An investigation of dietary intake, nutrition knowledge and hydration status of Gaelic Football players.

PURPOSE: To assess the dietary intake, nutrition knowledge and hydration status of Irish Gaelic footballers. METHOD: One hundred and sixty-eight male club/county level Irish Gaelic footballers (median [IQR]; age 23 years [20.0, 27.0]; height 1.79 m [1.74, 1.84]; body mass 78.0 kg [73.5, 84.8]) participated in this cross-sectional study. Dietary intake was assessed using a 4-day semi-quantitative food record, with the application of Goldberg cut-offs to define acceptable reporters (n = 62). Nutrition knowledge was assessed using the validated Nutrition for Sport Knowledge Questionnaire in a sub-group of athletes (n = 24), while hydration status was measured using urine specific gravity pre-exercise (USG) in 142 athletes. RESULTS: Dietary analysis indicated an energy deficit at the group level (485 kcal [IQR 751,6]) (p < 0.001), with carbohydrate intakes (3.6 g/kg [IQR 3.0,4.1]) below current guidelines for athletes participating in one hour moderate intensity exercise per day (5-7 g/kg; p < 0.001). Average vitamin D (3.8 µg [IQR 1.8, 5.5]) and selenium intakes (54.2 µg [47.2, 76.7]) were significantly below the reference nutrient intakes (p < 0.001). A high proportion of individual athletes also had sub-optimal intakes for: vitamin D (95.2%), selenium (72.6%), vitamin A (38.7%), potassium (30.6%), zinc (25.8%), magnesium (19.4%) and calcium (12.9%). Nutrition knowledge was deemed poor (40.2 ± 12.4%), while pre-exercise hydration status (median USG 1.010 [IQR 1.005, 1.017]) was significantly below the cut-off to denote dehydration (1.020; p < 0.001). CONCLUSIONS: Our findings suggest that Irish Gaelic footballers have sub-optimal dietary practices and lack nutrition knowledge. Individualised nutrition support may benefit these athletes to meet their nutrition requirements, to support health and performance.

Central connections of the trigeminal motor command system in the weakly electric Elephantnose fish (Gnathonemus petersii).

The highly mobile chin appendage of Gnathonemus petersii, the Schnauzenorgan, is used to actively probe the environment and is known to be a fovea of the electrosensory system. It receives an important innervation from both the trigeminal sensory and motor systems. However, little is known about the premotor control pathways that coordinate the movements of the Schnauzenorgan, or about central pathways originating from the trigeminal motor nucleus. The present study focuses on the central connections of the trigeminal motor system to elucidate premotor centers controlling Schnauzenorgan movements, with particular interest in the possible connections between the electrosensory and trigeminal systems. Neurotracer injections into the trigeminal motor nucleus revealed bilateral, reciprocal connections between the two trigeminal motor nuclei and between the trigeminal sensory and motor nuclei by bilateral labeling of cells and terminals. Prominent afferent input to the trigeminal motor nucleus originates from the nucleus lateralis valvulae, the nucleus dorsalis mesencephali, the cerebellar corpus C1, the reticular formation, and the Raphe nuclei. Retrogradely labeled cells were also observed in the central pretectal nucleus, the dorsal anterior pretectal nucleus, the tectum, the ventroposterior nucleus of the torus semicircularis, the gustatory sensory and motor nuclei, and in the hypothalamus. Labeled terminals, but not cell bodies, were observed in the nucleus lateralis valvulae and the reticular formation. No direct connections were found between the electrosensory system and the V motor nucleus but the central connections identified would provide several multisynaptic pathways linking these two systems, including possible efference copy and corollary discharge mechanisms.

Development and validation of diagnostic triage criteria for liver disease from a minimum data set enabling the 'intelligent LFT' pathway for the automated assessment of deranged liver enzymes.

