Laminar differences in bicuculline methiodide's effects on cortical neurons in the rat whisker/barrel system

Extracellular unit recordings were made at various depths within SmI barrel cortex of immobilized, sedated rats, in the presence and absence of titrated amounts of the GABA(A) receptor antagonist bicuculline methiodide (BMI). Principal and adjacent whiskers were moved singly, or in paired combination in a condition-test paradigm, to assess excitatory and inhibitory receptive field (RF) characteristics. Neurons were classified as regular- or fast-spike units, and divided into three laminar groups: supragranular, granular (barrel), and infragranular. BMI increased response magnitude and duration, but did not affect response latencies. The excitatory RFs of barrel units, which are the most tightly focused on the principal whisker, were the most greatly defocused by BMI; infragranular units were least affected. All three layers had approximately equal amounts of adjacent whisker-evoked, surround inhibition, but BMI counteracted this inhibition substantially in barrel units and less so in infragranular units. The effects of BMI were most consistent in the barrel; more heterogeneity was found in the non-granular layers. These lamina-dependent effects of BMI are consistent with the idea that between-whisker inhibition is generated mostly within individual layer IV barrels as a result of the rapid engagement of strong, local inhibitory circuitry, and is subsequently embedded in layer IV's output to non-layer IV neurons. The latter's surround inhibition is thus relatively resistant to antagonism by locally applied BMI. The greater heterogeneity of non-granular units in terms of RF properties and the effects of BMI is consistent with other findings demonstrating that neighboring neurons in these layers may participate in different local circuits.     

Does the cortical representation of body parts follow both injury to the related sensory peripheral nerve and its regeneration?

A study was made of the borderline between the physiological representations of the digits (D2, D3 and D4) and sinus whiskers in the rat primary somatosensory cortex after a contralateral infraorbital nerve crush. Following the injury, the physiological representation of the digits of the contralateral forepaw extended posterolaterally, occupying the anterolateral part of the whisker region (posteromedial barrel subfield). The extended physiological representation of the digits, though somewhat shrunken, remained after the reappearance of whisker-evoked responses, forming an overlapping area between the obligate digit and whisker representations. The findings emphasize the importance of afferent inputs in modulating cortical organization, but show that a reversible change in a sensory input (nerve damage) does not result in a perfectly reversible change in cortical representation.     

Widespread activation of barrel cortex by small numbers of neonatally spared whiskers

Activity-dependent plasticity in rodent whisker barrel cortex was examined by means of high-resolution 2-deoxyglucose (2-DG) with immunohistochemical double labeling. Hamsters with all but one, two, or four follicles ablated on postnatal day 7 received 2-DG injections as adults. Autoradiograms of follicle-ablated animals showed heavy activation of the entire barrel field during normal behavior, despite the missing whiskers. The intensity of 2-DG labeling was significantly reduced if the whiskers spared after follicle ablation were trimmed prior to the 2-DG injection, demonstrating that the widespread activation was driven by the spared whiskers. This widespread metabolic activation of the adult barrel field after neonatal follicle ablation was in sharp contrast to the somatotopically appropriate 2-DG labeling in barrel fields of normal adults subject to acute trimming of most whiskers, but was similar to that seen in normal adult animals with all whiskers intact. The results demonstrate large-scale plasticity of barrel circuitry following neonatal sensory deprivation, and provide a powerful functional anatomical setting to investigate underlying mechanisms.     

Optical intrinsic signal imaging responses are modulated in rodent somatosensory cortex during simultaneous whisker and forelimb stimulation

Optical intrinsic signal imaging (OIS) was used to investigate physiologic interactions between spatially and functionally distinct cortical somatosensory systems. The OIS response magnitude was evaluated after simultaneous stimulation of single whiskers and forelimb digits. Whisker C1 was deflected at a frequency of 10 Hz for 2 seconds while low- or high-intensity vibratory stimuli were applied to forelimb digits. The OIS responses to simultaneous whisker and forelimb stimulation were compared with lone whisker stimulated controls. Overall, addition of a second stimulus caused decreases in barrel cortex response magnitude. Three different response patterns were detected within individual trial sets. Modulation of barrel cortex evoked potentials provided evidence that changes in OIS responses observed here may be partially influenced by vascular responses to changes in neuronal activity. However, OIS responses in the barrel region during lone forelimb stimulation that were unaccompanied by evoked potentials suggested the possibility of independent vascular dynamic influences on response modulation. This study demonstrates that cortical responses at the level of primary sensory processing may be significantly influenced by activity in adjacent regions. Furthermore, it reveals that vascular and neuronal characteristics of interregional modulation do not co-localize and may produce responses in which one component increases while the other decreases.     

