Biomedical subjects

M S Cynader

Publications and source records attributed to M S Cynader.

At least 55 records · Page 3Linked to original sources

PubMed1993

Immunohistochemical localization of the S-100 beta protein in postnatal cat visual cortex: spatial and temporal patterns of expression in cortical and subcortical glia.

The ontogenic expression of the glial-specific protein S100 beta was examined in postnatal cat visual cortex using immunocytochemical methods. Astrocytes in visual cortex and oligodendrocytes in the subcortical white matter exhibited distinct spatio-temporal gradients in their expression of the S100 beta protein. In the visual cortex, S100 beta-immunoreactivity was detected in astroglial cytoplasm, as well as in the extracellular interstitium, in a lamina-specific manner throughout postnatal development. Using double labeling procedures, the S100 beta protein was found to be strictly colocalized with GFAP-immunoreactive astrocytes when GFAP was present. The glial fibrillary acidic protein (GFAP), a marker of mature astrocytes, was not present at high levels until the 4th postnatal week. From the 2nd through 5th postnatal weeks, the expression of S100 beta was highest in the thalamocortical recipient, layer IV, of visual cortical areas 17 and 18. At ages beyond 6 postnatal weeks, S100 beta-immunoreactivity increased disproportionately in supra- and infragranular layers such that areas 17 and 18 were demarcated from adjacent cortices by lower levels in layer IV. The S100 beta protein was also highly expressed in oligodendroglial somata and processes in the subcortical white matter between the 2nd and 6th postnatal weeks. The levels of S100 beta in the subcortical white matter progressively diminished to adult levels, where it was localized only to a few remaining oligodendroglial somata. The differential laminar expression of the S100 beta protein in astrocytes during the period within which the visual cortex exhibits input- and experience-dependent synaptic modifications suggests that astrocytes, possibly via their release of S100 beta, may play a special role in mediating plasticity in visual cortical development. A consistent feature of the appearance of the S100 beta protein was its expression in immature astroglia and oligodendroglia, well before they are considered morphologically mature. This characteristic underscores the potential of S100 beta as a marker of distinct populations of glial cells and of their role in normal and abnormal development.

Animals↗

PubMed1993

Activity-dependent expression of the transcription factor Zif268 reveals ocular dominance columns in monkey visual cortex.

The visualization of neuronal populations activated by sensory stimulation has been approached using a number of different methodologies. Recent developments in our understanding of transcription factors have provided a new window for observing neural activity. We have found that the transcription factor Zif268 is expressed throughout the visual cortex of the monkey at high basal levels and that monocular visual deprivation produces dramatic changes in its levels revealing ocular dominance columns in striate cortex with as little as 2 h of selective exposure. These results show that immunodetection for Zif268 may be used for labelling activated neuronal populations in the monkey with several key advantages over prior techniques.

Animals↗

PubMed1993

An improved staining technique for cytochrome C oxidase.

Cytochrome C oxidase (CO) has been shown to be an indicator of neuronal activity in the brain. In the primate visual cortex, CO staining also differentiates cell populations encoding visual properties such as color, contrast, ocularity, and movement. We have developed a modified method which dramatically enhances the intensity and contrast of CO staining. This method can be applied to both fixed and non-fixed tissues. The sensitivity of this method is sufficiently high that, even after years of storage, tissues can still be well stained for CO activity. Such tissue is poorly stained with current methods. This CO staining technique may also be useful for double labeling of CO with other anatomical markers.

Animals↗

PubMed1993

The EP2 receptor is the predominant prostanoid receptor in the human ciliary muscle.

Prostaglandins can reduce intraocular pressure by increasing uveoscleral outflow. We have previously demonstrated that the human ciliary muscle was a zone of concentration for binding sites (receptors) for prostaglandin F2 alpha and for prostaglandin E2. Here, we try to elucidate the types of prostanoid receptors in the ciliary muscle using competitive ligand binding studies in human eye sections and computer assisted autoradiographic densitometry. Saturation binding curves showed that the human ciliary muscle had a large number of binding sites with a high affinity for prostaglandin E2 compared with prostaglandin D2 and F2 alpha. The binding of tritiated prostaglandin E2 and F2 alpha in the ciliary muscle was displaced most effectively by prostaglandin E2 and 11-deoxy prostaglandin E1 (a selective EP2 prostanoid receptor agonist), whereas the binding of prostaglandin D2 was displaced most effectively by prostaglandin E2 and D2. These results indicate that the dominant prostanoid receptor in the human ciliary muscle is the EP2 subclass and that there is also a small number of DP receptors.

