Role of the cervico-ocular reflex in the "flying" pigeon: interactions with the optokinetic reflex.

We studied the cervico-ocular reflex (COR) alone and in combination with the optokinetic (OKN) reflex in head-fixed pigeons. We analyzed these responses in two behavioral conditions: (1) animals were hung in a harness ("resting" condition); and (2) animals were additionally submitted to a frontal airflow that provoked a flight posture ("flying" condition). In both conditions, cervical stimulation provoked a slow phase of very low gain (around 0.05) in the opposite direction to that of the stimulation and fast phases triggered near the head-body alignment in the same direction as the stimulation. The slow phase showed a phase lag of 20 deg at 0.5 Hz. The gain of the slow phase was not modified by the velocity, amplitude, or frequency of the stimuli. This gain was not changed by the presence of a fixed visual surround. When cervical stimuli (0.05-0.5 Hz) were added to an optokinetic stimulation (30 deg/s) in the "resting" condition, the slow phase velocity (SPV) of the optokinetic reflex was modulated with a time course close to that produced by the cervico-ocular reflex alone. The SPV was alternately increased and decreased round the SPV level corresponding to the steady-state OKN. In the "flying" condition, optokinetic-cervical stimulation provoked an eye beating field and a strong SPV modulation synchronized with the position of the cervical stimulation. The number of nystagmic beats (OKN) and the amplitude and velocity of the fast phases were modulated in correlation with the SPV. Consequently, the optokinetic response was increased or decreased according to whether the cervical stimuli were in the reverse direction or in the same direction as the optokinetic stimulation, respectively. These data are interpreted as an improvement of gaze stabilization by the COR. This mechanism is context dependent, since it is strongly reinforced during the flight.

Eye-neck coupling during optokinetic responses in head-fixed pigeons (Columba livia): influence of the flying behaviour.

The effects of the behavioural context on the properties of slow and fast phases of the horizontal optokinetic nystagmus (OKN) and on the electromyographic neck response (EMG) were investigated in head-fixed pigeons. Responses in two situations were compared: (i) animals were hung in a harness ('resting' condition); (ii) animals in harness were subjected to a frontal airflow that provoked a flight posture ('flying' condition). During optokinetic stimuli the neck muscles responded in synchrony and in synergy with the eye nystagmus in both the 'resting' and the 'flying' conditions. In the 'resting' condition the neck activity was essentially correlated to the slow phase velocity of the eyes (eye SPV) whereas in the 'flying' condition, the neck response was also correlated to the eye position. The neck response was independent of the retinal slip velocity during the OKN. The velocity of the slow and fast phases of the OKN was not modified by flight. However, the 'flying' condition provoked an increase of the neck response by augmenting both its velocity gain (neck EMG/eye SPV) and its position gain (neck EMG/eye position). These results show that although an optokinetic stimulation results in synchronised eye and head motor commands in head-fixed pigeons, only the head motor command is modified by the behavioural context ('flying' vs. 'resting'). This strategy could help pigeons in reorienting their gaze during the flight.

Role of basal ganglia and ectostriatum in the context-dependent properties of the optocollic reflex (OCR) in the pigeon (Columba livia): a lesion study.

The possible participation of basal ganglia and associated structures [dorsal striato-pallidum, nucleus spiriformis lateralis (SpL), ectostriatum] in the elaboration of the optocollic reflex (OCR) was investigated by making bilateral chemical lesions (ibotenic acid). Previous data have shown that both the slow and fast phases of the OCR are dependent on the behavioural context. The slow phase velocity (SPV) and the peak velocity of fast phases obtained in non-flying pigeons ('resting condition') were enhanced in pigeons in which a flying posture was experimentally provoked ('flying condition'). Therefore, the effect of lesions was analysed in pigeons standing in the 'resting' or 'flying' condition. In the 'resting' as in the 'flying' condition, all the lesions provoked a decrease in SPV, which augmented with the stimulation velocity. Velocity step stimuli revealed greater OCR deficits than velocity ramp stimuli. Extensive lesions (including the striato-pallidum, ectostriatum and a part of the neostriatum), as well as SpL lesions, provoked a greater SPV decrease over a longer time than lesions restricted to the striato-pallidum or the ectostriatum. The peak velocity of fast phases was only reduced by the 'extensive lesion' in the 'flying condition'. The present data show that the basal ganglia system is involved in the elaboration of optokinetic responses and suggest that, to work in an optimal range, the optokinetic centres need to receive integrated information from basal ganglia in addition to direct visual input.

