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ABSTRACT: Slow spontaneous rhythmic activity is generated and propagates in neocortical slices when bathed in an artificial cerebrospinal fluid with ionic concentrations similar to the ones in vivo. This activity is extraordinarily similar to the activation of the cortex in physiological conditions (e.g., slow-wave sleep), thus representing a unique in vitro model to understand how cortical networks maintain and control ongoing activity. Here we have characterized the activity generated in the olfactory or piriform cortex and endopiriform nucleus (piriform network). Because these structures are prone to generate epileptic discharges, it seems critical to understand how they generate and regulate their physiological rhythmic activity. The piriform network gave rise to rhythmic spontaneous activity consisting of a succession of up and down states at an average frequency of 1.8 Hz, qualitatively similar to the corresponding neocortical activity. This activity originated in the deep layers of the piriform network, which displayed higher excitability and denser connectivity. A remarkable difference with neocortical activity was the speed of horizontal propagation (114 mm/s), one order of magnitude faster in the piriform network. Properties of the piriform cortex subserving fast horizontal propagation may underlie the higher vulnerability of this area to epileptic seizures.
Cerebral Cortex 06/2008; 18(5):1179-92. · 6.54 Impact Factor
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ABSTRACT: Blind individuals often demonstrate enhanced non-visual perceptual abilities. Neuroimaging and transcranial magnetic stimulation experiments have suggested that computations carried out in the occipital cortex may underlie these enhanced somatosensory or auditory performances. Thus, cortical areas that are dedicated to the analysis of the visual scene may, in the blind, acquire the capacity to participate in other sensory processing. However, the neural substrate that underlies this transfer of function is not fully characterized. Here we studied the synaptic and anatomical basis of this phenomenon in cats that were visually deprived by dark rearing, either early visually deprived after birth (EVD), or late visually deprived after the end of the critical period (LVD); data were compared with those obtained in normally reared cats (controls). The presence of synaptic and spike responses to auditory stimulation was examined by means of intracellular recordings in area 17 and the border between areas 17 and 18. While none of the cells recorded in control and LVD cats showed responses to sound, 14% of the cells recorded in EVD cats showed both subthreshold synaptic responses and suprathreshold spike responses to auditory stimuli. Synaptic responses were of small amplitude, but well time-locked to the stimuli and had an average latency of 30+/-12ms. In an attempt to identify the origin of the inputs carrying auditory information to the visual cortex, wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was injected in the visual cortex and retrograde labeling examined in the cortex and thalamus. No significant retrograde labeling was found in auditory cortical areas. However, the proportion of neurons projecting from supragranular layers of the posteromedial and posterolateral parts of the lateral suprasylvian region to V1 was higher than that in control cats. Retrograde labeling in the lateral geniculate nucleus showed no difference in the total number of neurons between control and visually deprived cats, but there was a higher proportion of labeling in C-laminae in deprived cats. Labeled cells were not found in the medial geniculate nucleus, a thalamic relay for auditory information, in either control or visually deprived cats. Finally, immunohistochemistry of the visual cortex of deprived cats revealed a striking decrease in pavalbumin- and calretinin-positive neurons, the functional implications of which we discuss.
Progress in brain research 02/2006; 155:287-311. · 3.04 Impact Factor
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ABSTRACT: 1. In rat sympathetic ganglion cells, axotomy induces the appearance of a depolarizing after-potential (ADP) produced by a calcium-activated chloride current. Here we report that this current is also present in normal sympathetic neurones from the mouse. 2. In an in vitro preparation of the superior cervical ganglion, an ADP was observed after spike firing in 50% of the cells studied with single-electrode current- and voltage-clamp techniques. 3. When the cells were voltage clamped at -50 mV in the presence of tetrodotoxin (TTX) and tetraethylammonium chloride (TEA), depolarizing jumps evoked inward calcium currents which were contaminated by outward chloride currents, followed by slowly decaying inward chloride tail currents. 4. The ADP and the inward tail currents disappeared when calcium was removed from the extracellular solution or when cadmium was added. 5. The reversal potential for the inward tail current was approximately -24 mV and was displaced in agreement with the Nernst equation for chloride when the extracellular NaCl was replaced by sucrose or sodium isethionate. The chloride channel blocker anthracene-9-carboxylic acid (9AC) inhibited both the ADP and the tail current. 6. Using intracellular injection of neurobiotin, we found that cells with shorter dendrites had larger ADPs. In axotomized ganglia practically all cells showed very pronounced ADPs. 7. We conclude that normal mouse sympathetic ganglion cells have a calcium-activated chloride current that generates an ADP. The channels responsible for this current are probably located in the dendrites.