BACKGROUND: Liver function tests (LFTs) are commonly abnormal; most patients with 'incidental' abnormal LFTs are not investigated appropriately and for those who are, current care pathways are geared to find an explanation for the abnormality by a lengthy process of investigation and exclusion, with costs to the patient and to the health service. OBJECTIVE: To validate an intelligent automatable analysis tool (iLFT) for abnormal liver enzymes, which diagnoses common liver conditions, provides fibrosis stage and recommends management. DESIGN: A retrospective case note review from three tertiary referral liver centres, with application of the iLFT algorithm and comparison with the clinician's final opinion as gold standard. RESULTS: The iLFT algorithm in 91.3% of cases would have correctly recommended referral or management in primary care. In the majority of the rest of the cases, iLFT failed safe and recommended referral even when the final clinical diagnosis could have been managed in primary care. Diagnostic accuracy was achieved in 82.4% of cases, consistent with the fail-safe design of the algorithm. Two cases would have remained in primary care as per the algorithm outcome, however on clinical review had features of advanced fibrosis. CONCLUSION: iLFT analysis of abnormal liver enzymes offers a safe and robust method of risk stratifying patients to the most appropriate care pathway as well as providing reliable diagnostic information based on a single blood draw, without repeated contacts with health services. Offers the possibility of high quality investigation and diagnosis to all patients rather than a tiny minority.

Physiological evidence of sensory integration in the electrosensory lateral line lobe of Gnathonemus petersii.

Mormyrid fish rely on reafferent input for active electrolocation. Their electrosensory input consists of phase and amplitude information. These are encoded by differently tuned receptor cells within the Mormyromasts, A- and B-cells, respectively, which are distributed over the animal's body. These convey their information to two topographically ordered medullary zones in the electrosensory lateral line lobe (ELL). The so-called medial zone receives only amplitude information, while the dorsolateral zone receives amplitude and phase information. Using both sources of information, Mormyrid fish can disambiguate electrical impedances. Where and how this disambiguation takes place is presently unclear. We here investigate phase-sensitivity downstream from the electroreceptors. We provide first evidence of phase-sensitivity in the medial zone of ELL. In this zone I-cells consistently decreased their rate to positive phase-shifts (6 of 20 cells) and increased their rate to negative shifts (11/20), while E-cells of the medial zone (3/9) responded oppositely to I-cells. In the dorsolateral zone the responses of E- and I-cells were opposite to those found in the medial zone. Tracer injections revealed interzonal projections that interconnect the dorsolateral and medial zones in a somatotopic manner. In summary, we show that phase information is processed differently in the dorsolateral and the medial zones. This is the first evidence for a mechanism that enhances the contrast between two parallel sensory channels in Mormyrid fish. This could be beneficial for impedance discrimination that ultimately must rely on a subtractive merging of these two sensory streams.

Practical Use of Metal Oxide Semiconductor Gas Sensors for Measuring Nitrogen Dioxide and Ozone in Urban Environments.

The potential of inexpensive Metal Oxide Semiconductor (MOS) gas sensors to be used for urban air quality monitoring has been the topic of increasing interest in the last decade. This paper discusses some of the lessons of three years of experience working with such sensors on a novel instrument platform (Small Open General purpose Sensor (SOGS)) in the measurement of atmospheric nitrogen dioxide and ozone concentrations. Analytic methods for increasing long-term accuracy of measurements are discussed, which permit nitrogen dioxide measurements with 95% confidence intervals of 20.0 µ g m - 3 and ozone precision of 26.8 µ g m - 3 , for measurements over a period one month away from calibration, averaged over 18 months of such calibrations. Beyond four months from calibration, sensor drift becomes significant, and accuracy is significantly reduced. Successful calibration schemes are discussed with the use of controlled artificial atmospheres complementing deployment on a reference weather station exposed to the elements. Manufacturing variation in the attributes of individual sensors are examined, an experiment possible due to the instrument being equipped with pairs of sensors of the same kind. Good repeatability (better than 0.7 correlation) between individual sensor elements is shown. The results from sensors that used fans to push air past an internal sensor element are compared with mounting the sensors on the outside of the enclosure, the latter design increasing effective integration time to more than a day. Finally, possible paths forward are suggested for improving the reliability of this promising sensor technology for measuring pollution in an urban environment.

Post-hatching brain morphogenesis and cell proliferation in the pulse-type mormyrid Mormyrus rume proboscirostris.

