Biomedical subjects

P Heggelund

Publications and source records attributed to P Heggelund.

At least 19 recordsLinked to original sources

PubMed2006

Dynamics of spatial resolution of single units in the lateral geniculate nucleus of cat during brief visual stimulation.

Sharpness of vision depends on the resolution of details conveyed by individual neurons in the visual pathway. In the dorsal lateral geniculate nucleus (LGN), the neurons have receptive fields with center-surround organization, and spatial resolution may be measured as the inverse of center size. We studied dynamics of receptive field center size of single LGN neurons during the response to briefly (400-500 ms) presented static light or dark spots. Center size was estimated from a series of spatial summation curves made for successive 5-ms intervals during the stimulation period. The center was wide at the start of the response, but shrank rapidly over 50-100 ms after stimulus onset, whereupon it widened slightly. Thereby, the spatial resolution changed from coarse-to-fine with average peak resolution occurring approximately 70 ms after stimulus onset. The changes in spatial resolution did not follow changes of firing rate; peak firing appeared earlier than the maximal spatial resolution. We suggest that the response initially conveys a strong but spatially coarse message that might have a detection and tune-in function, followed by transient transmission of spatially precise information about the stimulus. Experiments with spots presented inside the maximum but outside the minimum center width suggested a dynamic reduction in number of responding neurons during the stimulation; from many responding neurons initially when the field centers are large to fewer responding neurons as the centers shrink. Thereby, there is a change from coarse-to-fine also in the recruitment of responding neurons during brief static stimulation.

Action Potentials↗

PubMed2002

Brainstem modulation of visual response properties of single cells in the dorsal lateral geniculate nucleus of cat.

The dorsal lateral geniculate nucleus (dLGN) transmits visual signals from the retina to the cortex. In the dLGN the antagonism between the centre and the surround of the receptive fields is increased through intrageniculate inhibitory mechanisms. Furthermore, the transmission of signals through the dLGN is modulated in a state-dependent manner by input from various brainstem nuclei including an area in the parabrachial region (PBR) containing cholinergic cells involved in the regulation of arousal and sleep. Here, we studied the effects of increased PBR input on the spatial receptive field properties of cells in the dLGN. We made simultaneous single-unit recordings of the input to the cells from the retina (S-potentials) and the output of the cells to the cortex (action potentials) to determine spatial receptive field modifications generated in the dLGN. State-dependent modulation of the spatial receptive field properties was studied by electrical stimulation of the PBR. The results showed that PBR stimulation had only a minor effect on the modifications of the spatial receptive field properties generated in the dLGN. The PBR-evoked effects could be described mainly as increased response gain. This suggested that the spatial modifications of the receptive field occurred at an earlier stage of processing in the dLGN than the PBR-controlled gain regulation, such that the PBR input modulates the gain of the spatially modified signals. We propose that the spatial receptive field modifications occur at the input to relay cells through the synaptic triades between retinal afferents, inhibitory interneurone dendrites, and relay cell dendrites and that the gain regulation is related to postsynaptic cholinergic effects on the relay cells.

Animals↗

PubMed2001

Muscarinic regulation of dendritic and axonal outputs of rat thalamic interneurons: a new cellular mechanism for uncoupling distal dendrites.

Inhibition is crucial for sharpening the sensory information relayed through the thalamus. To understand how the interneuron-mediated inhibition in the thalamus is regulated, we studied the muscarinic effects on interneurons in the lateral posterior nucleus and lateral geniculate nucleus of the thalamus. Here, we report that activation of muscarinic receptors switched the firing pattern in thalamic interneurons from bursting to tonic. Although neuromodulators switch the firing mode in several other types of neurons by altering their membrane potential, we found that activation of muscarinic subtype 2 receptors switched the fire mode in thalamic interneurons by selectively decreasing their input resistance. This is attributable to the muscarinic enhancement of a hyperpolarizing potassium conductance and two depolarizing cation conductances. The decrease in input resistance appeared to electrotonically uncouple the distal dendrites of thalamic interneurons, which effectively changed the inhibition pattern in thalamocortical cells. These results suggest a novel cellular mechanism for the cholinergic transformation of long-range, slow dendrite- and axon-originated inhibition into short-range, fast dendrite-originated inhibition in the thalamus observed in vivo. It is concluded that the electrotonic properties of the dendritic compartments of thalamic interneurons can be dynamically regulated by muscarinic activity.

