Pretectal Region Research Articles

Topographic organization of the projections of the retina to the pretectal region in the rat

The pattern of projection of the retina to the pretectal region and its retinotopic organization were investigated in the rat by autoradiographic and silver impregnation techniques for axonal pathways. The endings of retinal axons form three terminal fields in the pretectum in: 1, olivary pretectal nucleus (PO), bilaterally; 2, posterior pretectal nucleus (PP), bilaterally; and 3, nucleus of the optic tract (NTO), contralaterally. The following retinotopic pattern was observed in rats surviving peripheral retinal lesions and injections of 3H-proline in the same eye, when the positions occupied by terminal degeneration in Fink-Heimer stained sections were matched with the corresponding areas deficient in radiolabel in adjacent autoradiographic sections showing the surviving parts of the terminal fields. The nasal periphery of the retina maps along the adjoining edges of PO and PP, both of which extend obliquely, in a posterolateral direction, through the entire extent of the pretectum. Both nuclei map the line of representation of the anterior midline (in the temporal retina) along their opposite edges (anterolaterally, in PO; posteromedially, in PP). This mirror-image symmetry is completed by the representation of the ventral peripheral retina separately in the rostral poles and the dorsal peripheral retina separately in the caudal poles of both nuclei. The map in NTO is vertically oriented, with the temporal retina, dorsally, the nasal retina, ventrally, the ventral retina, rostrally, and the dorsal retina caudally represented. The binocular area of the terminal field in PO is subdivided by a terminal-free zone into two parts that may process separately events in the central and lateral visual field.

Correlation between behavioral and neuronal activities of toads Bufo bufo (L.) in response to moving configurational prey stimuli

Common toads are able to distinguish prey objects from predators and behaviorally irrelevant stimuli by their shape and direction of motion. Using computer programs for correlation analysis, the prey-catching activity in response to different moving configurational stimuli was compared with the activity of neurons recorded at different levels of the visual pathway. Among retinal ganglion cells, the class R2 neurons were found to be most sensitive, to moving configurational stimuli. Among neurons recorded from retinal projection fields in the optic tectum and thalamic pretectal region, the tectal T5(2) neurons exhibited configurational selectivity. The output of these neurons showed the best positive correlation with prey-catching when both the neuronal and behavioral activities were compared in response to stripes of different length moving with their axis in, or perpendicular to, the direction of motion.

Mechanism of morphine-induced mydriasis in the cat

Neurons that increased their firing rate in response to light stimulation were recorded from the pretectal region and the anterior oculomotor nucleus of sedated immobilized cats while morphine (2 mg/kg iv) was administered. The dose produced mydriasis and an increase in spontaneous firing rate of all light-sensitive neurons recorded from the anterior oculomotor nucleus. This suggested that morphine did not produce mydriasis through inhibition of the third nerve. Phenoxybenzamine, iv or topically, antagonized the mydriasis, indicating a peripheral source of sympathetic input as the basis for morphine-induced mydriasis. Morphine (2 mg/kg iv), administered 1 h after adrenalectomy, produced miosis and increased the spontaneous firing rate of light-sensitive neurons recorded from the oculomotor nucleus. These observations suggest that, in the cat, although morphine activates the oculomotor neurons to produce miosis, the effect is masked by the morphine-induced release of catecholamines, mainly from the adrenal glands, which produced mydriasis.

Reversibility of Parinaud syndrome in thalamic hemorrhage

Parinaud syndrome, associated with a left thalamic hemorrhage, disappeared completely in a 57-year-old woman after ventriculoperitoneal shunt. The syndrome may be attributed to increased intracranial pressure owing to mass effect on the pretectal region and tectum, or to tightness in the incisura causing hydrocephalus secondary to aqueduct compression. The lesions responsible for the syndrome may not be irreversible.

Comparative significance of pretectal and ventral lateral geniculate systems in functional recoveries after injuries to the posterior cortex

Rats with ablations of the pretectal region or ventral lateral geniculate bodies rapidly relearn a black-white discrimination. However, if combined with visual cortical ablations, pretectal ablations, but not LGNv ablations, markedly potentiate impairments of retention of the task. The results are discussed in relation to the putative role of sprouting in recoveries of functions.

Projections of precentral and premotor cortex to the red nucleus and other midbrain areas in Macaca fascicularis.