GABAergic neurons in barrel cortex show strong, whisker-dependent metabolic activation during normal behavior

Electrophysiological data from the rodent whisker/barrel cortex indicate that GABAergic, presumed inhibitory, neurons respond more vigorously to stimulation than glutamatergic, presumed excitatory, cells. However, these data represent very small neuronal samples in restrained, anesthetized, or narcotized animals or in cortical slices. Histochemical data from primate visual cortex, stained for the mitochondrial enzyme cytochrome oxidase (CO) and for GABA, show that GABAergic neurons are more highly reactive for CO than glutamatergic cells, indicating that inhibitory neurons are chronically more active than excitatory neurons but leaving doubt about the short-term stimulus dependence of this activation. Taken together, these results suggest that highly active inhibitory neurons powerfully influence relatively inactive excitatory cells but do not demonstrate directly the relative activities of excitatory and inhibitory neurons in the cortex during normal behavior. We used a novel double-labeling technique to approach the issue of excitatory and inhibitory neuronal activation during behavior. Our technique combines high-resolution 2-deoxyglucose (2DG), immunohistochemical staining for neurotransmitter-specific antibodies, and automated image analysis to collect the data. We find that putative inhibitory neurons in barrel cortex of behaving animals are, on average, much more heavily 2DG-labeled than presumed excitatory cells, a pattern not seen in animals anesthetized at the time of 2DG injection. This metabolic activation is dependent specifically on sensory inputs from the whiskers, because acute trimming of most whiskers greatly reduces 2DG labeling in both cell classes in columns corresponding to trimmed whiskers. Our results provide confirmation of the active GABAergic cell hypothesis suggested by CO and single-unit data. We conclude that strong activation of inhibitory cortical neurons must confer selective advantages that compensate for its inherent energy inefficiency.     

BDNF and NT-3 applied in the whisker pad reverse cortical changes after peripheral deafferentation in neonatal rats

It has been known for a long time that subcortical input drives the specification of cortical areas. Molecular signals mediating this instructive effect from the periphery are poorly understood. In foetal or neonatal rats, ablation of whisker follicles, transection of the infraorbital nerve, inhibition of axonal transport, but not impulse activity blockade, prevent formation of barrels in the primary somatosensory cortex (S1). These findings suggest that a chemical signal, possibly arising from the skin or the follicle, may be responsible for somatotopic pattern formation in S1. Neurotrophins promote survival and differentiation of primary sensory neurons, and are expressed in the whisker pad during development. Neonatal rats received gelfoam impregnated with NGF, BDNF or NT-3 under the whisker pad following surgical denervation of whisker rows D and E on P0. Barrel formation in S1 was assessed on P7 by acetylcholinesterase histochemistry and 5-HT-immunohistochemistry. BDNF and NT-3, but not NGF, promoted development of the cortical barrels corresponding to denervated whiskers. Furthermore, BDNF and NT-3 prevented the lesion-induced expansion of row C barrels, while NGF appeared to promote row C expansion. Our results suggest that BDNF and NT-3 arising from the whisker pad are involved in the formation and/or maintenance of the barrel pattern in S1. These findings are potentially relevant for the prevention of sensory disturbances possibly due to reorganization of central sensory circuits after peripheral nerve lesions in humans.     

