Restoration of retino-tectal connections in frogs during regeneration of the optic nerve

At various times after unilateral division of the optic nerve in the frogRana temporaria L. evoked potentials in response to electrical stimulation of the optic nerve were investigated in a segment distal to the site of operation, spike activity was recorded from endings of regenerating and intertectal axons when stimuli of different shapes were placed in the field of vision, and the distribution of axonal bulbs of growth by depth in the tectum mesencephal was studied electron-microscopically. During regeneration of the axons the responses of the retinal ganglionic cells to visual stimuli retained most of their individual features. Myelinated axons of the retinal ganglionic cells regenerate first (starting on the 21st day after operation). Myelination of these fibers lags significantly behind their growth and is complete more than 100 days after the operation. Unmyelinated axons of the retinal ganglionic cells grow up toward the tectum mesencephali after myelinated axons (80 or more days after the operation). Axonal bulbs of growth in the initial periods after the operation are located close to the pial surface and the level of spread of the myelinated axons of the retinal ganglionic cells differs significantly from their normal level of localization. Intertectal connections persist after division of the nerve and are activated by visual stimuli during regeneration of the axons of the retinal ganglionic cells. Connections were found mainly between intertectal fibers terminating superficially and retinal ganglionic cells belonging to class 1 and 2 detectors. Axons of the retinal ganglionic cells grow up toward the caudal region of the tectum mesencephali later than toward the rostral region.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 6, pp. 611–620, November–December, 1973.     

The antidromic activation of tectal neurons by electrical stimuli applied to the caudal medulla oblongata in the toad,Bufo bufo L.

In order to specify the tectal projection to the bulbar/spinal regions, the antidromic responses of the physiologically identified tectal neurons as well as the gross antidromic field responses in the optic tectum to electrical stimuli applied to the caudal medulla were examined in the paralyzed common toad, Bufo bufo. The antidromic field potential was recorded in the optic tectum in response to electrical stimuli applied to the ventral paramedian portion of the contralateral caudal medulla (where the crossed tecto-spinal pathway of Rubinson (1968) and Lázár (1969) runs), but generally not when they were applied to various parts of the ipsilateral caudal medulla. The antidromic field potential was largest at the superficial part of Layer 6 or at the border between Layers 6 and 7 of the optic tectum, indicating that neurons in these layers project to the contralateral caudal medulla. Mapping experiments of the antidromic field potential over the optic tectum showed that the antidromic field potential was recorded mainly in the lateral part of it, indicating that this part of the optic tectum is the main source of projection neurons to the contralateral caudal medulla. Various classes of tectal neurons as well as retinal ganglion neurons were identified from the characteristics of the response properties to moving visual stimuli and the properties of the receptive fields. Of these, the Class T1, T2, T3, T4, T5(1), T5(2), T5(3), and T5(4) tectal neurons were activated antidromically by stimuli applied to the contralateral caudal medulla. Only a limited proportion of the Class T5(1) neurons was activated antidromically by stimuli applied to the ipsilateral caudal medulla. On the other hand, the Class T7 and T8 neurons, as well as the Class R2, R3, and R4 retinal neurons, were not activated antidromically by stimuli applied to the caudal medulla of either side. These results suggest a possibility that these tectal neurons which project to the medullary regions form the substrate of the sensorimotor interfacing and contribute to the initiation or coordination of the visually guided behavior, such as prey-catching.     

Visual information coding in the frog optic tectum

The possible mechanisms of visual information coding in the frog optic tectum were studied by extracellular recording of unit activity. It was postulated that information is coded spatially and that its precision is increased by the use of various types of time codes, making wide use in particular of differences in response latencies. These differences are also important on their own account, and they act as a component of the time codes (latency-frequency, latency-structural, and so on). The uniform distribution of neurons processing visual information and, in particular, analyzing the different parameters of visual signals (direction-velocity, lightness-darkness, and so on), among the structures of the tectum is evidence that the mechanism of analysis of the parameters of visual stimulus movement is distributive in type.Research Institute of Neurocybernetics, State University, Rostov-on-Don. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 26–34, January–February, 1982.     