The Journal of Physiology 02/1997; 498 ( Pt 2):397-408. · 4.72 Impact Factor
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ABSTRACT: In sympathetic neurons, axotomy induces a marked depression in synaptic transmission. We asked whether the decrease in synaptic efficacy observed in a given axotomized cell is more severe if most of the postsynaptic neurons are also injured. Accordingly, we studied if the synaptic depression induced by axotomy in neurons with axons running in a postganglionic nerve is influenced by section of other postganglionic nerves. The excitatory postsynaptic potentials evoked by preganglionic stimulation were recorded intracellularly in an in vitro preparation of the superior cervical ganglion. Eight days after cutting the inferior postganglionic nerve, postsynaptic potentials recorded from neurons projecting through this nerve were smaller (median = 6 mV, n = 62) than the controls (median = 34 mV, n = 89), but were similar to those found after sectioning the inferior nerve plus most postganglionic nerves (median = 5 mV, n = 70). If the inferior nerve was left intact, but most postganglionic branches were cut, the synaptic potentials recorded from inferior nerve neurons were normal (median = 33 mV, n = 77). It is concluded that the synaptic depression induced by axotomy in a sympathetic neuron is not affected by axotomy of nearby ganglion cells, even if they share part of their presynaptic axons. This suggests that the effect of axotomy is restricted to the synaptic terminals on the injured neuron.
Neuroscience 09/1995; 67(3):689-95. · 3.38 Impact Factor
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ABSTRACT: 1. Seven to ten days after sectioning their axons, rat sympathetic neurons were studied using intracellular recording techniques in an in vitro preparation of the superior cervical ganglion. 2. In 75% of axotomized cells, an after-depolarization (ADP) was observed following spike firing or depolarization with intracellular current pulses. Discontinuous single-electrode voltage-clamp techniques were employed to study the ADP. When the membrane potential was clamped at the resting level just after an action potential, a slow inward current was recorded in cells that showed an ADP. 3. In the presence of TTX and TEA, inward peaks and outward currents were recorded during depolarizing voltage jumps, followed by slowly decaying inward tail currents accompanied by large increases in membrane conductance. The inward peak and tail currents activated between -10 and -20 mV and reached maximum amplitudes around 0 mV. With depolarizing jumps to between +40 and +50 mV, net outward currents were recorded during the depolarizing jumps but inward tail currents were still activated. 4. In the presence of the Ca2+ channel blocker cadmium, or when Ca2+ was substituted by Mg2+, the ADP disappeared. In voltage-clamped cells, cadmium blocked the inward tail currents. The reversal potential for the inward tail current was approximately -15 mV. Substitution of the extracellular NaCl by sucrose or sodium isethionate increased the amplitude of the inward tail current, and displaced its equilibrium potential to more positive values. Changes in extracellular [K+] did not appreciably affect the inward tail current amplitude or equilibrium potential. Niflumic acid, a blocker of chloride channels activated by Ca2+, almost completely blocked the tail current. 5. No ADPs were observed in non-axotomized neurons, and when depolarizing pulses were applied while in voltage clamp no inward tail currents were evoked in these normal cells. 6. It is concluded that axotomy of sympathetic ganglion cells produces the appearance of a Ca(2+)-dependent chloride current responsible for the ADP observed following spike firing.
The Journal of Physiology 04/1994; 475(3):391-400. · 4.72 Impact Factor
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ABSTRACT: Some of the marked biochemical and electrophysiological changes provoked by section of the axon in mature neurons suggest that the intracellular calcium concentration ([Ca2+]i) may be increased. We have measured the [Ca2+]i using the fluorescent indicator Indo-1 microinjected into rat superior cervical ganglion neurons. No differences in resting [Ca2+]i levels were found between control neurons and cells which had been axotomized 7-10 days before. However, the rise in [Ca2+]i evoked by orthodromic or antidromic stimulation and the recovery after the stimulating train were considerably slower in axotomized neurons than in control cells. We also found that the number of calbindin-D28k-immunopositive cells in the ganglion increases after axotomy, which could be related to the observed differences in calcium homeostasis.
