[Neuronal reactions of the inferior olive and cerebellum to light and stimulation of the superior colliculi of the corpora quadrigemina].
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Differential turnover of tubulin and neurofilament proteins in central nervous system neuron terminals.
The transport of tubulin and neurofilament protein subunits from the preterminal axons of guinea pig retinal ganglion cells into their presynaptic terminals in the superior colliculus was examined. Newly synthesized tubulin and neurofilament proteins were radiolabeled with tritiated amino acids in the cell bodies and were allowed to be axonally transported through the optic axons and into the terminals in the superior colliculi. Superior colliculi were harvested at appropriate times, synaptosomes were prepared, and radiolabeled proteins were examined by gel electrophoresis and fluorography. Proteins in the radiolabeled synaptosomes were compared with those in the portion of the optic tract immediately proximal to the superior colliculus. Tubulin subunits entered the terminals by 100 days after intraocular labeling, and at least one isoform of tubulin appeared to persist as long as 400 days. Neurofilament proteins, despite the fact that they are axonally transported and delivered to the terminals in concert with the tubulin subunits, disappear rapidly upon entry into the terminals themselves.
Animals↗
Control of cell number in the developing visual system. III. Effects of visual cortex ablation.
The effect of unilateral deletion of the visual cortex on early cell death and eventual cell number in various structures of the visual system was examined. At minimum, this manipulation potentially provides excess retinal afference to the superior colliculi, partially denervates the superior colliculi, reduces normal retinal terminal area and opens up potential target space for the retina and superior colliculus in those areas where they share terminal space with the visual cortex. All layers of the superior colliculus, bilaterally, showed an initial decrease in the rate of cell death relative to normal followed by an increase in cell death rates. No change in the number or distribution of cells in the retinal ganglion cell layer resulted despite a substantial loss of retinal terminal area, and a substantial alteration of the pattern of retinal central termination. These results are interpreted as evidence for two stages in normally occurring cell death, a first in which axons compete to colonize any available terminal space, and a second in which axon-to-target specificity must be matched. These results also provide evidence that the amount of target required for neuron survival is clearly variable.
Animals↗
Serotonin, the superior colliculus, and grooming behavior in cats with neocortical lesions.
Previous studies of cats with pontile lesions indicate that a serotonergic deficit exists in the superior colliculi and that this deficit is involved in the genesis of an abnormal grooming behavior. Cats with frontal neocortical lesions exhibit the same serotonergic deficit and the same abnormal grooming behavior. The present study established that the serotonergic deficit is involved in the mediation of the abnormal grooming behavior in cats with frontal neocortical lesions. Microinjections of 5-hydroxytryptophan (5-HTP) and 5-hydroxytryptamine (5-HT) into the superior colliculi abolished or signigicantly reduced the abnormal behavior in cats with frontal neocortical lesions, whereas no effects of 5-HTP were observed after injections into the cerebrospinal fluid above the superior colliculi, into the tegmentum beneath the superior colliculi, or into the medial dorsal nucleus rostral to the superior colliculi. Other substances (tryptophan, noradrenaline, and gamma-amino-butyric acid) had no effect on the abnormal behavior when injected into the superior colliculi. Further evidence implicating a serotonergic deficit in the mediation of the abnormal behavior was obtained by systemic injections: The abnormal behavior was abolished with 5-HTP in cats with frontal neocortical lesions and in adrenalectomized cats that were previously treated with p-chlorophenylalanine.. The present study also demonstrated that the abnormal grooming behavior is induced by frontal neocortical lesions and not by more caudal lesions of the neocortex. The anatomical relations between the frontal neocortex and the superior colliculus and the role of these structures in grooming behavior are discussed.
5-Hydroxytryptophan↗
Raphe lesions and 5,7-dihydroxytryptamine induce grooming reflexes in adrenalectomized cats.
Grooming reflexes are induced by frontal neocortical, pontile, or spinal lesions in dogs and cats. In intact cats, the combined treatments of adrenalectomy and para-chlorophenylalanine administration induce grooming reflexes. Two other ways of depleting serotonin (with 5,7-dihydroxytryptamine and raphe lesions) were combined with adrenalectomy in the present study as further tests that serotonin and glucocorticoid hormones are the critical factors in the induction of grooming reflexes. Because the deficit in serotonin is confined to the superior colliculi in cats with frontal and pontile lesions, 5,7-dihydroxytryptamine (5,7-DHT) was injected directly into the superior colliculi at eight sites, 2 microgram/site (1 microliter at .5 microliter/min). Electrolytic dc lesions of the dorsal and superior central raphe nuclei were made in another group, and then both groups were adrenalectomized. There were three control groups: (a) a group with vehicle injections in the superior colliculi and laporatomies, (b) a group with 5,7-DHT injections in the superior colliculi, and (c) a group with the raphe lesions. Large receptive fields for grooming reflexes occurred only in the groups with combined treatments. Thus the mechanism of induction of grooming reflexes by central nervous system lesions involves independent changes in a hormonal and a neurotransmitter system which combine to effect the change in behavior.