Response of neostriatal neurons to direct electrical stimulation of the optic tract and photic stimulation in awake cats

During acute experiments on awake cats the response of 98 neurons belonging to the head and tail of the caudate nucleus to direct electrical stimulation of the optic tract and presentation of photic stimuli was investigated using extracellular recording techniques. Of the test neurons 34.6% responded to stimulation of the optic tract and 36.2% to optic stimulation. Long latency (over 40 msec for the optic tract and over 80 msec for visual stimulation) excitatory responses prevailed in both cases. A small number of cells responded to optic tract stimulation with short latencies of 5–14 msec. Both types of stimulation were presented during investigations of 58 units of which eight were found to respond to both stimuli. The latter varied in their reaction to different stimuli and their response pattern. Findings are discussed in relation to the possible pathways by which visual information reaches the cortical structure under study.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 4, pp. 476–485, July–August, 1986.     

Spatial organization of detector neurons in the caudo-medial part of the frog tectum opticum

Investigation of the spatial organization of detector neurons of the frog tectum opticum showed that these neurons are mainly in the nuclear layers. When responding to a photic stimulus they form a mosaic of groups of synergically excited cells separated by inhibited or nonresponding neurons. Inhibited neurons are much more numerous than excited. Different photic stimuli (shaped or diffuse) evoke the appearance of mosaics of different structure; mosaics connected with different forms of detection are to a considerable degree stratified.Rostov State University. Research Institute of Neurocybernetics, Rostov-on-Don. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 468–475, September–October, 1973.     

The tecto-thalamo-telencephalic system of the tortoise (electrophysiological investigation)

Using tortoises immobilized with diplacin to which chloralose had been added, or under chloralose — nembutal narcosis, we investigated the distribution of evoked potentials and neuronal responses in the thalamus and forebrain induced by electrical excitation of the optic tectum and by flashes of light. In the thalamus the main mass of cells that reacted to these stimuli was concentrated in the nucleus rotundus and the tecto-thalamic tract; in the forebrain it was concentrated in the general cortex, the pallial thickening, and the neostriatum. In the two latter structures responses with shorter latent periods than those in the general cortex predominated. Visual and tectal neuronal responses, especially those of convergent cells, displayed correlation in their latent periods and types of response, which was more clearly shown in the thalamus. Submaximal tetanization of the optic tectum had a facilitating effect on cortical responses produced by light flashes and excitation of the nucleus rotundus. Complete blocking of transmission of tectal impulsation to the forebrain was observed on destruction of the tecto-thalamic tract region bounded by the lateral bundle of the forebrain, the lateral geniculate body, and the nucleus rotundus. High-frequency excitation of the nucleus rotundus produced only partial blocking of transmission (of the late components). It is concluded that there are various pathways of tectal impulsation through the thalamus to the forebrain.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 2, No. 3, pp. 296–306, May–June, 1970.     

Excitation and inhibition in the visual center of Rana temporaria

Analysis of postsynaptic unit responses in the visual center ofRana temporaria showed that optic nerve fibers with high and low conduction velocities usually converge on a single neuron of the tectum opticum (TO). In response to stimulation of the optic nerve a complex depolarization potential consisting of 3 (or possibly 4) EPSPs was recorded in one group of neurons; these EPSPs were probably generated through excitation of several groups of afferent fibers. Either an increase or a decrease in the EPSPs can be observed in the TO neurons in response to repetitive and paired stimulation of the optic nerve. Postsynaptic inhibitory responses of some TO neurons, probably of direct and recurrent origin, are discussed.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 3, No. 6, pp. 637–643, November–December, 1971.     

Distribution of MAP1A,MAP1B,and MAP2A&;B during layer formation in the optic tectum of developing chick embryos

The expression patterns of three microtubule-associated proteins (MAP1A, MAP1B, and MAP2A&B) were investigated in the developing optic tectum. Expression of MAP1B and middle-molecular-weight peptide of neurofilament (NF-M) was first observed in the same mesencephalic cells on day 3 of incubation, indicating that neuroblasts had been produced. At day 5, MAP1A and MAP2A&B expression appeared in the cellular layer containing the first neuroblasts that differentiate into large multipolar cells. The NF-M⁺ neurites in the striatum album centrale (SAC) and the striatum opticum (SO) were MAP1B⁺ up to day 19, but the intensity of MAP1B immunoreactivity decreased with development. All three MAPs were expressed in large multipolar neurons in the developing stratum griseum centrale from the beginning of maturation. Stratum griseum et fibrosum centrale cellular layers, containing radially arranged piriform neurons, were MAP1A^–/MAP2A&B^– on day 11 but became MAP1A⁺/MAP2A&B⁺ during later stages. These results suggest that the timing of MAP expression in neuronal maturation of large multipolar cells differs from that of piriform cells. The expression of MAPs has revealed specific cellular events in the developing optic tectum. Based on our observations, the development of the optic tectum can be divided into four periods.     