Action Potentials↗

PubMed2001

AMPA receptor properties at the synapse between retinal afferents and thalamocortical cells in the dorsal lateral geniculate nucleus of the rat.

The thalamocortical (TC) cells in dorsal lateral geniculate nucleus transfer signals from retinal afferents to the primary visual cortex. The excitatory retinal input to the TC cells is mediated by ionotropic receptors of the N-methyl-D-aspartate (NMDA) and non-NMDA type. In the present study the excitatory postsynaptic current (EPSC) mediated by non-NMDA receptors in this synapse was characterised by means of voltage-clamp recordings from TC neurons in rat thalamic slices. The specific alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor antagonist GYKI-53655 fully blocked the non-NMDA mediated EPSC, evoked by optic tract stimulation. The EPSC peak amplitudes were linearly related to the command voltage, suggesting that the receptor complex includes the GluR2 subunit. The EPSC amplitude and decay time increased during application of the desensitisation blocker, cyclothiazide, showing that the EPSC was partly controlled by fast desensitisation.

2-Amino-5-phosphonovalerate↗

PubMed1998

Roles of N-methyl-D-aspartate receptors in ocular dominance plasticity in developing visual cortex: re-evaluation.

We have re-examined whether N-methyl-D-aspartate receptors play a specific role in experience-dependent plasticity in kitten visual cortex. A specific antagonist of this glutamate receptor subtype, D,L-2-amino-5-phosphonovaleric acid, was directly and continuously infused into kitten striate cortex for one week concurrently with monocular lid suture. In the hemisphere infused with 50 mM antagonist, we found the usual shift in ocular dominance toward the open eye with only a few binocular cells remaining. The changes were accompanied by an extremely high incidence (38%) of abnormal cells lacking orientation selectivity across different ocular dominance groups. In kitten cortex infused with 10 mM antagonist concurrently with monocular deprivation for a week, recording from a drug-affected region near the infusion centre, we again found the U-shaped ocular dominance distribution with the high incidence of non-selective cells. In antagonist-infused, otherwise normal striate cortex of adult cats, we found that the proportion of binocular cells decreased by one-half in two cellular populations: one recorded during the continuous infusion of 10 mM antagonist under general anaesthesia and paralysis, and the other about two days after stopping the infusion. We also established that in vivo concentrations of chronically infused 10 mM antagonist decreased, not near-exponentially, but linearly with increasing distance from the infusion site. Thus, the effects of a directly and continuously infused, concentrated antagonist of N-methyl-D-aspartate receptors on receptive-field properties of visuocortical cells are complex. The present findings strongly suggest that the antagonist effects in the developing cortex may be due primarily to blockade of normal synaptic transmission rather than specific disruption of an experience-dependent mechanism underlying ocular dominance plasticity.

2-Amino-5-phosphonovalerate↗

PubMed1996

Quantal properties of spontaneous EPSCs in neurones of the guinea-pig dorsal lateral geniculate nucleus.