Alterations in visual receptive fields in the superior colliculus induced by amphetamine

Visual response properties were examined in the superficial layers of the superior colliculus (SC) of anesthetized, paralyzed cats before and after i.v. administration of d-amphetamine. Receptive fields (RFs) of single SC units were plotted using small spots of light presented to the contralateral eye. Within the first hour following d-amphetamine injections, RF size gradually increased, reaching a maximum 86 min post-injection. On average, the area of the RF increased by 5.6 times and RF expansion was observed in all single units examined in the superficial layers. Over the subsequent 4-8 h following the injection, RF area gradually decreased and returned to control dimensions. Most RFs displayed asymmetrical patterns of expansion, showing relatively more horizontal than vertical growth. As RF expansion developed, responses to stimuli flashed "on" and "off" at various locations both inside and outside the borders of the control RF became progressively more vigorous. In contrast, no significant changes were noted in direction-selective responses at any time after d-amphetamine injections. Using an array of light bar stimuli of different lengths, the strength of surround suppression was found to be significantly diminished by d-amphetamine. The reduction in surround suppression was especially clear for bar lengths which exceeded the diameter of the control RF. No RF expansion was observed in the superficial layers of the SC when d-amphetamine was injected intravitreally. Furthermore, d-amphetamine had no discernable effect on the RF sizes of cells in the visual cortex. These results suggest that the RF changes in the SC were not of either retinal or cortical origin. We conclude that the mean retinal area which can potentially influence the activity of RFs in the superficial layers of the SC may be on average over 5 times greater than the RF area determined using conventional methods and criteria. These findings raise the interesting possibility that the relatively small size and sharp borders characteristic of RFs in the superficial layers arise from local inhibitory networks which delimit a broader field of excitatory activity supplied by retinal and cortical afferent terminals. Thus, in order to generate the RF changes observed here, either these local inhibitory circuits are amphetamine sensitive, or more likely, these inhibitory networks are dynamically modulated by an, as yet unidentified, amphetamine-sensitive input affecting visual RFs in the superficial layers.     

Frequency-specific receptive field plasticity in the medial geniculate body induced by Pavlovian fear conditioning is expressed in the anesthetized brain.

Fear conditioning modifies the processing of frequency information; receptive fields (RFs) in the auditory cortex and the medial geniculate body (MGB) are altered to favor processing the frequency of the conditioned stimulus/stimuli (CS) over the pretraining best frequency (BF) and other frequencies. This experiment was designed to determine whether brief conditioning in the waking state produces RF plasticity that is expressed under general anesthesia. Guinea pigs bearing electrodes in the MGB received 20 trials on tone-shock pairing in a single training session. RFs were determined with animals under ketamine anesthesia before conditioning and 1–3 hrs and 24 hrs after conditioning. Frequency-specific RF plasticity was evident for both postconditioning periods: The BF shifted toward or to the CS frequency, responses to the BF decreased, and responses to the CS increased. Broadly tuned cells developed greater RF plasticity than narrowly tuned neurons. Results demonstrate that the specific neuronal results of brief learning experiences can be expressed in the anesthetized brain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of D-AP5 and NMDA microiontophoresis on associative learning in the barrel cortex of awake rats

Experiments involving single-unit recordings and microiontophoresis were carried out in the barrel cortex of awake, adult rats subjected to whisker pairing, an associative learning paradigm where deflections of the recorded neuron's principle vibrissa (S2) are repeatedly paired with those of a non-adjacent one (S1). Whisker pairing with a 300 ms interstimulus interval was applied to 61 cells. In 23 cases, there was no other manipulation whereas in the remaining 38, pairing occurred in the presence of one of three pharmacological agents previously shown to modulate learning, receptive field plasticity and long-term potentiation: N-methyl-D-aspartic acid (NMDA) (n=8), the NMDA receptor antagonist AP5 (n=17) or the nitric oxide synthase inhibitor L-nitro-arginine-N-methyl-ester (L-NAME) (n=13). Non-associative (unpaired) experiments (n=14) and delivery of pharmacological agents without pairing (n=14) served as controls. Changes in neuronal responsiveness to S1 following one of these procedures were calculated and adjusted relative to changes in the responses to S2. On average, whisker pairing alone yielded a 7% increase in the responses to S1. This enhancement differed significantly from the 17% decrease obtained in the non-associative control condition and could not be attributed to variations in the state of the animals because analysis of the cervical and facial muscle electromyograms revealed that periods of increased muscular activity, reflecting heightened arousal, were infrequent (less than 4% of a complete experiment on average) and occurred randomly. The enhancement of the responses to S1 was further increased when whisker pairing was performed in the presence of L-NAME (27%) or NMDA (35%) whereas AP5 reduced it to 1%. During the delivery period, NMDA enhanced both neuronal excitability and responsiveness to S1 whereas AP5 depressed them. However, the effects of both substances disappeared immediately after administration had ended. L-NAME did not affect the level of ongoing activity and responses to S1 significantly. From these data, we concluded that, since the changes in the responses to S1 lasted longer than the periods of both whisker pairing and drug delivery, they were not residual excitatory or inhibitory drug effects on neuronal excitability. Thus, our results indicate that, relative to the unpaired controls, whisker pairing led to a 24% increase in the responsiveness of barrel cortex neurons to peripheral stimulation and that these changes were modulated by the local application of pharmacological agents that act upon NMDA receptors and pathways involving nitric oxide. We can infer that somatosensory cerebral cortex is one site where plasticity emerges following whisker pairing.     