Multisensory convergence on neurons of the motor cortex in unanesthetized cats

Postsynaptic potentials (PSPs) of 83 neurons in the motor cortex of unanesthetized cats in response to electrodermal, photic, and acoustic stimulation were investigated by intra-and quasi-intracellular recording methods. Most cells responded to stimulation of at least one limb. About 60% of neurons of the posterior and over 75% of neurons of the anterior sigmoid gyrus responded to stimulation of two (or more) limbs. In 29 of 39 neurons of the anterior and 12 of 44 of the posterior sigmoid gyrus PSPs with a short (less than 50 msec) and stable latent period were evoked by flashes and clicks. On presentation of two somesthetic stimuli complete blocking (if the interval was less than 30–60 msec) or weakening (interval 30–200 msec) of responses to the second (testing) stimulus was observed. On presentation of paired photic (or acoustic) stimuli or paired stimuli of different modalities at various intervals from 0 to 100 msec, the testing response was often potentiated. The character of the responses and their interaction thus differed from those obtained under chloralose anesthesia [6, 7]. It is postulated that under the action of chloralose a system of neurons with strong excitatory feedback is formed in the motor cortex which may respond to stimuli of different modalities by something resembling the "all or nothing" principle.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 6, pp. 563–573, November–December, 1971.     

Visual Stimuli Evoked Action Potentials Trigger Rapidly Propagating Dendritic Calcium Transients in the Frog Optic Tectum Layer 6 Neurons

The superior colliculus in mammals or the optic tectum in amphibians is a major visual information processing center responsible for generation of orientating responses such as saccades in monkeys or prey catching avoidance behavior in frogs. The conserved structure function of the superior colliculus the optic tectum across distant species such as frogs, birds monkeys permits to draw rather general conclusions after studying a single species. We chose the frog optic tectum because we are able to perform whole-cell voltage-clamp recordings fluorescence imaging of tectal neurons while they respond to a visual stimulus. In the optic tectum of amphibians most visual information is processed by pear-shaped neurons possessing long dendritic branches, which receive the majority of synapses originating from the retinal ganglion cells. Since the first step of the retinal input integration is performed on these dendrites, it is important to know whether this integration is enhanced by active dendritic properties. We demonstrate that rapid calcium transients coinciding with the visual stimulus evoked action potentials in the somatic recordings can be readily detected up to the fine branches of these dendrites. These transients were blocked by calcium channel blockers nifedipine CdCl₂ indicating that calcium entered dendrites via voltage-activated L-type calcium channels. The high speed of calcium transient propagation, >300 μm in <10 ms, is consistent with the notion that action potentials, actively propagating along dendrites, open voltage-gated L-type calcium channels causing rapid calcium concentration transients in the dendrites. We conclude that such activation by somatic action potentials of the dendritic voltage gated calcium channels in the close vicinity to the synapses formed by axons of the retinal ganglion cells may facilitate visual information processing in the principal neurons of the frog optic tectum.     

GABA-immunohistological observations, at the electron-microscopical level, of the neurons of isthmic nuclei in chicken, Gallus domesticus

Following a demonstration of Golgi-impregnated neurons and their terminal axon arborization in the optic tectum, the neurons of the nucleus parvocellularis and magnocellularis isthmi were studied by means of postembedded electron-microscopical (EM) γ-aminobutyric acid (GABA)-immunogold staining. In the parvocellular nucleus, none of the neuronal cell bodies or dendrites displayed GABA-like immunoreactivity in EM preparations stained by postembedded GABA-immunogold. However, numerous GABA-like immunoreactive and also unlabeled terminals established synapses with GABA-negative neurons. GABA-like immunoreactive terminals were usually found at the dendritic origin. Around the dendritic profiles, isolated synapses of both GABA-like immunoreactive and immunonegative terminals established glomerulus-like structures enclosed by glial processes. All giant and large neurons of the magnocellular nucleus of the isthmi displayed GABA-like immunoreactivity. Their cell surface was completely covered by GABA-like immunoreactive and unlabeled terminals that established synapses with the neurons. These neurons are thought to send axon collaterals to the parvocellular nucleus; their axons enter the tectum opticum. The morphological characteristics of neurons of both isthmic nuclei are like those of interneurons, because of their numerous axosomatic synapses with both asymmetrical and symmetrical features. These neurons are not located among their target neurons and exert their modulatory effect on optic transmission in the optic tectum at a distance.     