European Journal of Neuroscience 02/1994; 6(1):9-17. · 3.63 Impact Factor
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ABSTRACT: 1. The electrical properties of rat superior cervical ganglion cells were examined in vitro with intracellular microelectrodes after axotomy or atrophy of the submandibular salivary gland. 2. Membrane time constant, input resistance and excitatory synaptic potentials (EPSPs) were decreased to about 50% of their control values 7-10 days after axotomy. 3. Axotomized ganglion cells also showed reduced action potentials and after-hyperpolarizations (AHPs). The AHP duration was reduced to 40% of the control value. 4. In 25% of the axotomized cells, the action potential was followed by an after-depolarization (ADP) instead of the AHP that was always present in control cells. In eleven out of seventeen axotomized cells with ADP, preganglionic stimulation failed to evoke an EPSP, whereas the failure of the synaptic response was never observed in control cells and occurred only in two of fifty-three axotomized cells with AHP. 5. In some axotomized cells with AHP, a depolarizing potential developed after a train of action potentials. This was never observed in control cells. 6. Sympathetic neurones innervating the submandibular gland in control animals had membrane properties similar to those observed in other ganglion cells. 7. The properties of neurones innervating the submandibular gland remained unaltered after the experimentally induced atrophy of the gland. 8. It is concluded that the marked effects of short-term axotomy on membrane properties of sympathetic ganglion cells are not reproduced by long-term atrophy of the target tissue.
The Journal of Physiology 12/1993; 471:801-15. · 4.72 Impact Factor
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ABSTRACT: Intercellular communication is considered to have a role during pattern specification processes in early embryonic development. This report analyzes the changing gap junctional communication properties of chick neuroepithelial cells depending on their position relative to the segmental partitions of the rhombencephalon. Intercellular electrical coupling and dye transfer were studied with microelectrode techniques. Neuroepithelial cells were electrically coupled irrespective of their location relative to interneuromeric boundaries. Iontophoretic injection of biocytin or Lucifer Yellow into single cells inside the rhombomeres was followed by transjunctional diffusion to the surrounding cells. In contrast, dye transfer was strictly limited when the diffusion zone contacted the cells forming the interneuromeric limits. Label injected into the boundary cells did not spread to other cells at all. Avian interrhombomeric boundaries are thus sites of reduced junctional permeability during early morphogenesis.
Development 01/1993; 116(4):1069-76. · 6.60 Impact Factor
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ABSTRACT: 1. The possibility that a modified Ca2+ channel mediates chemical and thermal excitation of nociceptors was examined in single polymodal nociceptive fibres of the cat's cornea. 2. Ca2+ channel blockers cadmium (2.5 mM) and diltiazem (1 mM), and high external [Ca2+] (40 mM), markedly reduced nociceptive responses to topical acidic solutions (pH 4.5). 3. Decreasing the pH to 6.5 did not cause excitation, but reduced the subsequent response to pH 4.5 buffer. 4. Diltiazem (1 mM), applied after repeated stimulation with stepped heating pulses (35 to 47-49 degrees C in 2 degrees C steps) decreased the impulse responses elicited by heat. The decrease in threshold to thermal stimulation produced by repeated heating was blocked by diltiazem. 5. Mechanical threshold and mechanical responsiveness of corneal polymodal nociceptors was not modified by Ca2+ antagonists or by a high-Ca2+ solution. 6. These results offer indirect evidence that proton-activated Ca2+ channels mediate stimulation of nociceptors by acidic solutions. The same type of ionic channel appears to be involved in the response of nociceptors to heat and in sensitization, but not in their responsiveness to mechanical stimulation. The blockade of nociceptive responses by Ca2+ antagonists opens the possibility of using Ca2+ blockers as selective analgesic drugs.
