Neurophysiological properties of magnetic cells in the pigeon's visual system

Summary Single unit electrical activity was recorded extracellularly in the nucleus of the basal optic root (nBOR) and in the optic tectum under earth-strength magnetic stimulation. Units in the nBOR which were stimulated while the eyes were illuminated by light of different wavelengths exhibited peaks of magnetic responsiveness at 503 nm and 582 nm.Magnetically directional selective cells were found in the stratum griseum et fibrosum superficiale of the optic tectum. They also showed directional selectivity to dynamic photic stimuli. Response peaks varied with the orientation of the pigeon in the horizontal plane. This confirmed that the magnetic responses contained directional information. The results suggest that the receptor and neural organisation of the pigeon's visual system provides an adequate substrate for the detection and elaboration of magnetic compass information.     

The role of γ-aminobutyric acid and its receptors in the nucleus of basal optic root in pigeons

The effects of γ-aminobutyric acid (GABA) and its antagonists bicuculline and 2-hydroxysaclofen on neuronal firings in the nucleus of basal optic root (nBOR) in pigeons were studied by using extracellular recording and microiontophoretic techniques. The results suggest that GABA may be an inhibitory neurotransmitter or modulator within nBOR, functioning by means of main mediation of GABA_A receptors and of minor mediation of GABA_B receptors. Furthermore, GABA and its GABA_A receptors are involved in the modulation of directional selectivity in part of nBOR neurons. Project supported by the National Natural Science Foundation of China and Amherst College.     

Responses of optokinetic neurons in the pretectum and accessory optic system of the pigeon to large-field plaids

The accessory optic system and pretectum are highly conserved brainstem visual pathways that process the visual consequences of self-motion (i.e. optic flow) and generate the optokinetic response. Neurons in these nuclei have very large receptive fields in the contalateral eye, and exhibit direction-selectivity to large-field moving stimuli. Previous research on visual motion pathways in the geniculostriate system has employed "plaids" composed of two non-parallel sine-wave gratings to investigate the visual system's ability to detect the global direction of pattern motion as opposed to the direction of motion of the components within the plaids. In this study, using standard extracellular techniques, we recorded the responses of 47 neurons in the nucleus of the basal optic root of the accessory optic system and 49 cells in the pretectal nucleus lentiformis mesencephali of pigeons to large-field gratings and plaids. We found that most neurons were classified as pattern-selective (41-49%) whereas fewer were classified as component-selective (8-17%). There were no striking differences between nucleus of the basal optic root and lentiformis mesencephali neurons in this regard. These data indicate that most of the input to the optokinetic system is orientation-insensitive but a small proportion is orientation-selective. The implications for the connectivity of the motion processing system are discussed.     

Electroretinographic study of the magnetic compass in European robins

Migratory birds are known to be sensitive to external magnetic field (MF). Much indirect evidence suggests that the avian magnetic compass is localized in the retina. Previously, we showed that changes in the MF direction could modulate retinal responses in pigeons. In the present study, we performed similar experiments using the traditional model animal to study the magnetic compass, European robins. The photoresponses of isolated retina were recorded using ex vivo electroretinography (ERG). Blue- and red-light stimuli were applied under an MF with the natural intensity and two MF directions, when the angle between the plane of the retina and the field lines was 0° and 90°, respectively. The results were separately analysed for four quadrants of the retina. A comparison of the amplitudes of the a- and b-waves of the ERG responses to blue stimuli under the two MF directions revealed a small but significant difference in a- but not b-waves, and in only one (nasal) quadrant of the retina. The amplitudes of both the a- and b-waves of the ERG responses to red stimuli did not show significant effects of the MF direction. Thus, changes in the external MF modulate the European robin retinal responses to blue flashes, but not to red flashes. This result is in a good agreement with behavioural data showing the successful orientation of birds in an MF under blue, but not under red illumination.     

Facial-expression and gaze-selective responses in the monkey amygdala

The social behavior of both human and nonhuman primates relies on specializations for the recognition of individuals, their facial expressions, and their direction of gaze. A broad network of cortical and subcortical structures has been implicated in face processing, yet it is unclear whether co-occurring dimensions of face stimuli, such as expression and direction of gaze, are processed jointly or independently by anatomically and functionally segregated neural structures. Awake macaques were presented with a set of monkey faces displaying aggressive, neutral, and appeasing expressions with head and eyes either averted or directed. BOLD responses to these faces as compared to Fourier-phase-scrambled images revealed widespread activation of the superior temporal sulcus and inferotemporal cortex and included activity in the amygdala. The different dimensions of the face stimuli elicited distinct activation patterns among the amygdaloid nuclei. The basolateral amygdala, including the lateral, basal, and accessory basal nuclei, produced a stronger response for threatening than appeasing expressions. The central nucleus and bed nucleus of the stria terminalis responded more to averted than directed-gaze faces. Independent behavioral measures confirmed that faces with averted gaze were more arousing, suggesting the activity in the central nucleus may be related to attention and arousal.     