Electrophysiological investigation of tecto-thalamo-telencephalic relations in frogs

Projections of the tectum mesencephali to the thalamus and telencephalon were investigated inRana temporaria. Individual cells in the optic neuropil of the lateral zone of the thalamus (corpus geniculatum thalami, n. Bellonci) and n. geniculatus lateralis respond to stimulation of the tectum mesencephali and to flashes but not to somatic stimuli. Many of the tectally reactive neurons in the medio-central zone of the thalamus, including n.postero-centralis, n.postero-lateralis, and n.rotundus, and in the telencephalon (the primordium of the hippocampus and septum) are convergent for somatic and visual impulses. The character of the macroresponses and spike responses to stimulation of the tectum mesencephali is the same for both zones of the thalamus. Tetanization within the lateral zone of the thalamus inhibits the conduction of visual and tectal impulses to the telencephalon, whereas during tetanization of the medio-central zone only the later components of visual and tectal evoked potentials of the telencephalon are suppressed. Responses with shorter latency than to stimulation of the medio-central zone arise in the telencephalon (primordium of the hippocampus) in response to electrical stimulation of the lateral zone by single pulses. In frogs the two divisions of the visual system — thalamo-telencephalic and tecto-thalamo-telencephalic — thus overlap considerably at the level of the thalamus and completely at the telencephalic level. In vertebrate phylogeny there is a progressive demarcation and specialization of these two visual channels.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 2, pp. 147–155, March–April, 1973.     

Axonal transport of lipid in goldfish optic axons

After injection of labeled glycerol, choline, or serine into the eye of goldfish, labeled lipids were axonally transported along the optic nerve to the optic tectum. although the different precursors were presumably incorporated into somewhat different lipid populations, all three were approximately equally effective in labeling the lipids transported to the tectum, but the amount of transported material remaining in the nerve was different, being highest with choline and lowest with serine. The labeled lipids appeared in the tectum within 6 hr of the injection, indicating a fast rate of transport, but continued to accumulate over a period of 1–2 weeks, which presumably reflects the time course of their release from the cell body. Since there was a gradual increase in the proportion of labeled lipid in the tectum during this period, some other process in addition to fast axonal transport may have affected the distribution of the lipids along the optic axons. When [³H]choline was used as precursor, the transported material included a small amount of TCA-soluble material, which was probably mainly phosphorylcholine, with labeled acetylcholine appearing in only insignificant amounts. With serine, which gave rise to a large amount of axonally transported protein in addition to lipid, a late increase in the amount of labeled lipid in the tectum was seen, accompanied by a decrease in labeling of the protein fraction.     

Enkephalin-immunoreactive cells in the mesencephalic tegmentum project to the optic tectum of the teleosts Salmo gairdneri and Salmo salar

Summary Immunocytochemistry using antibodies against Met-enkephalin and Leu-enkephalin has demonstrated a group of large enkephalin-immunoreactive neurons in the nucleus of the rostral mesencephalic tegmentum (mRMT) of two teleost fish, Salmo gairdneri and Salmo salar. Injections of cobalt-lysine in the medial optic tectum retrogradely labeled the above group of tegmental neurons. Tegmental neurons were labeled only ipsilaterally to the injection site. This indicates that enkephalinergic neurons in the nRMT project to the optic tectum, and that at least some of the enkephalinergic axons observed in the optic tectum belong to a tegmento-tectal pathway. Comparable enkephalinergic pathways have been described in reptiles and birds, where pretectal-mesencephalic nuclei contribute to the enkephalin-containing fibers that project to the optic tectum.     