5,7-Dihydroxytryptamine↗
Vying for dominance: dynamic interactions control visual fixation and saccadic initiation in the superior colliculus.
By the time you have reached this point, your daily count of alternating saccades and fixations will have increased considerably. So too will have your understanding of the dynamic interactions model. In the superior colliculi, visual fixation and saccadic initiation may be viewed as independent motor plans that compete for dominance across the intermediate layers. Extrinsic input modifies a point location on the retinotopic motor map that is shaped into a motor plan through the intrinsic circuitry of the superior colliculi. Independent motor plans compete for selection in a push-pull fashion and when a saccadic plan ultimately reaches threshold, it produces a strong burst of action potentials that shuts down the remaining regions of the intermediate layers. Modifying the activity of the intermediate layers changes these dynamic interactions in predictable ways. Enhancing the activity of one region facilitates nearby locations and inhibits distant locations. Diminishing the activity of one region inhibits nearby locations and facilitates distant locations. Such effects have been demonstrated in the neurophysiological activity of single cells (Munoz and Istvan, 1998; Olivier et al., 1999) and in behavior (Hikosaka and Wurtz, 1985; Munoz and Wurtz, 1993b). In addition to explaining visual fixation and saccadic initiation during basic saccadic tasks, the dynamic interactions model can explain changes in the timing of saccadic initiation that are observed when this task is modified. Namely, the gap effect, or decreased saccadic reaction times as a consequence of a gap period, occurs because removing fixation decreases the activity of fixation regions and, correspondingly, increases the excitability of saccadic regions. Express saccades, are a special instance of such dynamic interactions, in which decreased fixation activity and heightened motor preparation signals cause the target-related activity to be translated into a saccadic signal immediately. Finally, the slowing of saccadic initiation for antisaccades, can be interpreted as the consequence of multiple competing signals across the intermediate layers. It should be emphasized that the dynamic interactions that we have described in this chapter are not limited to the superior colliculi. On the contrary, similar interactions take place at many levels of the neuraxis (Moschovakis et al., 1996; Leigh and Zee, 1999; Schall and Thompson, 1999; Hikosaka et al., 2000; Munoz et al., 2000; Glimcher, 2001; Scudder et al., 2002). At this juncture, however, the dynamic interactions involved in producing visual fixation and saccadic initiation are better understood in the superior colliculi because of its well-organized motor map and its well-characterized neuronal elements. Although we are a long way from understanding how the brain controls visual fixation and saccadic initiation, we have made substantial progress in understanding these behaviors in the superior colliculi.
Fixation, Ocular↗
Clinicopathological study of atypical motor neuron disease with vertical gaze palsy and ballism.
The case of a 38-year-old patient with rapidly progressing motor neuron disease, complicated by major dysfunction of the extrapyramidal system and of vertical gaze is described. Neuropathological examination revealed a degenerative process that severely affected the lower motor neurons, as well as the neurons of the pars compacta of the substantia nigra, the nucleus of Darkschewitsch, the nucleus interstitialis of Cajal, the colliculi superiores, and the pallidum. The long tracts were unaffected at all levels of the brain stem and spinal cord. There was no convincing evidence for the presence of a multiple system atrophy or progressive supranuclear palsy; the results rather revealed a pattern of vulnerability characteristic of a variant of motor neuron disease.
Adult↗
The combined effects of unilateral enucleation and rearing in a "dim" red light on synapse-to-neuron ratios in the rat superior colliculus.
Rats whose right eyes were enucleated on day 1 after birth and nonenucleated rats were raised in either "light" or "dark" (red light) conditions from birth until 39 days of age. This resulted in 4 groups of animals: light-reared nonenucleated, light-reared enucleated, dark-reared nonenucleated, and dark-reared enucleated. At 39 days of age, the animals were killed by perfusion with 2.5% sodium cacodylate buffered glutaraldehyde. The superior colliculi were dissected out and processed for embedding in resin. Stereological procedures at the light and electron microscopical levels were used to estimate the synapse-to-neuron ratios in the superficial layers of these colliculi. Light-reared, nonenucleated rats had about 1,850 synapses-per-neuron in both the right and left superior colliculi. Rearing nonenucleated rats in the dark reduced this value to about 1,200. Enucleated rats reared in the light showed a differential response in the 2 colliculi. Thus, the contralateral (to the enucleated eye) colliculi showed a decrease, whereas the ipsilateral colliculi showed an increase in the synapse-to-neuron ratio compared with light-reared, nonenucleated rats. When enucleated rats were reared in the red light, there was a decrease in the ratio in both colliculi, although the extent of this decrease was more marked in the contralateral than the ipsilateral colliculi. However, the decrease in the contralateral colliculi was not significantly greater than that observed in the corresponding colliculi from dark-reared, nonenucleated rats. These results provide useful information on the combined and separate effects of unilateral enucleation at around birth and dark (red light) rearing during early life on the interneuronal connectivity of both the ipsi- and contralateral superior colliculi of rats. They also show the vast importance of visual stimulation for the normal development of the subcortical visual centers.
