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J T Schmidt

Publications and source records attributed to J T Schmidt.

47 records · Page 3Linked to original sources
PubMed1980

Localization of alpha-bungarotoxin binding sites to the goldfish retinotectal projection.

The optic tectum of the goldfish Carassius auratus is a rich source of alpha-bungarotoxin (alpha-Btx) binding protein. In order to determine whether some fraction of these receptors is present at retinotectal synapses, we have compared the histological distribution of receptors revealed by the use of [125I]alpha-Btx radioautography to the distribution of optic nerve terminals revealed by the use of cobalt and horseradish peroxidase (HRP) techniques. The majority of alpha-Btx binding is concentrated in those tectal layers containing primary retinotectal synapses. The same layers contain high concentrations of acetylcholinesterase (AChE), revealed histochemically. Following enucleation of one eye, there is a loss of alpha-Btx binding in the contralateral tectum, observed both by radioautography and by a quantitative binding assay of alpha-Btx binding. Approximately 40% of the alpha-Btx binding sites are lost within two weeks following enucleation. By contrast, no significant change in AChE activity could be demonstrated up to 6 months following enucleation. These results are discussed in light of recent studies which show that the alpha-Btx binding protein and the nicotinic acetylcholine receptor are probably identical in goldfish tectum. We conclude that the 3 main classes of retinal ganglion cells projecting to the goldfish tectum are nicotinic cholinergic and that little or no postdenervation hypersensitivity due to receptor proliferation occurs in tectal neurons following denervation of the retinal input.

Acetylcholine↗
PubMed1980

Electrophysiologic evidence that retinotectal synaptic transmission in the goldfish is nicotinic cholinergic.

A previous study identified, by conduction velocity following optic nerve shock, 3 classes of retinal fibers which project to 3 distinct laminae of the goldfish optic tectum. In the present study, the effect of various pharmacological agents on the synaptic efficacy of each of the 3 classes of retinal fibers was assessed by the use of current source-density analysis. All 3 classes of optic fibers appear to be nicotinic cholinergic. Six different nicotinic antagonists were tested. All 6 were effective in decrementing the responses of all 3 classes to a criterion level: alpha-bungarotoxin (10-8 M), alloferin (10-5 M), curare (10-4 M), metocurine (10-4 M), hexamethonium (10-4 M) and gallamine (10-3 M). Atropine, a muscarinic antagonist, had only a slight effect even at 10-3 M. Five nicotinic agonists tested also decremented synaptic responses: nicotine (10-5 M), carbamylcholine (10-4 M), acetylcholine (10-4 M), succinyl choline (10-4 M) and decamethonium (10-3 M), presumably via cellular depolarization and receptor desensitization. Two inhibitors of acetylcholinesterase prolonged the response at 10-4 M and decremented it as well at 10-3 M. Hemicholinium 3, an inhibitor of the high affinity uptake of choline, produced a gradual activity-dependent decrement in the responses. Beta-bungarotoxin, a presynaptically-acting toxin, abolished not only the postsynaptic components but also the presynaptic components at 10-6 M. In all other cases the presynaptic deflections were generally unaffected, and with the exception of the toxins, a return to at least 90% of the control value was achieved. In contrast, GABA (10-3 M) and bicuculine (10-4 M) both produced no discernible effect on the 3 classes of responses, and glutamate (10-3 M) produced only a slight decrement, which probably represents a non-specific effect.

Animals↗
PubMed1979

The laminar organization of optic nerve fibres in the tectum of goldfish.

Potentials in the tectum of large (12--20 cm) goldfish, evoked by stimulation of the optic nerve, were recorded extracellularly with double-barrelled electrodes (d.c., saline and a.c., Woods metal--Pt). Four fibre groups (E, M1, M2, M3) were recorded at latencies of approximately 2, 3, 5 and 8 ms after stimulation (conduction velocities of approximately 7, 5, 3 and 2 m/s). The same four groups were recorded from the optic nerve when the tectum was stimulated. The fastest fibre groups (E) did not give rise to a postsynaptic wave. Fibre groups M1, M2 and M3 gave rise to postsynaptic potentials which, following computation of their second spatial derivatives with depth, were found to have current sinks at depths of approximately 100-150 micrometers, 150--200 micrometers and 250--350 micrometers respectively. Thus the fastest conducting retinotectal fibres make their synapses most superficially, the opposite of the arrangement in the frog tectum. These postsynaptic waves fatigued at repetitive stimulus rates of 20--50 per second, and in twin pulses at interstimulus intervals of 10--15 ms; and they were reversibly blocked by topical application of pentobarbitol. The fibre potentials, however, were virtually undecremented under these conditions. To compare these electrophysiological findings with the anatomy, the cobalt procedure was used to visualize the profiles of the optic fibres in the various tectal laminae. A thick dense projection filled the superficial grey and white (s.g.w.) layer, and there was a thin satellite band just superficial to it. In addition, there were two deeper bands of sparse innervation, in the middle of the central grey zone (c.g.) and in the deep white (d.w.) layer. These bands were associated with the field potential sinks through lesions made with recording electrodes. The two deep bands correspond to the M3 fibre group. The dense s.g.w. innervation contains both the M1 and M2 fibre groups, the M1 just superficial to the M2. The fastest fibre group, E, which had no postsynaptic wave associated with it, persisted at least six weeks after retinal removal, and probably represents efferent cells with fibres projecting back through the optic nerve to the retina. Filled cell profiles could not be positively identified with the cobalt technique, but could be seen with the HRP technique, when the optic afferents were first allowed to degenerate. The filled cells were the pyramidals of the s.g.w. layer.

