Head and body movements produced by electrical stimulation of superior colliculus in rats: effects of interruption of crossed tectoreticulospinal pathway

Behavior evoked by electrical stimulation of the hamster superior colliculus

Syrian golden hamsters were implanted with fixed or moveable stimulating electrodes aimed at the superior colliculus (SC). Behavior was observed in response to trains of 0.1 ms pulses at 200 Hz while the animals were moving freely in an open arena or in their home cages. At threshold stimulating currents, the responses consisted almost entirely of freezing or contraversive turning, which occurred in two forms: fast turns, resembling orienting movements to sunflower seeds, and slow turns that were smooth and continuous. Other responses, including head raising and lowering, ipsiversive turning and backing movements were seen occasionally. Increasing the stimulating current usually gave a variety of responses, including circling movements, prolonged freezing, ipsilateral movements and running escape behavior. The sites in SC giving freezes at threshold tended to be located superficially (SO and above), or deep (SGP and below), while sites giving turns were in the intermediate layers. Most freeze sites occurred in the rostro-medial SC that represents the upper visual field, while turn sites occurred predominantly in caudo-lateral SC. Apart from the turns, most of the stimulated responses resembled natural defensive behavior, supporting the view that SC in rodents plays a role in organizing responses to predators, as well as in orienting behavior.

Turning responses evoked by stimulation of visuomotor pathways

Lateral eye, head, and body movements are produced by electrical stimulation of many brain regions from frontal cortex to pons. A new collision method shows that at least 5 separate axon bundles mediate stimulation-elicited lateral head and body movements in rats. One bundle passes between the rostromedial tegmentum and medial pons, with conduction velocities of 0.8-18 m/s. A second bundle passes between the superior colliculus and contralateral medial pons, with conduction velocities of 1.7-13 m/s. A third bundle passes between the superior colliculus and ventrolateral pons, with conduction velocities of 1.3-20 m/s. A fourth bundle passes between the internal capsule and medial substantia nigra, with conduction velocities of 0.9-4.4 m/s. A fifth bundle passes between the anteromedial cortex and rostral striatum, with conduction velocities of 2.4-36 m/s. Collision effects have not been observed between the anteromedial cortex and the internal capsule, medial substantia nigra, superior colliculus, rostromedial tegmentum, or medial pons, which suggests that these sites are not connected by axons mediating turning. Possible synaptic linkages between the 5 bundles and possible transmitters are discussed.

Origins of descending projections to the medulla oblongata and rostral medulla spinalis in the urodele Salamandra salamandra (amphibia)

Descending projections to the medulla oblongata and rostral medulla spinalis have been examined in the urodele Salamandra salamandra with retrograde horseradish peroxidase tracing. Ipsilateral projections originate from the striatum and the nucleus ventrolateralis thalami and reach the medulla oblongata. The ipsilateral nucleus praeopticus magnocellularis reaches the medulla spinalis. The rostral part of the nucleus tuberculi posterioris projects to the ipsilateral medulla oblongata; its caudal part projects further caudally. Tectal efferents and the efferents of the nucleus praetectalis profundus project bilaterally, the nucleus praetectalis superficialis, nucleus mesencephalicus nervi trigemini, torus semicircularis, nucleus Darkschewitsch, and nucleus fasciculi longitudinalis medialis project ipsilaterally to the medulla oblongata. The nucleus mesencephalicus nervi trigemini, nucleus fasciculi longitudinalis medialis, and tectal efferents reach the rostral medulla spinalis. The nucleus ruber projects mainly via the contralateral dorsolateral funiculus to the medulla spinalis. A largely crossed medullary projection arises in the nucleus dorsalis tegmenti pars anterior, a bilateral projection arises in the nucleus dorsalis tegmenti pars posterior, and an ipsilateral projection arises in the nucleus ventralis tegmenti pars anterior. Cerebellar and statoacoustic efferents descend to the medulla spinalis. The nucleus reticularis isthmi, superior, medius and inferior as well as the nucleus raphes exhibit spinal trajectories. The nucleus vestibularis magnocellularis projects bilaterally, the nucleus vestibularis medialis projects ipsilaterally spinalward. The supposed nucleus descendens nervi trigemini descends mainly contralaterally. A small spinal projection arises in the nucleus tractus solitarii. The results indicate that salamander brains display elaborate descending connections which are similar to those in other vertebrates despite their scarcely differentiated neuronal cytoarchitecture.

Food wrenching and dodging: use of action patterns for the analysis of sensorimotor and social behavior in the rat

Developments of a procedure to study two movements, food wrenching (stealing food from a conspecific) and dodging (escaping with food from a conspecific), used in the competition for food by rats is described. These include, (A) procedures for adaptation, (B) procedures for filming and scoring, and (C) procedures for measuring dimensions of movements. The character of the movements have features of action patterns in the sense that the term is used by ethologists. It is suggested that they can be used to study the neural basis of complex sequencing of behavior as well as to study the neural basis of sensorimotor behavior and sensorimotor asymmetries.