Experience-dependent changes in function and anatomy of adult barrel cortex

Manipulations of sensory input to vibrissal mechanoreceptors can modify columnar functioning of the barrel cortex in adult animals. In mice, partial vibrissectomy sparing one row of vibrissae in young adults results 7 days later in an increase in the functional cortical column activated by the spared whiskers and visualized with 2-deoxyglucose autoradiography. The increase in the extent of the labelled area is visible in all cortical layers, but particularly in layer V, where the metabolic labelling is more intense in the representation of the spared vibrissae. Two months after vibrissectomy the enlargement of the labelled area is accentuated. Deprivation of a row of vibrissae results in a decrease in the areal extent of its cortical representation. Investigations of cortico-cortical connections carried out in living slices of the barrel cortex of mice 2 months after vibrissectomy sparing one row of whiskers, revealed elongation and increased branching of axons originating in the spared cortical column. The dendritic spine density was increased on the basal dendrites of layer V pyramidal neurons of the spared column and decreased on layer III apical dendrites of the deprived column. Thus, prolonged changes in functional activation of adult barrel cortex are accompanied by rearrangement of cortico-cortical circuitry.     

Basal forebrain stimulation induces discriminative receptive field plasticity in the auditory cortex.

Learning alters receptive field (RF) tuning in the primary auditory cortex (ACx) to emphasize the frequency of a tonal conditioned stimulus. RF plasticity is a candidate substrate of memory, as it is associative, specific, discriminative, rapidly induced, and enduring. The authors hypothesized that it is produced by the release of acetylcholine in the ACx from the basal forebrain (BasF), caused by presentation of reinforced but not nonreinforced conditioned stimuli. Waking adult male Hartley guinea pigs (n?=?16) received 1 of 2 tones followed by BasF stimulation, in a single session of 30 pseudo-random order trials each. RFs from neuronal discharges before and after differential pairing revealed the induction of predicted plasticity, as well as increased responses to the paired tone and decreased responses to the unpaired tone. Thus, highly specific, learning-induced RF plasticity in the ACx may be produced by activation of the BasF by a reinforced conditioned stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of context in the expression of learning-induced plasticity of single neurons in auditory cortex.

Classical conditioning produces frequency-specific plasticity of receptive fields (RFs) of single neurons in cat auditory cortex (D. M. Diamond and N. M. Weinberger; see record 1987-14817-001). In this article we show that although plasticity may be observed during both training trials and determination of RFs, it is usually expressed in a qualitatively different form (e.g., decreased response during conditioning vs. increased response to this same conditioned stimulus in the postconditioning RF). This differential expression of learning-induced plasticity provides evidence for a role of context in neurophysiological mechanisms of learning in auditory cortex. A model of cortical neurons functioning within a mosaic of influences is presented. The Functional Mosaic model views the induction and expression of plasticity as separate processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Velocity invariance of receptive field structure in somatosensory cortical area 3b of the alert monkey

