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J Lannou

Publications and source records attributed to J Lannou.

At least 19 recordsLinked to original sources
PubMed1997

Hemispheric asymmetries of visual evoked potentials in relation to spatial frequency, handedness and familial left-handedness.

The effects of handedness and of familial left-handedness on the asymmetry of the cerebral hemispheres were investigated by means of visual evoked potentials. Square gratings of different spatial frequencies were presented, at 1 Hz in ON-OFF mode to 60 subjects: 30 right-handers and 30 left-handers, 15 with familial handedness and 15 without in each group. The results show that the patterns of hemispheric asymmetry differ in right- and left-handers. They also show that in left-handers these patterns depend on the presence or absence of familial left-handedness, whereas in right-handers the role of this genetic factor is less evident.

Adolescent↗
PubMed1992

Role of the cerebellum in habituation exploration behavior in the rat.

Adult control and cerebellectomized DA/HAN-strained male rats were submitted to habituation of exploration behavior in a test environment consisting of a novel cage in which four objects were displayed. Seven days after the initial session of habituation, retention of the habituation was tested. Within-session habituation was observed in cerebellectomized and control rats. However, retention of habituation was impaired in rats that were cerebellectomized after the initial session but not in those cerebellectomized before the session. These results are consistent with the hypothesis that the cerebellum has a role in memory of habituation to environmental stimuli.

Animals↗
PubMed1992

Role of the cerebellum in spatial orientation in the rat.

Adult DA/HAN strain rats were submitted to a spatial orientation task consisting of finding a reward in an open field. They were first submitted to an initial learning session and 10 days later to a retrieval test. The animals were divided into four groups of five rats each: animals that were cerebellectomized before the initial learning session or after the initial learning session, sham-operated rats, and control (intact) animals. Different parameters that characterize the spatiotemporal organization of the rat's exploratory behavior were quantified. From the results, it can be concluded that the cerebellum is not absolutely necessary in the processes that sustain spatial learning but that it is involved in the mechanisms sustaining focused spatial memory and in the cognitive processes of the motor program elaboration and not only in the regulation of the movement being done.

Animals↗
PubMed1989

Effects of kainic acid lesions of the nucleus reticularis tegmenti pontis on fast and slow phases of vestibulo-ocular and optokinetic reflexes in the pigmented rat.

The nucleus reticularis tegmenti pontis (NRTP) and adjacent pontine reticular formation were lesioned chemically using the neurotoxic agent kainic acid, and the effects of these lesions on horizontal ocular optokinetic and vestibular nystagmus were examined. Eye position was measured in the alert, NRTP-lesioned animals with the electromagnetic search coil technique. Optokinetic and vestibular stimuli consisted of steps of rotations or sinusoidal oscillations of a fullfield visual pattern surrounding the animal or of the animal in total darkness, respectively. In a first group of animals, small unilateral NRTP lesions were produced by placing a single kainic acid injection in the area of the left NRTP. In one third of the animals, ipsilateral quick phases of optokinetic and vestibular nystagmus were abolished. In the remaining animals, quick phases were deficient to various degrees or not affected at all. There were no changes in the characteristics of optokinetic step responses to ipsilateral pattern rotations which activate predominantly optokinetic pathways on the side of the brainstem lesion. In animals with ipsiversive quick phase deficits, contralateral pattern rotations elicited tonic eye deviations. In a second group of animals, large uni- or bilateral lesions were produced by injecting kainic acid into three separate rostral, middle and caudal levels of the right NRTP. These animals had uni- or bilateral quick phase deficits during optokinetic and vestibular nystagmus. Optokinetic nystagmus in response to velocity steps of pattern rotation towards the lesion side was strongly reduced in gain even in those animals that had no apparent deficits in the fast contraversive reset phases. In four out of six animals, responses to sinusoidal optokinetic pattern oscillations were reduced in gain and showed increased phase lags compared to controls. Vestibulo-ocular responses to velocity steps of head rotations were of normal gain but reduced in duration (measured from onset of stimulation to reversal of nystagmus). Sinusoidal vestibulo-ocular responses evoked by head oscillations exhibited reduced gain values and strongly increased phase leads in the frequency range below 0.5 Hz. The vestibular time constant was found to be around 4.5 s in animals with NRTP lesions compared to about 7.5 s in control animals. The present results show that large kainic acid lesions of the NRTP (and adjacent area) do not abolish optokinetic eye movements in the rat, in contrast to what has been reported after electrolytic lesions.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Development of optokinetic neuronal responses in the pretectum and horizontal optokinetic nystagmus in unilaterally enucleated rats.