Midbrain projections from the precentral and premotor cortex were studied autoradiographyically in seven macaques. Earlier findings of Kuypers and Lawrence (1967) based on silver impregnated axonal degeneration were largely confirmed and partly extended. Laminar projections into the parvocellular red nucleus were found bilaterally from the somatotopic representation areas of the precentral cortex and three main divisions of premotor cortex (ventral, dorsal, and medial). The heaviest contralateral projection was recorded from the medial hemispheric aspects of area 6 (partly identical with the supplementary motor cortex). Homolateral projections were found from the limb areas of the precentral motor cortex to the magnocellular portion of the red nucleus and direct evidence for the overlap between corticorubral projections and corresponding areas of origin of the rubrospinal tract was obtained. Other projections concerned N. Darkschewitsch, N. Edinger-Westphal, suprarubral and dorsal mesencephalic reticular formation and adjacent lateral periaqueductal grey, substantia nigra, pretectal region, superior colliculus and N. tegmenti pedunculo-pontinus.

Regeneration of monoaminergic and cholinergic neurons in the mammalian central nervous system

Regeneration of monoaminergic and cholinergic neurons in the mammalian central nervous system

The neuronal pathway subserving the pupillary light reflex

The pupillary light reflex was investigated using electrical stimulation along the pathway and recording in the short ciliary nerves. The discharge of single units in the ciliary ganglion was compared during diffuse light stimuli and electrical stimuli. It was concluded that the early reflex discharge in the short ciliary nerves following electrical stimulation on the optic tract is due to excitation of fibres active during the pupillary light reflex. The light reflex is conveyed by slow (< 10 m/sec) optic tract fibers which synapse in the medial part of the pretectal area. In turn, pretectal neurones with conduction velocities of about 6 m/sec pass to the Edinger-Westphal complex from which the preganglionic ‘pupilloconstrictor’ neurones originate. Latency measurements show that there are synapses in the pretectal region and the Edinger-Westphal nucleus. The amplitude of the ‘pupilloconstrictor’ responses in the short ciliary nerves can be used as a measure of the excitability in the pathway of the pupillary light reflex under various conditions, e.g. following conditioning stimuli of other interacting pathways. In addition to the ‘pupilloconstrictor’ response there is also another short-latency discharge in the short ciliary nerves following stimulation of the posterior commissure and the Edinger-Westphal nucleus. That discharge is presumably due to activation of fibres which cause accomodation of the lens.

Application of cobalt-filling technique to show retinal projections in the frog

Cobaltous-lysine complex was used to fill the axons of the cut optic nerve in the frog, Rana esculenta. After intensification in a physical developer, fibres containing black precipitate could be detected in the nucleus of Bellonci, in the lateral geniculate body, in the pretectal region, in the optic tectum and in the basal optic nucleus on both sides. The axial optic tract was described in detail. Fibres of this tract terminate in the posterior entopeduncular nucleus, in the ventrolateral area of the thalamus, in the lateral geniculate nucleus, in the posterolateral nucleus and in layers F, G and 6 of the optic tectum contralateral to the cobalt-filled optic nerve. The existence of a hypothalamic optic root was also verified. Cobaltous-lysine complex proved to be an excellent marker to show the projections of a central pathway. This compound covered longer distances and gave heavier precipitate than cobaltous chloride alone. Fibres of 0.6–3 μm in diameter were well-filled in the majority of cases. In the best preparations, fibres with a calibre of 0.3–0.5 μm were also found. The thinnest fibres are probably unmyelinated.

Analgesia from rostral brain stem stimulation in the rat

Rats implanted with bipolar stimulating electrodes in the rostral medial brain stem were tested for brain stimulation-produced analgesia using tail-flick, pinch and hot-plate tests. Potent analgesia across all three tests was obtained from stimulation of sites in the gray matter surrounding the aqueduct and the caudal portion of the third ventricle, the posterior hypothalamus, the midline area of the caudal thalamus and the pretectal region of the meso-diencephalic junction. The analgesia obtained from these sites was comparable to that produced by stimulation of the previously studied caudal periaqueductal gray matter: it outlasted the period of brain stimulation, was not due to a generalized motor debilitation of the animal, and was not correlated with changes in electrographic activity. Stimulation of sites in the caudal thalamus and pretectal area yielded analgesia without stimulation-induced aversive reactions, confirming the potential of these sites for use in the relief of clinical pain in man.

