²⁺ saline into the neuropile associated with the neurone. Rates were determined before and after the training procedure was applied. It was found that a stable increase in the mean frequency of the pacemaker occurred during up-learning and a decrease during down-learning. The pacemaker shift accounted for a little over half the overall learning change. The remainder was attributed to changes in the activities of interneurones that directly, or indirectly, affect the motoneurone pacemaker. Conventional synaptic potentials that could have accounted for the remainder were not conspicuous in the soma recordings.

In Windermere charr, Salvelinus willughbii, are either (1) autumn spawners, main breeding period November, most spawning on the lake shore, in shallow water, some in the main inflowing stream; or (2) spring spawners, main breeding period February-March, spawning in the lake only and in deep water. The comparison of these two is mainly based on the autumn spawners netted on the lake spawning grounds at Low Wray Bay and Bed Nab, and on a river spawning ground in Brathay, at Purdom’s Dub, and on the spring spawners netted on the spawning ground at Holbeck Point. Information on their breeding habits was obtained by rearing fish in hatchery ponds and on their spawning behaviour by observation in the field and in aquaria. This paper, which deals with the breeding habits of the two types of spawners and the implications arising from them, is divided into two parts, with the Discussion in between. Part I describes the breeding habits of the autumn and spring spawners and shows how these separate the two types from each other. It is concerned with the question of whether these autumn and spring spawners so isolated represent distinct populations. (There is a note on the charr from other English Lake District waters.) The Discussion comes at the end of Part I. Part II gives further details of breeding habits of autumn and spring spawners and describes early stages in the life history of the charr. Aspects of the reproductive life of autumn and spring spawners are compared between themselves and also with other Salmonidae. Some of the information given expands that mentioned in Part I. Part I The difference in spawning times of autumn and spring spawners cannot be explained by reference to the light penetration and temperature conditions during the spawning periods, but day-length may be a factor associated with spawning time. Although the spawning places of autumn and spring spawners differ markedly in depth, both are characterized by a stony substratum, an essential feature of the breeding site. Autumn and spring spawners tagged on their breeding grounds were all recovered in subsequent seasons on their previous breeding grounds. Furthermore among autumn spawners the consistent return to a particular spawning place (tested by displacement experiments) further emphasizes the constancy of the spawning habits of individual Windermere charr. Thus Windermere charr ‘home' in the sense of repeatedly returning to the same place to spawn and to this extent autumn and spring spawners keep separate. There is some indirect evidence, from experimental planting of eggs and fry, that spawners home in the sense of returning to spawn in their natal stream. Of characteristics in which autumn and spring spawners differ two are of particular significance: the pattern of early scale growth and the mean number of gill rakers. The difference in the pattern of scale growth and in the number of gill rakers may be associated with environmental conditions but they are good evidence that autumn spawners breed autumn spawners and spring spawners breed spring spawners. Thus it is highly probable that there are two distinct self-perpetuating populations of charr in Windermere: the distinction may be imposed on each generation or be genetical. Evidence from rearing experiments in hatchery ponds shows that the time of spawning is not genetically fixed and there is no barrier to cross-fertilization. Experiments on homing (return of the adult to spawn in the natal stream) suggest that the difference in spawning sites of autumn and spring spawners is not genetic but that without genetical aid the two spawning populations can be kept separate. The difference in depth of autumn and spring-spawning sites is explained by the selective effect of temperature on the developing eggs. Although the possibility of some genetical difference cannot be ruled out, the evidence so far suggests that imposition and imprinting are sufficient to explain the division of Winder-mere charr into autumn and spring breeding populations. The Discussion considers other examples of situations comparable to that in Windermere in Europe and in the British Isles in view of which the taxonomic status of the Windermere charr is discussed. Theories are suggested of the possible origin of the autumn and spring-populations. It is noted that in none of the other Lake District waters have two populations been found. Part II Comparative information is given on frequency of return of spawners to the breeding ground, time spent there, proportions of the sexes, estimated number of spawners and estimated survival rates. The spawning behaviour (based on observations in field and aquaria) is briefly described. Comparison of the female’s weaving (undulating) and cutting actions with similar activities in the genus Salmo leads to the suggestion that in Salvelinus weaving is replacing the cutting-to-cover activity of Salmo and that cutting of any kind is becoming vestigial in Salvelinus . On the evidence from rearing and field observation, the eggs of autumn spawners hatch about the first week in March and those of spring spawners about the first week in May. Therefore the former have 2 months longer growing time which may account for their being larger than the spring-spawned fish at the end of their first year of life. It also seems likely that there is an association between the hatching of eggs in May and the habit of spawning-in deep water. Observations on alevins and fry indicate that the latter are not territorial. Predation, which is on both adult charr and their eggs, is much greater on the autumn than on the spring spawners.

