Evolution of Nucleus Isthmi

2008 ◽  
pp. 1258-1262
Author(s):  
Elizabeth Dudkin ◽  
Edward Gruberg
Keyword(s):  
Nucleus Isthmi

Responses of the teleostean nucleus isthmi to looming objects and other moving stimuli

2006 ◽  
Vol 23 (2) ◽  
pp. 209-219 ◽  
Author(s):  
SHAWN P. GALLAGHER ◽  
DAVID P.M. NORTHMORE
Keyword(s):  
Visual Field ◽  
Neural Activity ◽  
Three Dimensional ◽  
Object Motion ◽  
Activity Levels ◽  
Nucleus Isthmi ◽  
Spike Density ◽  
Ball Size ◽  
Longitudinal Body Axis ◽  
The Right

Visually evoked extracellular neural activity was recorded from the nucleus isthmi (NI) of goldfish and bluegill sunfish. When moving anywhere within the right eye's visual field, three-dimensional checkered balls or patterns on a computer screen evoked bursts of spikes in the left NI. Object motion parallel to the longitudinal body axis gave responses that habituated markedly upon repetition, but movement into recently unstimulated regions of the visual field gave vigorous responses. Thus, while NI's response is not visuotopic, its habituation is. An object approaching the animal's body generated a rising spike density, whereas object recession generated only a transient burst. During the approach of a checkered stimulus ball, average NI spike density rose linearly as the ball-to-eye distance decreased and at a rate proportional to the ball's speed (2.5–30 cm/s). Increasing ball size (2.2–9.2 cm) did not affect the rate of activity rise at a given speed, but did increase overall activity levels. NI also responded reliably to expanding textures of fixed overall size. The results suggest that NI signals changes in motion of objects relative to the fish, and estimates the proximity of approaching objects.

Central Mechanisms of Frog Calling

Behaviour ◽  
1966 ◽  
Vol 26 (3-4) ◽  
pp. 251-285 ◽  
Author(s):  
Robert S. Schmidt
Keyword(s):  
Rana Pipiens ◽  
Hormone Receptors ◽  
Acoustic Stimulus ◽  
Control Mechanisms ◽  
Nucleus Isthmi ◽  
Hyla Cinerea ◽  
Midbrain Tegmentum ◽  
Inspiratory Phase ◽  
Ventral Thalamus ◽  
The Brain

AbstractRelease calling and warning crying in Rana pipiens are described and compared with breathing. Vokalizations consist of a vocal phase, which is merely a modification of the expiratory phase of breathing, followed by an inspiratory phase, which is identical to inspiratory phase of breathing. Electrical and mechanical stimulation of the brain and brain lesions are used to locate some of the central mechanisms controlling release calling and warning crying in Rana pipiens, and mating calling in Rana pipiens and a number of hylids (mainly Hyla cinerea). It is concluded that the main control mechanisms are in the trigeminoisthmic tegmentum (below the nucleus isthmi). Mating calling requires, in addition, input transmitted through the ventral thalamus from hormone receptors in the preoptic area. Mating calling can be evoked in hylids by presenting them with recordings of specific calls. The mechanisms for responding to an acoustic stimulus are probably located in the anterior medulla and midbrain tegmentum (below the nucleus isthmi). Mating calling was evoked in two Hyla cinerea females after replacing the ovaries with Rana testes and injecting Rana pituitaries. It is suggested that release calling evolved from breathing, and that warning crying and mating calling may then have evolved from release calling.

Development of the nucleus isthmi in Xenopus, II: Branching patterns of contralaterally projecting isthmotectal axons during maturation of binocular maps

1989 ◽  
Vol 2 (2) ◽  
pp. 153-163 ◽  
Author(s):  
Susan B. Udin
Keyword(s):  
Optic Nerve ◽  
Horseradish Peroxidase ◽  
Visual Cues ◽  
Visual Fields ◽  
Physiological Data ◽  
Nucleus Isthmi ◽  
Anterograde Transport ◽  
Branching Patterns ◽  
Juvenile Stages ◽  
Contralateral Eye

AbstractThe tectum of Xenopus frogs receives input from both eyes. The contralateral eye's projection reaches the tectum directly, via the optic nerve, and the ipsilateral eye's projection reaches the tectum indirectly, via the nucleus isthmi. Under normal conditions, the topography of the ipsilateral map relayed from the nucleus isthmi is in register with the topography of the retinotectal map from the contralateral eye. During development, the process of aligning the two maps is complicated by the dramatic changes in binocular overlap of the two eyes' visual fields which take place during late tadpole and juvenile stages. The goal of this study is to determine the branching patterns of contralaterally projecting isthmotectal axons before, during, and after the period of rapid eye migration.Isthmotectal axons were filled by anterograde transport of horseradish peroxidase (HRP) from the nucleus isthmi. The results show that crossed isthmotectal axons enter the entire extent of the tectum before binocular overlap begins to increase. Therefore, binocular overlap is not necessary for the initial isthmotectal projection to span the tectum. The density of isthmotectal branches rises dramatically at the same time that the eyes begin to shift. During the period when eye migration is most rapid, many isthmotectal axons form arbors which resemble adult arbors but which extend over greater proportions of the tectal surface.The axons appear to be directed toward appropriate mediolateral positions as they enter the tectum. Their trajectories are roughly rostocaudal, with relatively little change along the mediolateral dimension. These data, when combined with available physiological data, suggest that mediolateral order is initially established by vision-independent mechanisms but can be altered by vision-dependent mechanisms. Rostrocaudal order becomes discernable only at the time when binocular visual cues become available and appears to be established primarily on the basis of the activity of the retinotectal and isthmotectal axons.

GABAergic visual pathways in the frog Rana pipiens

2001 ◽  
Vol 18 (3) ◽  
pp. 457-464 ◽  
Author(s):  
ZHENG LI ◽  
KATHERINE V. FITE
Keyword(s):  
Optic Tectum ◽  
Rana Pipiens ◽  
Visual Pathways ◽  
Second Order ◽  
Gamma Aminobutyric Acid ◽  
Nucleus Isthmi ◽  
Double Labeling ◽  
Inhibitory Neurotransmitter ◽  
Vertebrate Brain ◽  
Pretectal Nucleus

Gamma-aminobutyric acid (GABA) is the most prevalent inhibitory neurotransmitter in the vertebrate brain. It can exert its influence either as GABAergic projection pathways or as local interneurons, which play an essential role in many visual functions. However, no GABAergic visual pathways have been studied in frogs so far. In the present study, GABAergic pathways in the central visual system of Rana pipiens were investigated with double-labeling techniques, combining immunocytochemistry for GABA with Rhodamine microspheres for retrograde tracing. Three GABAergic visual pathways were identified: (1) a retino-tectal projection, from retina to the contralateral optic tectum (OT); (2) an ipsilateral projection from the nucleus of the basal optic root (nBOR) to the pretectal nucleus lentiformis mesencephali (nLM); and (3) a second-order pathway from the nucleus isthmi (NI), bilaterally, to the optic tectum. These results indicate that GABA is involved in both first-order (retina to optic tectum) as well as second-order (nucleus isthmi to optic tectum) visual projections in Rana pipiens, and may play a major role in mediating visuomotor reflexs such as optokinetic nystagmus or other visually guided behaviors.

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