The anatomical organization of African Mormyrids' brain is a clear example of departure from the average brain morphotype in teleosts, probably related to functional specialization associated to electrosensory processing and sensory-motor coordination. The brain of Mormyrids is characterized by a well-developed rhombencephalic electrosensory lobe interconnected with relatively large mesencephalic torus semicircularis and optic tectum, and a huge and complex cerebellum. This unique morphology might imply cell addition from extraventricular proliferation zones up to late developmental stages. Here we studied the ontogeny of these brain regions in Mormyrus rume proboscirostris from embryonic to adult stages by classical histological techniques and 3D reconstruction, and analyzed the spatial-temporal distribution of proliferating cells, using pulse type BrdU labeling. Brain morphogenesis and maturation progressed in rostral-caudal direction, from 4day old free embryos, through larvae, to juveniles whose brain almost attained adult morphological complexity. The change in the relative size of the telencephalon, and mesencephalic and rhombencephalic brain regions suggest a developmental shift in the relative importance of visual and electrosensory modalities. In free embryos, proliferating cells densely populated the lining of the ventricular system. During development, ventricular proliferating cells decreased in density and extension of distribution, constituting ventricular proliferation zones. The first recognizable one was found at the optic tectum of free embryos. Several extraventricular proliferation zones were found in the cerebellar divisions of larvae, persisting along life. Adult M. rume proboscirostris showed scarce ventricular but profuse cerebellar proliferation zones, particularly at the subpial layer of the valvula cerebelli, similar to lagomorphs. This might indicate that adult cerebellar proliferation is a conserved vertebrate feature.

Modeling latency code processing in the electric sense: from the biological template to its VLSI implementation.

Understanding the coding of sensory information under the temporal constraints of natural behavior is not yet well resolved. There is a growing consensus that spike timing or latency coding can maximally exploit the timing of neural events to make fast computing elements and that such mechanisms are essential to information processing functions in the brain. The electric sense of mormyrid fish provides a convenient biological model where this coding scheme can be studied. The sensory input is a physically ordered spatial pattern of current densities, which is coded in the precise timing of primary afferent spikes. The neural circuits of the processing pathway are well known and the system exhibits the best known illustration of corollary discharge, which provides the reference to decoding the sensory afferent latency pattern. A theoretical model has been constructed from available electrophysiological and neuroanatomical data to integrate the principal traits of the neural processing structure and to study sensory interaction with motor-command-driven corollary discharge signals. This has been used to explore neural coding strategies at successive stages in the network and to examine the simulated network capacity to reproduce output neuron responses. The model shows that the network has the ability to resolve primary afferent spike timing differences in the sub-millisecond range, and that this depends on the coincidence of sensory and corollary discharge-driven gating signals. In the integrative and output stages of the network, corollary discharge sets up a proactive background filter, providing temporally structured excitation and inhibition within the network whose balance is then modulated locally by sensory input. This complements the initial gating mechanism and contributes to amplification of the input pattern of latencies, conferring network hyperacuity. These mechanisms give the system a robust capacity to extract behaviorally meaningful features of the electric image with high sensitivity over a broad working range. Since the network largely depends on spike timing, we finally discuss its suitability for implementation in robotic applications based on neuromorphic hardware.

Impact of clinical pharmacists in the emergency department of an Australian public hospital: A before and after study.

OBJECTIVE: To evaluate the impact of an ED pharmacy service on ED clinical staff and hospital pharmacist activity. METHODS: A prospective study measuring pharmacist activities and surveying ED staff attitudes and experience before and after commencement of an ED pharmacy service. RESULTS: There were 2275 and 2072 hospital-wide pharmacist occasions of service recorded over a 1 month period before and after implementation of the ED pharmacy service, respectively; 339 (16.4%) of these occurred in the ED post-implementation. ED pharmacists most commonly were involved in obtaining medication histories (74% of ED occasions of service); 43% of all pharmacist-performed medication histories occurred in the ED. Post-implementation of the service, 26% of medication interventions occurred in the ED with the number of medication errors identified by ward pharmacists decreasing by 11%; 59% of ED pharmacist medication interventions were clinically significant. ED clinicians perceived the greatest impact of the service to be on patient education and medication safety. Qualitative feedback was overwhelmingly positive. CONCLUSIONS: Pharmacy staff can rapidly become a vital component of clinical service provision in the ED, contributing to medication safety from the point of patient entry into the hospital and impacting ED clinicians and whole of hospital activity for pharmacists.