In Rhodnius most of the haemoglobin ingested is broken down in the lumen of the gut to protohaematin which is excreted unchanged. But a small amount is absorbed and circulates in the haemolymph as kathaemoglobin (parahaematin). This is taken up by the salivary glands where it appears as a cherry-red pigment with properties similar to haemalbumin. Blood pigment is also transferred to the yolk of the eggs and becomes concentrated in the stomach of the newly hatched nymph as a bright red fluid (parahaematin). In the next few days most of this is digested in the gut to give protohaematin; some is transferred to the salivary glands to give rise to their usual pigment.

By using the patch–clamp technique the effect of 2-decenoic acid (DA) on Ca ²⁺ -activated potassium (K ⁺ ) channels in the membrane of smooth muscle cells from the human aorta was studied. In the presence of 0.5 μM Ca ²⁺ and 2 mM Mg ²⁺ on the cytoplasmic side of the membrane, a more than tenfold elevation in the probability of the channels being open ( p _o ) was observed under the effect of DA. With divalent cation concentrations of less than 1 nM DA caused a more than twofold elevation in p _o . In the DA-treated membranes Mg ²⁺ ions, which normally fail to activate the channels, brought about a nearly threefold increase in the channel activity when applied to the inner membrane surface. Channel sensitivity to the activating effect of cytoplasmic Ca ²⁺ ions did not increase with the application of DA. Single-channel conductance was unchanged by DA exposure. We suggest that DA alters the Ca ²⁺ -binding mechanism of the channel, increasing its sensitivity to Mg ²⁺ ions, presumably owing to membrane fluidization.

The new antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), which blocks responses to kainate and quisqualate, has been used in conjunction with D-2-amino-5-phosphonovalerate (APV), which blocks selectively responses to N -methyl-D-aspartate (NMDA), to determine the role of excitatory amino acid receptors in synaptic transmission. An excitatory postsynaptic potential (EPSP) – inhibitory postsynaptic potential (IPSP) sequence was evoked in CA1 neurons by stimulation of the Schaffer collateral–commissural pathway in rat hippocampal slices. CNQX (10 μm) substantially reduced the EPSP without having any effect on input resistance or membrane potential. The IPSP was also reduced provided that the stimulating electrode was place approximately 1 mm from the recording electrode. The EPSP that remained in the presence of CNQX had characteristics of an NMDA receptor-mediated potential; it had a slow timecourse, summated at high frequencies, was blocked reversibly by APV, increased greatly in size in Mg ²⁺ -free medium. and showed an anomalous voltage dependence in Mg ²⁺ -containing medium. In the presence of CNQX, an APV-sensitive polysynaptic GABAergic IPSP could be evoked, indicating that NMDA receptors can mediate suprathreshold EPSPS in inhibitory interneurons. It is suggested that either NMDA or non-NMDA receptors can, under different circumstances, mediate the synaptic excitation of pyramidal neurons and inhibitory interneurons in area CA1 of the hippocampus.

By means of electron microscopy applied to wild material prepared as dry whole mounts, descriptions are given of external morphology, including lorica construction, of four new species of collared flagellates, namely: Pleurasiga caudata, Salpingoeca longicaudata, Parvicorbicula serrulata and Diaphanoeca aperta . Reasons are given for the choice of generic names although future changes in some generic boundaries are expected. Aspects of the ecology and geographical distributions are discussed in a preliminary way.