Characteristics of slow and fast phases of the optocollic reflex (OCR) in head free pigeons (Columba livia): influence of flight behaviour.

The effect of behavioural context on the properties of slow and fast phases of the horizontal optocollic reflex (OCR) were investigated in head free pigeons for two situations, i.e.: (i) animals were hung in a harness ('resting condition'); (ii) animals were additionally submitted to a frontal airflow that provoked a flight posture ('flying condition') [Bilo and Bilo (1983) J. Comp. Physiol., 153, 111]. A 'transient flight' was also provoked in the 'resting condition' by tapping the breastbone region. Stimuli consisted either of velocity steps (30-300 degrees/s) or of an increasing velocity stimulus (0-300 degrees/s). The amplitude of nystagmic beats and the OCR gain increased in the 'flying condition' and during 'transient flight' as compared to the 'resting condition'. The OCR working range was considerably extended toward high velocities by the flying behaviour. In the 'resting condition', spontaneous head oscillations generally triggered a high-gain OCR, close to that obtained in the 'flying condition'. One-third of the animals showed a higher gain in response to an increasing velocity stimulus than with step stimuli, in the high velocity range. The linear relation between amplitude and peak velocity of OCR fast phases was independent of the stimulation velocity in the 'resting condition', whereas the amplitude and peak velocity increased with the stimulation velocity in the 'flying condition'. In this condition, the fast phase velocity was correlated with the slow phase velocity, but not with the retinal slip velocity. Thus, both the slow and fast phases of the OCR are dependent on the behavioural context.

Characteristics of cervico-ocular responses in the chameleon.

The cervico-ocular reflex (COR) was investigated in the chameleon. Two kinds of responses were observed by oscillating the body (sine-wave stimuli) in the fixed-head animal: a "smooth response" of very low gain (around 0.08) and a saccadic response composed of 1-12 saccades per cycle of stimulation (depending on the stimulation frequency). Both responses were elicited in the compensatory direction (same direction as the stimulation) and exhibited a frequency dependence with low-pass properties. The saccadic response was especially developed and displayed a higher gain (up to 0.4) than the smooth response. In darkness, the saccades were triggered near the zero point (head-body alignment), whereas in the presence of a fixed visual surround they were elicited more regularly throughout the stimulation cycle. The amplitude of saccades was increased in the light. Consequently, the gain and the phase lag of the saccadic response were enhanced by the visual input. No visuo-cervical interaction was observed for the smooth response. Oscillating the body at a constant velocity (seesaw or ramp stimuli) revealed a frequency effect on the number of saccades (during a cycle of stimulation), but not on the gain of the response. Increasing the amplitude of oscillations augmented only very slightly the amplitude of saccades and consequently decreased the gain. Hence, the best working range of the saccadic response corresponds to body or head movements of low amplitude (up to +/- 20 deg) and low frequency (up to 0.25 Hz), and is improved by a visual input. These properties are discussed on a comparative point of view. It is proposed that, in chameleons, the saccadic response could contribute to gaze stabilization and add to the vestibulo-ocular and the optokinetic responses.

Muscarinic receptor stimulation increases the spontaneous [3H]GABA release in the rat substantia nigra through muscarinic receptors localized on striatonigral terminals.