Visual-vestibular convergence in the vestibular nuclei of the cat

Responses from neurons of the vestibular nuclei were recorded in N₂O-anaesthetized cats. Most neurons in the rostral parts of the nuclei responded to bimodal visual-vestibular stimulation, following a trapezoidal velocity profile. Both combinations of the two stimuli were tested: rotation of the animal with stationary visual field and rotation with overtaking visual field, i.e. the visual pattern running in the same direction as the turntable with twice the velocity. Some correlation of physiological data with results in corresponding psychophysical experiments were found. As a possible biological function of visual-vestibular convergence a phylogenetic solution for discrimination of body and outer world movement is discussed.     

Effects of Near-Threshold Stimulation of the Vestibular Apparatus on Postural Responses Evoked by Displacements of the Visualized Surrounding

In healthy subjects in the relaxed upward stance and perceiving a virtual visual environment (VVE), we recorded postural reactions to isolated visual and vestibular stimulations or their combinations. Lateral displacements of the visualized virtual scene were used as visual stimuli. The vestibular apparatus was stimulated by application of near-threshold galvanic current pulses to the proc. mastoidei of the temporal bones. Isolated VVE shifts evoked mild, nonetheless clear, body tilts readily distinguished in separate trials; at the same time, postural effects of isolated vestibular stimulation could be detected only after averaging of several trials synchronized with respect to the beginning of stimulation. Under conditions of simultaneous combined presentation of visual and vestibular stimuli, the direction of the resulting postural responses always corresponded to the direction of responses induced by VVE shifts. The contribution of an afferent volley from the vestibular organ depended on the coincidence/mismatch of the direction of motor response evoked by such a volley with the direction of response to visual stimulation. When both types of stimulations evoked unidirectional body tilts, postural responses were facilitated, and the resulting effect was greater than that of simple summation of the reactions to isolated actions of the above stimuli. In the case where isolated galvanic stimulation evoked a response opposite with respect to that induced by visual stimulation, the combined action of these stimuli of different modalities evoked postural responses identical in their magnitude, direction, and shape to those evoked by isolated visual stimulation. The above findings allow us to conclude that the effects of visual afferent input on the vertical posture under conditions of our experiments clearly dominate. In general, these results confirm the statement that neuronal structures involved in integrative processing of different afferent volleys preferably select certain type of afferentation carrying more significant or more detailed information on displacements (including oscillations) of the body in space.     

Activity of Caudate Nucleus Neurons in a Visual Fixation Paradigm in Behaving Cats

Beside its motor functions, the caudate nucleus (CN), the main input structure of the basal ganglia, is also sensitive to various sensory modalities. The goal of the present study was to investigate the effects of visual stimulation on the CN by using a behaving, head-restrained, eye movement-controlled feline model developed recently for this purpose. Extracellular multielectrode recordings were made from the CN of two cats in a visual fixation paradigm applying static and dynamic stimuli. The recorded neurons were classified in three groups according to their electrophysiological properties: phasically active (PAN), tonically active (TAN) and high-firing (HFN) neurons. The response characteristics were investigated according to this classification. The PAN and TAN neurons were sensitive primarily to static stimuli, while the HFN neurons responded primarily to changes in the visual environment i.e. to optic flow and the offset of the stimuli. The HFNs were the most sensitive to visual stimulation; their responses were stronger than those of the PANs and TANs. The majority of the recorded units were insensitive to the direction of the optic flow, regardless of group, but a small number of direction-sensitive neurons were also found. Our results demonstrate that both the static and the dynamic components of the visual information are represented in the CN. Furthermore, these results provide the first piece of evidence on optic flow processing in the CN, which, in more general terms, indicates the possible role of this structure in dynamic visual information processing.     