Alprostadil↗

PubMed1993

Autoradiographic localization of serotonin receptor subtypes in cat visual cortex: transient regional, laminar, and columnar distributions during postnatal development.

Postnatal changes in the distribution of 5-HT receptor subtypes in the visual cortex of cats were assessed both qualitatively and quantitatively using in vitro autoradiographic methods. The 5-HT 1A, 1C, 2, and 3 receptor subtypes and the 5-HT uptake (5-HTUp) site were visualized with 3H-8-hydroxy-2(di-n-propyl-amino)tetralin, 3H-mesulergine, (2,5-dimethoxy-4-125I-iodophenyl)-2-aminopropane, 3H-BRL43694, and 3H-cyanoimipramine, respectively. Although specific labeling of 5-HT3 receptors was not detected in the cat visual cortex at any age, each of the remaining 5-HT receptor subtypes exhibited unique temporal, regional, and laminar patterns of expression in visual cortical areas 17, 18, and 19 and lateral suprasylvian cortex (LS). 5-HT1A receptors were the earliest to demonstrate visual cortex-specific changes in expression. They exhibited peak levels of expression in all visual cortical areas, predominantly in supra- and infragranular layers, between postnatal day 10 (PD10) and PD30. Their levels in all areas declined progressively with increasing age. 5-HT1c receptors demonstrated their highest levels of expression in the deeper half of layer IV, but only in area 17, between PD40 and PD75. The most striking feature of their distribution throughout this period was that, in layer IV and extending into layer III, the 5-HT1c receptors were concentrated in columns that were 400 microns wide and had a center-to-center spacing of about 900 microns. This transient pattern of expression was not present beyond PD90. 5-HT2 receptors were most densely expressed in layer IV between PD40 and PD120, but they displayed a distinctly different distribution pattern. The densest binding of 5-HT2 receptors was limited to the upper half of layer IV and found in areas 17, 18, and LS. The distribution of layer 5-HT2 receptors along the dense band in layer IV of area 17 was discontinuous, exhibiting patches that were found in the same vertical columns as were the 5-HT1c receptors. Intermediate binding levels for the 5-HT2 receptors were found through layers I-III, the remainder of layer IV, and the subcortical white matter. The levels of 5-HT uptake sites increased gradually to reach adult levels by PD40, but with a distribution pattern that was basically homogeneous, both across cortical regions and across laminae.(ABSTRACT TRUNCATED AT 400 WORDS)

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1992

Neurons in cat primary auditory cortex sensitive to correlates of auditory motion in three-dimensional space.

Amplitude modulation at the receiver's ears is a characteristic of moving sound sources. When a sound source moves from side to side, stimulus intensity decreases in one ear and increases in the other. When a sound source moves toward or away from the organism, the two ears receive correlated increases or decreases in sound level. We recorded from single cells in the auditory cortex while presenting amplitude modulated pure tones to the two ears which stimulated motion either toward or away from the organism, or from side to side. Our results indicate that auditory cortex neurons can be highly sensitive to these correlates of auditory motion in three dimensional space. Three major classes of neurons were encountered. These included 1) neurons sensitive to azimuthal stimulus motion, 2) neurons sensitive to motion directly toward or away from the organism, and 3) monaural-like neurons. More toward-preferring neurons than away-preferring neurons were encountered, and more units preferred contralateral-directed than ipsilateral-directed movement. The different classes of direction-selective neurons were spatially segregated from each other within the cortex and appear to occur in columns. In addition to their selectivity for different directions of simulated sound source motion, auditory cortex neurons could also be highly selective to AM ramp rate and excursion; these are correlates of sound source velocity.