The effect of muscarinic agonists on the spontaneous release of [3H]GABA was investigated in vitro on rat substantia nigra slices. Acetylcholine (5 x 10(-5) M) in the presence of eserine (5 x 10(-5) M) induced a 12.3% increase of the spontaneous release of [3H]GABA. Similarly, carbachol (5 x 10(-4) M) enhanced by 9% the release of [3H]GABA. This effect was Ca(2+)-dependent, it was abolished in the presence of 0.4 mM Ca2+ and enhanced from 9 to 17% when Ca(2+)-concentration of the superfusion medium was increased from 1.3 to 2.4 mM. The carbachol effect was mediated by muscarinic receptors since it was abolished by atropine (2 x 10(-6) M). The pharmacologically M2 muscarinic receptor subtypes seems to be involved as the carbachol-induced effect was abolished by AF-DX384MS (10(-6) M), an M2 antagonist and was only partially reversed by pirenzepine (10(-5) and 10(-4) M), an M1 antagonist which at these doses also block the M2 receptors. The absence of effect of SCH23390 (10(-6) M) a D1 antagonist as well as the lack of effect of CNQX (10(-5) M) and dizocilpine maleate (10(-6) M), two glutamate antagonists, on the carbachol-induced effect indicated that neither dopamine (through D1 receptors) nor glutamate (through ionotropic receptors) were involved in the response. In addition, the persistence of the carbachol-induced effect in the presence of tetrodotoxin (2 x 10(-7) M) suggests a direct muscarinic-mediated modulation of [3H]GABA. The localization of muscarinic receptors on striatonigral fibres was confirmed by autoradiographic studies showing a decrease of [3H]pirenzepine binding in the substantia nigra after a unilateral striatal lesion induced by kainic acid injection. This latter result provides evidence of the presence of M1 receptors on striatonigral terminals as the concentration of [3H]pirenzepine used (10 nM) is M1-selective. These results indicate a cholinergic modulation of GABA release in the rat substantia nigra mediated by muscarinic receptors localized on striatonigral terminals. The involvement of the m4 muscarinic receptor subtype that have a M1/M2 pharmacology is discussed.

Visual and vestibular reflexes that stabilize gaze in the chameleon.

Spontaneous eye movements as well as visual, vestibular, and proprioceptive cervical reflexes which contribute to gaze stabilization were investigated in the chameleon using the magnetic search-coil technique. The oculomotor range of each eye was very large (180 deg horizontally x 80 deg vertically). Spontaneous ocular saccades were independent in the two eyes and could have very large amplitudes. The fast phases of nystagmus during the stabilization reflexes were also independent in the eyes. In the head-restrained condition, optokinetic nystagmus (OKN) had a low gain in both horizontal and vertical planes (0.35 at 5 deg/s) and showed little binocular interaction. The vestibulo-ocular reflex (VOR) exhibited a low gain (0.2-0.3 from 0.05-1 Hz) and a high-phase lead at low frequency (140 deg at 0.05 Hz). Rotation of the animal in the presence of a visible surround increased the overall gain of gaze stabilization to 0.4-0.5 (P < 0.01) and considerably reduced the phase lead (38 deg at 0.05 Hz). In the head-free condition, head and eye reflexes were active simultaneously during both optokinetic and vestibular stimulation, but nystagmic head movements appeared only occasionally with a rather loose eye-head coordination. During optokinetic stimulation, eye movements contributed more than head movements to gaze stabilization, whereas, during vestibular or visuo-vestibular stimulation, the relative contribution of eye and head responses varied with stimulus frequency. When the head was freed, overall gain for gaze stabilization increased from 0.35 to 0.45 (P < 0.05) for optokinetic stimulation at 5 deg/s and from 0.2-0.3 to 0.4-0.75 (P < 0.001) for vestibular stimulation at 0.05-1 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of [3H]clonidine binding sites in the brain of the convulsive mutant quaking mouse: a radioautographic analysis.

The radioautographic analysis of [3H]clonidine binding was performed on brain slices from the convulsive mutant mice quaking and their controls of the same strain. In the quaking mice significant increases were observed mostly in the brainstem and the cerebellum, but also in a few regions of the forebrain, such as the lateral and medial thalamic nuclei, the medial geniculate nucleus, the amygdala and the hypothalamus. Other regions, such as the cerebral cortex and the hippocampus, which are classically involved in various models of epilepsy, but not in the quaking mice, did not show any modification of [3H]clonidine binding. A high degree of correlation was found between the structures with an increased density of alpha 2-adrenoceptor binding sites and the distribution of regions from which seizures can be elicited by intracerebral electrical stimulation in head-restrained quaking mice. This comparison emphasizes the role of noradrenaline acting at the level of alpha 2-adrenoceptors in the epileptic syndrome of the quaking mutants.

Spontaneous saccades under different visual conditions in the pigeon.