Responses of single units to constant-velocity rotations of the visual surround (0.25-10 degrees/s) were studied in the pretectum of unilateral enucleated rats at different ages. Enucleation was performed either in the first postnatal week ("early" enucleated rats) or in the adult stage ("late" enucleated rats). Pretectal unitary responses were recorded in early enucleated animals at postnatal day 20-21, 36-49 and, in both experimental groups, in the adult stage. Optokinetic ocular nystagmus was studied in early and late enucleated rats in the adult stage. Gain of optokinetic nystagmus in temporo-nasal stimulus direction was not changed for visual surround rotations of up to 20 degrees/s compared to controls in monocular viewing conditions. At higher stimulus velocities, however, the gain dropped. In naso-temporal stimulus direction, optokinetic nystagmus was improved in gain for optokinetic pattern motions of up to 5-10 degrees/s. There were only minor differences in the gain behaviour of optokinetic nystagmus obtained from early or late enucleated rats. The optokinetic responses of pretectal neurons obtained from early and late enucleated rats were reduced in sensitivity by more than 50%. The response patterns of neurons recorded in the contralateral pretectum relative to the intact eye were shifted by a large amount from directional selective to directional nonselective response types. No such changes were obtained in the ipsilateral pretectum. In contrast to normal rats, there were very few directional selective units responding to temporo-nasal pattern motion. On the other hand, a large proportion of directional selective units responded to naso-temporal pattern motion. These latter units were found in both early and late enucleated rats. A similar response type has previously been described for intact young rats but not for adult rats. The velocity tuning curve of pretectal units studied in the adult stage was similar in shape in early and late enucleated rats and resembled that obtained from enucleated or intact young animals. Our results show that response sensitivity, direction and velocity tuning of pretectal units depend crucially on retinal afferent input originating from both eyes. The data suggest that the response characteristics of many of the pretectal units that are considered to be important for mediating optokinetic reflexes depend on interpretectal signal processing using commissural connections. There is very little evidence for an adaptative structural plasticity of the optokinetic system following loss of one eye. The reduced asymmetry observed in gain of optokinetic responses correlated in both early and late enucleated rats with the shifts observed in the distribution of pretectal unitary response patterns.

Action Potentials↗
PubMed1988

Responses of nucleus reticularis tegmenti pontis neurons to vestibular stimulation in the rat.

Forty-nine neurons were recorded in the nucleus reticularis tegmenti pontis (NRTP) during horizontal vestibular and/or optokinetic stimulation in immobilized pigmented rats. During optokinetic stimulation, the response of NRTP neurons was either unidirectional (51%) or bidirectional (49%). Histological reconstruction showed that unidirectional neurons were located in the dorsal-medial part of NRTP, and bidirectional neurons in the lateral part. All neurons exhibited a response during pure vestibular sinusoidal stimulation in the frequency range 0.025 Hz-0.2 Hz. NRTP neurons were divided into two groups according to their threshold to vestibular stimulation. Group A neurons had a low threshold, a low spontaneous activity and their firing frequency slowly increased with acceleration. Group B neurons showed opposite characteristics. Phase and gain analysis suggested that NRTP neurons carry a head velocity signal. After hemiflocculectomy, the gain of the vestibular response of contralateral NRTP neurons increased. From these data, the role of NRTP in the horizontal vestibulo-oculomotor is discussed.

Action Potentials↗
PubMed1987

Dynamic characteristics of vestibular nuclear neurons responses to vestibular and optokinetic stimulation during vestibular compensation in the rat.

