PubMed Health⌕ Search

Biomedical subjects

O Hardy

Publications and source records attributed to O Hardy.

31 records · Page 2Linked to original sources
PubMed1985

[Discharge mechanism of pigeon optic tectum neurons in an in vitro preparation].

The pattern of discharge of neurones of the pigeon's optic tectum to directly injected depolarizing current was investigated in in vitro slice preparation. Three patterns of discharge were found: some neurones (types I and II) give a tonic response: type I-neurones exhibited a repetitive firing whereas type II-neurones showed grouped discharges (doublets or triplets). Type III-neurones displayed a phasic response formed by a few action potentials of decreasing amplitude, triggered at the onset of the current pulse. Each pattern of response was associated with a specific shape of action potential.

Action Potentials↗
PubMed1984

Postsynaptic potentials in neurons of the pigeon's optic tectum in response to afferent stimulation from the retina and other visual structures: an intracellular study.

The responses of the cells in the pigeon's optic tectum to electrical stimulation of the contralateral optic nerve, the ipsilateral visual Wulst and the opposite optic tectum were intracellularly recorded. Optic nerve or visual Wulst stimulation elicited 3 types of responses: (1) a pure EPSP which gave rise to one or two action potentials; (2) an EPSP which sometimes gave rise to a spike, followed by an IPSP; and (3) a pure IPSP. Opposite tectum stimulation evoked in the tectal cells either a pure IPSP or a pure EPSP. The mono- or polysynaptic nature of the pathways involved in the excitatory and inhibitory responses of the tectal cells was assessed by increasing the frequency of the optic nerve stimulation. At low stimulus rates (2-6 Hz), all the excitatory events showing latencies longer than 5 ms were blocked suggesting that they were polysynaptic. Excitatory events having latencies shorter than 5 ms were generally able to follow high rate frequencies of optic nerve stimulation (40, 50 or 90 Hz) and we considered them to be monosynaptic. All but 3 IPSPs evoked by optic nerve stimulation, were blocked by stimulus rates beyond 5 Hz. Thus, although most IPSPs are generated through polysynaptic paths, direct retino-tectal inhibitory paths may also exist. The latency of the responses of individual cells to optic nerve, visual Wulst and opposite tectum stimulation show that the polysynaptic IPSPs to optic nerve stimulation did not involve relays in the visual Wulst or the opposite tectum.

Afferent Pathways↗
PubMed1984

Suppressive regions in the visual receptive fields of single cells of the pigeon's optic tectum.

Single unit extracellular recordings were obtained from non-directional and from directionally selective cells in the pigeon's optic tectum. Non-directional cells were classified according to their excitatory dynamic profiles into three classes. Class A: cells showing spatially superimposed light and dark regions in their fields. Class B: cells showing spatially separated light and dark regions in their fields. Class C: cells which responded exclusively to one sign of contrast. Most of the cells in our sample showed a suppressive region outside the excitatory area from where moving stimuli were able to reduce the units' "spontaneous" background firing. Suppressive regions were found in directionally selective as well as in non-directional cells, regardless of their dynamic excitatory profiles, with the exception of Class C cells. Evidence of spatial overlapping between the excitatory and the suppressive region was obtained with both moving and flashed stimuli. Furthermore, suppressive antagonistic effects were observed in Class B cells.

Action Potentials↗
PubMed1983

Receptive field properties of single cells in the pigeon's optic tectum during cooling of the 'visual wulst'.

In birds, efferents from the visual telencephalon (visual wulst) terminate in the ipsilateral and contralateral optic tectum. This study concerns the influence of a bilateral cryogenic block of the wulst on the receptive field properties of the visual tectal cells in the pigeon. Tectal units were tested for their responses to static and moving stimuli before, during and after cooling the wulst. For some units the cryogenic block of the wulst was repeated twice. The responsiveness to static and moving stimuli was decreased in most of the tectal cells when the neural activity of the wulst was blocked. In contrast, in some units cooling the wulst provokes an increase of responsiveness. These results indicate that the wulst-tectum path is able to convey both excitatory and inhibitory influences. Other receptive field properties such as the spatial location of the light and dark excitatory regions in the field, the effect of the surround, the size and shape of the excitatory region, the relative responsiveness to static and moving stimuli and the 'spontaneous activity' were not affected by wulst cooling. Directional tuning curves were obtained in 18 directionally selective cells before, during and after wulst cooling. In 6 of them the cryogenic block provoked a reduction in directional selectivity either by way of a reduction of the preferred response (4 cells) or by way of an increase of the non-preferred responses (2 cells). In two others directionally selective cells, cooling the wulst provoked a total loss of directional selectivity due to a reduction of the response to the preferred direction together with an increase of the response to the null direction. These results show: (1) that the retinal directional selective input to the tectum is affected by the cryogenic block of the wulst; and (2) that the visual wulst provokes a sharpening of the directional tuning at the optic tectum level.

Animals↗
PubMed1982

[Influence of visual telencephalon (wulst) on directional selective neurons of pigeon's optic tectum (author's transl)].

The influence of the visual telencephalic projection area (Wulst) upon directional selective cells in the Pigeon's optic tectum was studied through reversible cold block of this telencephalic region. About half of the cells studied were affected during Wulst cooling. The effect was either a total loss or a marked reduction of the cell directional selectivity. These results indicate that the Wulst plays an important role in controlling the directional selectivity in the Pigeon's optic tectum.

Animals↗
PubMed1982

The spatial organization of the excitatory regions in the visual receptive fields of the pigeon's optic tectum.

The spatial location of the excitatory regions in the receptive field of cells in the pigeon's optic tectum was analyzed with light and dark edges moving at a constant velocity. The tectal cells were classified into two main groups: 1-cells showing spatially overlapping light and dark excitatory regions in their receptive field (60%); cells showing spatially separated light and dark excitatory regions in their receptive field (32%). A small number of cells discharged only to one sign of contrast. These results were confirmed by testing the cells with light bars of various widths. Latency studies were carried out with single edges moving at a series of constant velocities. In most cases, for any given cell the light and dark edge discharges were shown to have similar latencies. These results also indicate that the relative location of the excitatory regions in the receptive field of most tectal cells was not significantly affected by the latency of the discharges.

Animals↗
PubMed1978

Brain stem nuclei giving fibers to lobules VI and VII of the cerebellar vermis.

The HRP method has been used to identify all the brain stem nuclei, which may project to lobule VI and/or VII of the posterior cerebellar vermis. Three tentative degrees of labeling of the different structures have been assigned: 'massive', 'clear' and 'discrete'. (1) Massive projections have been found to reach lobule VI and VII from the inferior olive and lobule VII only from the nucleus reticularis tegmenti pontis. (2) Clear projections have been found to reach lobule VI only from the pontine nuclei, the nucleus reticularis tegmenti pontis, the nucleus reticularis lateralis and the reticularis paramedianus; lobule VII only from the raphe nuclei, and both VI and VII from the perihypoglossal and vestibular nuclei. (3) Discrete projections have been found to reach lobule VI and VII from the deep cerebellar nuclei; lobule VI only from the nucleus tracti solitarii and nucleus cuneatus externus; lobule VII only from the nucleus lemnisci lateralis pars ventralis, the nuclei parabrachiales and the nucleus subcoeruleus.

Animals↗