Sustained potential shifts and changes in acoustic evoked potentials after presentation of a non-acoustic priming stimulus to carp (Cyprinus carpio)

Potassium signalling in the brain: its role in behaviour

This paper examines evidence that glial cells respond to changes in extracellular potassium ([K+]e) in ways that contribute to modulation of neuronal activity and thereby behaviour. Glial cells spatially (and probably directionally) redistribute potassium from regions of increasing concentration to those with a lesser concentration. This redistribution is largely responsible for slow potential shifts associated with behavioural responses of animals. These slow shifts are related in amplitude to the level of 'arousal' of an animal, and its motivational state. In addition, glia, especially astrocytes, respond to changes in [K+]e, the presence of transmitters like nor-adrenaline and glutamate and at least some hormones with changes in their metabolism and/or the morphological characteristics of the cell. The ionic, metabolic and morphological responses of glia to changes in extracellular potassium after neuronal activity have been associated with at least some forms of learning, including habituation, one trial passive avoidance learning and changes associated with enriched environments. The implication of these effects of potassium signalling in the brain is that there is considerable involvement of glia in a number of processes crucial to neuronal activity. Glia may also form another route for information distribution in the brain that is at least bi-directional, though less specific than its neuronal counterparts. It is evident that the Neuroscience of the future will have to incorporate much more study of neuron-glial interactions than hitherto.

Comparative physiology of acoustic and allied central analyzers

To exploit comparisons among classes of vertebrates and invertebrates, and between higher and lower levels of the brain, and between modalities, some important needs and opportunities for new research into the way central processing of acoustic input takes place are pointed out. Most of these are suggested by unfamiliar results on fish and reptiles that call for new controls in mammalian experiments as well as more systematic study of nonmammalian taxa. Three frameworks or basic agendas are outlined; i) systematic comparison of dynamical properties to acoustic variables including especially repetition at different rates and the related states of expectation; ii) comparison of response measures, including especially sequences such as oscillations and measures of assembly cooperativity such as synchrony, coherence and bicoherence; and iii) comparison of auditory subsystems, including especially modal categories such as complex feature selective regions and small sets. Some recent and some new results are summarized on human acoustic and non-mammalian event related potentials (ERPs) in response to expectations. When a regular and frequent standard stimulus is omitted, the omitted stimulus potential (OSP) after conditioning with low repetition rates (long ISIs--1-3 s) is a slow, broad positivity P600-900), previously known. With high rates (ISI < 1 s), a new form of response appears, with fast components (P22), different dynamics and less dependence on attention. Slow and fast OSPs each show a constant peak latency after the due-time of the missing stimulus, as though a temporal expectation has been learned. Unlike the visual OSP we have reported earlier, both fast and slow can occur together in the 1-2 Hz range. Very few conditioning stimuli suffice to create the "expectation" that causes an OSP--only two for the slow type. These and more familiar ERPs, considered in human subjects to index cognitive events, need to be compared in other classes of vertebrates and invertebrates.

Physiological stress responses of Anguilla anguilla to fenitrothion

The present communication deals with the effect of fenitrothion (0.04 ppm) on the carbohydrate metabolism of the european eel Anguilla anguilla and its recovery from intoxication. Analysis of various parameters such as glycogen, lactate and glucose was made on different eel tissues after 2, 8, 12, 24, 32, 48, 56, 72 and 96 hr of fenitrothion exposure. Subsequently, the fish were allowed recovery periods of 8, 12, 24, 48, 72, 96, 144 and 192 hr in clean water, and the same parameters were evaluated. Muscle glycogen content decreased significantly during the exposure time, while blood glucose levels increased markedly. Gill, muscle and blood lactate values increased during pesticide exposure. Most of the metabolic disorders did not persist after allowing recovery in clean water during less than a week. The observed effects of fenitrothion on fish metabolism are discussed in relation to a stress syndrome and probable reasons for alterations have been exposed.

Sustained potential shift responses and their relationship to the ecg response during arousal in the goldfish (Carassius auratus)

1. Goldfish, when presented with a 10 sec light-on stimulus against a background of 2 hr of sensory restriction, exhibited sustained potential shift (SPS) activity, of differing polarity, at each of four surface recording sites, on the medulla, cerebellum, optic tectum and telencephalon. 2. Principle components analysis (PCA) indicated that SPS responses from each region comprised superimposed early and late waveforms. At the cerebellar, tectal and telencephalic surfaces, neuronal activity appeared to contribute strongly to the early (less than 2 sec) SPS waveform. 3. While, in response to repeated stimulus presentations, habituation was apparent in the early SPS waveforms recorded from the medulla, cerebellum and telencephalon, an increase in negativity occurred in late SPS waveforms throughout the brain. 4. The tectal SPS response was directly proportional to the telencephalic SPS response both in terms of average SPS amplitudes following the first presentation of the light-on stimulus and in terms of their increasing negativity in response to stimulus repetition. 5. The increasing negativity of the telencephalic SPS was also associated with the habituation of the ECG response over repeated trials. 6. Results are discussed with regard to a possible neuromodulatory role for glia.