Effect of background illumination on evoked potentials of the visual system in the turtle

We discovered an enhancing effect of background illumination on amplitude and total duration of electrical reactions of the tectum of the midbrain and pallial thickening in response to a flash and electrical stimulation of the optic nerve. This effect is analogous to the phenomenon of photic potentiation known for the visual system of mammals. Changes of evoked potentials in the contralateral pallial thickening and tectum were fairly stable and survived throughout the course of the entire period of illumination (up to 30 min). The effect was intensified with an increase of illumination intensity. Intensification of response on the part of the tectum and pallial thickening during steady illumination was accompanied by a weakening of slow background electrical activity. During the action of background illumination, the excitability of the tectum rose considerably with direct electrical stimulation. The influence of prolonged illumination on responses of the tectum and pallial thickening was more clearly detected at submaximal strengths of stimulation of the optic nerve or tectum. All of the effects of photic potentiation are confined to centers contralateral to the illuminated eye. This indicates the absence of diffuse effects on excitability of the turtle brain.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 1, No. 2, pp. 219–224, September–October, 1969.     

Ultrastructural localization of acetylcholinesterase in retino-deprived optic tectum of the goldfish

The ultrastructural localization of AChE has been studied in the optic tectum of the goldfish after unilateral eye ablation. 1 or 4 months after the operation the patterns of enzyme localization were essentially the same in the normal and affected optic tectum, despite structural modifications caused by the degeneration of retinal terminals and dendritic atrophy of some tectal neurons. The results are discussed in relation to the different hypotheses put forward concerning possible cholinergic mechanisms in the optic tectum of teleosts.     

Layer by layer analysis of synaptic organization in the optic tectum of the prog

The distribution of axo-axonal and axo-dendritic synapses, nerve endings, and bodies of neurons by depth in the optic tectum ofRana temporaria L. was investigated under normal conditions and 6–9, 60, and 134 days after removal of the contralateral eye. Counting was carried out on long oriented sections examined in the electron microscope. In outer plexiform layer 9 the density of synapses was greatest near the surface of the tectum and decreased in the direction away from it; no inner sublayers with differing density of synapses could be distinguished. In the outer zone of layer 9 (to a depth of about 30 ) many axo-axonal synpases were discovered. Endings of myelinated optic fibers of large diameter ("dark" terminal degeneration) were widely distributed in the same layer. The density of axo-dendritic synapses in deep plexiform layer 5 was similar to that in layer 9. Many nerve endings containing granular vesicles as well as pale synaptic vesicles were found in layer 5 and neighboring zones.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 2, pp. 130–136, March–April, 1979.     

Reactions of neurons of the orbitofrontal cortex to stimulation of optic thalamic nuclei

The reactions of 288 neurons of the orbitofrontal cortex (OFC) to stimulation of the posteroventral (VP), ventral anterior (VA), and reticular (R) nuclei, as well as the median center (CM) of the thalamus, were investigated in acute experiments on cats. OFC neurons can be divided into four groups by their reactions to stimulation of thalamic nuclei: 1) those which respond with an increase in the frequency of the discharges to single and serial stimuli with a frequency of up to 20/sec; 2) those which respond doubtfully to single stimuli with a frequency of 4–12/sec; 3) those which respond with inhibition of the background impulses; 4) those which do not respond to stimulation of the nuclei. Stimulation of the thalamic nuclei evoked responses of OFC neurons with a large scatter of the latent period duration. The responses of neurons to stimulation of the VP (mean latent period 19.1±6.1 msec) had the shortest latent period (sometimes less than 3–4 msec). Reactions with a longer latent period developed upon stimulation of the VA (23.8±7.4 msec) and CM (42.8±12.8 msec). The uniqueness of the links of the OFC with the various optic thalamic nuclei is shown in an analysis of the material obtained and possible methods of the activation of the neurons of this region from thalamic structures are discussed.State Medical Institute, Kemerovo. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 350–358, July–August, 1971.     

Spatiotemporal organization of unit activity in the frog tectum and its modification by visual stimuli

Unit activity was recorded in the tectum of curarized frogs during presentation of various visual stimuli (on- and off-responses to diffuse illumination and movement of an object of recognizable shape). It was shown that different types of stimulation lead to the organization of a different distribution of unit activity in the tectum, in the form of excitatory-inhibitory neuronal mosaics; inhibitory responses, limiting and exacerbating the excitatory responses of other neurons, predominate. The differences observed in the spatiotemporal characteristics of the neuronal mosaics under the influence of different stimuli may be evidence of specificity of coding of visual impulses carrying different information from the retina in the tectum.