New cellular mechanisms of gap junction degradation and recycling.

BACKGROUND INFORMATION: Connexins (Cxs), the constitutive proteins of gap junctions, are key actors of many physiological processes. Therefore, alterations of Cx expression and degradation lead to the development of physiopathological disorders. Because of the formation of a double membrane vesicle termed annular gap junction (AGJ), gap junction degradation is a unique physiological process for which many cellular aspects remain unclear. RESULTS: By using a combination of time-lapse fluorescence microscopy and high-resolution transmission electron microscopy, we evidenced new specific cellular events concerning gap junction degradation and recycling. Indeed, by time lapse video microscopy we demonstrated, for the first time to our knowledge, that an entire AGJ can be fully recycled back to the plasma membrane. Moreover, we dissected the degradative processes of gap junction by electron microscopy approaches. Interestingly, in addition to canonical autophagy and heterophagy pathways, previously described, we discovered that both pathways could sometimes intermingle. Strikingly, our results also highlighted a new lysosome-based autophagy pathway that could play a pivotal role in common autophagy degradation. CONCLUSIONS: The present investigation reveals that AGJ degradation is a more complex process that it was previously thought. First, a complete recycling of the gap junction plaque after its internalisation could occur. Second, the degradation of this peculiar double membrane structure is possible through autophagy, heterophagy, hetero-autophagy or by lysosomal-based autophagy. Altogether, this work underlines novel aspects of gap junction degradation that could be extended to other cell biology processes.

More a finger than a nose: the trigeminal motor and sensory innervation of the Schnauzenorgan in the elephant-nose fish Gnathonemus petersii.

The weakly electric fish Gnathonemus petersii uses its electric sense to actively probe the environment. Its highly mobile chin appendage, the Schnauzenorgan, is rich in electroreceptors. Physical measurements have demonstrated the importance of the position of the Schnauzenorgan in funneling the fish's self-generated electric field. The present study focuses on the trigeminal motor pathway that controls Schnauzenorgan movement and on its trigeminal sensory innervation and central representation. The nerves entering the Schnauzenorgan are very large and contain both motor and sensory trigeminal components as well as an electrosensory pathway. With the use of neurotracer techniques, labeled Schnauzenorgan motoneurons were found throughout the ventral main body of the trigeminal motor nucleus but not among the population of larger motoneurons in its rostrodorsal region. The Schnauzenorgan receives no motor or sensory innervation from the facial nerve. There are many anastomoses between the peripheral electrosensory and trigeminal nerves, but these senses remain separate in the sensory ganglia and in their first central relays. Schnauzenorgan trigeminal primary afferent projections extend throughout the descending trigeminal sensory nuclei, and a few fibers enter the facial lobe. Although no labeled neurons could be identified in the brain as the trigeminal mesencephalic root, some Schnauzenorgan trigeminal afferents terminated in the trigeminal motor nucleus, suggesting a monosynaptic, possibly proprioceptive, pathway. In this first step toward understanding multimodal central representation of the Schnauzenorgan, no direct interconnections were found between the trigeminal sensory and electromotor command system, or the electrosensory and trigeminal motor command. The pathways linking perception to action remain to be studied.

Receptive field properties of neurons in the electrosensory lateral line lobe of the weakly electric fish, Gnathonemus petersii.

The receptive field of a sensory neuron is known as that region in sensory space where a stimulus will alter the response of the neuron. We determined the spatial dimensions and the shape of receptive fields of electrosensitive neurons in the medial zone of the electrosensory lateral line lobe of the African weakly electric fish, Gnathonemus petersii, by using single cell recordings. The medial zone receives input from sensory cells which encode the stimulus amplitude. We analysed the receptive fields of 71 neurons. The size and shape of the receptive fields were determined as a function of spike rate and first spike latency and showed differences for the two analysis methods used. Spatial diameters ranged from 2 to 36 mm (spike rate) and from 2.45 to 14.12 mm (first spike latency). Some of the receptive fields were simple consisting only of one uniform centre, whereas most receptive fields showed a complex and antagonistic centre-surround organisation. Several units had a very complex structure with multiple centres and surrounding-areas. While receptive field size did not correlate with peripheral receptor location, the complexity of the receptive fields increased from rostral to caudal along the fish's body.

