Evolutionary evaluation of reciprocity of connections in the turtle tectofugal visual system

In two turtle species—Emys orbicularis and Testudo horsfieldi—by the method of anterograde and retrograde traicing at the light and electron microscopy level, the existence is proven of direct descending projections from the thalamic nucleus of the tectofugal visual system n. rotunds (Rot) to the optic tectum. After injection of tracers into Rot alone and into Rot with involvement of the tectothalamic tract (Trtth), occasional labeled fibers with varicosities and terminals are revealed predominantly in the deep sublayers of SGFS of the rostral optic tectum, while in the lower amount—in other tectal layers. After the tracer injections into the optic tectum, a few retrogradely labeled neurons were found mainly in the Rot ventral parts and within Trtth. Their localization coincides with that of GABA-immunoreactive cells. Electron microscopy showed the existence of many retrogradely labeled dendrites throughout the whole Rot; a few labeled cell bodies were also present there, some of them being also GABA-immunoreactive. These results allow us to conclude about the existence of reciprocal connections between the optic tectum and Rot in turtles, these connections being able to affect processing of visual information in tectum. We suggest that reciprocity of tectothalamic connections might be the ancestral feature of the vertebrate brain; in the course of amniote evolution the functional significance of this feature can be decreased and even lost in parallel with a rise of the role of direct corticotectal projections.     

Calcium-binding proteins and metabolic activity in thalamotelencephalic parts of the turtle visual system

Distribution of three calcium-binding proteins (CaBPr) calbindin (CB), calretinin (CR) and parvalbumin (PV) in parallel with metabolic activity (cytochrome oxidase, CO) was studied in telencephalic projection zones of the tecto- and thalamofugal visual pathways in experiments on the Horsfield's terrapin Testudo horsfieldi and the pond turtle Emys orbicularis. It was shown that the nucleus rotundus (Rot) and dorsal lateral geniculate nucleus (GLd) terminal fields in both zones (dorsolateral region of the anterior ventricular ridge, Advrdl and dorsolateral cortex, Cxdl, respectively) were CB-immunoreactive (-ir) in the both studied turtle species. The highest density of CB-ir terminals and the focus of rotundal projections in the Advrdl core coincided precisely. The GLd terminal field in Cxdl also was CR-ir. The PV contribution to innervation of both projectional zones was much lower, especially to innervation of Cxdl from GLd. In spite of similar CB-ir innervation, the projectional field of the tectofugal pathway of Advrdl had the much higher CO activity than of that of the thalamofugal pathway in Cxdl. The neurons immunoreactive to all three CaBPr types were distributed in Cxdl in different ratios in each of layers. In the visual Advrdl area the overwhelming majority were PV-ir neurons, whereas CB-ir neurons were absent. The conclusion is made that in spite of the CB- or CB/CR-immunoreactivity predominates over the PV-immunoreactivity in both thalamotelencephalic pathways of the visual system, the tectofugal (rotundo-Advrdl) pathway having the higher metabolic activity.     

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.     

Nonlinear characteristics in the Frog's visual system

The receptive fields of retinal fibers in the visual tectum of the frog are mapped with different techniques and the spatial summation characteristics are examined, by presenting stimuli of various shapes and sizes in the center of the receptive field. When the size is increased gradually from the center of the stimulus, for constant stimulus intensity, the maximum response is obtained for stimuli of approximately the size of the most responsive part of the RF. Using a clustering technique to obtain stimuli that are part of the RF and combinations of these parts, it is evident that the spatial summation characteristics are not linear. A model is developed that describes the nonlinear form of these results, based on a power law.     

Dark and light neurons in the cortical plate of the forebrain of the swamp turtle]

Electron microscopic study of the neuronal composition of Emys orbicularis cortical zones as compared with the light microscopy data has revealed that the distinctions in the cell cytoplasm ultrastructure with respect to the dendrite branching pattern and the peculiarities of their localization in the cortical plate are suggestive of a possible metabolic heterogeneity and can serve as a foundation of the morpho-functional characteristics of the neurons. A few neuronal types of neurons have been revealed: 1. light neurons distinguished by the cytoplasm matrix devoid of any electron density, a poorly developed endoplasmic reticulum and a few cytoplasmatic organells and inclusions; 2. light neurons having slight osmophility of the cytoplasm matrix, a more developed endoplasmic reticulum with elongated cisternae, a great number of organells including neurofilaments; 3. dark neurons having a high degree of cytoplasm matrix and the nucleus, a large number of the nuclei, cytoplasm, dendrites and axons in contrast to the above described patterns.     

Morphological characteristics of the pituitary-gonad system in high altitude hypoxia

The experiments on male rats showed that their sojourn at high altitude resulted in alterations of functional relationship between the gonadotropic pituitary cells and tests. That was characterized by synthesis inhibition and hormone release by gonadotropocytes. In the testes we found impairments in the barrier function and active substance transport in sustentocytes. Intensification of destructive processes in sustentocytes, with prolongation of adaptation duration, are mediated to a greater extent by a direct destructive high altitude factors. A decrease in hormone producing function of glandulocytes as a result of destruction processes has aggravated dysharmony of the pituitary-testes system which by the end of the second month was manifested by a marked inhibition of gonadotropic cell hormone release with preservation of the synthesis high level in them.     