Acoustic Stimulation↗

PubMed1992

Auditory cortex neurons sensitive to correlates of auditory motion: underlying mechanisms.

Neuronal response properties such as phasic vs. tonic, onset vs. offset, monotonicity vs. non-monotonicity, and E/E vs. E/I, can be shown to act synergistically suggesting underlying mechanisms for selectivity to binaural intensity correlates of auditory sound source motion. Both identical (diotic), and oppositely directly dichotic AM ramps were used as stimuli in the lightly anesthetized cat, simulating motion in four canonical directions in 3-dimensional space. Motion in either azimuthal direction evokes selective activity in cells which respond best to the onset of monaural sound in one ear and show a decreased response to binaural stimulation (E/I or I/E). In some cells specificity is increased by "off" components in the non-dominant ear. Although these cells fire only at the onset of stationary sound, they fire throughout oppositely directed AM ramps. Motion toward or away from the head evokes responses from EE cells; strong binaural facilitation increases selectivity for motion in depth. The sharpness of direction of tuning was related to the degree of binaural facilitation in E/E cells. Selectivity for sound moving away from the head is correlated with "off" responses, while "on" responses correlate with preference for motion toward the head. Most units showed a monotonic rate function as AM ramp excursion and rate was increased. One third were selective for slower rates of intensity change and may therefore encode slower rates of stimulus motion, as well as direction of movement. The findings suggest that neural processing of auditory motion involves neural mechanisms distinct from those involved in processing stationary sound location and that these mechanisms arise from interactions between the more traditionally studied response properties of auditory cortex neurons.

Acoustic Stimulation↗

PubMed1992

GABAA receptor immunoreactivity in the white matter.

Using immunohistochemical methods with polyclonal antibodies directed against a specific sequence of the beta 1-subunit of the GABAA receptor, we found strong immunoreactivity in the white matter of cat brain. The immunopositive products were present primarily on processes of glial cells, especially astrocytes. Immunoreactivity appeared also on the cell bodies of astrocytes and on the cytoplasmic membranes of neurons. The abundant immunostaining in the white matter suggests that (1) GABAA receptors are present on glial cells in vivo, (2) GABAA receptors may be localized on non-synaptic membranes in the white matter and (3) activation of GABAA receptors may have some trophic effects on preservation of the structure and functional properties of the white matter.

Amino Acid Sequence↗

PubMed1992

Localisation of prostaglandin F2 alpha and E2 binding sites in the human eye.

Prostaglandin F2 alpha reduces intraocular pressure possibly by increasing uveoscleral outflow. To further understand the mechanism of its action binding sites for prostaglandin F2 alpha and, for comparison, prostaglandin E2 were localised in sections of human cadaveric eyes using an in vitro ligand-binding technique and autoradiography. Specific binding sites for both prostaglandin F2 alpha and E2 were co-localised at a high level in the areas of the ciliary muscles and iris sphincter muscles, and at a lower level in the iris epithelium and the retina. The results suggest that prostaglandin F2 alpha and also prostaglandin E2, could modulate uveoscleral outflow by binding to their receptors located on the ciliary muscles and inducing their relaxation.

Binding Sites↗

PubMed1992

Localization of alpha-2 adrenergic receptors in the human eye.

To elucidate sites of the action of alpha-2 adrenergic drugs, we localized binding sites for a potent alpha-2 adrenergic agonist, UK-14,304, in sections of the human cadaveric eye by an in vitro ligand-binding technique and autoradiography. Its specific binding sites were found in the iris epithelium and ciliary epithelium at a high level, and also in the ciliary muscle, retina, retinal pigment epithelium (and/or choroid). Binding of UK-14,304 to the ocular pigments was prevented by preincubating the eye sections with chloroquine, which reduced the non-specific binding to a low level.

Adrenergic alpha-Agonists↗

PubMed1991

Aural intensity for a moving source.