Question of prey feature detectors in the toad'sBufo bufo (L.) visual system: A correlation analysis

1. ToadsBufo bufo (L.) prefer as prey “worm-like” objects with long axis orientation parallel to the movement direction rather than the same objects oriented “antiworm-like” with their long axis perpendicular to the movement direction. 2. By means of statistical correlation methods with computer programs it was analyzed to what extent neurons from different regions of the visual pathway respond sensitively, selectively or specifically to moving configurational stimuli, such as worm-like and antiworm-like objects of equivalent sizes. 3. Neurons withsensitivity to particular moving configurational stimuli were found in the retina (classes R2, R3, R4) and the retinal projection fields in the thalamic pretectal region (class TH3) and the optic tectum (class T5(1)). 4. Neurons withselective responses to moving configurational stimulus objects, corresponding to the behavior, were found in a particular population of tectal neurons (class T5(2)). 5. No neurons were found withspecific responses to a stimulus of a certain configuration.

Neurons of the toad's (Bufo bufo L.) visual system sensitive to moving configurational stimuli: A statistical analysis

1. The activity of 59 neurons situated at different points along the visual pathway of the toadBufo bufo (L.) were investigated quantitatively by extracellular microelectrode recording methods. The activity was recorded in response to a variety of moving configurational stimuli which traversed the excitatory receptive fields of these neurons: Various sized squares and stripes of different length, oriented either in or perpendicular to the direction of movement, were used as visual stimuli. The stimuli were moved at constant visual angular velocity. The neuronal activities were evaluated by five different methods (Fig. 1A-E). The electrode positions in the brain tissue for all neurons investigated were reconstructed histologically (Fig. 2A-C). 2. In the central layers of the optic tectum two statistically different neuronal populations were identified (Fig. 3A and B). Neurons of one population, class T5(1), were sensitive to the area of a moving stimulus and were activated mainly by configurational stimuli elongated in the direction of movement rather than by the extension of the same stimulus object perpendicular to the direction of movement (Fig. 5). Neurons of another population in the same layers of the optic tectum, class T5 (2), were found to be activated by elongation of a configurational stimulus in the direction of movement, but inhibited by extension perpendicular to the direction of movement (Figs. 4 and 6). 3. In the thalamic pretectal region neurons (class TH3) were recorded showing sensitivity to the area of a moving stimulus. They were activated mainly by configurational stimuli elongated perpendicular to the direction of movement rather than by extension in the direction of movement (Fig. 8). 4. The present data confirm our earlier results on stimulus configurationsensitivity andselectivity by neurons in the toad'sBufo bufo (L.) visual system.

An autoradiographic study of the projections of the pretectum in the rhesus monkey (macaca mulatta): evidence for sensorimotor links to the thalamus and oculomotor nuclei

Autoradiographic tracing methods were used to determine the differential projections of the pretectal nuclei, in the rhesus monkey, in relation to their inputs. The sublentiform (SL) and olivary (ON) nuclei receive projections from the visual cortex, superior colliculus (SC) and an equal bilateral projection from the retina. The nucleus of the posterior commissure (NPC) and its subdivisions do not receive any of these inputs. The projections of the pretectum involve a number of structures within the thalamus and brain stem and there are differences in the projection targets of the pretectal region which receives direct visual input (i.e., SL and ON) and the region which does not (i.e., nucleus of the posterior commissure, NPC). For example, while all pretectal regions project within the pretectum and to the SC, accessory oculomotor nuclei, reticular formation, intralaminar nuclei and hypothalamus, it is only the retino-recipient zone which projects to rostral regions such as the visceral oculomotor nuclei, the lateral pulvinar, the border between the lateral pulvinar and medial pulvinar, the oral pulvinar as well as to the thalamic reticular nucleus, ventral lateral geniculate nucleus, zona incerta and other structures. It is concluded that the retina, SC and cortex which influence the visceral oculomotor nuclei can only do so by virtue of their projections to the pretectum, and that any consideration of accommodative and pupillary reflexes must view the pretectum as an obligatory link through which various structures can influence the intrinsic musculature of the eye. In contrast to the SC, the pretectum does not project to any of the visual relay nuclei of the thalamus, such as the inferior pulvinar, which project to the visual cortices. Instead, the pretectum projects directly to visuomotor, visceromotor and arousal systems.