Modeling of the vertebrate visual system. II. Application to the turtle cone retina

The model of the vertebrate cone retina was adapted to the turtle retina with its red cone- and L-channel-dominances. The model consists of an ordering of four spatial organizations of unit hexagons, weighted inputs for all cones in the receptive fields, and linear polarization factors based on data from literature on turtle retina. Data generated by the model for spatial and chromatic patterns of receptive fields, intensity-response curves, dynamic ranges for cones, horizontal and bipolar cells proved remarkably consistent with literature. The model also generates observed phenomena such as near-field enhancement of cones due to stray light effects and electrical coupling of like-cones and far-field decrease in responses due to negative feedback from L-type horizontal cells to cones. Annular stimuli were shown to be more effective than spot stimuli for horizontal cells. The formal approach of the model demonstrates factors which play roles in various observed phenomena and all aspects of model can be displayed and tested both qualitatively and quantitatively.     

Morphological characteristics of chemosensory,visual, and statocyst pathways in the snailHelix lucorum

The following structural characteristics of the chemosensory, visual, and vestibular pathways of the snail (Helix lucorum) were demonstrated by using a variety of histological techniques. Large and small neurons of the tentacle ganglion, the bipolar cells of the olfactory nerve, and a proportion of optic tentacle bulb chemoreceptors within the olfactory nerve all send their processes to the CNS of the mollusk. Here they are divided up into numerous bundles of fibers in the neuropil of the ipsilateral cerebral ganglion. They are joined by processes from the central nervous system put out by all neurons of the protocerebrum and the cluster of cells of the commissural section of the metacerebrum. Ocular receptors do not send processes down below the enlargement of the upper optic nerve. This enlargement is also the site where processes from cells within the CNS and the nerve itself terminate. An area of arborization of processes from the visual pathway cells is located in the neuropil of the pleural portion of the metacerebrum. Hair cells of statocysts put out processes to the cerebral ganglion, whence axons of small metacerebral neurons extend towards the organ of balance. Some processes from vestibular pathway cells form an arborization zone at the ipsilateral cerebral ganglion, while others pass through the cerebral commissure to form their area of arborization in the contralateral ganglion. Processes from vestibular and visual pathway cells arborize in exactly the same area.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 7–16, January–February, 1986.     

Response properties of visual neurons in the turtle nucleus isthmi

The optic tectum holds a central position in the tectofugal pathway of non-mammalian species and is reciprocally connected with the nucleus isthmi. Here, we recorded from individual nucleus isthmi pars parvocellularis (Ipc) neurons in the turtle eye-attached whole-brain preparation in response to a range of computer-generated visual stimuli. Ipc neurons responded to a variety of moving or flashing stimuli as long as those stimuli were small. When mapped with a moving spot, the excitatory receptive field was of circular Gaussian shape with an average half-width of less than 3°. We found no evidence for directional sensitivity. For moving spots of varying sizes, the measured Ipc response-size profile was reproduced by the linear Difference-of-Gaussian model, which is consistent with the superposition of a narrow excitatory center and an inhibitory surround. Intracellular Ipc recordings revealed a strong inhibitory connection from the nucleus isthmi pars magnocellularis (Imc), which has the anatomical feature to provide a broad inhibitory projection. The recorded Ipc response properties, together with the modulatory role of the Ipc in tectal visual processing, suggest that the columns of Ipc axon terminals in turtle optic tectum bias tectal visual responses to small dark changing features in visual scenes.     

Propagating waves in visual cortex: a large-scale model of turtle visual cortex

This article describes a large-scale model of turtle visual cortex that simulates the propagating waves of activity seen in real turtle cortex. The cortex model contains 744 multicompartment models of pyramidal cells, stellate cells, and horizontal cells. Input is provided by an array of 201 geniculate neurons modeled as single compartments with spike-generating mechanisms and axons modeled as delay lines. Diffuse retinal flashes or presentation of spots of light to the retina are simulated by activating groups of geniculate neurons. The model is limited in that it does not have a retina to provide realistic input to the geniculate, and the cortex and does not incorporate all of the biophysical details of real cortical neurons. However, the model does reproduce the fundamental features of planar propagating waves. Activation of geniculate neurons produces a wave of activity that originates at the rostrolateral pole of the cortex at the point where a high density of geniculate afferents enter the cortex. Waves propagate across the cortex with velocities of 4 m/ms to 70 m/ms and occasionally reflect from the caudolateral border of the cortex.     