Functional foveae in an electrosensory system.

Several species of Mormyrid weakly electric fish have a mobile chin protuberance that serves as a mobile antenna during prey detection, tracking behaviors, and foraging for food. It has been proposed that it constitutes a fovea of the electrosensory system. The distribution of the three types of receptor organs involved in active imaging of the local surroundings, prey detection, and passive electroreception, and their central projection to the electrosensory lobe (ELL), have been studied in Gnathonemus petersii. Density distributions were compared for different body regions. Primary afferent projections were labeled with biocytin or biotinylated dextrans. This showed that there is considerable central "over-representation" of the mandibular and nasal regions of the sensory surface involved in electrolocation, at the expense of the other body regions investigated. This over-representation is not a mere effect of the very high density of receptor organs in these areas, but is found to be due to central magnification. This magnification differs between the subclasses of electroreceptors, suggesting a functional segregation in the brain. We conclude that the chin protuberance and the nasal region are the regions of greatest sensitivity for the resistive, capacitive, and low-frequency characteristics of the environment, and are probably most important in prey detection, whereas other regions of the skin with a lesser resolution and sensitivity to phase distortion of the EOD, in particular the trunk, are probably designed for imaging larger, inanimate features of the environment. Our data support the hypothesis that the chin appendage and nasal region are functionally distinct electrosensory foveae.

Electric imaging through active electrolocation: implication for the analysis of complex scenes.

The electric sense of mormyrids is often regarded as an adaptation to conditions unfavourable for vision and in these fish it has become the dominant sense for active orientation and communication tasks. With this sense, fish can detect and distinguish the electrical properties of the close environment, measure distance, perceive the 3-D shape of objects and discriminate objects according to distance or size and shape, irrespective of conductivity, thus showing a degree of abstraction regarding the interpretation of sensory stimuli. The physical properties of images projected on the sensory surface by the fish's own discharge reveal a "Mexican hat" opposing centre-surround profile. It is likely that computation of the image amplitude to slope ratio is used to measure distance, while peak width and slope give measures of shape and contrast. Modelling has been used to explore how the images of multiple objects superimpose in a complex manner. While electric images are by nature distributed, or 'blurred', behavioural strategies orienting sensory surfaces and the neural architecture of sensory processing networks both contribute to resolving potential ambiguities. Rostral amplification is produced by current funnelling in the head and chin appendage regions, where high density electroreceptor distributions constitute foveal regions. Central magnification of electroreceptive pathways from these regions particularly favours the detection of capacitive properties intrinsic to potential living prey. Swimming movements alter the amplitude and contrast of pre-receptor object-images but image modulation is normalised by central gain-control mechanisms that maintain excitatory and inhibitory balance, removing the contrast-ambiguity introduced by self-motion in much the same way that contrast gain-control is achieved in vision.

Active sensing in a mormyrid fish: electric images and peripheral modifications of the signal carrier give evidence of dual foveation.

Weakly electric fish generate electric fields with an electric organ and perceive them with cutaneous electroreceptors. During active electrolocation, nearby objects are detected by the distortions they cause in the electric field. The electrical properties of objects, their form and their distance, can be analysed and distinguished. Here we focus on Gnathonemus petersii (Günther 1862), an African fish of the family Mormyridae with a characteristic chin appendix, the Schnauzenorgan. Behavioural and anatomical results suggest that the mobile Schnauzenorgan and the nasal region serve special functions in electroreception, and can therefore be considered as electric foveae. We investigated passive pre-receptor mechanisms that shape and enhance the signal carrier. These mechanisms allow the fish to focus the electric field at the tip of its Schnauzenorgan where the density of electroreceptors is highest (tip-effect). Currents are funnelled by the open mouth (funnelling-effect), which leads to a homogenous voltage distribution in the nasal region. Field vectors at the trunk, the nasal region and the Schnauzenorgan are collimated but differ in the angle at which they are directed onto the sensory surface. To investigate the role of those pre-receptor effects on electrolocation, we recorded electric images of objects at the foveal regions. Furthermore, we used a behavioural response (novelty response) to assess the sensitivity of different skin areas to electrolocation stimuli and determined the receptor densities of these regions. Our results imply that both regions - the Schnauzenorgan and the nasal region - can be termed electric fovea but they serve separate functions during active electrolocation.

