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L Cazin

Publications and source records attributed to L Cazin.

64 records · Page 4Linked 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

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↗
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↗
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↗