Response of neostriatal neurons to direct electrical stimulation of the optic tract and photic stimulation in awake cats

During acute experiments on awake cats the response of 98 neurons belonging to the head and tail of the caudate nucleus to direct electrical stimulation of the optic tract and presentation of photic stimuli was investigated using extracellular recording techniques. Of the test neurons 34.6% responded to stimulation of the optic tract and 36.2% to optic stimulation. Long latency (over 40 msec for the optic tract and over 80 msec for visual stimulation) excitatory responses prevailed in both cases. A small number of cells responded to optic tract stimulation with short latencies of 5–14 msec. Both types of stimulation were presented during investigations of 58 units of which eight were found to respond to both stimuli. The latter varied in their reaction to different stimuli and their response pattern. Findings are discussed in relation to the possible pathways by which visual information reaches the cortical structure under study.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 4, pp. 476–485, July–August, 1986.     

Responses to magnetic stimuli recorded in peripheral nerves in the marine nudibranch mollusk <Emphasis Type="Italic">Tritonia diomedea</Emphasis>

Prior behavioral and neurophysiological studies provide evidence that the nudibranch mollusk Tritonia orients to the earth’s magnetic field. Earlier studies of electrophysiological responses in certain neurons of the brain to changing ambient magnetic fields suggest that although certain identified brain cells fire impulses when the ambient field is changed, these neuron somata and their central dentritic and axonal processes are themselves not primary magnetic receptors. Here, using semi-intact animal preparations from which the brain was removed, we recorded from peripheral nerve trunks. Using techniques to count spikes in individual nerves and separately also to identify, then count individual axonal spikes in extracellular records, we found both excitatory and inhibitory axonal responses elicited by changes in the direction of ambient earth strength magnetic fields. We found responses in nerves from many locations throughout the body and in axons innervating the body wall and rhinophores. Our results indicate that primary receptors for geomagnetism in Tritonia are not focally concentrated in any particular organ, but appear to be widely dispersed in the peripheral body tissues.     

Response properties of visual neurons in the turtle nucleus isthmi

The optic tectum holds a central position in the tectofugal pathway of non-mammalian species and is reciprocally connected with the nucleus isthmi. Here, we recorded from individual nucleus isthmi pars parvocellularis (Ipc) neurons in the turtle eye-attached whole-brain preparation in response to a range of computer-generated visual stimuli. Ipc neurons responded to a variety of moving or flashing stimuli as long as those stimuli were small. When mapped with a moving spot, the excitatory receptive field was of circular Gaussian shape with an average half-width of less than 3°. We found no evidence for directional sensitivity. For moving spots of varying sizes, the measured Ipc response-size profile was reproduced by the linear Difference-of-Gaussian model, which is consistent with the superposition of a narrow excitatory center and an inhibitory surround. Intracellular Ipc recordings revealed a strong inhibitory connection from the nucleus isthmi pars magnocellularis (Imc), which has the anatomical feature to provide a broad inhibitory projection. The recorded Ipc response properties, together with the modulatory role of the Ipc in tectal visual processing, suggest that the columns of Ipc axon terminals in turtle optic tectum bias tectal visual responses to small dark changing features in visual scenes.     

Effect of static magnetic fields on the budding of yeast cells

The effect of static magnetic fields on the budding of single yeast cells was investigated using a magnetic circuit that was capable of generating a strong magnetic field (2.93 T) and gradient (6100 T² m^?1). Saccharomyces cerevisiae yeast cells were grown in an aqueous YPD agar in a silica capillary under either a homogeneous or inhomogeneous static magnetic field. Although the size of budding yeast cells was only slightly affected by the magnetic fields after 4 h, the budding angle was clearly affected by the direction of the homogeneous and inhomogeneous magnetic fields. In the homogeneous magnetic field, the budding direction of daughter yeast cells was mainly oriented in the direction of magnetic field B. However, when subjected to the inhomogeneous magnetic field, the daughter yeast cells tended to bud along the axis of capillary flow in regions where the magnetic gradient, estimated by B(dB/dx), were high. Based on the present experimental results, the possible mechanism for the magnetic effect on the budding direction of daughter yeast cells is theoretically discussed. Bioelectromagnetics 31:622–629, 2010. © 2010 Wiley‐Liss, Inc.     