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Bilateral projections from the superior colliculus to the suprageniculate nucleus in the cat: a WGA-HRP/double fluorescent tracing study.
Following WGA-HRP injection into the right suprageniculate nucleus of the cat brain, retrogradely-labeled neurons were found not only in the ipsilateral, but also in the contralateral superior colliculi. After WGA-HRP injection into the unilateral superior colliculus, anterogradely-labeled axon terminals were observed in the bilateral suprageniculate nuclei, and electron microscopic examination revealed that these were large terminals which made asymmetric synaptic contacts with dendrites. When a different kind of fluorescent tracer was injected into each suprageniculate nucleus (Fast blue and Nuclear yellow), double-labeled neurons were observed in the rostral and middle portions of both superior colliculi. These results suggest that there are direct bilateral projections from the superior colliculus to the suprageniculate nuclei, and that some of these projections originate from branching colliculo-suprageniculate axons.
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Biological bases for the integration of appetitive and consummatory grooming behaviors in the cat: a review.
Cats with pontile lesions, frontal neocortical lesions, and thyroidectomized cats display a dissociation of the appetitive and consummatory components of grooming behavior following tactile stimulation of the body surface, an abnormal behavior which waxes and wanes with the seasons of the year. Tryptophan hydroxylase activity and serotonin levels were significantly decreased in the superior colliculi (but not other brain regions) in cats with pontile lesions or frontal neocortical lesions, but not in thyroidectomized cats. Systemic administration of 5-hydroxytryptophan or monoamine oxidase inhibition plus tryptophan administration abolishes the abnormal grooming behavior in each group of cats, and microinjections of 5-hydroxytryptophan or serotonin into the superior colliculi has the same effect, indicating that the change in a serotonergic system is a critical aspect of the abnormal behavior in cats with lesions and that a serotonergic system may also be involved in the genesis of the abnormal grooming behavior in thyroidectomized cats. Functional inactivation of the serotonergic system by p-chlorophenylalanine, LSD, or serotonin receptor blockade does not induce the abnormal grooming behavior in normal cats, indicating that other factors are involved. Cats with lesions and thyroidectomized cats display a rhythmic dysfunction in the excretion of glucocorticoids and glucocorticoid administration abolishes the abnormal grooming behavior, suggesting that glucocorticoids are the other critical factor. Adrenalectomized cats do not display the abnormal grooming behavior, but when adrenalectomized cats are treated with p-chlorophenylalanine, the abnormal behavior appears. Thus, a serotonergic system in the superior colliculi, operating at some level of glucocorticoid function, is involved in the integration of appetitive and consummatory grooming behaviors.
5-Hydroxytryptophan↗
Visual modulation of vestibularly-triggered air-righting in rats involves the superior colliculus.
Vision plays two roles in air-righting, it can trigger air-righting in the absence of the labyrinths, and it can modulate the onset and speed of air-righting depending upon the height of the fall. While the visual cortex is known to be necessary for visual triggering, the neural systems necessary for visual modulation are unclear. In this study, the role of the visual cortex and the superior colliculus in visual modulation by rats was analysed. Rats can visually modulate vestibularly-triggered righting, but not trigger righting visually in the absence of the labyrinths. Adult rats with complete neonatal decortication, and adult rats with more specific ablation of the visual cortex were able to visually modulate air-righting. Ablation of the superior colliculi as well as the visual cortex, or ablation of the superior colliculi alone, resulted in loss of the ability to visually modulate air-righting. It is concluded that the superior colliculus is necessary for visual modulation in rats. It is hypothesized that in cats also, the superior colliculus, not the visual cortex, is necessary for visual modulation.
Animals↗
[Characteristics of the evoked electrical reactions of the nucleus lateralis posterior in the rabbit thalamus and their dependence on cortical and reticular formation function].
The electrical responses of n. lateralis posterior of the thalamus (nLP) to light stimuli of different intensity were recorded in alert rabbits, and their interrelationships with the reactions of retina, superior colliculi and visual cortex were analysed. The retina rather than superior colliculi appeared to play a major role in afferent supply of nLP in rabbit. The organized mechanism of facilitating reticular control of the nLP function was shown, with the adrenoreactive mechanism playing the most important role in the reticular influence. The inhibitory influence of visual and sensomotor cortical areas upon neuronal mechanism of nLP forming the responses to photostimuli, was revealed. The effects of visual cortex were the most expressive and stable.