Considerable, highly specific information is available to the auditory system concerning the trajectory of a moving sound source. This paper delineates the set of stimuli that motion-sensitive systems might use. General expressions for the sound intensity, the interaural intensity difference, and their first time derivatives, are derived for a source moving along an arbitrary trajectory. The general expressions are then made explicit for three special cases of motion of an omnidirectional constant level source: a source moving directly away from or toward the observer, a source moving around the observer's head, and a source moving in a straight line across the auditory field of the observer. The later special case combine characteristics of the two first ones. The functions are plotted and their characteristics compared. The combination of all four functions provides a unique signature for each source trajectory. The first time derivative of the monaural spectrum level function is found to be directly proportional to the velocity scaled by the distance of the source for omnidirectional sources of constant intensity. This makes the first time derivative of the spectrum level especially attractive as a component of a specialized source detection system in the brain.

Auditory Perception↗

PubMed1991

Position-specific adaptation in simple cell receptive fields of the cat striate cortex.

1. Responses of simple cells in cat striate cortex were studied with flashed light-slit stimuli. The responses to bars flashed in different positions in the receptive field were assessed quantitatively before and after periods of prolonged stimulation of one small region. This type of prolonged stimulation resulted in reduced responsivity over a limited zone within the simple cell receptive field. 2. The adaptation-induced responsivity decrement was generally confined to the receptive-field subregion that was adapted (either ON or OFF). Prolonged stimulation within an ON region did not usually result in adaptation effects that spread into neighboring OFF regions. Furthermore, the adaptation-induced response decrement did not necessarily spread throughout the subregion in which the adapting stimulus was presented. The adaptation effects from prolonged stimulation at a single receptive-field position spread throughout the subregion in nearly one-half of the 25 cells examined for position-specific adaptation. Another subpopulation of neurons (n = 12) displayed adaptation effects that spread through only one-half of the subregion, whereas in two neurons the spread of the adaptation effect was even more restricted and encompassed only one-fourth of the subregion. 3. The spread of adaptation was not systematically related to the size of the stimulus presented, the size of the receptive field, or the magnitude of the adaptation-induced response decrements but was significantly correlated with the spatial wavelength of the cell (the reciprocal of the cell's preferred spatial frequency) and with the size of the subregion in which the adapting stimulus was presented. Cells with large receptive-field subregions and long wave-lengths showed adaptation effects that spread further than those of cells with small subregions. 4. The adaptation effects from repeated stimulation at a single receptive-field position did not spread symmetrically across the receptive field, and the preferred direction of motion for a given cell indicated the direction of the asymmetric spread of the adaptation. Receptive-field positions that would be stimulated by a light slit originating at the point of adaptation and moving in the preferred direction (preferred side) showed greater adaptation-induced response decrements than did receptive-field positions that would be stimulated by a light slit moving in the opposite direction from the point of adaptation (nonpreferred side). There was significant enhancement of responses at some receptive-field positions on the nonpreferred side of the point of adaptation.(ABSTRACT TRUNCATED AT 400 WORDS)

Acclimatization↗

PubMed1990

Protein kinase C immunoreactivity in kitten visual cortex is developmentally regulated and input-dependent.

Immunocytochemistry with polyclonal antibodies directed against protein kinase C (PKC) was utilized to investigate the development of the kinase in kitten visual cortex neurons. The immunoreaction product was found at postsynaptic sites at all ages studied. However, PKC was localized in presynaptic terminals only during the first few weeks of postnatal life, during the period when the cortex is most susceptible to visual experience. The overall level of PKC immunoreactivity was high at early postnatal ages (up to 6 weeks) and declined afterwards till adulthood. This decline in reactivity was not equal across the cortex and was particularly marked in the middle cortical layers, especially layer IV. The reduction of PKC immunoreactivity in all cortical layers but layer IV was abolished by isolating a portion of cortex from its neuronal inputs early in life. Indirect evidence points to the lateral geniculate nucleus as the source of input that is required for input-dependent maturational changes in the kinase level. The results reported here suggest that the expression of PKC in kitten visual cortex in not only developmentally regulated but is also use-dependent.

Aging↗

PubMed1990

Functional organization of the cortical 17/18 border region in the cat.