In albino rats and pigmented rats, neurons were recorded extracellularly in the vestibular nuclei during the first 2 weeks after unilateral labyrinthectomy in order to study the neuronal events occurring during vestibular compensation and the effect of unilateral vestibular lesion on the optokinetic responses of neurons in the vestibular nuclei. It was found in albino rats that a re-equilibration took place in the gains of type I neurons between both lesioned and intact sides. The gain of the rare type I neurons on the deafferented side, which was low just after the lesion (t less than 48 h) subsequently increased (48 h less than t less than 14 d) while on the intact side the gain was greater just after the lesion, and then decreased. This re-equilibration of the gains of type I neurons is considered to be the neuronal equivalent of behavioural effects which occur after hemilabyrinthectomy. In pigmented rats, most type I and II VN neurons recorded on both sides 24 to 96 h after the lesion did not respond to pure horizontal OKS, while in controls almost all of them responded. It seems evident that the tonic activation of VN neurons by vestibular afferences is necessary for their responsiveness to pure OKS. However, when comparing the gain/phase of their responses to pure, vestibular and combined optokinetic-vestibular stimulations, it was found that optokinetic inputs improved the performance of type I and II VN neurons on both lesioned and intact sides. Finally, the time course of vestibular compensation is shorter in pigmented rats than in albino rats, since the re-equilibration in gains between the two sides was already reached 4 days after the lesion in the former.

Animals↗
PubMed1984

Responses of prepositus hypoglossi neurons to optokinetic and vestibular stimulations in the rat.

The responses of 47 nucleus prepositus hypoglossi neurons to vestibular optokinetic stimulations in the horizontal plane were recorded in immobilized, pigmented rats. During sinusoidal vestibular stimulation in the dark, type II (62%) and type I (38%) responses were recorded. In addition to the sinusoidal modulation of firing rate, units often showed fast rhythmic increases or decreases in firing (nystagmic modulation). The mean phase of the response relative acceleration measured at 0.025 and 0.2 Hz were 19 and 84 deg., respectively. Some units (25%) showed larger phase-lags. The sensitivities of unit responses at 0.025 and 0.2 Hz were 1.6 and 0.5 spikes X s-1/deg X s-2, respectively. The responses of NPH neurons to binocular optokinetic stimulation were divided in 2 classes: (i) neurons with unidirectional responses (18%) were excited by stimuli moving towards the side of recording and showed no change in firing on oppositely directed stimulation; all of them showed a type II pattern during vestibular stimulation; (ii) bidirectional responses showed an increase in one direction and a decrease in firing for stimulation in the opposite direction. In every case the optokinetic responses were synergistic with the vestibular responses, which consisted of both type I and type II units. On the basis of the directionality of their optokinetic response, the value of their time constants and the shape of their velocity tuning curves, it is suggested that unidirectional type II NPH neurons could serve as relays in the optokinetic pathways between NRTP (or PT) and vestibular neurons. Some other neurons, having time constants particularly long and different for the rising and falling of the response, probably serve other functions.

Animals↗
PubMed1984

An electrophysiological study of pathways mediating optokinetic responses to the vestibular nucleus in the rat.

Intra- and extracellular responses of neurons in the pretectum (Pt), the nucleus reticularis tegmenti pontis (NRTP), the prepositus hypoglossal complex (NPH) and the vestibular nuclei (VN) were recorded during orthodromic/antidromic stimulation of their afferent/efferent fibers. In the Pt, many neurons were excited by stimulation of the contralateral optic nerve (ONc). Comparison of the latencies of evoked presynaptic action potentials and EPSPs yielded a time difference corresponding to one synaptic delay. Forty five per cent of these monosynaptically driven neurons were also excited antidromically from the ipsilateral NRTP. In the NRTP, ONc and Pt stimulations evoked disynaptic and monosynaptic EPSPs, respectively. Thirty six per cent of NRTP neurons orthodromically driven from ONc and/or ipsilateral Pt stimulation were also antidromically invaded from either the contralateral (67%) or the ipsilateral (33%) flocculus but never from both. In the NPH, both ipsilateral Pt and NRTP stimulations excited type II neurons monosynaptically. In addition, EPSPs evoked by Pt stimulation could be mediated to the NPH via a disynaptic route involving the NRTP. In the VN, type II neurons were excited by ipsilateral Pt stimulation. When comparing the latencies of action potentials and EPSPs evoked by Pt stimulation in the NPH and in VN type II neurons respectively, a short, possibly monosynaptic connection, may be postulated between the NPH and the VN. Our results suggest that vestibular neurons may be optokinetically driven from the contralateral eye both via Pt-NPH connections and Pt-NRTP-NPH paths. They also confirm the existence of a transcerebellar route from the Pt via the NRTP to the ipsior contralateral flocculi.

Animals↗
PubMed1982

Non-cerebellar visual afferents to the vestibular nuclei involving the prepositus hypoglossal complex: an autoradiographic study in the rat.