The Journal of Physiology 06/1992; 450:179-89. · 4.72 Impact Factor
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ABSTRACT: We have examined the effect of axotomy on the conduction velocity of unmyelinated sensory fibres in the vagus nerve of the rabbit. In an in vitro preparation of the nodose ganglion, conduction velocity was calculated for each cell from the latency of the intracellularly recorded action potential evoked by vagus nerve stimulation. The average velocity of sensory fibres conducting at less than 1.1 m/s, was 0.53 m/s in 287 control cells and 0.45 m/s in 269 neurones recorded 10 days after cutting the vagus nerve. Therefore, peripheral axotomy decreases conduction velocity in mammalian unmyelinated sensory axons.
Brain Research 08/1990; 523(2):298-300. · 2.73 Impact Factor
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ABSTRACT: 1. The properties of sensory neurones in the petrosal ganglion of the cat were examined in vitro with intracellular electrodes 2-30 days after cutting the carotid or the glossopharyngeal nerve or 30-120 days after crushing the nerves and allowing time for peripheral reinnervation. Both glossopharyngeal and carotid neurones with conduction velocities faster than 2 m/s and humps on the falling phase of their action potentials were studied. 2. Two days after axotomy, the action potential of glossopharyngeal cells showed increased maximum rate of depolarization and decreased after-hyperpolarization (AHP) amplitude. These cells also showed a decrease in time-dependent inward rectification and conduction velocity. No significant changes were observed in carotid neurones at this stage. 3. Four days after axotomy, these changes were still present in glossopharyngeal cells and the duration of the AHP had also decreased. Among carotid neurones there was an increase in spike duration and a decrease in time-dependent rectification and in the amplitude and duration of the AHP. 4. Eight days after axotomy glossopharyngeal cells additionally showed an increased spike duration and decreased rheobase, while carotid neurones had also decreased in conduction velocity. 5. All the changes described were still present 16 days after cutting the nerves. In addition, the input resistance increased in both types of cells. 6. The effects of axotomy persisted 30 days after cutting the nerve, except for the AHP amplitude in both types of cells and the spike duration in glossopharyngeal neurones which had recovered to near control values. 7. Thirty days after crushing the carotid nerve, some carotid neurones showed chemosensory activity, indicating that reinnervation of the carotid body had taken place. In these cells, the properties altered by axotomy had recovered except for the conduction velocity. 8. Four months after crushing the glossopharyngeal nerve, activity evoked by mechanical and chemical stimulation of the tongue could be recorded from the nerve, indicating that sensory reinnervation had taken place. The electrical properties of the glossopharyngeal cells were normal except for conduction velocity which was still slower than the control value. 9. It is concluded that the electrical membrane properties altered by axotomy revert to normal after peripheral sensory regeneration.
The Journal of Physiology 12/1988; 405:219-32. · 4.72 Impact Factor
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ABSTRACT: 1. The properties of sensory neurones in the petrosal ganglion of the cat were examined in vitro with intracellular electrodes 8 days after section of the central (bulbar roots) or peripheral process. Two types of cells, both with conduction velocities faster than 2 m/s and with humps on the falling phases of their action potentials (H-neurones), were studied: glossopharyngeal neurones arising from the tongue and pharynx, and carotid neurones originating in the carotid body and carotid sinus. 2. Peripheral axotomy produced an increase in action potential duration and a marked decrease in the amplitude and duration of the spike after-hyperpolarization in both glossopharyngeal and carotid neurones. 3. The maximum rate of depolarization of the action potential increased after peripheral axotomy in glossopharyngeal cells but did not change in carotid neurones. 4. The time-dependent inward rectification in response to hyperpolarizing pulses was markedly reduced in both types of cells after peripheral axotomy. 5. Section of the peripheral process produced a decrease of the rheobase of glossopharyngeal cells, but not of carotid neurones. After axotomy the proportion of cells giving tonic discharges in response to long depolarizing pulses increased from 13 to 54% among carotid neurones but did not change in glossopharyngeal cells. 6. No significant changes in membrane potential or input resistance of either group of cells were found after peripheral axotomy. 7. Central axotomy did not produce any changes in the electrophysiological properties of glossopharyngeal or carotid neurones. 8. Peripheral conduction velocity was decreased in both types of cells after peripheral axotomy, but did not change after section of the bulbar roots. 9. It is concluded that the electrical properties of sensory neurones are modified after peripheral axotomy but not after central axotomy. Furthermore, the changes produced by peripheral axotomy are different in neurones innervating different peripheral targets. 10. The possibility that some electrical properties of sensory neurones are maintained by their peripheral targets is discussed.