Animals↗
PubMed1978

Independent biaxial reorganization of the retinotectal projection: a reassessment.

It has been previously suggested that the retinotectal projection can reorganize independently along two orthogonal tectal axes. This possibility was reexamined by removing roughly a quarter of the retina and slightly less than a quarter of the tectum. In the tectal case, the unseated fibers arborized rostral to the ablation, but not lateral to it, and the projection shifted irrespective of tectal axes to maintain topographic order and a roughly uniform representation of retinal areas. In the retinal case, expansion into the denervated quadrant was only from the rostral, never from the medial or lateral directions. Analysis of the movements of fiber arbors shows that they respond to local competition for tectal space rather than following tectal axes.

Animals↗
PubMed1978

The paths and destinations of the induced ipsilateral retinal projection in goldfish.

Adult goldfish had one tectal lobe removed surgically, and several months later, the eye contralateral to the missing tectum was injected with radioactive proline. Radioautographs of the brains were studied to trace the paths and termination sites of the optic fibers. The optic tract decussated at the chiasm, as normally, but then ran caudally in a large neuroma on the tectum-less side of the brain. Substantial numbers of fibers left this neuroma to enter two or more of five commissures, through which they recrossed the midline. These commissures: transverse, minor, horizontal, posterior and ansate, ordinarily contain few or no optic fibers. All are normally linked with the tectum. Negligible numbers of aberrant optic fibers recrossed the midline elsewhere. On the intact side of the brain, ipsilateral to the injected eye, the optic fibers innervated some or all of the nuclei and areas normally served by contralateral retinal fibers. An earlier behavioral study of these same fish had shown that some of them made reversed optokinetic nystagmus in response to stripe movement seen by the eye projecting ipsilaterally; others failed to respond to stimuli through this eye. In all the reversed responders, a caudal group of retinal projection sites was labeled ipsilaterally. This included the basal optic nucleus and the caudal portions of nucleus dorsolateralis thalami and area pretectalis. In the non-responders, these targets were not labeled ipsilaterally. Together, these results suggest that one or more of these three sites is or are responsible for optokinetic nystagmus in normal goldfish.

Animals↗
PubMed1977

Bilateral tectal innervation by regenerating optic nerve fibers in goldfish: a radioautographic, electrophysiological and behavioral study.

Following unilateral enucleation and optic nerve crush in goldfish, the remaining nerve regenerates and innervates both optic tecta. Approximately 5% of the nerve fibers reach the ipsilateral optic tectum (IOT) via the ipsilateral tract at the chiasma. Comparable debris in both tracts was not sufficient to result in an IOT projection since when both nerves were crushed simultaneously the usual pattern was seen, i.e., each nerve innervated a contralateral optic tectum (COT). When the arrival of one nerve at the chiasma was delayed by staggering the nerve crushes, the nerve that first arrived at the chiasma partially innervated the Iot. In most instances the entire IOT was innervated, however, the stratigraphic distribution of fibers in the various tectal lamina was atypical. Electrophysiological analysis indicated that fibers from each area of the retina innervated the IOT visuotopically. The COT was ablated in order to determine whether the IOT projection could mediate behavior. All fish failed to respond to changes in illumination as measured by respiration and failed to swim with or against the stripes in an optomotor drum. Thus, the IOT input, possibly because of its sparseness, could not be shown to be behaviorally functional.

Animals↗
PubMed1977

Reversed visuomotor behavior mediated by induced ipsilateral retinal projections in goldfish.