Radioactive amino-acids were injected into the nucleus reticularis tegmenti pontis (NRTP) and the pretectum (PT) in the rat. Beside the labeling of the several nuclei which are known to receive afferents of either the NRTP and/or the PT, monosynaptic projections from these two structures to the prepositus hypoglossal complex (PHN) were demonstrated. Pretectal visual inputs to the vestibular nuclei (VN) may thus be conveyed not only by the classical PT-inferior olive-cerebellar route, but also by two other non-cerebellar ones involving the strong efferent projections of the PHN onto the VN. These last two pathways are strong candidates to account for the residual visual sensitivity of VN neurons after cerebellectomy or inferior olive lesions.

Animals↗
PubMed1982

Optokinetic, vestibular, and optokinetic-vestibular responses in albino and pigmented rats.

Horizontal eye movements and neuronal activity in the vestibular nuclei and pretectum were recorded in albino and pigmented rats in response to optokinetic, vestibular (VS), combined visual-vestibular (VVS) sinusoidal stimulations. 1. VOR slow phase velocity in VS condition leads head velocity. This phase lead is smaller in albino than in pigmented rats. 2. Presence of vision (VVS) improves the phase angle of the VOR in both strains, especially at low frequencies. In pigmented rats the VOR is perfectly compensatory with respect to phase at all frequencies whereas in albinos the eye velocity still leads the head velocity. 3. There is no difference in the response characteristics of vestibular nuclear neurons (VN) to VS between albino and pigmented rats which could explain the difference in their VORs. 4. In the pigmented rat, there is a strong optokinetic input to VN which provokes a shift of the response peak towards peak head velocity. These visual-vestibular interactions at VN level are in agreement with the changes in the phase angle of the VOR. 5. In albino rat, there are no differences in the response characteristics of VN between VS and VVS, thus the decrease of the VOR phase lead observed in VVS compared to VS is due either to visual-vestibular interactions outside of the vestibular nuclei or to some general arousing effect of light. 6. Recording of responses of pretectal neurons to visual stimulation in albino rats has shown that they are activated in a phasic or tonic way by light on ("On cells") or off ("Off cells"). Contrary to the pigmented rat, pretreated neurons in albino exhibited no detectable direction specific optokinetic responses.

Animals↗
PubMed1980

Development of optokinetic responses in vestibular nuclear neurons in the young rat.

Responses of vestibular nuclear neurons (Vn) of the horizontal canal system to optokinetic stimulation could not be elicited before postnatal day 22. Between days 22 and 29 response magnitude gradually increased whereas response phase remained constant. At the end of the first postnatal month the sensitivity of the optokinetic responses was still much less than that measured in adult animals.

Afferent Pathways↗
PubMed1980

Firing characteristics of neurons mediating optokinetic responses to rat's vestibular neurons.

1) The responses of single units in the pretectum (Pt) and in the n. reticularis tegmenti pontis (NRTP) to constant velocity horizontal rotation (0.25--60 deg/s) of a large-field visual pattern were studied in immobilized, non-anesthetized DA-HAN rats. In addition, responses of Pt and NRTP neurons to pure vestibular stimuli (rotation in the dark) were studied. 2) Pt neurons showed seven response types to optokinetic stimulation (Table 1). The most frequent response (48%) consisted of a very rapid increase in firing to steady state on temporonasal motion stimulation of the contralateral eye; nasotemporal stimuli yielded no change in resting rate as did stimulation of the ipsilateral eye. The response maximum occurred at a retinal slip velocity of 1 deg/s. None of the Pt units tested responded to pure vestibular stimuli. 3) NRTP neurons - as Pt units - most frequently (43%) increased their discharge rate on temporonasal stimulation of the contralateral eye and maintained a constant resting rate during nasotemporal motion. Peak response amplitudes also occurred with retinal slip velocites of 1 deg/s. Contrary to the fast time-to-peak of the responses of Pt neurons NRTP units showed a slow rise in frequency of firing to peak response levels. 4) NRTP neurons responded to pure vestibular stimuli (horizontal angular acceleration in the dark). The vestibular responses were synergistic with those evoked in the same neurons by optokinetic stimuli. Thus, the most frequently encountered type of optokinetic response (s. above) showed a type II vestibular response. 5) Comp]arison of OKN and Vn optokinetic responses with those of Pt and NRTP suggests that the unidirectional-selective Pt and NRTP neurons are important links in the central optokinetic path. In addition, the NRTP may represent the site at which the retinal slip signal and the eye velocity signal converge. This convergence has been postulated in models of the system [12].