Internuclear connections between the pretectum and the accessory optic system in Salamandra salamandra

Summary Application of horseradish peroxidase into the posterior thalamic and basal optic neuropils of Salamandra salamandra (L.) revealed strong reciprocal connections between the pretectum and the accessory optic system. Pretectal neurons located within the periventricular gray matter project to the basal optic neuropil distributing their terminals over the whole extent of this neuropil. A well developed nucleus of the basal optic neuropil, with its neurons within and medial to this neuropil, projects to the posterior thalamic neuropil. Its terminals appear to be located selectively within the core of the posterior thalamic neuropil which receives no ipsilateral retinal afferents.The pretectum and the accessory optic system are reciprocally connected to a ventral tegmental nucleus, which has not previously been described in urodeles. This nucleus is located immediately dorsal to the oculomotor and trochlear nuclei and extends from the oculomotor root to the middle of the trochlear nucleus.Dendrites of the nucleus of Darkschewitsch reach the posterior thalamic neuropil but mainly enter the rostral tegmental neuropil, while the dendrites of the nucleus of the medial longitudinal fasciculus ramify within the basal optic neuropil and the anterior tegmental neuropil with minor branches in the caudal posterior thalamic neuropil.     

Microelectrophoretic study of unit responses of the rabbit amygdaloid nucleus to acetylcholine and noradrenaline

Responses of 152 neurons of the basal and lateral nuclei of the amygdala and of the anterior amygdaloid field to microelectrophoretic application of acetylcholine and noradrenalin, in the case of 115 neurons to both substances, were investigated in immobilized, unanesthetized rabbit. In the basal nucleus 35% of neurons tested responded to acetylcholine, most often by an increase in discharge frequency (34%), and 63% of cells responded to noradrenalin, most of them giving inhibitory responses (53%). A response to only one of the two substances applied in turn was given by 45% of neurons. Among neurons responding to both acetylcholine and noradrenalin, 23% of cells did so in the opposite direction and only 11% in the same direction.     

Afferent signals from pigeon extraocular muscles modify the vestibular responses of units in the abducens nucleus.

Although the extraocular muscles contain stretch receptors it is generally believed that their afferents exert no influence on the control of eye movement. However, we have shown previously that these afferent signals reach various brainstem centres concerned with eye movement, notably the vestibular nuclei, and that the decerebrate pigeon is a favourable preparation in which to study their effects. If the extraocular muscle afferents do influence oculomotor control from moment-to-moment they should exert a demonstrable effect on the oculomotor nuclei. We now present evidence that extraocular muscle afferent signals do, indeed, alter the responses of units in an oculomotor nucleus (the abducens, VI nerve nucleus, which supplies the lateral rectus muscle) to horizontal, vestibular stimulation induced by sinusoidal oscillation of the bird. Such stimuli evoke a vestibulo-ocular reflex in the intact bird. The extraocular stretch receptors were activated by passive eye movement within the pigeon's saccadic range; such movements modified the vestibular responses of all 19 units studied which were all, histologically, in the abducens nucleus. The magnitude of the effects, purely inhibitory in 15 units, depended both on the amplitude and the velocity of the eye movement and most units showed selectivity for particular combinations of plane (e.g. horizontal versus vertical) and direction (e.g. rostral versus caudal) of eye movement. The results show that an afferent signal from the extraocular muscles influences vestibularly driven activity in the abducens nucleus to which it carries information related to amplitude, velocity, plane and direction of eye movement in the saccadic range. They thus strongly support the view that extraocular afferent signals are involved in the control of eye movement.     

Representation of lateral line and electrosensory systems in the midbrain of the axolotl,Ambystoma mexicanum

Summary The study focussed on the representation of the electrosensory and lateral line units in the midbrain of the axolotl Ambystoma mexicanum. In addition, the responses to photic and acoustic/vibrational stimuli were determined. Unit properties were characterized with respect to baseline activity, sensitivity, latency, directional specificity and number of input modalities. The anatomical arrangement of the units was determined using stereotactic and histological measurements of the electrode positions.Of 106 units recorded, 29 units were unimodal, 77 units responded to more than one modality. Most units discharged only in response to stimuli. Thresholds of electrosensory units were about 100 V/cm field strength; lateral line units had thresholds below 5 m pp amplitude. The shortest latencies (8–17 ms) were found for responses to visual stimuli. Lateral line and vestibular units responded after 35–58 ms, electroreceptive units after 79–150 ms. All electrosensory and about 50% of the lateral line units were sharply tuned to definite stimulus directions.Electrosensory and lateral line units formed topographical maps in the tectum. The map in each tectal hemisphere contained information about the contralateral surroundings. The electrosensory, lateral line and visual representations were only partly in register; especially in the caudal areas of the midbrain the alignment was poor.     