Spontaneous saccades of both eyes were recorded in head-restrained pigeons placed in 6 different visual conditions (darkness and biocular, uniocular, frontal or lateral viewing). Most saccades (95%) were biocular and directed forward (around the beak axis) and backward (around the horizontal line). In the dark, the proportions of forward and backward saccades were different, they became symmetrical when the visual input involved either the left eye, the lateral fields or both eyes. This spatial reorganization could be mediated by one 'dominant' eye through the lateral and foveal vision. Although some biocular saccades were strictly convergent, divergent or conjugate, most of them showed a higher independence since they had different directions and amplitudes for each eye.

Seizures can be triggered by stimulating non-cortical structures in the quaking mutant mouse.

Mutant Quaking mice (C57BL/6J) display convulsive tonic-clonic seizures that can be either spontaneous or triggered by manipulation of the animal or by auditory stimulation. Several abnormalities have been found (especially in the noradrenergic system) in the brainstem of this mutant strain. We first verified by electrophysiological recording that the cerebral cortex was not involved in the generation or in the development of these fits. Then we showed that tonic-clonic seizures similar to those obtained in the freely moving animal were triggered by low-threshold (LT, 5-50 microA) or high-threshold (HT, 55-150 microA) stimuli performed during head restraint. LT stimuli were mostly efficient in a number of ponto-bulbar and mesencephalic structures, including several reticular nuclei, the locus coeruleus, the nucleus subcoeruleus and the red nucleus, whereas HT stimuli were generally necessary to trigger fits by stimulating the nuclei pontis, the substantia nigra, the central gray area and the cerebellar nuclei. Seizures were also provoked at the diencephalic level with LT stimulation delivered in the medial thalamic area, the nucleus reticularis thalami and some subthalamic regions (zona incerta, H field of Forel). In contrast, no fits were obtained by stimulating the cerebellar cortex and the inferior colliculus, the ventral and lateral groups of thalamic nuclei or the telencephalic regions (hippocampus, amygdala, caudate nucleus, putamen and cerebral cortex), with the exception of the globus pallidus.

[Psychophysical study of the chromatic discrimination in pigeons after lesions of thalamic nuclei Rotundus (RT) and Geniculatus Lateralis ventralis (GLv)]. / Etude psychophysique de la discrimination chromatique du pigeon après lésion des noyaux thalamiques Rotundus (RT) et Geniculatus Lateralis ventralis (GLv).

The discrimination threshold at 510 and 640 nm has been measured before and after the bilateral lesion with kaïnic acid of two main thalamic structures: the nucleus rotundus (Rt) and the nucleus geniculatus lateralis ventralis (GLv). When the lesion destroys the GLv and the lower part of the Rt, thresholds increase followed by a progressive recuperation. In contrast, when the Rt lesion is complete, and whether the GLv is touched or not, the threshold increase is both higher and does not come down to the pre-operatory levels even after 15 post-operatory sessions.

Role of the nucleus geniculatus lateralis ventralis (GLv) in the optokinetic reflex: a lesion study in the pigeon.

Several functions have been proposed for the avian GLv (color vision, pupillary reflex, optomotor mechanisms). In the present paper we have examined the role of the GLv in optomotor responses. For this purpose, horizontal and vertical optokinetic nystagmus (OKN) were quantified in response to different stimulation velocities, before and after chemical (kainic acid) lesions. Unilateral lesion of the GLv produced a marked increase of the horizontal OKN gain when the eye contralateral to the lesion was stimulated in the temporonasal (T-N) direction and, to a lesser extent, when the ipsilateral eye was stimulated in the naso-temporal (N-T) direction. Biocular integration was reduced after the lesion, since the biocular stimulation corresponding to these two monocular stimulations (ipsiversive to the lesion) produced only a moderate gain increase. When stimulations were delivered in the opposite direction (contraversive to the lesion), the horizontal OKN gain was slightly increased for the N-T monocular stimulation of the eye contralateral to the lesion, but was unchanged for other stimulations. A bilateral lesion of the GLv provoked only a slight increase of the horizontal OKN gain. The vertical OKN was not affected by the GLv lesions. Thus, the GLv system is probably involved in the modulation of optomotor responses and could mediate visuo-optokinetic interactions, each nucleus (and its associated system) exerting an inhibitory (or disfacilitatory) effect on the horizontal OKN in one direction.