The representation of the visual field in the 17/18 border region of the cat's visual cortex, and the layout of orientation and ocular dominance columns, were studied by making many closely spaced electrode penetrations into the superficial layers of the flattened dorsal region of the marginal gyrus and recording response properties at each location. The 17/18 border region was defined by measuring the change in the horizontal component of receptive field position within the gyrus: as the position of the recording electrode moved from medial to lateral, the receptive fields moved towards the vertical midline, indicating that the electrode was in area 17; as penetrations were made in increasingly lateral positions, the trend reversed, and receptive field positions moved away from the midline, indicating that the electrode was in area 18. The receptive fields of cells close to the border straddled, or lay within 2 degrees-3 degrees on either side of the vertical midline. In addition, patches of cortex were sometimes encountered in which cells had receptive field centers located up to 7 degrees in the ipsilateral visual field. Experiments in which maps were made in the left and right hemispheres of a single animal showed that these patches had a complementary distribution in the two hemispheres. Cells within the patches behaved as though driven by Y-cell inputs: they usually had large receptive fields and responded to rapidly-moving stimuli. They were broadly tuned for orientation and strongly dominated by the contralateral eye. Fourier spectral analysis of orientation selectivity maps showed that iso-orientation bands had an average spacing of 1.14 +/- 0.1 mm and tended to be elongated in a direction orthogonal to the 17/18 border. Individual bands crossed the border without obvious interruption, although singularities (points of discontinuity in the layout of orientations) were more frequently observed in the border region than in adjacent areas. Two dominant periodicities could be measured in the maps of ocular dominance, one at around 0.8 +/- 0.2 mm and a second at 2.0 +/- 0.3 mm. No constant direction of elongation was noted. These are close to the periods present within areas 17 and 18 respectively.

Animals↗

PubMed1990

Cellular and subcellular localization of protein kinase C in cat visual cortex.

Polyclonal antibodies against 3 protein kinase C (PKC) subtypes (I, II and III) were applied to localize the kinase in cat visual cortex. These antibodies exclusively stained neuronal cells. Both pyramidal and non-pyramidal cells exhibiting PKC-like immunoreactivity were concentrated in layers, II, III, V and VI with relatively few cells in layer IV. Electron microscopic examination did not reveal any presynaptic localization of the kinase. PKC immunoreactivity remained normal in a zone of cortex surgically isolated from the rest of the brain by an undercut procedure. These results suggest that PKC is heterogenously distributed in adult cat visual cortex; the kinase recognized by the polyclonal antibodies is localized postsynaptically in intracortical neurons of the superficial and deep cortical layers and the expression of the kinase is not regulated by extracortical input.

Animals↗

PubMed1989

Endstopping and curvature.

Hypercomplex or endstopped visual cortical neurons are usually supposed to be concerned with length or end point analysis. However, recent evidence demonstrates that endstopped neurons are curvature-selective, a connection that we explore here in some detail. A model of endstopped simple cells is developed and a variety of computational simulations examine the connection of the model to the reported length and orientation responses of endstopped neurons. Even and odd versions of the model are described, both of which are shown to be curvature-selective. Even-symmetric instances of the model respond well to thin curves over a range of curve orientation and curvature, independent of sign of curvature. In contrast, odd-symmetric instances respond to both thin and thick curves while exhibiting a more complex curvature-sign dependence--responding in a sign-selective fashion to curved lines but not to curved edges. Finally, the response of the endstopped model to curve singularities is explored, and the possible role of nonendstopped and endstopped cells in building curve descriptions is discussed.

Contrast Sensitivity↗

PubMed1989

Characterization of muscarinic acetylcholine receptors in rat cerebral cortex slices with concomitant morphological and physiological assessment of tissue viability.