Animals↗
Role of the functional state of the central nervous system in the mechanism forming responses from the peripheral and central parts of the visual analyzer.
Chronic experiments on rabbits showed that changes in the functional state of the central nervous system induced by Nembutal and changes in the brainstem reticular formation induced by aminazine had significant effects on the formation of the early receptor potential, a-wave, and oscillatory potentials of retinal ERG signals, as well as on oscillatory potentials in the superior colliculi and visual cortex. Nembutal inhibited the formation of the early receptor potential, the a-wave, and the second and third ERG oscillatory potentials, and had similar effects on the oscillatory potentials of the superior colliculi and the visual cortex. Only the first oscillatory potential was enhanced in all visual system structures. Aminazine had long-lasting enhancing effects on the formation of the early receptor potential and the a-wave and on the oscillatory potentials of the retina, superior colliculi, and visual cortex. This enhancement may be associated with "release" of the retina and central structures from the constant inhibitory influences of the brainstem reticular formation.
Animals↗
[Serotonin binding activity of light and heavy synaptosomes from different animal brain structures following light deprivation].
The extent of interaction between serotonin (ST) with light and heavy synaptosomes from different brain regions of normal and dark-reared rabbits was studied by the author's technique, using gel filtration. The activity of this interaction in the heavy synaptosomes of the visual cortex and the colliculi superiores of the control rabbits was the same and significantly higher than that in the motor cortex. The light synaptosomes of all the investigated regions were similar by the extent of this process activity. In dark-reared rabbits the activity of ST binding by heavy synaptosomes in the visual cortex and the colliculi superiores decreased by 74--81 per cent only. A fall in the ST binding by light synaptosomes in all the regions was the same (approximately 73 per cent as compared to the control). The results obtained are discussed in the light of a possible mediator or modulator role of ST in the visual system structures.
Animals↗
Similarities in the physiological bases of an abnormal grooming behavior in thyroidectomized cats and in cats with lesions of the central nervous system.
Thyroidectomized cats display a dissociation of the appetitive and consummatory components of grooming behavior when the body surface is tactually stimulated, an abnormal behavior that also occurs in cats with pontile or frontal neocortical lesions. Systemic administration of 5-hydroxytryptophan (5-HTP) abolishes the abnormal behavior, whereas dihydroxyphenylalanine administration does not, and p-chlorophenylalanine (PCPA) administration induces the abnormal grooming behavior in thyroidectomized cats that are not displaying the abnormal behavior because of spontaneous seasonal reversions. Microinjections of 5-HTP or serotonin into the superior colliculi also abolish the abnormal grooming behavior in thyroidectomized cats. Lesions of the superior colliculi prevent the development of the abnormal behavior after thyroidectomy, even with PCPA treatment. These pharmacological results in thyroidectomized cats parallel the behavioral effects observed in cats with pontile or frontal neocortical lesions.
Animals↗
[The effect of activation of the superior colliculus on the convulsive activity during picrotoxin-induced kindling].
Bilateral administration of picrotoxin, bicucullin or benzilpenicillin to the colliculi superior induced high-amplitude hypersynchronous discharges in rats. In these conditions, a suppression of generalized seizures induced with picrotoxin, was observed. The superior colliculi seem to play a significant part in antiepileptic system, the part being realized through generator mechanism.
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Oculomotor areas in the rabbits midbrain and pretectum.
The role of some meso- and diencephalic structures in eye movements was investigated by ablation and stimulation experiments. Optokinetic nystagmus was abolished by small lesions in the lateral pretectum, but not by complete removal of the superior colliculi. Stimulation of the superior colliculus and other visual centers was effective in eliciting nystagmus (slow phase ipsilateral), but the most efficient trigger zones are found in the lateral pretectum and the midbrain tegmentum. Only from these areas could nystagmus still be elicited after degeneration of the primary optic fibers. The lateral pretectal trigger zone is probably identical with the nucleus of the optic tract. It is postulated that this nucleus is an essential station for horizontal optokinetic reactions. Saccades were obtained by stimulation of the mesencephalic central grey, but not for any visual centers such as the superior colliculus.
Animals↗
Opposing basal ganglia processes shape midbrain visuomotor activity bilaterally.
The manner in which the nervous system allocates limited motor resources when confronted with conflicting behavioural demands is a crucial issue in understanding how sensory information is transformed into adaptive motor responses. Understanding this selection process is of particular concern in current models of functions of the basal ganglia. Here we report that the basal ganglia use simultaneous enhancing and suppressing processes synergistically to modulate sensory activity in the superior colliculi, which are bilaterally paired midbrain structures involved in the control of visual orientation behaviours. These complementary processes presumably ensure accurate gaze shifts mediated by the superior colliculi despite the presence of potential distractors.
Animals↗