1. Spontaneous non-NMDA glutamate receptor-mediated EPSCs were recorded with the whole-cell patch-clamp technique from twenty-six neurones in the dorsal lateral geniculate nucleus in thalamic slices from guinea-pig. 2. Amplitude distributions of the EPSCs were skewed towards larger values. The skewness could be accounted for by multiquantal properties. The multiquantal properties were most clearly demonstrated in four cells that had prominent peaks in the amplitude distribution, and peak separation approximately corresponding to the modal value. The amplitude distribution for all cells could be adequately fitted by a quantal model consisting of a sum of Gaussians with means equal to integer multiples of a quantal unit. The variance of each Gaussian was equal to the sum of the noise variance of the recordings and an additional non-negative variance which increased linearly with the number of the Gaussian in the series. The estimated mean quantal size was 152 +/- 37 pS. The estimated mean quantal coefficient of variation was 15%. Addition of tetrodotoxin did not significantly change any of the quantal parameters (n = 5). 3. The waveform of the EPSCs was similar for small and large events, and similar to that of events evoked by stimulation of retinal input fibres. There was a positive correlation between peak amplitude and rise time. This is the opposite of that expected if differences in electrotonic distances were to explain differences in amplitude. 4. The spontaneous EPSCs occurred randomly at an average frequency of 3.1 Hz. The events with amplitudes approximately equal to multiples of the quantal size were, in most cells, more numerous than could be accounted for by coincidence of randomly occurring events of quantal size. 5. The results indicate that spontaneous EPSCs can reflect more than a single quantum, and suggest that quantal events may be coupled due to action potential-independent near-synchronous multiquantal release of transmitter.

2-Amino-5-phosphonovalerate↗

PubMed1995

Brainstem modulation of signal transmission through the cat dorsal lateral geniculate nucleus.

We studied changes in retinogeniculate transmission that occur during variation of modulatory brainstem input and during variation of stimulus contrast. Responses of single cells in the dorsal lateral geniculate nucleus (dLGN) to a stationary flashing light spot of varying contrast were measured with and without electrical stimulation of the peribrachial region (PBR) of the brainstem. PBR stimulation increased the contrast gain (slope of response versus contrast curve) and the dynamic response range (range between spontaneous activity and maximal firing). Lagged and nonlagged X-cells reached the midpoint of the dynamic response range at lower contrasts during PBR stimulation than in the controls. No comparable change was seen for Y-cells. Only minor changes of threshold contrast were seen. The characteristics of the retinogeniculate transmission were directly studied by comparing the response of dLGN cells with their retinal input (slow potentials, S-potentials). With increasing contrast there was a marked increase in the transfer ratio (proportion of impulses in the input that generates action potentials in the dLGN cell). The transfer ratio seemed to be primarily determined by the firing rate of the retinal input. The transfer ratio increased with increasing input rates from low values near threshold to values that could approach 1 at high-input firing rates. PBR stimulation increased the transfer ratio, particularly at moderate input firing rates. The increased transfer ratio, caused by increasing input firing rates, enhanced the response versus contrast characteristics through an increase in contrast gain and dynamic response range. The modulatory input from the PBR further enhanced these characteristics.

Animals↗

PubMed1994

The quantal size at retinogeniculate synapses determined from spontaneous and evoked EPSCs in guinea-pig thalamic slices.

1. To determine the quantal size at retinogeniculate synapses, spontaneous and evoked excitatory postsynaptic currents (EPSCs) were recorded in twelve neurones of the dorsal lateral geniculate nucleus in guinea-pig thalamic slices using the whole-cell patch-clamp technique. We limited our study to the fast non-N-methyl-D-aspartate (NMDA) component of the EPSCs by adding the NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid to the perfusion medium. 2. Spontaneous EPSCs occurred at a frequency between 0.5 and 6.6 Hz (mean 2.5 Hz). The modal value of the peak conductance change of spontaneous excitatory events varied between cells from 102 to 179 pS. 3. EPSCs were evoked by electrical stimulation in the optic tract. The peak conductance change of EPSCs evoked by stimulation of a putative single input fibre ranged from 0.6 to 3.4 nS (mean 1.7 nS). 4. To resolve the quantal components of evoked EPSCs the external Ca2+ concentration was reduced and the external Mg2+ concentration increased for four cells. In this condition failures occurred and the amplitude histograms were multimodal with approximately equidistant peaks. 5. These multimodal histograms could be fitted by a sum of Gaussian functions with mean values corresponding to integer multiples of the modal value of the spontaneous EPSCs for the same cell. Thus, the quantal size of evoked EPSCs was the same as the modal value of spontaneous EPSCs. The mean of the apparent quantal conductance change was 138 pS. The estimated number of quanta released by stimulating a putative single input fibre in the control condition ranged from 4 to 27 (mean 13).(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗

PubMed1994

Response variability of single cells in the dorsal lateral geniculate nucleus of the cat. Comparison with retinal input and effect of brain stem stimulation.