This is the second in a series of studies of the neural representation of tactile spatial form in cortical area 3b of the alert monkey. We previously studied the spatial structure of 330 area 3b neuronal receptive fields (RFs) on the fingerpad with random dot patterns scanned at one velocity (40 mm/sec; ). Here, we analyze the temporal structure of 84 neuronal RFs by studying their spatial structure at three scanning velocities (20, 40, and 80 mm/sec). As in the previous study, most RFs contained a single, central, excitatory region and one or more surrounding or flanking inhibitory regions. The mean time delay between skin stimulation and its excitatory effect was 15.5 msec. Except for differences in mean rate, each neuron's response and the spatial structure of its RF were essentially unaffected by scanning velocity. This is the expected outcome when excitatory and inhibitory effects are brief and synchronous. However, that interpretation is consistent neither with the reported timing of excitation and inhibition in somatosensory cortex nor with the third study in this series, which investigates the effect of scanning direction and shows that one component of inhibition lags behind excitation. We reconcile these observations by showing that overlapping (in-field) inhibition delayed relative to excitation can produce RF spatial structure that is unaffected by changes in scanning velocity. Regardless of the mechanisms, the velocity invariance of area 3b RF structure is consistent with the velocity invariance of tactile spatial perception (e.g., roughness estimation and form recognition).     

Effects of erythromycin on membrane-bound chloroplast ribosomes from wild-type Chlamydomonas reinhardi and erythromycin-resistant mutants

The properties of peripheral cutaneous units in the hairy skin of cat's forelimb were studied by single-fiber recordings with tungsten microelectrodes. The response properties and receptive field (RFs) of total 193 units in superficial branch of radial nerve (SRN) were studied. The SRN sample included the following five major types of mechanoreceptive units; two types of low-threshold units (type I and II, slowly adapting), two types of hair units (G and D, rapidly adapting) and field units (F, responding principally to slow skin movement). Afferent conduction velocities of these units ranged from 9.0 to 56.0 m/sec. D hair fibers conducted much slower than other types of afferents and their conduction velocities were between 9.0 and 23.3 m/sec. Most of the smaller RFs of G, D and F units were found in the paw and digits. The disto-proximal increase of the mean size of RFs was marked in D hair units. The distributions of the RFs of simultaneously recorded paired units, which were supposed to be adjacent fibers, were examined. Among 23 paired units, more than half of them were homonymous combinations of unit types and there were no marked prevalence of particular types in heteronymous combinations. The RFs of paired units were close to each other, but showed little overlaps and some were separated by up to several cm over the skin surface. Some functional properties of cutaneous afferents from the forelimb were discussed.     

A solution to the rheumatoid factor paradox: pathologic rheumatoid factors can be tolerized by competition with natural rheumatoid factors

Rheumatoid factors (RF) associated with arthritic joint erosion are only seen transiently, if at all, in nondiseased individuals. Therefore, a tolerance mechanism must exist that prevents pathologic RF B cells from expressing Abs. Surprisingly, it has been shown that pathologic RF B cells are not tolerized by any previously established tolerance mechanism such as deletion, receptor editing, anergy, or prevention of memory establishment. How are pathologic RF cells tolerized? By simulating the RF response with a cellular automaton model immune system, we demonstrate that pathologic RFs can be tolerized by the novel mechanism of "competitive tolerance" with natural, nonpathologic RFs. We then demonstrate that competitive tolerance can be broken when a sequestered pool of expanding B cells are inappropriately subjected to chronic stimulation (as appears to occur in MRL/lpr mice and in patients with rheumatoid arthritis).     