[Stabilization of the gaze in chameleons: visual and vestibular reflexes]. / Stabilisation du regard chez le caméléon: réflexes visuels et vestibulaires.

Some visual, vestibular and proprioceptive reflexes which contribute to gaze (head + eye) stabilization were quantified in the chameleon. All the reflexes were analysed in the horizontal plane, and the visual reflexes were also studied in the vertical plane. In restrained-head animals, both the optokinetic nystagmus (OKN) and the vestibulo-ocular reflex (VOR) had low gains. In free-head animals, the head (opto-collic or vestibulo-collic reflex) and eye (OKN or VOR) responses added their effects, thus improving gaze stabilization, especially during vestibular stimulation. Cervical stimulation provoked both a cervico-ocular reflex (COR) in the compensatory direction and a large number of saccades. The saccadic response was especially marked in the presence of patterned visual surroundings.

Stabilizing gaze reflexes in the pigeon (Columba livia). II. Vestibulo-ocular (VOR) and vestibulo-collic (closed-loop VCR) reflexes.

The vestibulo-ocular reflex (VOR) and the closed-loop vestibulo-collic reflex (CL-VCR) were investigated in the pigeon. The animals, placed either in the fixed-head condition (VOR) or in the free-head condition (CL-VCR) were rotated in darkness (vestibular responses) or in the presence of visual surroundings (visuo-vestibular responses). The linear range of the reflexes were determined both in the frequency and in the velocity domains. Results show that: 1. Pigeons develop a strong VOR, which presents the same asymmetry observed with the OKN, the gain being higher when the slow-phase occurs in the T-N direction. This asymmetry persists in the light (VOR + OKN). In the free-head condition, both the eye and the head display a synchronized nystagmus whose effects are additive. The head reflex (CL-VCR) contributes about 80% of the gaze stabilization. 2. In the medium-low frequency range, the head response (CL-VCR) has a lower gain than the VOR (head-fixed), but the gain of both reflexes increases with frequency, up to about 1 at 0.6-1 Hz. The gaze response (eye + head) presents an optimal gain above 0.06 Hz. The phase lead is higher for the VOR than for the CL-VCR (40 degrees and 32 degrees respectively at 0.03 Hz), but both phases also become nul around 1 Hz. The time constants are 6.5 s for the VOR, 8.5 s for the CL-VCR and 9.6 s for the gaze response (VOR + CL-VCR). 3. While the VOR gain shows a saturation at peak stimulation velocities (PV) higher than 20 degrees/s (at 0.3 Hz), the CL-VCR gain is linear at least up to 60 degrees/s (the highest PV used). However, the phase lead declines when the PV is greater than 20 degrees/s, both for the VOR and the CL-VCR. 4. When the vestibular stimulation is delivered in the light (visuo-vestibular stimulation), there is no phase shift. The VOR gain (fixed-head) is optimal and linear over the entire frequency range, but it saturates for PV higher than 40 degrees/s. In the free-head condition, while the gaze gain is linear and close to 1 in both the frequency and the velocity domains, the head response gain (CL-VCR) remains lower especially in the low frequency and in the low velocity ranges.

Stabilizing gaze reflexes in the pigeon (Columba livia). I. Horizontal and vertical optokinetic eye (OKN) and head (OCR) reflexes.