1. We studied the degree and source of response variability in different classes of cell in the dorsal lateral geniculate nucleus (dLGN). The response of single cells to a series of contrasts of a stationary flashing light spot was measured. The variability analyses were based on the mean and SD of the response to a number of repeated stimulus presentations. The relative variability was expressed by the coefficient of variation (Cv; SD/mean). 2. At a given contrast, the Cv for lagged cells was larger than for nonlagged cells. No difference was found between the Cv of X and Y cells. The magnitude of the Cv was about the same as previously found for cells in striate cortex. Accordingly, little variability is added at the cortical level. The Cv decreased with increasing contrast showing that the reliability of response and the signal-to-noise ratio was improved with increasing contrast. 3. For some cells, the retinal input was determined by recording S potentials in addition to action potentials. The Cv of the retinal input was smaller than the Cv of the dLGN cells at a given contrast. Thus in the paralyzed and anesthetized preparation, variability was added at the geniculate relay. 4. The additional variability was related to modulatory input from the brain stem. This was shown by comparing Cv versus contrast curves for the dLGN cells obtained during electrical stimulation of the peribrachial region of the brain stem (PBR) with corresponding curves obtained without PBR stimulation. During PBR stimulation, which presumably mimics the effects of arousal on the dLGN cell, the Cv at a given contrast was reduced toward the value for the retinal input to the cell. Furthermore PBR stimulation increased the signal-to-noise-ratio of the cell to the level of the retinal input. 5. When Cv was plotted against response rather than against contrast, approximately the same function was found for the various dLGN cell classes. This indicated that the variability basically depended on firing rate rather than on stimulus contrast. No difference of Cv was seen between lagged and nonlagged cells at a given level of response. The difference found at a given level of contrast reflected differences in firing rate of the two cell classes. During PBR stimulation, there was no clear difference between the Cvs of the dLGN cell and its retinal input at a given level of response.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1993

The effect of acetylcholine on the visual response of lagged cells in the cat dorsal lateral geniculate nucleus.

We examined the influence of acetylcholine (ACh) on the visual response properties of lagged cells in the dorsal lateral geniculate nucleus of anaesthetised cats. By means of electrophysiological techniques, the response of single cells was recorded before, during and after ionophoretic application of ACh. ACh evoked a clear enhancement of the visual response. The initial suppression that a visual stimulus evokes in lagged cells was resistant to the effects of ACh. The characteristic anomalous response component of lagged cells was also present during application of ACh. The difference in latency to half-rise and to half-fall of the visual response that is found between lagged and non-lagged cells was maintained during application of ACh. Taken together, the results support previous evidence from experiments with brain stem stimulation that the fundamental visual response characteristics of lagged cells are state independent.

Acetylcholine↗

PubMed1993

Simultaneous luminance contrast with chromatic colors.

The variations in the color of a test field of constant luminance during changes in the luminance of a contiguous inducing field was measured psychophysically. The fields had the same hue (red, green, or blue). The colors induced in the test field could be specified by the strength of a chromatic quality, and by the strength of the opponent qualities luminous/black. The psychophysical relationship between the two kinds of perceptive variables and test and inducing luminance followed distinctly different functions. The luminous/black variable varied linearly with contrast over a large range, as previously found for achromatic colors. The contrast gain of the luminous/black variable for the red and green colors was the same as for achromatic colors. The gain for the blue colors was twice the gain for the other colors. The chromatic variables were primarily related to the local luminance. For a given test luminance they were maximal near zero contrast. They followed the same function as the white component of achromatic colors. It is suggested that the luminous/black variable is related to spectrally broadband cells with a strong center/surround antagonism, while the chromatic variables and white are related to cells that lack a spectrally broadband surround in their receptive field.