Cholinergic transmission in subcortical and cortical visual centers of rats: No evidence for the involvement of primary optic system

The effect of unilateral enucleation, ablation of the visual cortex or coagulation of the lateral geniculate nucleus (LGN) upon the activity of choline acetyltransferase (ChAc) and acetylcholinesterase (AChE) in different structures of the visual system of albino rats was studied. The localization and extent of the degeneration pattern were followed up by histological silver degeneration methods. Afferents from the retina project mainly contralaterally to the dorsal and ventral LGN, the pretectal region and the superior colliculus. Afferent fibres from the dorsal LGN enter the visual cortex in area 17 only. Neurons of this area project back ipsilaterally to the LGN and the superior colliculus (SC). No significant decrease in the activity of the cholinergic marker enzyme choline acetyltransferase could be observed under any of the experimental conditions; there was rather a tendency to increased activity in the subcortical centres. AChE as a less specific marker also exhibited no gross changes in activity in the lesioned animals. The results add more direct proof to pharmacological and physiological evidence that ACh is not involved in the synaptic transmission of the direct optic projections in rats, either at the subcortical or at the cortical level.

A Golgi study on the habenular nucleus of the cat

The habenular nucleus of kittens was studied using the rapid Golgi and the Golgi-Kopsch silver impregnation methods. The neurons of the medial habenular nucleus (MH) were classified into two types. The type I neurons, the main constituents of the MH, had piriform cell bodies with a mean diameter of 12 mum by 18 mum and two to five primary dendrites; dendrites had many spines. The type II neurons (14 X 23 mum) were fusiform in shape and one to three primary dendrites arose from each pole of the cell bodies; dendrites had few spines. The axons of both types of neurons were traced into the fasciculus retroflexus Meynerti (FR), and intranuclear axon-collaterals arose from axons of the type I neurons. The neurons of the lateral habenular nucleus (LH) were divided into four groups. Type I, II and III neurons were projection neurons of large, medium and small size, respectively. The type I neurons (27 X 43 mum) with four to seven primary dendrites were located mainly in the rostral and ventral areas of the LH. The type II neurons (15 X 33 mum) with two to four primary dendrites, the main constituents of the LH, were distributed throughout the LH. The type III neurons (15 X 25 mum) with two primary dendrites emerging from each pole of the soma were localized to the mediocaudal areas of the LH. The vast majority of axons of these projection neurons passed ventrally or ventrocaudally to enter the FR; only a few axons of these neurons were traced into the stria medullaris thalami (SM). The type IV neurons (12 X 25 mum) were small cells with short axons, suggesting the existence of a neural circuitry intrinsic to the LH. Bundle formation and glomerular arrangement of dendrites were observed in the medium-sized LH neurons. The afferent fibers terminating within the MH coursed in the most part of the SM. These afferents were classified into medium-caliber type I and fine type II fibers; both of these fibers emitted many intranuclear collaterals. There were also observed many fibers of passage which ran between the SM and FR, or between the habenular commissure (HC) and FR. The afferent fibers to the LH were divided into three groups; afferents via the HC, ascending and descending afferents. Most of the descending afferents entered the LH through the SM; some of them traversed the LH to join the FR or HC, or to extend to the pretectal region. The vast majority of the ascending afferents entered the LH via the FR; some of them extended rostrally to enter the SM. Some fibers in the HC also terminated within the LH. In addition to these afferents, many fibers of passage were seen to run through the LH and to bridge over between the SM and FR, or between the SM and HC.

Trial sequence of changed unit activity in auditory system of alert rat during conditioned response acquisition and extinction.

1. The activity of units in the auditory system of alert, freely moving rats was studies during the acquisition and extinction of a tone-signaled, appetitive classically conditioned response. Responses of neurons in inferior colliculus (N = 28), medial geniculate (N = 32), posterior nucleus of thalamus (N = 28), pretectal region (N = 19), and cortex (N = 100) were studies in 74 rats across 10-trial blocks. 2. During behavioral acquisition, neurons in posterior nucleus of thalamus were the first to show response increments to CS+ onset. They were followed by neurons in cortex, pretectal region, medial geniculate, inferior colliculus and by movement behavior. 3. Prestimulus background rates during acquisition showed significant decrements in cortical neurons. These background decrements began to be evidenced in the trial series before the response increases in posterior nucleus. These data strengthened the suggestion of a previous study that posterior nucleus responses could be dependent on tonic modulation from cortex. 4. Extinction appeared to be largely a reverse of acquisition. Cortex and behavior showed response decrements first in the trial series. They were followed by medial geniculate, pretectal region, posterior nucleus, and inferior colliculus neurons. 5. The hypothesis was advanced that the auditory lemniscal adjunct afferent system may play a primary role in the early phases of auditory conditioned-response acquisition.