Binocular visual integration in the crustacean nervous system

Although the behavioral repertoire of crustaceans is largely guided by visual information their visual nervous system has been little explored. In search for central mechanisms of visual integration, this study was aimed at identifying and characterizing brain neurons in the crab involved in binocular visual processing. The study was performed in the intact animal, by recording intracellularly the response to visual stimuli of neurons from one of the two optic lobes. Identified neurons recorded from the medulla (second optic neuropil), which include sustaining neurons, dimming neurons, depolarizing and hyperpolarizing tonic neurons and on-off neurons, all presented exclusively monocular (ipsilateral) responses. In contrast, all wide field movement detector neurons recorded from the lobula (third optic neuropil) responded to moving stimuli presented to the ipsilateral and to the contralateral eye. In these cells, the responses evoked by ipsilateral or contralateral stimulation were almost identical, as revealed by analysing the number and amplitude of the elicited postsynaptic potentials and spikes, and the ability to habituate upon repeated visual stimulation. The results demonstrate that in crustaceans important binocular processing takes place at the level of the lobula.     

Effects of postural changes and vestibular lesions on genioglossal muscle activity in conscious cats.

Previous studies in humans showed that genioglossal muscle activity is higher when individuals are supine than when they are upright, and prior experiments in anesthetized or decerebrate animals suggested that vestibular inputs might participate in triggering these alterations in muscle firing. The present study determined the effects of whole body tilts in the pitch (nose-up) plane on genioglossal activity in a conscious feline model and compared these responses with those generated by roll (ear-down) tilts. We also ascertained the effects of a bilateral vestibular neurectomy on the alterations in genioglossal activity elicited by changes in body position. Both pitch and roll body tilts produced modifications in muscle firing that were dependent on the amplitude of the rotation; however, the relative effects of ear-down and nose-up tilts on genioglossal activity were variable from animal to animal. The response variability observed might reflect the fact that genioglossus has a complex organization and participates in a variety of tongue movements; in each animal, electromyographic recordings presumably sampled the firing of different proportions of fibers in the various compartments and subcompartments of the muscle. Furthermore, removal of labyrinthine inputs resulted in alterations in genioglossal responses to postural changes that persisted until recordings were discontinued approximately 1 mo later, demonstrating that the vestibular system participates in regulating the muscle's activity. Peripheral vestibular lesions were subsequently demonstrated to be complete through the postmortem inspection of temporal bone sections or by observing that vestibular nucleus neurons did not respond to rotations in vertical planes.     

Mechanism of perception of changes in the magnetic field by ampullae of lorenzini of elasmobranchs

The mechanisms of reception of changes in the magnetic field by electroreceptor formations were investigated in experiments on Black Sea rays in which spike activity was recorded from single nerve fibers connected with the ampullae of Lorenzini. The responses of the ampullae of Lorenzini to magnetic stimulation were shown to be due to induced electric currents creating potential gradients in the body tissues of the fish and the sea water. On the basis of differences in responses of different ampullae to magnetic stimulation, it is possible to distinguish between magnetic stimuli and other stimuli acting on the electroreceptor system. Potentiation of the receptor response to magnetic stimulation was found as the fish came closer to the "shore." The mechanisms and biological importance of reception of changes in the magnetic field by the ampullae of Lorenzini are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 10, No. 1, 75–83, January–February, 1978.     

The intrinsic neuronal organisation of the nucleus of the basal optic root in the domestic chicken; a light and electron microscopic study using anterograde tracers and postembedding GABA-immunostaining

The intrinsic neuronal organisation in the nucleus of the basal optic root of chickens was investigated. The divergent connections with various areas and the functional complexity of the nucleus require a complex intrinsic structural arrangement. Therefore, an analysis of Golgi impregnated material, ultrastructure, GABA-immunocytochemistry and biotinylated dextran-amine anterograde tracer analysis of the nucleus was carried out. In the Golgi analysis, a characteristic dendritic ramification pattern of two types of putative projection neurons was observed. These neurons form dendritic nests with their overlapping dendritic terminal sections, that develop synaptic fields with the optic fibre terminals. These synaptic fields were confirmed by electron microscopy. GABA-immunopositive terminals synapse with distinct loci of the dendritic trees of projection neurons; they may therefore play an important role in the inhibitory-modulatory system of the nucleus of the basal optic root. The GABA-immunopositive terminals derive from small and/or elongated local circuit neurons which receive retinal afferents, and from myelinated fibres afferents to the nucleus of unknown origin.