Color Perception↗

PubMed1993

Brain stem modulation of spatial receptive field properties of single cells in the dorsal lateral geniculate nucleus of the cat.

1. We studied the effect of electrical stimulation of the peribrachial region (PBR) in the brain stem on the visual response of single cells in the dorsal lateral geniculate nucleus (dLGN) to a light slit presented in a series of positions across the receptive field. The response was plotted against slit position, giving a spatial receptive field profile. 2. PBR stimulation markedly increased the visual response. In the middle of the receptive field center, the absolute response increase was considerably larger than in the peripheral parts of the receptive field or than the increase of spontaneous activity. The PBR stimulation also led to a small increase of the diameter of the receptive field center. 3. The maximum steepness of the receptive field profile for the dLGN cells increased by PBR stimulation. We suggest that the visual resolution in the dLGN cell is directly related to this maximal slope of the receptive field profile rather than to the width of the receptive field center. This would mean that increased input from the PBR, as presumably occurs during arousal, increases the visual resolution of the dLGN cells. 4. For some of the cells we could record S-potentials (slow potentials) in addition to action potentials. This allowed us to directly compared the receptive field center size of a dLGN cell with that of its retinal input. For these cells, the center size was considerably reduced by the geniculate relay. During PBR stimulation, the center size of these cells also increased slightly, but even in this condition it was reduced compared with the retinal input. The maximal slope of the receptive field profile in the dLGN cell during PBR stimulation was larger than for the retinal input. 5. We also examined the effect of ionophoretical application of acetylcholine (ACh) and bicuculline methchloride (BMC) on the spatial receptive field properties of dLGN cells. The effects of ACh were similar to those of PBR stimulation. Application of BMC, on the other hand, made the receptive field profile more similar to that of retinal ganglion cells.

Acetylcholine↗

PubMed1992

A bidimensional theory of achromatic color vision.

The theory is based on a perceptive color system where the achromatic colors are specified by their degree of similarity to the three qualities white, black and luminous. Black and luminous are treated as opponent variables. It is assumed that white and luminous/black are determined by different kinds of visual processes termed the w- and the b-process. The relationship between these processes and luminance parameters in a simple disc/ring configuration is derived from available data. The b-process is related to stimulus contrast in a simple manner. It is assumed to involve cells with antagonistic center/surround organization of the receptive field. The w-process is primarily determined by the local luminance, and it is assumed to involve cells that lack a center/surround organization of the receptive field. The w-process has properties similar to the processes involved in chromatic color vision. The theory can account for different kinds of psychophysical data on achromatic colors like data on simultaneous contrast, color scaling, and color constancy.

Color Perception↗

PubMed1992

The effect of contrast on the visual response of lagged and nonlagged cells in the cat lateral geniculate nucleus.

The response vs. contrast characteristics of different cell classes in the dorsal lateral geniculate nucleus (LGN) were compared. The luminance of a stationary flashing light spot was varied stepwise while the background luminance was constant. Lagged X cells had lower slope of the response vs. contrast curve (contrast gain), and they reached the midpoint of the response range over which the cells' response varied (dynamic response range) at higher contrast than nonlagged X cells. These results indicated that nonlagged cells are well suited for detection of small contrasts, whereas lagged cells may discriminate between contrasts over a larger range. The contrast gain and the contrast corresponding to the midpoint of the dynamic response range were similar for X and Y cells. The latency to onset and to half-rise of the visual response decreased with increasing contrast, most pronounced for lagged cells. Even at the highest contrasts, the latency of lagged cells remained longer than for nonlagged cells. For many lagged cells, the latency to half-fall decreased with increasing contrast. It is shown that the differences in the response vs. contrast characteristics between lagged and nonlagged X cells in the cat are similar to the differences between the parvocellular and magnocellular neurones in the monkey.