Etomidate reduces initiation of backpropagating dendritic action potentials: implications for sensory processing and synaptic plasticity during anesthesia.

Anesthetics may induce specific changes that alter the balance of activity within neural networks. Here we describe the effects of the GABA(A) receptor potentiating anesthetic etomidate on sensory processing, studied in a cerebellum-like structure, the electrosensory lateral line lobe (ELL) of mormyrid fish, in vitro. Previous studies have shown that the ELL integrates sensory input and removes predictable features by comparing reafferent sensory signals with a descending electromotor command-driven corollary signal that arrives in part through parallel fiber synapses with the apical dendrites of GABAergic interneurons. These synapses show spike timing-dependent depression when presynaptic activation is associated with postsynaptic backpropagating dendritic action potentials. Under etomidate, almost all neurons become tonically hyperpolarized. The threshold for action potential initiation increased for both synaptic activation and direct intracellular depolarization. Synaptically evoked inhibitory postsynaptic potentials (IPSPs) were also strongly potentiated and prolonged. Current source density analysis showed that backpropagation of action potentials through the apical dendritic arborization in the molecular layer was reduced but could be restored by increasing stimulus strength. These effects of etomidate were blocked by bicuculline or picrotoxin. It is concluded that etomidate affects both tonic and phasic inhibitory conductances at GABA(A) receptors and that increased shunting inhibition at the level of the proximal dendrites also contributes to increasing the threshold for action potential backpropagation. When stimulus strength is sufficient to evoke backpropagation, repetitive association of synaptic excitation with postsynaptic action potential initiation still results in synaptic depression, showing that etomidate does not interfere with the molecular mechanism underlying plastic modulation.

Sensory and motor effects of etomidate anesthesia.

The effects of anesthesia with etomidate on the cellular mechanisms of sensory processing and sensorimotor coordination have been studied in the active electric sense of the mormyrid fish Gnathonemus petersii. Like many anesthetics, etomidate is known to potentiate GABA(A) receptors, but little is known about the effects on sensory processing at the systems level. A better understanding is necessary for experimental studies of sensory processing, in particular regarding possible effects on the dynamic structure of excitatory and inhibitory receptive fields and to improve the knowledge of the mechanisms of anesthesia in general. Etomidate slowed the electromotor discharge rhythm, probably because of feedback inhibition at the premotor level, but did not alter the structure of the electromotor command. Sensory translation through primary afferents projecting to the cerebellum-like electrosensory lobe (ELL) was not changed. However, central interneurons and projection neurons were hyperpolarized under etomidate, and their spiking activity was reduced. Although the spatial extent and the center/surround organization of sensory receptive fields were not changed, initial excitatory responses were followed by prolonged inhibition. Corollary discharge input to ELL was maintained, and the temporal sequence of excitatory and inhibitory components of this descending signal remained intact. Later inhibitory corollary discharge responses were prolonged by several hundred milliseconds. The result was that excitatory reafferent sensory input was conserved with enhanced precision of timing, whereas background activity was greatly reduced. Anti-Hebbian synaptic plasticity evoked by association of sensory and corollary discharge input was still present under anesthesia, and differences compared with the nonanesthetized condition are discussed.

Dendritic spike back propagation in the electrosensory lobe of Gnathonemus petersii.