A recurrent system incorporating characteristics of the visual system: a model for the function of backward neural connections in the visual system

A recurrent system is constructed in order to investigate the role of the backward neural connections found in the primate visual system. The system incorporates a layer to perform localized spatial frequency analysis of input images, a function which has been assumed to take place in the primary visual cortex. The function of the system is examined by simulation. The results show that the system can separate an object pattern from its background, irrespective of its precise position. The acceptable displacement range for input images is determined from the width of the window function used to calculate the local Fourier transform. A multilayer version of the above recurrent system is also constructed.     

Morphological and physiological identification of medulla interneurons in the visual system of the tiger beetle larva

The morphology of visual interneurons in the tiger beetle larva was identified after recording their responses. Stained neurons were designated as either medulla or protocerebral neurons according to the location of their cell bodies. Medulla neurons were further subdivided into three groups. Afferent medulla neurons extended processes distally in the medulla neuropil and a single axon to the brain through the optic nerve. They received their main input from stemmata on the ipsilateral side. Two distance-sensitive neurons, near-by sensitive and far-sensitive neurons, were also identified. Atypical medulla neurons extended their neurites distally in the medulla and proximally to the brain, as afferent medulla neurons, but their input patterns and the shapes of their spikes differed from afferent neurons. Protocerebral neurons sent a single axon to the medulla neuropil. They spread collateral branches in the posterior region of the protocerebrum on its way to the medulla neuropil. They received main input from stemmata on the contralateral side. Medulla intrinsic neurons did not extend an axon to the brain, and received either bilateral or contralateral stemmata input only. The input patterns and discharge patterns of medulla neurons are discussed with reference to their morphology.     

The photosynthetic characteristics of papyrus in a tropical swamp

Summary Photosynthesis and transpiration was measured in the large emergent C₄ sedge Cyperus papyrus (papyrus) which occupies wide areas of wetland on the African continent. The maximum observed value of net assimilation was 35 mol CO₂ m^-2 s^-1 at full sunlight but light saturation of photosynthesis did not occur. The quantum yield of photosynthesis obtained from the initial slope of the light response curves (0.06 mol mol^-1 incident light) was relatively high and close to previously recorded values for some C₄ grasses. Measurements made over two days showed that stomatal conductance was sensitive to the ambient air vapour pressure deficit (VPD) and was consistently lower on the day when VPD's were higher. There was, however, no marked midday closure of the stomata. Photosynthesis was also reduced on the day when VPD's were higher. The relationship between net photosynthesis and stomatal conductance was close to linear over the range of measurement conditions, with the result that intercellular CO₂ concentrations (C _i ) did not vary markedly. There was some evidence that C _i decreased at high VPD's. The regulation of stomatal movement in papyrus appears to minimise excessive water loss while not severely limiting photosynthesis. The significance of this strategy for a wetland species with plentiful supplies of water is discussed.     

Morphological and morphometrical characteristics of the esophageal intrinsic nervous system in the golden hamster

Very little is known about esophageal innervation in the hamster. In the present study, we used protein gene product 9.5 (PGP 9.5) to determine immunohistochemically the architectural features of the enteric nervous system in the hamster esophagus. The myenteric plexus consisted of a loose and irregular network of ganglia and interganglionic nerve bundles. The density of the neurons in the myenteric plexus was relatively low (479 +/- 75/cm(2), n = 5), with a preferentially higher density in the upper cervical portion than other parts of the esophagus. Regional differences in the number of PGP 9.5-positive neurons and ganglia were observed. PGP 9.5-immunoreactive fibers in the ganglia often branched, giving rise to expanding nerve endings of laminar morphology resembling intraganglionic laminar endings described in rats and cats. Fine varicose fibers originating from the secondary plexus were occasionally observed near the motor endplates, suggested a dual innervation of the striated muscle. The submucosal plexus was free from ganglionated plexus. A regional difference in the submucosal nervous network was observed. The number of motor endplates in the inner muscle layer was higher than that in the outer muscle layer.     

Morphological characteristics of the acetabulum

The aim of this research was to accurately measure the surface of the semi lunar articular surface of the pelvis (facies lunata acetabuli) and the variability of the acetabular geometry, as well as to determine the correlation between measured parameters. 30 macerated anatomical specimens of pelvic bones were measured. The radius and depth were measured in the classical way, while cartilaginous surface area was measured using small fragments of measuring paper to avoid errors in measurement due to the curvature of the surface. Computerized calculations provided accurate surface values. In our research, facies lunata acetabuli measured 2294+/-329 mm2. Diameter of the opening of the acetabulum measured 25.8+/-1.9 mm. Acetabular depth was 30+/-3.2 mm. Correlations between the surface area of the facies lunata acetabuli and the radius of the acetabular opening curvature (r=0.71), surface area of the facies lunata acetabuli and the depth of the acetabulum (r=0.80) and the radius of the acetabular opening curvature and the depth of the acetabulum (r=0.80) were confirmed. For precise assessment of the facies lunata acetabuli surface area, the simplest and the cheapest method is the method of measurement using small fragments of measuring paper and software analysis. There is a significant correlation between the depth, opening of the acetabulum and surface area of the facies lunata.