Animals↗

PubMed1990

Neurotransmitter receptors mediating excitatory input to cells in the cat lateral geniculate nucleus. I. Lagged cells.

1. Synaptic mechanisms that might explain the functional properties of the recently discovered class of lagged cells in the dorsal lateral geniculate nucleus (LGN) were analyzed with electrophysiological and pharmacologic techniques. To study the type of excitatory amino acid (EAA) receptor that mediates visual responses of lagged cells, we recorded the response of single cells to a stationary flashing light spot before, during, and after microiontophoretic application of antagonists and agonists to EAA receptors. 2. The visual response of the lagged cells could be almost completely blocked by an antagonist to the N-methyl-D-aspartate (NMDA) receptor. The degree of suppression was dose dependent, and the average maximum degree of suppression for all the cells was 94%. NMDA enhanced the response, and this enhancement was antagonized by NMDA antagonists. A quisqualate/kainate receptor antagonist had no significant effect on the lagged cells. 3. These findings indicate that the visual response in lagged cells is dependent upon activation of NMDA receptors, which may directly result from activation of retinal inputs. 4. No pharmacologic difference was seen between lagged X- and Y-cells, or between lagged ON- and OFF-center cells. 5. gamma-Aminobutyric acid-A (GABA-A) receptor antagonists were used to study whether the characteristic lag of the visual response and the suppression of the initial transient response component of the lagged cells are dependent on geniculate inhibition. Beside enhancement of the visual response, the GABA antagonists strongly reduced the lag of the visual response, and an initial transient response component occurred instead of the initial suppression. The lag remained slightly longer than for nonlagged cells, and the peak firing rate of the transient was below values typical for nonlagged cells, indicating that the lagged cell properties are dependent on other factors beside GABA-A receptor-mediated inhibition. 6. The enhanced visual response during iontophoresis of GABA antagonists could be completely blocked by simultaneous iontophoresis of an NMDA-receptor antagonist. This gives further support to the hypothesis that the retinal input to these cells is mediated by NMDA receptors. 7. The NMDA-receptor/ionophore complex mediates excitatory postsynaptic potentials (EPSPs) characterized by slow rise and decay times and long duration. The ionophore is characterized by a voltage-dependent blockade that makes these receptors particularly sensitive to inhibitory input. The temporal interplay between the slow NMDA receptor-mediated EPSPs and the fast GABA receptor-mediated inhibitory postsynaptic potentials (IPSPs) may explain the characteristic response properties of the lagged cells.

Afferent Pathways↗

PubMed1990

Neurotransmitter receptors mediating excitatory input to cells in the cat lateral geniculate nucleus. II. Nonlagged cells.

1. We studied the type of receptor for excitatory amino acids (EAA) that mediates visual responses of nonlagged cells in the dorsal lateral geniculate nucleus (LGN) by recording the visual response of single cells to a stationary flashing spot before, during, and after iontophoretical application of antagonists and agonists to EAA receptors. 2. The visual response of the nonlagged cells was strongly suppressed, in a dose-dependent manner, by the specific quisqualate/kainate receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX). The average degree of suppression was 74%. Quisqualate enhanced the visual response. 3. Specific antagonists to the N-methyl-D-aspartate (NMDA) receptor had a weak suppressing effect on most nonlagged cells. The average degree of suppression was 22%. Measurement of such weak effects was complicated by the considerable spontaneous fluctuations of responsivity in the LGN cells. In the majority of cells where the visual response was suppressed by NMDA antagonists, the tonic response component was more strongly suppressed than the initial transient response component. The visual response was enhanced by NMDA, and this enhancement was antagonized by NMDA antagonists. 4. These findings suggest that the excitatory input from the retina to nonlagged LGN cells is mainly mediated by non-NMDA receptors. The non-NMDA receptors mediate fast EPSPs, and this can explain the fast onset and offset of the visual response of the nonlagged cells. 5. The generally small contribution from NMDA receptors to the visual response of the nonlagged cells might reflect a minor involvement of these receptors in the retinal input, or it could be related to the excitatory input to LGN from the visual cortex. 6. To study whether the expression of NMDA receptors was related to modulatory brain stem input to LGN, we examined the effects of the NMDA antagonists when the visual response was enhanced with gamma-aminobutyric acid (GABA) antagonists or acetylcholine (ACh). Neither of these pharmacologic manipulations consistently increased the relative contribution of NMDA receptors to the visual response. 7. No pharmacologic difference was found between nonlagged X- and Y-cells, or between ON- and OFF-center cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗

PubMed1989

Response to rates of luminance change of sustained and transient cells in the cat lateral geniculate nucleus and optic tract.

We recorded the response of sustained (X) and transient (Y) cells in the cat lateral geniculate nucleus (LGN) and optic tract to a stationary spot while the spot luminance was increased and decreased with a constant rate (linear luminance functions), or modulated sinusoidally. The spot filled the receptive field center, and was surrounded by an annulus of fixed luminance. The LGN X cells seemed to perform a differentiation-like operation in the time domain at slow temporal modulations, giving information about rate of luminance change. To the linear luminance functions the cells responded with a constant firing rate. The on-center cells were activated during increasing luminance, the off-center cells during decreasing luminance. This firing rate increased monotonically with rate of luminance change. To low-frequency sinusoidal modulations the cells had a marked negative phase shift. The response of the LGN Y cells had a transient component shortly after the luminance started to increase (on-center cells) or decrease (off-center cells), followed by a secondary, gradually changing component. The peak of the transient component occurred on average when the response of the X cells increased most rapidly. To low-frequency sinusoidal modulation the average negative phase shift of this peak was twice the average of the X cells. The Y system could accordingly provide information about rate of change in the response of the X system. In the optic tract the X fiber response resembled the LGN X cell response in most respects. The Y fibers had only a weak transient response component, so this component was accentuated in the thalamic relay. Also the sensitivity for rate of luminance change was increased in LGN.

Action Potentials↗

PubMed1989

Postnatal development of glutamatergic, GABAergic, and cholinergic neurotransmitter phenotypes in the visual cortex, lateral geniculate nucleus, pulvinar, and superior colliculus in cats.

We have analyzed the postnatal development of glutamatergic/aspartergic, GABAergic, and cholinergic neurotransmitter systems in the visual cortical Areas 17 and 18, lateral geniculate nucleus (LGN), pulvinar, and the visual and non-visual parts of superior colliculus (SC) in kittens. High-affinity uptake of D-aspartate (HA D-Asp), glutamate decarboxylase (GAD), and choline acetyltransferase (ChAT) activities were measured as a means of probing the development of the respective transmitter systems. HA D-Asp exceeded the adult level several-fold in all areas during the postnatal period which corresponded with the period of maximal dendritic/axonal branching patterns and synapse densities in the respective regions. GAD exhibited a gradual increase towards adult levels during the first month. The adult level was reached during postnatal week (PNW) 5-6 in Areas 17 and 18, during PNW3 within LGN, pulvinar, and the visual part of SC. In the nonvisual part of SC, the adult GAD level was reached as early as PNW2. ChAT exhibited biphasic developmental profiles in Areas 17 and 18. An initial peak of near adultlike activity in PNW2 was followed by a decline and subsequently by a slow increase towards adult levels during PNW5-17. ChAT developed very slowly in LGN and pulvinar, and in the latter structure only approximately 70% of the adult activity had been attained by PNW17. In both subdivisions of SC, ChAT had reached adult levels during PNW3-5. Dark-rearing from birth until PNW6 moderately attenuated GAD development in all areas and increased ChAT activity in Areas 17 and 18 but did not affect development of HA D-Asp in any part of the kitten visual system. Our neurochemical findings in the developing cat visual system are consistent with available evidence regarding localization of neurotransmitter systems, as well as postnatal changes in terms of cytoarchitectonics, synaptogenesis, functional development, and susceptibility to neonatal dark-rearing in visual pathways.

Animals↗