The role of the pretectum in the acquisition and retention of visual discrimination habits in monkeys

Seven rhesus monkeys were trained to discriminate between each of three pairs of stimulus plaques, namely (1) black vs. white, (2) horizontal vs. vertical stripes, and (3) triangle vs. diamond. Six animals were then subjected to subcortical electrolytic lesions. The three subjects that received bilateral damage to the pretectal region exhibited a significant loss in the retention of the horizontal vs. vertical stripe discrimination as compared to normal or brain-operated controls. Subjects that sustained bilateral damage to the area immediately ventral to the pretectal region showed significantly poorer retention of the triangle vs. diamond task compared to the other subjects. In addition, monkeys with bilateral pretectal damage needed significantly more trials to learn a new visual discrimination task than the control group. The pretectal animals were not impaired relative to controls on the number of trials necessary to learn a 5-sec delayed alternation task. Possible functions of the pretectal region are discussed in light of the present results.

Effects of pretectal lesions on rats wearing light-diffusing occluders

The study provides behavioral evidence that the pretectal region of the subcortical visual system primarily mediates responses to diffuse rather than to patterned light stimuli: pretectal lesions induced greater transoperative deficits in performance of a light-dark discrimination task for rats wearing light-diffusing occluders than for non-occluded animals. Pretectal lesions also produced less transoperative disruption in animals trained to perform a pattern discrimination task (horizontal vs. vertical stripes). These results are precisely the opposite of those which follow ablation of visual cortex.

Morphologisch-histochemische Untersuchungen über die verbindungen der mesencephalen reticulären formation (Area cuneiformis) zu subcorticalen strukturen des visuellen systems: Morpho-histochemical investigations about the connection of the mesencephalic reticular formation (Area cuneiformis) to the subcortical structures of the visual system

There was investigated the connection of the mesencephalic reticular formation (Area cuneiformis) with subcortical structures of the visual system. After coagulation of the reticular formation we studied the connections by degeneration and enzymhistochemistric methods. Terminal degeneration in different intensity was observed in the ventral part of the lateral geniculate in the nucleus lateralis posterior, the pretectal region and in the lower laminae (IV ... VII) of the superior colliculus. The findings are mainly ipsilateral. A direct projection to the dorsal part of the lateral geniculate could not be observed. By enzymhistochemic methods we localized the AchE intracellular in the rostral part of the area cuneiformis. After destruction of this area there was observed a clear diminishing of the AchE activity in the ventral lateral geniculate and in the area pretectalis. These results were confirmed by biochemical methods.

The ascending projections of the superior colliculus in the rhesus monkey (Macaca mulatta).

We studied and compared the ipsilateral efferents of the superficial and deep layers of the superior colliculus of the rhesus monkey. Using a stereotaxic method, microelectrodes were inserted through the contralateral hemisphere in order to make electrolytic lesions of the superior colliculus. Large lesions involved all layers of the superior colliculus, while smaller lesions involved either the superficial or the deep layers of the superior colliculus. Following various survival times, the brains were prepared with the Fink-Heimer technique ('67). Following lesions of the superficial layers of the superior colliculus, definite degenerated axonal endings were found in the dorsal and ventral lateral geniculate nuclei, inferior pulvinar, centrointermediate nucleus, magnocellular dorsomedial nucleus, anterior pretectal nucleus and pretectal region. Sparse degenerated axonal endings were found in the limitans nucleus, lateral posterior nucleus and some intralaminar nuclei following lesions of the superficial layers in the rostral portion of the superior colliculus. Following lesions of the deep layers of the superior colliculus, degenerated axonal endings were found in the central gray, magnocellular medial geniculate nucleus, suprageniculate nucleus, limitans nucleus, lateral posterior nucleus, medial and oral pulvinar, nucleus of the accessory optic tract, zona incerta, subdivisions of the ventral lateral and ventral posterior lateral nuclei, ventral posterior inferior nucleus, denosocellular and multiform dorsomedial nuclei, all intralaminar nuclei, inferior colliculus, parabigeminal nucleus, olivary nucleus, reunions nucleus, Forel's Field H and an undefined midbrain nucleus. In general the projections were topographically organized in that the caudal portion of the superior colliculus projected to the rostral portions of thalamic nuclei and the rostral portion of the superior colliculus projected to the caudal portions of thalamic nuclei. All the degeneration patterns seen after lesions of the superficial and deep layers were accounted for by large lesions which involved all layers of the superior colliculus. It is concluded that the superficial and deep layers of the rehesus monkey superior colliculus have different ascending projections. The finding, are related to the organization of visual and multimodal thalamocortical systems in primates and other mammals.