Biomedical subjects

M S Cynader

Publications and source records attributed to M S Cynader.

At least 19 recordsLinked to original sources

PubMed1994

A study of tachykinin-immunoreactivity in the cat visual cortex.

The localization of tachykinin-immunoreactivity in the cat visual cortex (area 17) was investigated using immunohistochemical methods. Strong laminar specificity was observed, with immunoreactivity highest in layer V, followed by layers I, VI, II and III, and the lowest density in layer IV. Most of the immunoreactive product was localized in neuronal processes. A few immunopositive cell bodies were also present. The immunopositive neurons were non-pyramidal, multipolar, or bipolar in shape, and mostly found in layer V. There were particularly dense immunopositive fibers and varicosities around somata in layer V. These may represent tachykinin-containing presynaptic terminals (boutons). The results provide anatomical evidence that tachykinins may primarily affect layer V neurons in the cat visual cortex.

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↗

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↗

PubMed1989

Phorbol 12,13-dibutyrate regulates muscarinic receptors in rat cerebral cortical slices by activating protein kinase C.

Stimulation of muscarinic acetylcholine receptors (mAChR) elicits phosphatidylinositol turnover, which yields inositol phosphates (InsP) and diacylglycerol (DG) the latter activating protein kinase C (PKC). Activating PKC with phorbol esters inhibits mAChR agonist-stimulated phosphoinositide hydrolysis and InsP production. A possible mechanism of this inhibition may be down-regulation of mAChR by PKC. In the present work, rat cortical slices were preincubated with phorbol 12,13-dibutyrate (PDBu) followed by binding assays for [3H]quinuclidinyl benzilate [( 3H]QNB), [N-methyl-3H]scopolamine [( 3H]NMS) or [3H]pirenzepine [( 3H]PZ). Our data demonstrate that activation of PKC by phorbol esters causes a rapid down-regulation of muscarinic cholinergic receptors. This down-regulation is also rapidly reversible. Receptors on the cell surface appear to be more sensitive to the effect of PKC than do internal ones. This down-regulation occurs by a decrease in the number of receptors, rather than by changes in receptor affinity. The results suggest that PKC may exert negative feedback on its own activation by down-regulating the receptors that normally elicit phosphatidylinositol turnover.

Animals↗

PubMed1989

Adaptation in single units in visual cortex: the tuning of aftereffects in the spatial domain.

Cat striate cortical neurons were investigated using a new method of studying adaptation aftereffects. Stimuli were sinusoidal gratings of variable contrast, spatial frequency, and drift direction and rate. A series of alternating adapting and test trials was presented while recording from single units. Control trials were completely integrated with the adapted trials in these experiments. Every cortical cell tested showed selective adaptation aftereffects. Adapting at suprathreshold contrasts invariably reduced contrast sensitivity. Significant aftereffects could be observed even when adapting at low contrasts. The spatial-frequency tuning of aftereffects varied from cell to cell. Adapting at a given spatial frequency generally resulted in a broad response reduction at test frequencies above and below the adapting frequency. Many cells lost responses predominantly at frequencies lower than the adapting frequency. The tuning of aftereffects varied with the adapting frequency. In particular, the strongest aftereffects occurred near the adapting frequency. Adapting at frequencies just above the optimum for a cell often altered the spatial-frequency tuning by shifting the peak toward lower frequencies. The fact that the tuning of aftereffects did not simply match the tuning of the cell, but depended on the adapting stimulus, implies that extrinsic mechanisms are involved in adaptation effects.

Adaptation, Physiological↗

PubMed1989

Adaptation in single units in visual cortex: the tuning of aftereffects in the temporal domain.

Adaptation-induced changes in the temporal-frequency tuning and direction selectivity of cat visual cortical cells were studied. Aftereffects were induced largely independent of direction. Adapting in either direction reduced responses in both directions. Aftereffects in the direction opposite that adapted were only slightly weaker than were aftereffects in the adapted direction. No cell showed any enhancement of responses to drifting test stimuli after adapting with moving gratings. Adapting in a cell's null direction usually had no effect. Dramatic differences between the adaptation characteristics of moving and stationary stimuli were observed, however. Furthermore, aftereffects were temporal frequency specific. Temporal frequency-specific aftereffects were found in both directions: adapting in one direction induced frequency-specific effects in both directions. This bidirectionality of frequency-specific aftereffects applied to the spatial domain as well. Often, aftereffects in the direction opposite that adapted were more narrowly tuned. In general, adaptation could shift a cell's preferred temporal frequency. Aftereffects were most prominent at high temporal frequencies when testing in the adapted direction. Aftereffects seemed to be more closely linked to temporal frequency than to velocity matching. These results constrain models of cortical connectivity. In particular, we argue against schemes by which direction selectivity is generated by inhibiting a cell specifically when stimulated in the nonpreferred direction. Instead, we argue that cells receive bidirectional spatially and temporally tuned inputs, which could combine in spatiotemporal quadrature to produce direction selectivity.

Adaptation, Physiological↗