We have begun studies on regulatory mechanisms of muscarinic acetylcholine receptors (mAChRs) in slices of rat cerebral cortex. This paper, the first of two, deals with the viability of the cells in the slices (a prerequisite for studying receptor regulation) and provides a characterization of binding sites for [3H]N-methyl scopolamine ([3H]NMS) and [3H]quinuclidinyl benzylate ([3H]QNB) in this preparation. Trypan blue exclusion tests in 400-microns-thick cortical slices showed a number of dead cells in a 100 microns zone from each cut edge, for a total of about 15-30% of all cells in the slice. In agreement with previous reports, electron microscopy revealed healthy tissue in the middle of the slice, but after incubation for several hours, swollen cells and dendrites were seen without cytoplasmic organelles. Axon terminals, however, were still seen to synapse upon these processes. Electrophysiological single unit recordings showed spontaneous action potentials in the slices. For receptor binding experiments, slices were incubated with either [3H]NMS, a hydrophilic mAChR ligand which does not penetrate the cell membrane, or the lipophilic ligand [3H]QNB which readily enters cells. For both ligands, equilibrium binding was reached after 8 h at 4 degrees C, and after 3 h at 30 degrees C. Binding of both ligands could be displaced by unlabelled atropine sulphate, NMS or QNB. Saturation binding curves yielded a Bmax of 2187 fmol/mg protein for [3H]QNB (reflecting all mAChRs) and 1335 fmol/mg protein for [3H]NMS (only mAChRs on the cell surface) at 30 degrees C. Kd values were 8.2 and 5.2 nM for [3H]QNB and [3H]NMS, respectively. These values are high compared with values obtained from homogenates, frozen sections or dissociated cells, and presumably reflect the use of intact, living tissue. These data are probably a better reflection of the actual, in vivo mAChR number and affinity than those obtained from dead tissue. This slice preparation suggests itself as a simple but effective method with which to study the regulation of mAChRs in living brain tissue.

Animals↗

PubMed1989

A role for potassium channels in the regulation of cortical muscarinic acetylcholine receptors in an in vitro slice preparation.

The rules underlying muscarinic acetylcholine receptor (mAChR) regulation in an in vitro cortical slice preparation of adult rats were examined following various alterations of bioelectric activity and following agonist stimulation. Muscarinic ACh antagonists [3H]N-methyl scopolamine ([3H]NMS) or [3H]quinuclidinyl benzylate ([3H]QNB) were used to label cell surface vs total (i.e. surface and internal) receptors, respectively. Depolarization of neural membranes for 4 h at 22-37 degrees C using veratridine or high external potassium (K+) led to a temperature-dependent down-regulation of surface mAChR of 26.2% and 11.3%. Total mAChRs decreased by 37.6% and 8.1%. Addition of picrotoxin and glutamic acid also led to decreases in mAChRs. Increases in inward chloride ion current induced by gamma-aminobutyric acid (GABA) or gold chloride had no significant effect on mAChRs. Blockade of calcium channels and synaptic transmission by magnesium or cobalt and postsynaptic calcium channels with nifedipine showed a significant effect on mAChRs only in the latter case. In contrast, agonist stimulation using carbachol led to a large down-regulation for both [3H]NMS and [3H]QNB (26.1%, 35.9%). ACh decreased [3H]QNB binding by 33.9%, but had little effect on [3H]NMS binding (6.3%). For [3H]QNB binding sites the effects of carbachol appeared to summate with those of veratridine. Down-regulation of [3H]NMS labelled mAChRs by carbachol and veratridine had an estimated half-time of 30 min and 2 h, respectively. Neither the effects of veratridine nor carbachol could be antagonized by tetrodotoxin (TTX), showing that the effects were not due to an increase in sodium ion currents. However, a common thread linking the various agents which induce mAChR down-regulation appears to involve changes in potassium (K+) current. Potassium channel blockers tetraethylammonium chloride (TEA), 4-aminopyridine (4-AP) and apamin had little independent effect on mAChR number, but prevented veratridine-induced down-regulation, presumably through a blockade of K+- and Ca2+-dependent K+-channels. Only TEA and 4-AP diminished carbachol-induced down-regulation suggesting that this effect involves only the non Ca2+-dependent K+-channels. It thus appears that mAChR regulation in the rat cerebral cortex is linked to changes in active K+-channel currents: activation of the K+-channel by depolarization-induced changes in K+ current or by agonist stimulation leading to changes in the selective K+ currents stimulate mAChR down-regulation; blockage of the K+-channels prevents this down-regulation.

4-Aminopyridine↗