1. When one optic lobe of a goldfish is removed and the optic nerve from the contralateral eye is deflected ipsilaterally, the nerve innervates the intact, previously foreign side. When the control eye is left intact, the animal shows normal swimming and coordination of head and eyes. In some cases, however, optokinetic nystagmus evoked through the experimental eye is reversed, indicating a functional ipsilateral projection which was apparently outweighed by the normal projection during swimming. 2. When the same surgical procedure is accompanied by partial or complete destruction of the control eye, the animals show overt reversal of visuomotor behavior soon after the ipsilateral projection is established. They make a spontaneous nystagmus and circle continuously. The nystagmus and the circling persist in total darkness for days before they are extinguished. They resume as soon as the animal returns to light. 3. The vestibuloocular reflex is biased differently from normal, but the sign of the gain is normal. 4. We conclude that the neurological reversal of vision triggered the nystagmus and the circling, and that the many months with reversed vision resulted in some longer lasting change in the nervous system such that the behaviors persisted even in the absence of moment-to-moment visual stimulation.

Animals↗
PubMedDate not supplied

Nucleus isthmi in goldfish: in vitro recordings and fiber connections revealed by HRP injections.

Recordings of field potentials in nucleus isthmi (NI) were obtained in an in vitro preparation of goldfish brain using a lateral approach. Horseradish peroxidase (HRP) was injected from recording electrodes to verify recordings within the nucleus and to label axonal pathways and cell bodies. Activity in NI was repetitive and could be elicited by stimulation of the optic nerve, tectum, pretectum, or tectobulbar tract. Spontaneous activity was present in some preparations and consisted of bursts with intervening silent periods. Anatomical and electrophysiological evidence indicated that the primary isthmotectal pathway is composed of fine fibers that exit NI rostrally and pass through pretectum to enter tectum rostrally. An afferent pathway consisting of both fine- and large-diameter fibers entered NI ventromedially; the large diameter axons have been previously reported in percomorph fishes, but were not thought to be present in cyprinids such as goldfish. The large diameter axons arise from labeled cell bodies in the region of the lateral thalamic nucleus. No labeled cell bodies were seen in ipsilateral nucleus pretectalis superficialis, pars magnocellularis, where they are seen in percomorphs. The fine axons, which have not been reported in percomorph fishes, were shown to arise from tectal bipolar (type VI) neurons. As in percomorphs, tectal type XIV neurons were also labeled. This and corroborating recordings from nucleus isthmi constitute the fist demonstration of a tectoisthmic projection in a cyprinid fish.

Animals↗
PubMedDate not supplied

The modulatory cholinergic system in goldfish tectum may be necessary for retinotopic sharpening.

The cholinergic circuit within the tectum and the cholinergic input from the nucleus isthmi mediate a presynaptic augmentation of retinotectal transmitter release via nicotinic receptors. In this study, the cholinergic systems were either eliminated using the cholinergic neurotoxin AF64A or blocked using nicotinic antagonists to test for effects on the activity-driven sharpening of the regenerating retinotectal projection. The effectiveness of the AF64A was verified by recording field potentials elicited by optic tract stimulation and by immunohistochemical staining for choline acetyltransferase (ChAT). At 1 week after intracranial (IC) injection of AF64A (12 to 144 nmoles) into the fluid above the tectum, field potentials showed a selective dose-dependent decrement of the cholinergic polysynaptic component with no effect on the amplitude of the glutamatergic monosynaptic component. The decrement was only partially recovered in recordings at 2 and 6 weeks. In normal fish, the ChAT antibody stains a population of periventricular neurons, their apical dendrites, and a dense plexus within the optic terminal lamina that consists of their local axons and fine dendrites and of input fibers from the nucleus isthmi. One week after IC AF64A injection (48-72 nmoles), most immunostaining in superficial tectum was lost but most neuronal somas in the deep tectum could still be seen, and staining in the tegmentum below the tectum was completely intact. At 2 weeks and later, the staining of neuronal somata largely recovered, but staining of the superficial plexus did not. AF64A treatment at 18 days after nerve crush, when regenerating retinal fibers are beginning to form synapses, prevented retinotopic sharpening of the projection. Recordings showed a rough retinotopic map on the tectum but the multiunit receptive fields (MURFs) at each tectal point averaged 34 deg vs. 11 deg in vehicle-injected control regenerates. AF64A treatment before nerve crush also blocked sharpening, ruling out a direct effect on retinal growth cones or retinal fibers, as AF64A rapidly decomposes, whereas its effect on the cholinergic fibers is long-lasting. IC injection or minipump infusion of the nicotine antagonists alpha-bungarotoxin (alpha BTX), neuronal bungarotoxin (nBTX), and pancuronium during regeneration also prevented sharpening (MURFs averaging 29.4 deg, 33.0 deg, and 31.4 deg, respectively). Control Ringer's solution infusions or injections over the same period (19-37 days postcrush) had no effect on regenerated MURF size (11.7 deg). The results show that the cholinergic innervation, which modulates transmitter release, is required for activity-driven retinotopic sharpening, thought to be triggered by NMDA receptor activation.

Action Potentials↗