A quantitative study of horizontal and vertical optokinetic nystagmus (OKN) and optocollic reflex (OCR) has been performed in the pigeon using the search-coil technique. The reflexes were analysed in response to either velocity steps or sinusoidal stimulation. Results show that: 1. In response to a velocity step stimulation, the slow phase velocity of both OKN and OCR increases gradually to reach a steady state level. When the stimulation stops in the dark, After Responses (OKAN-I, OKAR-I) occur. Time constants of the OKN charge (or OCR charge) and of the After Responses are lower for vertical than for horizontal responses. 2. In the free-head condition, both the head and the eye display a synchronized nystagmus which add their effects. However, the head reflex (OCR) accounts for about 80-90% of the entire linear gaze response (head + eye), except for the vertical steady state responses which are wholly accomplished by the head (OCR). 3. Both closed-loop and open-loop gains of steady state responses are higher for horizontal than for vertical reflexes. Vertical OCR, horizontal OKN and vertical OKN show properties of binocular integration, the response gain being higher for binocular than for monocular stimulations. By contrast, the horizontal OCR shows little binocular integration but displays a higher response gain for monocular stimulation, compared to horizontal OKN. 4. The horizontal OKN elicited by both monocular and binocular stimulation is asymmetrical, the gain being higher when the eye is driven by a temporo-nasal stimulation. In contrast, both vertical OKN and vertical OCR are practically symmetrical. 5. While both the gain of horizontal OKN and its linear range (up to 20 degrees/s) are improved when the head is free (gaze gain close to 1 up to 40 degrees/s), the vertical OKN and the vertical OCR have similar gain profiles and similar domains of linearity (up to 10 degrees/s). 6. In response to increasing the frequency of a sinusoidal stimulation at constant peak velocity, all the reflexes display a drop in gain and a strong increase of phase lag. The phase increase is greater for horizontal than for vertical reflexes. On the other hand, both gain and phase are higher for OCR than for OKN, both in the horizontal plane as well as in the vertical plane. 7. For sinusoidal stimulations, when the peak velocity (PV) is increased at a constant frequency (0.03 Hz), nonlinearities appear (drop in gain, phase increase) both for OKN and OCR.(ABSTRACT TRUNCATED AT 400 WORDS)

Single unit activity in the nucleus of the basal optic root (nBOR) during optokinetic, vestibular and visuo-vestibular stimulations in the alert pigeon (Columbia livia).

Extracellular recordings were performed in the nucleus of the basal optic root (nBOR) of alert pigeons during optokinetic nystagmus (OKN), vestibulo-ocular reflex (VOR) and combined visuo-vestibular stimulation. Cell identification was assessed either by histological control or by electrophysiological testing (antidromic response to vestibulo-cerebellar or oculomotor complex stimulation). 1) OKN was induced in 8 directions by a binocular stimulation. During the fast phase of OKN, optokinetic after nystagmus (OKAN) or reversed OKAN, most cells showed an inhibition which varied in magnitude independent of the direction of stimulation. A few cells however showed a phasic discharge for some OKN directions. 2) During the slow phase of OKN induced by a binocular stimulation, cells displayed either a tonic activation or a more or less strong inhibition according to the direction of the OKN. Cells were classified in 4 groups, according to their degree of directional specificity. The best OKN direction (slow phase) for maximal cell activation was upwards and naso-upwards, and next to best, naso-temporal and downwards. Maximal cell inhibition occurred during downward, and for some cells during upward, directions. 3) During OKN induced by stimulating the eye contralateral to the recorded nBOR, cell responses resembled those obtained during binocular stimulation, but, during ipsilaterally induced OKN, the cells lost their directional specificity. As a result of binocular integration, neuronal activation seems to originate from contralateral input whereas cell inhibition would mainly come from ipsilateral input. 4) During sinusoidal optokinetic stimulation induced in the temporo downward-naso upward axis, cells showed a more or less marked modulation (according to their directional selectivity) that was closely in phase with the stimulation velocity, and therefore probably with retinal slip. 5) nBOR cells appeared generally unaffected during both the slow phase and the fast phase of the VOR. However, some cells showed a slight but irregular modulation which might imply a weak vestibular input. During visuo-vestibular stimulation, the response resembled that obtained with sinusoidal optokinetic stimulation but the fast phase inhibition was often strengthened in the downwards direction (fast phase).

Optokinetic nystagmus in the pigeon (Columba livia). II. Role of the pretectal nucleus of the accessory optic system (AOS).