Animals↗
PubMed1980

Response of central vestibular neurons to horizontal linear acceleration in the rat.

Responses of central vestibular neurons to horizontal sinusoidal translation (F:0.25Hz) were recorded in albino rat. 57.5% of vestibular neurons were responding to this stimulation by a modulation of their firing rate, the mean phase angle of the response, averaged from the whole population being 22 +/- 79 deg. lag, relative to the peak of contralateral acceleration. Dynamic characteristics of phase and gain were studied and appeared to be different from previous reports on primary afferents: the gain decreased or was flat with increasing acceleration at one frequency, and the phase lag which was flat in the same conditions increased with increasing frequency. A phase lead of some units has been observed at low frequency (0.1 Hz). Regarding the convergence between otolith and canal inputs on nuclear vestibular neurons, it was shown that the major pattern of convergence is between canal and otolith inputs of same polarity.

Acceleration↗
PubMed1980

Pathways mediating optokinetic responses of vestibular nucleus neurons in the rat.

1. The effects of various brain lesions on the responses of vestibular nuclear neurons (Vn) of the horizontal semicircular canal system to optokinetic stimulations were studied to elucidate the optokinetic path from the retina to the vestibular nuclei. A previous study performed in intact rats served as a control [2]. 2. It was shown that the pretectal region including the n. of the optic tract is the first central relay in the optokinetic path; it receives its functionally effective input from the contralateral eye. Unilateral lesions of this area rendered all Vn responses unidirectional when tested with binocular stimulation. Lesions of other visual centers such as the superior colliculi or visual cortices had no influence on the optokinetic response properties of Vn. 3. The area of the n. reticularis tegmenti pontis (NRTP) proved to be an important link between pretectum and vestibular nuclei: Unilateral lesions produced effects similar to those described for pretectal lesions. Pretectal axons to NRTP descend lateral to the MLF and tectospinal tract. 4. It was demonstrated that the vestibular commissure plays the crucial role in mediating the mirror image optokinetic effects to Vn on the opposite side and assures the bidirectionality of the responses to binocular stimulation. 5. Cerebellectomy did not significantly affect the Vn responses to the optokinetic stimuli presented in this study. 6. Electrical stimulation of the pretectum excited type II and inhibited type I Vn ipsilaterally and had the opposite effect on Vn located on the opposite side. NRTP stimulation excited type II and inhibited type I ipsilaterally; latency analysis of these effects suggested that the pretectal stimuli excited opsilateral NRTP neurons which, in turn, excited ipsilateral type II Vn. Ipsilateral type I inhibition as well as the concurrent contralateral type II inhibition and type I excitation are produced by the inhibitory action of type II on type I and the commisural system. 7. Systemic application of picrotoxin abolished all optokinetic responses of Vn except the type II activation. This finding further supports the hypothesis described above. 8. Unilateral pretectal or NRTP lesions abolished OKN to surround motion in the direction of the lesion.

Animals↗
PubMed1979

The postnatal development of functional properties of central vestibular neurons in the rat.

The postnatal development of the responses of rat central vestibular neurons to horizontal angular acceleration was studied in the time and frequency domain. The resting discharge was very low and irregular during the first postnatal days, increased gradually and became more regular throughout the first month and reached adult values approximately by the end of the first month. The relative distribution of type I and type II units was the same in all age groups. Threshold for frequency increase to angular acceleration and sensitivity of unit responses became lower and higher, respectively, as time elapsed after birth. Adult values were reached approximately by the end of the first month. There was a slight tendency towards shorter time constants and smaller phase lags in one-month-old animals when compared with the younger animals. The results are discussed in conjunction with similar work performed in vestibular afferents and correlated with known morphological and behavioral studies.

Acceleration↗
PubMed1976

Responses to tilting of fibers of the frog's saccular nerve.

The activity of single fibers from the saccular nerve has been recorded in isolated head preparations in the frog (Rana esculenta). Nearly all the fibers present an activation or a depression of their activity during the tilting movement in a given direction. This is considered to correspond to the existence of two anatomical populations of haircells in the saccular macula which differ in their functional polarization. The activity of only some units (about 40%) remained increased or decreased when the head was in a tilted position for 4-5 min. This shows that the sacculus is sensitive to the direction of gravity.

Animals↗