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W Precht

Publications and source records attributed to W Precht.

At least 55 records · Page 3Linked to original sources
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

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↗
PubMed1980

The role of the crossed and uncrossed retinal fibres in mediating the horizontal optokinetic nystagmus in the cat.

While the horizontal optokinetic nystagmus (OKN) was studied in cats in which the optic chiasma was completely split thus leaving only uncrossed retinofugal fibers intact it was found that both temporonasal and nasotemporal surround motion generated symmetrical OKN. Similar findings were obtained when one optic tract was sectioned and the eye ipsilateral (uncrossed fibers only) or contralateral (crossed fibers only) to the lesion was covered. It is concluded that in the cat the crossed and uncrossed retinofugal fibers are equipotent in mediating symmetrical OKN.

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↗
PubMed1979

Mechanisms of compensation for vestibular deficits in the frog. I. Modification of the excitatory commissural system.

In hemilabyrinthectomized frogs excitatory responses of central vestibular neurons to electrical stimulation of the remaining vestibular nerve were recorded extra- and intracellulary at different stages (0, 3, and 60 days) after the operation. The output pattern of ipsilateral vestibular neurons sending an axon across the midline via the vestibular commissure to the deafferented nucleus did not change postoperatively. The synaptic efficacy of these commissural axons ending on partially deafferented vestibular neurons on the lesioned side increased with time. This enhanced synaptic potency was associated with a shortening in time to peak and duration and an increase in amplitude of the evoked EPSPs. As a result most vestibular neurons were readily excited by single shock stimulation of the contralateral vestibular nerve, a finding which was rarely observed in control animals. These plastic changes are explained by the assumption of reactive synaptogenesis. The consequences of this modification for the readjustment of static and dynamic vestibular reflexes are discussed.

Afferent Pathways↗
PubMed1979

Mechanisms of compensation for vestibular deficits in the frog. II. Modification of the inhibitory Pathways.

In hemilabyrinthectomized frogs inhibitory responses of central vestibular neurons to electrical stimulation of the remaining vestibular nerve were recorded extra- and intracellularly at different stages (0, 3, and 60 days) after the operation. In acute animals inhibition of vestibular neurons following stimulation of the VIIIth nerve is rarely observed. In chronic animals about 30% of the vestibular neurons on the partially deafferented side and about 15% of the vestibular neurons on the intact side are inhibited. The distribution of the latencies of these inhibitory responses is bimodal with ranges from 4 to 14 ms and 18 to 24 ms. Removal of the cerebellum reduced the number of inhibited vistibular neurons and picrotoxin abolished all inhibitory responses. The vestibular input to the cerebellar dorsal rim is bilateral. In chornic animals excitation of Purkinje cells was similar as in acute preparations but many more cells were disfacilitated. Inhibition of partially deafferented vestibular neurons by cerebellar and brain stem neurons increases in parallel with their excitatory commissural input. The balance between these plastic changes may be crucial for the functional recovery of appropriate compensatory reflexes.

Afferent Pathways↗
PubMed1979

Timing of bilateral cerebellar output evoked by unilateral vestibular stimulation in the frog.

Electrical stimulation of one VIIIth nerve evoked simple spike activity in Purkinje cells located on either side of the cerebellum. This cellebullar output was delayed by ca. 10 ms with respect to its mossy fiber-parallel fiber input. The onset of the cerebellar output occurs on the average simultaneously on either side of the corpus cerebelli. The delay is explained by slowly rising EPSPs in PC induced by primary afferent and by second and higher order vestibular fibers. The latter inputs are stronger and terminate ipsi- and contralaterally in the granular layer.

Action Potentials↗
PubMed1979

Effects of cerebellectomy on the cat's vertical vestibuloocular reflex.

The effects of cerebellectomy on the semicircular canal evoked responses recorded from individual vertical and oblique eye muscles were studied in cats anesthetized with Ketamine. The phase lag relative angular acceleration of the electromyographic response was consistently smaller over the frequency range tested (0.02--1.0 Hz) in cerebellectomized than in intact animals. This finding indicates that the time constant of the central, neural integrator was shifted towards smaller values by the lesion. This was also suggested when the vertical eye movements generated by rotation about the pitch axis were recorded in the fully alert animal. In addition, the EOG data show that the phase of the VOR in the low frequency range was not altered following cerebellectomy suggesting that the macular influences were still present. When the EMG responses of the superior oblique (SO) and superior rectus (SR) muscles were studied in their presumed main mode, i.e. roll-canal and pitch-canal, respectively, no difference was noted in hemicerebellectomized animals when compared to intact control animals. However, when SO and SR were studied in pitch-canal and roll-canal rotation, respectively, dramatic changes in the response pattern were noted in lesioned animals.

Animals↗
PubMed1979

Functional deficits in the optokinetic system of albino rats.

Vestibular nuclear neurons of the horizontal canal system (Vn) of albino rats (Wistar) failed to respond to optokinetic stimulation. Similarly, optokinetic nystagmus (OKN) could not be elicited in these animals. Brown (DA--HAN) rats, however, consistently showed optokinetic responses of Vn and OKN to identical stimuli.

Animals↗