The Journal of Physiology 11/1987; 391:39-56. · 4.72 Impact Factor
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ABSTRACT: 1. The effects of chronic conduction block with tetrodotoxin (TTX) of the cervical sympathetic trunk on synapses in the superior and stellate ganglia were examined in vitro with intracellular recording techniques. 2. The mean maximum amplitude of excitatory post-synaptic potentials (e.p.s.p.s) evoked in superior cervical ganglion neurones by stimulation of the cervical sympathetic trunk was increased significantly after 2 or 4 days of block. The electrical properties of the ganglion cells were not appreciably changed by the period of inactivity. 3. Chronic conduction block for 4 days also resulted in a significant increase in the amplitude of the e.p.s.p.s. evoked in stellate ganglion cells by active collaterals of the blocked fibres. 4. The number of steps in the synaptic response elicited in individual stellate ganglion neurones by graded stimulation of the ansa subclavia and the subclavian trunk (which join to form the cervical sympathetic trunk) was increased after 4 days of conduction block. 5. These results show that elimination of impulse activity in the cervical sympathetic trunk increased synaptic efficacy at the disused synapses in the superior cervical ganglion and at the active synapses in the stellate ganglion. In the latter case, collaterals of the blocked fibres apparently formed new synaptic connexions on stellate ganglion cells.
The Journal of Physiology 02/1987; 382:449-62. · 4.72 Impact Factor
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ABSTRACT: Petrosal ganglion chemoreceptor neurones were impaled with glass microelectrodes in an 'in vitro' preparation maintained at 36.5 degrees C. For each cell, the input conductance and the axonal conduction velocity were calculated from the voltage change produced by a hyperpolarizing pulse, and from the latency of the spike evoked by carotid nerve stimulation. In 34 neurones, the average values for these variables were 3.7 X 10(-8) Siemens and 10 m/s. The two parameters were related by a power function with an exponent of 0.9, which is lower than the value of 2 expected on the basis of simple linear relations between soma and axon diameters and between axon diameter and conduction velocity.
Neuroscience Letters 12/1984; 52(1-2):117-22. · 2.11 Impact Factor
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ABSTRACT: The properties of chemoreceptor and baroreceptor neurones in the petrosal ganglion of the cat were examined in vitro with intracellular micro-electrodes. Chemoreceptor neurones with myelinated axons (average conduction velocity, 11 m/s) showed action potentials with a hump on the falling phase, followed by a prolonged after-hyperpolarization (average duration, 260 ms). The duration of the hump present in the action potential of chemoreceptor neurones was positively correlated with the duration of the after-hyperpolarization. In response to prolonged depolarization, chemoreceptor neurones showed only one or a few action potentials at the beginning of the depolarization. Two types of baroreceptors neurones with myelinated axons were found: fast (F) baroreceptors (average conduction velocity, 33 m/s) and slow (S) baroreceptors (average conduction velocity, 10 m/s). F baroreceptors had action potentials without a hump followed by a short after-hyperpolarization (average duration, 43 ms), while S baroreceptors had spikes similar to those found in chemoreceptors except for a shorter hyperpolarization (average duration, 145 ms). Both types of baroreceptor neurones fired repetitively throughout prolonged depolarization. It is concluded that, in the petrosal ganglion, primary sensory neurones originating a given type of sensory terminal share a particular set of electrophysiological properties.
The Journal of Physiology 10/1983; 342:603-14. · 4.72 Impact Factor
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ABSTRACT: The possibility that carotid chemoreceptors respond to changes in plasma osmolality was investigated in the cat, perfusing the carotid artery with blood made hyper- or hypo-osmotic and recording chemoreceptor activity from carotid nerve fibers. Blood made hyperosmotic with sucrose or NaCl reduced the chemoreceptor discharge, while hypoosmotic blood increased chemoreceptor activity. The minimal osmolality variation necessary to obtain a detectable frequency change was 3--8% of the control. Frequency changes of 30% of the control were obtained with a 20% variation in osmolality. The frequency variations produced by the osmotic changes lasted as long as the infusion was maintained (up to 15 min). In some instances a rebound was observed when iso-osmotic saline was perfused again. A transient change in frequency and a clear rebound were obtained when blood made hypersomotic with glycerol was perfused. These effects probably reflect a rapid change in intracellular osmolality due to the free passage of glycerol across cellular membranes. The modifications in chemoreceptor activity consecutive to osmolality variations are the opposite of those observed in isolated and superfused carotid bodies. As it is known that osmolality values affect the smooth muscle of the blood vessels, we conclude that our results are mainly produced by changes in carotid body blood flow due to a direct effect of hyper- and hypo-osmotic solutions on vascular muscle tone. Chemoreceptor excitation during a decrease in blood osmolality may contribute reflexly to the increased vascular resistance observed during acute osmolality reductions in man.