In birds, the accessory optic system (AOS) includes two nuclei: the nucleus ectomamillaris (nEM) and the pretectal nucleus superficialis synencephali (nSS). The role of the nSS in the production of a horizontal optokinetic nystagmus (OKN) was studied in the pigeon, by comparing the OKN before and after a unilateral lesion of this nucleus. The lesions were performed either by electrolysis or by local application of kainic acid (KA); the KA lesions gave more stable modifications of the OKN than the electrolytic lesions. A quantitative analysis of the slow-phase velocity (V) of the OKN was carried out on the animals receiving KA lesions. Lesion of the nSS provokes the almost total disappearance of the OKN for stimulation of the contralateral eye in the temporo-nasal direction, and a reduction of the OKN for stimulation in the naso-temporal direction. Thus, the nSS is essential for the production of the OKN in the temporo-nasal direction, but it also participates in the production of the OKN in the naso-temporal direction (slow-phase direction). The same lesion produces a large increase of the OKN (V) when the ipsilateral eye is stimulated in the temporo-nasal direction, and a smaller increase following stimulation in the naso-temporal direction. These increases suggest some kind of inhibitory (or disfacilitatory) interactions between the nSS (or the associated system) on one side, and the contralateral optokinetic centers. The lesion of one nSS does not provoke a deficit when the stimulation is binocular. This result probably reflects the combined effect of both monocular inputs. After a pretectal KA injection, a spontaneous nystagmus of the contralateral eye, in the naso-temporal direction, can be seen for several hours. The mechanism is still unknown, but it might be related to a reverse optokinetic after nystagmus (R-OKAN). The anatomical and physiological data so far available consistently support the hypothesis of a functional equivalence between the nSS in birds and the nucleus of the optic tract in mammals.

Optokinetic nystagmus in the pigeon (Columba livia). III. Role of the nucleus ectomamillaris (nEM): interactions in the accessory optic system (AOS).

The accessory optic system (AOS) in birds is composed of two structures: the nucleus Superficialis Synencephali (nSS), essential for the production of an optokinetic nystagmus (OKN) in the temporo-nasal direction (slow phase) for the eye contralateral to the nucleus, and the nucleus Ectomamillaris (nEM), or nucleus of the basal optic root (nBOR). The objectives of the present work were: (1) to study the importance of the nEM for the horizontal OKN, (2) to study the interactions between the nSS and the nEM. Experiments were realized by combining different kinds of lesion. (1) Results show that the nEM is essential for the production of an OKN in the naso-temporal direction (direction of the slow-phase), but it also participates in the temporo-nasal response. (2) After bilateral lesion of the nEM or the nSS, only a residual nystagmic response remains. (3) Synergic effects exist between (I) the homolateral nEM and nSS, or between the systems related to them; we call this relation "homolateral synergy", (II) a nEM and the contralateral nSS (or systems related to these nuclei). The synergic effect exerted by one nEM upon the contralateral nSS appears to be stronger than the reciprocal effect. (4) The effects obtained after combined lesions, either homolateral (nEM and nSS on the same side) or heterolateral (nEM and nSS on opposite sides) confirm the previous results and show that heterolateral interactions are stronger than homolateral interactions. (5) For all the lesions studied, the results obtained from binocular stimulation are compatible with a model of convergence of monocular inputs. The role of the nuclei of the AOS in birds is discussed in terms of existing anatomical and physiological data.

[Single unit activity in the nucleus ectomamillaris (nem) during optokinetic nystagmus, in the pigeon]. / Analyse unitaire du nucleus ectomamillaris (nem) chez le pigeon durant le nystagmus optocinétique.

Extra-cellular recordings of single units were obtained in the nucleus ectomamillaris (nEM) in waking Pigeons, during optokinetic nystagmus (OKN). OKN was obtained for 8 directions of stimulation (horizontal, vertical and oblique) in monocular and binocular vision. For half of the units the responses were synchronized, showing activation during the slow-phase and inhibition during the fast phase of the OKN. This response pattern was more common for the horizontal OKN, both in the Nasal to Temporal (N-T) and in the Temporal-to-Nasal (T-N) directions. With contralateral stimulations, most cells showed directional selective responses for upwards and backwards directions, the activity being inhibited for the other directions. Some units showed a less marked directional selectivity or were unaffected by the stimulations. Ipsilateral stimulations provoked no directional selectivity, but rather a reduction of the firing level. With binocular stimulation, responses were very close to those obtained with contralateral stimulation, with an increase of the directional selectivity. The nEM seems to be involved in the control of OKN, specially for the N-T and upwards directions, and less significantly for the T-N direction.