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At least 397 records · Page 22Linked to original sources
PubMed2002

Morphological characteristics and central projections of two types of interneurons in the visual pathway of Hermissenda.

The synaptic interactions between photoreceptors in the eye and second-order neurons in the optic ganglion of the nudibranch mollusk Hermissenda are well characterized. However, the higher-order neural circuitry of the visual system, consisting of cerebropleural interneurons that receive synaptic input from photoreceptors and project to pedal motor neurons that mediate visually guided behaviors, is only partially understood. In this report we have examined the central projections of two identified classes of cerebropleural interneurons that receive excitatory or inhibitory synaptic input from identified photoreceptors. The classification of the interneurons was based on both morphological and electrophysiological criteria. Type I interneurons received monosynaptic excitatory or inhibitory synaptic input from identified photoreceptors and projected to postsynaptic targets within the cerebropleural ganglion. Type II interneurons, characterized here for the first time, received polysynaptic excitatory or inhibitory synaptic input from identified photoreceptors and projected to postsynaptic targets in either the ipsilateral pedal ganglion or the contralateral cerebropleural ganglion. Type I interneurons exhibited unique intraganglionic projections to different regions of the cerebropleural ganglion, depending on whether they received excitatory or inhibitory synaptic input from identified photoreceptors. Type I interneurons that received monosynaptic excitatory input from identified B photoreceptors terminated near the cerebropleural commissure and had multiple regions of varicosities located at branches that projected from the primary axon. Type I interneurons that received monosynaptic inhibitory input from identified B photoreceptors projected to the anterior cerebropleural ganglion and exhibited varicosities localized to the terminal region of the primary axonal process. Type II interneurons that received polysynaptic inhibitory input from identified photoreceptors projected to the contralateral cerebropleural ganglion. Most type II interneurons that projected to the pedal ganglia received polysynaptic excitatory input from identified photoreceptors. These results indicate that there is at least one additional interneuron in the higher-order visual circuit between type I interneurons and pedal motor neurons responsible for the generation of phototactic locomotion in Hermissenda.

Action Potentials↗
PubMed1993

A possible visual pathway to the cat caudate nucleus involving the pulvinar.

Electrical stimulation of the thalamic nucleus pulvinar was found to influence unit activity in the feline caudate nucleus. Twenty-six (18.3%) units were encountered, in this subcortical region of the brain, that responded to activation of the pulvinar input in anesthetized cats and 41 (54%) in awake animals. In the two types of experiments, stimulation of the pulvinar induced mainly an initial excitatory reaction (81% and 78% of responsive cells, respectively). A latency analysis indicated that the majority of responses occurred at a long latency, while 9 (34.6%) cells in anesthetized cats and 5 (12%) in awake animals were excited at a short latency. The short latency is compatible with the involvement of a monosynaptic pathway between the pulvinar and the caudate nucleus. Units that responded to thalamic stimulation were found predominantly in the posterior regions of the caudate nucleus. These results confirm previous neuroanatomical findings of a direct projection from the pulvinar to the feline caudate nucleus. In awake animals, neurons activated by pulvinar stimulation were also tested, using visual stimuli of various orientations. Out of 41 units, 63% were classified as having "visual responses". Of these, 5 cells were found to respond selectively to a particular orientation of the visual stimulus. Three of these were excited at a short latency by pulvinar stimulation. The possible involvement of a direct pathway from the pulvinar to the caudate nucleus in the processing of visual information is discussed.

Animals↗
PubMed1976

[A new visual pathway in an anour amphibian, Discoglossus pictus].

The retino-tectai projections of the Anura Discoglossus pictus were examined on seventeen adult specimens unilaterally enucleated. After a postoperative survival period of 9 to 105 days, the degenerating fibers and terminals were shown by Nauta and electromicroscopic techniques. This work points out the existence of a direct ipsilateral retino-tectal pathway in Anura. Typical terminal degenerations were seen in the postero-medial part of the ipsilateral tectum. The implications of this new anatomical pathway in binocular vision is discussed.

Animals↗
PubMed1981

Visual pathways and acuity hooded rats.

Three experiments on the effects of lesions of the visual system on contrast-detection in hooded rats are described, in which the ability of rats to detect stationary high-contrast square-wave gratings of various fundamental frequencies presented in the central visual field was measured before and after operation. The results suggested the following conclusions: (i) The pathways from retina to striate cortex via dorsal lateral geniculate nucleus (dLGN) conveys information about high spatial frequencies sufficient for normal detection of these gratings, that is up to about 1 cycles/deg. It may be the only pathway to carry this information, and may thus play a unique role in the analysis of fine detail. The high-frequency information is probably relayed from striate cortex to extrastriate cortex, rather than to subcortical sites. (ii) The superior colliculus receives information from the retina up to at least 0.7 cycles/deg, which it then relays to extrastriate visual cortex, probably via the lateral posterior nucleus of the thalamus. (iii) Neither the projections from superior colliculus to other, non-thalamic sites nor the remaining pathways from the retina (e.g. to ventral LGN) appear to carry contrast information higher than 0.3 cycles/deg. These sets of projections therefore do not appear to be used for precise analysis of stationary scenes. These findings suggest that there are considerable similarities between the visual systems of rats and other mammals with respect to the routing of information about stationary spatial contrast, and may help to explain the results of some experiments that have used tasks besides contrast-detection to assess the visual capacities of rats after lesions.

Animals↗