Pflügers Archiv - European Journal of Physiology 06/1979; 380(1):53-8. · 4.46 Impact Factor
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Experimental Eye Research 11/1974; 19(4):331-4. · 3.26 Impact Factor
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Brain Research 09/1972; 43(1):25-35. · 2.73 Impact Factor
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ABSTRACT: In sympathetic neurons, axotomy induces a marked depression in synaptic transmission. We asked whether the decrease in synaptic efficacy observed in a given axotomized cell is more severe if most of the postsynaptic neurons are also injured. Accordingly, we studied if the synaptic depression induced by axotomy in neurons with axons running in a postganglionic nerve is influenced by section of other postganglionic nerves. The excitatory postsynaptic potentials evoked by preganglionic stimulation were recorded intracellularly in anin vitro preparation of the superior cervical ganglion. Eight days after cutting the inferior postganglionic nerve, postsynaptic potentials recorded from neurons projecting through this nerve were smaller (median = 6 mV,n = 62) than the controls (median = 34 mV,n = 89), but were similar to those found after sectioning the inferior nerve plus most postganglionic nerves (median = 5 mV,n = 70). If the inferior nerve was left intact, but most postganglionic branches were cut, the synaptic potentials recorded from inferior nerve neurons were normal (median = 33 mV,n = 77).It is concluded that the synaptic depression induced by axotomy in a sympathetic neuron is not affected by axotomy of nearby ganglion cells, even if they share part of their presynaptic axons. This suggests that the effect of axotomy is restricted to the synaptic terminals on the injured neuron.
Neuroscience.
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ABSTRACT: Blind individuals often demonstrate enhanced non-visual perceptual abilities. Neuroimaging and transcranial magnetic stimulation experiments have suggested that computations carried out in the occipital cortex may underlie these enhanced somatosensory or auditory performances. Thus, cortical areas that are dedicated to the analysis of the visual scene may, in the blind, acquire the capacity to participate in other sensory processing. However, the neural substrate that underlies this transfer of function is not fully characterized. Here we studied the synaptic and anatomical basis of this phenomenon in cats that were visually deprived by dark rearing, either early visually deprived after birth (EVD), or late visually deprived after the end of the critical period (LVD); data were compared with those obtained in normally reared cats (controls). The presence of synaptic and spike responses to auditory stimulation was examined by means of intracellular recordings in area 17 and the border between areas 17 and 18. While none of the cells recorded in control and LVD cats showed responses to sound, 14% of the cells recorded in EVD cats showed both subthreshold synaptic responses and suprathreshold spike responses to auditory stimuli. Synaptic responses were of small amplitude, but well time-locked to the stimuli and had an average latency of 30±12 ms. In an attempt to identify the origin of the inputs carrying auditory information to the visual cortex, wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was injected in the visual cortex and retrograde labeling examined in the cortex and thalamus. No significant retrograde labeling was found in auditory cortical areas. However, the proportion of neurons projecting from supragranular layers of the posteromedial and posterolateral parts of the lateral suprasylvian region to V1 was higher than that in control cats. Retrograde labeling in the lateral geniculate nucleus showed no difference in the total number of neurons between control and visually deprived cats, but there was a higher proportion of labeling in C-laminae in deprived cats. Labeled cells were not found in the medial geniculate nucleus, a thalamic relay for auditory information, in either control or visually deprived cats. Finally, immunohistochemistry of the visual cortex of deprived cats revealed a striking decrease in pavalbumin- and calretinin-positive neurons, the functional implications of which we discuss.
Progress in Brain Research.