Spike timing-dependent plasticity that follows anti-Hebbian rules has been demonstrated at synapses between parallel fibers and inhibitory interneurons known as medium ganglionic layer (MG) neurons in the cerebellum-like electrosensory lobe of mormyrid fish. This plasticity is expressed when presynaptic activation is associated with a characteristically broad, postsynaptic action potential, lasting 7-15 ms, occurring within a window of up to 60-80 ms following synaptic activation. Since the site of plastic change is presumably in the apical dendrites, it is important to know where, when and how this broad spike is generated and the manner in which such events propagate within the intrinsic network of the electrosensory lobe. The electrosensory lobe has a strict layered organization that makes the preparation suitable for one dimension current source density analysis. Using this technique in an 'in vitro' interface slice preparation, we found that following either parallel fiber stimulation or an orthogonal field stimulus, a sink appeared in the ganglionic layer and propagated into the molecular layer. Intracellular records from MG somata showed these stimuli evoked broad action potentials whose timing corresponds to this sink. TTX application in the deep fiber layer blocked the synaptically evoked ganglionic layer field potential and the 'N3' wave of the outer molecular layer field potential simultaneously, while the molecular layer 'N1' and 'N2' waves corresponding to synaptic activation of the apical dendrites remained intact. These results confirm the hypothesis that the broad spikes of MG cells originate in the soma and propagate through the molecular layer in the apical dendritic tree, and suggest the possibility that this backpropagation may contribute to 'boosting' of the synaptic response in distal apical dendrites in certain circumstances.

Pre-receptor profile of sensory images and primary afferent neuronal representation in the mormyrid electrosensory system.

Afferent responses to the fish's own electric organ discharge were explored in the electrosensory lobe of the mormyrid fish Gnathonemus petersii. In order to understand the neural encoding of natural sensory images, responses were examined while objects of different conductivities were placed at different positions along the skin of the fish, i.e. at different points within, and also outside, peripheral receptive fields. The presence of an object in the fish's self-generated electric field produces local modulation of transcutaneous current density. Measurement of the local electric organ discharge shows that object images formed at the electroreceptive sensory surface have an opposing center-surround, 'Mexican hat' profile. This is a pre-receptor phenomenon intrinsic to the physical nature of the sensory stimulus that takes place prior to neural lateral inhibition and is independent of such central inhibition. Stimulus intensity is encoded in the latency and number of action potentials in the response of primary afferent fibers. It is also reflected in changes in the amplitude and area of extracellular field potentials recorded in the deep granular layer of the electrosensory lobe. Since the object image consists of a redistribution of current density over the receptive surface, its presence is coded by change in the activity of receptors over an area much larger than the skin surface facing the object. We conclude that each receptor encodes information coming from the whole scene in a manner that may seem ambiguous when seen from a single point and that, in order to extract specific object features, the brain must process the electric image represented over the whole sensory surface.

Dye coupling without gap junctions suggests excitatory connections of gamma-aminobutyric acidergic neurons.

After injections of the low-molecular-weight tracer neurobiotin into the preeminential nucleus of the brain of the mormyrid fish Gnathonemus petersii, we observed that retrogradely labeled, large fusiform projection neurons (LFd cells) of the deep granular layer of the electrosensory lobe (ELL) were surrounded by 30-50 labeled satellite granular cells. More superficially located projection cells, including large fusiform cells in the superficial granular layer (LFs) and large ganglionic (LG) cells in the ganglionic layer, were never surrounded by labeled satellites. LFd-satellite cells have a small soma (diameter 5-8 microm), a few small dendrites, and an apical axon that terminates in the plexiform and ganglionic layers of the ELL. They contact LFd projection neurons with dendrodendritic, dendrosomatic, and somatodendritic puncta adhaerentia-like appositions, designated here as "neurapses." In the electron microscope, these contacts resemble synapses without presynaptic vesicles. Because no gap junctions were found between LFd and satellite granule cells, we suggest that the neurapses allow the passage of neurobiotin, though not biocytin or biotinylated dextran amine. These contacts may provide the intermediate substrate for the postulated, but so far unknown, excitatory connection between primary afferent input and LFd projection neurons, via gamma-aminobutyric acid (GABA)-ergic granular cells. We suggest that certain puncta adhaerentia-like contacts might not be only adhesive structures and that LFd-satellite granular cells might both excite LFd projection cells via neuraptic contacts of their dendrites and cell bodies and inhibit more superficial LF and LG cells via their GABAergic axonal synapses. Our results suggest that puncta adhaerentia-like contacts could be responsible in some cases for the electrical coupling found electrophysiologically in local inhibitory circuits.