Contralateral head movements produced by microinjection of glutamate into superior colliculus of rats: evidence for mediation by multiple output pathways

One of the major efferent pathways of the superior colliculus crosses midline to run caudally in the contralateral predorsal bundle, innervating targets in the brain stem and eventually reaching the cervical spinal cord. A variety of evidence suggests that this tecto-reticulo-spinal pathway may mediate the orienting movements that can be evoked by tectal stimulation. However, we have recently found that orienting head movements can still be obtained in rats after section of the tecto-reticulo-spinal pathway, implying that additional pathways are also involved. The present study sought to test this implication, by taking advantage of the fact that in rats the cells of origin of the tecto-reticulo-spinal pathway are largely segregated within the lateral part of the stratum album intermediate. It is thus possible to find out whether orienting head movements can be produced by a cell-excitant from tectal regions that contain few cells of origin of the tecto-reticulo-spinal pathway. Hooded rats in an open field were filmed during microinjections of sodium L-glutamate (50 mM, 200 nl) into the superior colliculus, and the films analysed for the appearance of contralaterally directed movements of the head and body. Subsequent histological reconstruction of the injection sites indicated that such movements could be obtained from widespread areas within the superior colliculus, including not only lateral stratum album intermediale but also the deep layers, and parts of the medial superficial and intermediate layers. Moreover, sites in or close to lateral stratum album intermediate often gave circling movements with downward pointing head, whereas some sites outside lateral stratum album intermediale gave sustained immobility with the head pointing contralaterally and upwards. This evidence supports the view that tectal efferent pathways besides the tecto-reticulo-spinal pathway are involved in the control of head movement. In addition, at least some of these pathways are not collaterals of the tecto-reticulo-spinal pathway, since the movements were obtained from collicular regions with few tecto-reticulo-spinal pathway cells. Finally, the results are consistent with the view that different collicular output pathways mediate movements that have different functions.

Movements of cats on a rotating cylinder: role of the substantia nigra pars reticulata and the deeper layers of the superior colliculus

Recently it has been shown that the substantia nigra pars reticulata (SNR) is required for adjusting the body position. In this study the role of the SNR in the execution of movements was investigated. Therefore, the effects of bilateral SNR injections of picrotoxin (500 ng/0.5 microliter) and muscimol (200 ng/1 microliter) were investigated on movements of cats which were trained to cross a rotating cylinder. SNR injection of picrotoxin suppressed the movements that were executed by cats injected with distilled water (0.5 microliter), i.e. 'normal movements'. While crossing the rotating cylinder, picrotoxin-injected cats mainly executed movements that almost never occurred in distilled water treated cats. Picrotoxin-injected cats executed 'special movements', i.e. forward locomotion in which the hindlimbs were affected, and 'counter-movements'. While executing the latter movements no forward locomotion occurred at all; the cats solely executed lateral fore- and hindlimb movements opposite to the direction in which the cylinder rotated. SNR application of muscimol enhanced the execution of 'normal movements'. Since the SNR sends information to the deeper layers of the superior colliculus (dl-SC) via GABAergic fibers, it was also investigated whether pharmacological stimulation (muscimol) and inhibition (picrotoxin) of the GABAergic dl-SC activity affected these movements on the rotating cylinder: no changes were observed after injecting otherwise effective doses of muscimol (75 ng/1 microliter) and picrotoxin (100 ng/0.5 microliter). In order to compare the function of the SNR and dl-SC in programming a different type of movements, the effects of GABAergic agents in the dl-SC (picrotoxin 100 ng/0.5 microliter and muscimol 75 ng/1 microliter) and the SNR (picrotoxin 500 ng/0.5 microliter and muscimol 200 ng/1 microliter) were investigated on the feline ability to execute goal-directed movements in an experimental set-up that prevented the occurrence of targeting movements which were continuously guided by external, i.e. auditory, visual, tactile and olfactory stimuli. For that purpose cats were trained to step out of a startbox on a rotating cylinder, i.e. the target. Dl-SC injection of muscimol or SNR application of picrotoxin prevented the cats from stepping out of the startbox on the rotating cylinder. In contrast, cats injected with muscimol into the SNR or picrotoxin into the dl-SC stepped out of the startbox, although dl-SC application of picrotoxin elicited forelimb misplacements: frequently the cats placed their forelimbs alongside of, but not on the cylinder when trying to leave the startbox.(ABSTRACT TRUNCATED AT 400 WORDS)

Further evidence for segregated output channels from superior colliculus in rat: ipsilateral tecto-pontine and tecto-cuneiform projections have different cells of origin

Two of the targets of the ipsilateral descending pathway from the superior colliculus are the cuneiform area (immediately ventral to the inferior colliculus), and the dorsolateral basilar pons. The cells of origin of the projections to these targets in rat were studied with a retrograde double-labelling technique, using the fluorescent tracers True blue and Diamidino yellow. Although many tectal cells were single-labelled by injections into basilar pons or the cuneiform area, less than 5% were double-labelled. The two projections thus appear to arise mainly from separate populations of cells within the superior colliculus.