On the basis of wild material processed into dry who mounts immediately following collection in two arctic localities (Hudson Bay and under sea ice in North Alaska), new insight has been obtained into lorica structure and development in Diaphanoeca grandis (Choanoflagellata) by means of scanning electron microscopy supplementing transmission electron microscopy and light microscopy. The more important new findings include demonstration of tectiform replication and of the two-layered nature of the lorica wall, the outer layer being limited throughout to longitudinal costae only. Details of transverse costae and of the fibrillar or membranous components involved in suspension of the protoplast are also described and illustrated. Outstanding problems, notably those involved in nutrient uptake, are discussed and the nature of the observations most needed to resolve them indicated. A revised description of the species replaces a summary.

The chemical evidence for the enzymic activity of lysozyme will be discussed in detail by other speakers at this meeting, but in order to describe our crystallographic studies of the interactions between the enzyme and its substrates it is necessary to summarize briefly what was known about them at the beginning of our work. Simultaneously with his discovery of lysozyme Fleming (1922) discovered a Gram-positive species of bacteria, Micrococcus lysodeikticus , which is particularly susceptible to the action of the enzyme. It was not until much later, however, that Salton (1952) demonstrated that the substrate is located entirely within the bacterial cell wall and it is only very recently that its chemical constitution has been established. Valuable early experiments (for example, by Meyer, Palmer, Thomson & Khorazo 1936; Meyer, Hahnel & Steinberg 1946; and by Epstein & Chain 1940) showed that lysozyme releases N -acetyl-amino sugars from M. lysodeikticus , but the first indication of the type of linkage attacked by lysozyme came when Berger & Weiser (1957) showed that lysozyme also degrades chitin, the linear polymer of N -acetylghicosamine.

It was previously shown that the addition of cytochrome c to a heart-muscle preparation greatly increases its power of catalysing the oxidation of such substances as p -phenylene diamine, hydroquinone, cysteine and ascorbic acid. It was demonstrated that the oxidations of these substances, which can be used for the detection and estimation of intracellular oxidase, are catalysed not directly by the oxidase but through the co-operation of cytochrome. The only direct function of the oxidase, so far ascertained, is the oxidation of reduced cytochrome, and the enzyme can therefore be considered as cytochrome oxidase (Keilin and Hartree 1938 a ). Several properties which have been previously ascribed to it do not complete cytochrome-oxidase system. The object of this paper is the study of the mechanism of oxidation and reduction of cytochrome in order to determine the properties and the nature of cytochrome oxidase.

Retinoic acid (vitamin A acid), the carboxylic acid corresponding to the primary alcohol retinol (vitamin A), has previously been thought to fulfil all the functions of vitamin A except in vision, since rats fed a diet deficient in retinol but supplemented with retinoic acid grow well, outwardly appearing healthy, yet become blind. This paper reports that female rats on such a diet had normal oestrous cycles and became pregnant when mated, but always resorbed the foetuses and no litters were born. The first abnormalities detected were necrosis and slight polymorph infiltration around the periphery of the placental disk about the sixteenth day of pregnancy. Supplementation with retinol as late as the tenth day resulted in the birth of a healthy litter. Retinoic acid therefore maintained the early but not the later stages of gestation. When very small amounts of retinol were given during pregnancy, dead or weak young were born; on higher supplements of the vitamin, litters were weaned successfully. By this means young rats were produced with negligible stores of retinol. Male rats fed retinoic acid but not retinol had small and often oedematous testes. The germinal epithelium sloughed off and in some tubules the lumen was obliterated, but in others the lumen remained, and in these some spermatocytes and spermatogonia were held tenaciously. The seminal vesicles were smaller than in controls given retinol. In rats born with negligible stores of retinol—see above—and maintained on retinoic acid, the testes remained infantile; spermatids were never formed. Feeding retinol restored spermatogenesis in degenerate testes and promoted the normal development of testes that had remained infantile; it also ensured the growth of the seminal vesicles. Retinoic acid did not therefore serve in reproduction, although it replaced the true vitamin in maintaining life, growth and general health. Besides the latter so-called systemic function, vitamin A must have a discrete and specific role in reproduction, viz. that performed by retinol but not by retinoic acid. From among the many previously reported features of disordered reproduction in vitamin A-deficient animals, it was possible to distinguish which had arisen from a failure of this specifically ‘reproductive’ role and which from a ‘systemic’ deficiency. The inactivity of retinoic acid in reproduction demonstrates that in rats vitamin A has not two, as previously thought, but three dissociable modes of action: (1) systemic; (2) in vision; and (3) in reproduction.