Role of cyclooxygenase-2 in the healing of gastric ulcers in rats

Extracellular activity was recorded from single spinal dorsal horn neurons in both chronic cat and acute rat models. This was done to define the effects of anesthesia on the processing of sensory information elicited by nonnoxious tactile stimulation of peripheral receptive fields (RFs). In the chronic cat model, baseline data were obtained in physiologically intact, awake, drug-free animals before anesthetic administration (halothane 1.0-2.0%). This made it possible to compare and contrast activity of each cell in the drug-free and anesthetized state. Halothane effects were confirmed in the acute rat model (anesthetized, spinally transected, and in some cases decerebrate). In addition, the gamma-aminobutyic acid-A (GABAA)-receptor antagonist picrotoxin (2 mg/kg) was administered intravenously to verify that the observed halothane effect on spinal dorsal horn neurons was mediated by an interaction with GABAA-receptor systems. Halothane effects on three separate measures of response to nonnoxious tactile stimuli were observed in the chronic cat model. Halothane produced a significant, dose-dependent reduction in the low-threshold RF area of the neurons studied. Halothane also caused a significant reduction in neuronal response to RF brushing (dynamic stimulus) and to maintained contact with the RF (static stimulus). A dose dependency was not observed with these latter two effects. Neurons with a predominant rapidly adapting response seemed to be less susceptible to halothane suppression than slowly adapting cells. In the acute rat model an increase in halothane caused a reduction in neuronal response similar to that seen in the cat. The intravenous administration of 2 mg/kg of picrotoxin by itself caused no significant change in RF size or response to brushing. However, the same amount of picrotoxin did cause a 50% reversal of the halothane-induced reduction in RF size without causing a significant change in the halothane effect on response to RF brushing. In contrast to work recently reported in a chronic sheep model, halothane causes a significant reduction in spinal dorsal horn neuronal response to tactile stimulation of peripheral RFs. This effect is caused by, in part, but not exclusively, to GABAA-neurotransmitter systems. However, the relative influence of GABAA systems may vary with the nature of the stimulus.     

Induction of long-term receptive field plasticity in the auditory cortex of the waking guinea pig by stimulation of the nucleus basalis.

Learning induces neuronal receptive field (RF) plasticity in primary auditory cortex. This plasticity constitutes physiological memory as it is associative, highly specific, discriminative, develops rapidly, and is retained indefinitely. This study examined whether pairing a tone with activation of the nucleus basalis (NB) could induce RF plasticity in the waking guinea pig and, if so, whether it could be retained for 24 hrs. Subjects received 40 trials of a single frequency paired with electrical stimulation of the NB at tone offset. The physiological effectiveness of NB stimulation was assessed later while subjects were anesthetized with urethane by noting whether stimulation produced cortical desynchronization. Subjects in which NB stimulation was effective did develop RF plasticity and this was retained for 24 hrs. Thus, activation of the NB during normal learning may be sufficient to induce enduring physiological memory in auditory cortex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Immediate and simultaneous sensory reorganization at cortical and subcortical levels of the somatosensory system

The occurrence of cortical plasticity during adulthood has been demonstrated using many experimental paradigms. Whether this phenomenon is generated exclusively by changes in intrinsic cortical circuitry, or whether it involves concomitant cortical and subcortical reorganization, remains controversial. Here, we addressed this issue by simultaneously recording the extracellular activity of up to 135 neurons in the primary somatosensory cortex, ventral posterior medial nucleus of the thalamus, and trigeminal brainstem complex of adult rats, before and after a reversible sensory deactivation was produced by subcutaneous injections of lidocaine. Following the onset of the deactivation, immediate and simultaneous sensory reorganization was observed at all levels of the somatosensory system. No statistical difference was observed when the overall spatial extent of the cortical (9.1 +/- 1.2 whiskers, mean +/- SE) and the thalamic (6.1 +/- 1.6 whiskers) reorganization was compared. Likewise, no significant difference was found in the percentage of cortical (71.1 +/- 5.2%) and thalamic (66. 4 +/- 10.7%) neurons exhibiting unmasked sensory responses. Although unmasked cortical responses occurred at significantly higher latencies (19.6 +/- 0.3 ms, mean +/- SE) than thalamic responses (13. 1 +/- 0.6 ms), variations in neuronal latency induced by the sensory deafferentation occurred as often in the thalamus as in the cortex. These data clearly demonstrate that peripheral sensory deafferentation triggers a system-wide reorganization, and strongly suggest that the spatiotemporal attributes of cortical plasticity are paralleled by subcortical reorganization.     

Morphology and Growth Kinetics of Straight and Kinked Tin Whiskers

Time-lapse SEM studies of Sn whiskers were conducted to estimate growth kinetics and document whisker morphologies. For straight whiskers, growth rates of 3 to 4 microns per day were measured at room temperature. Two types of kinked whiskers were observed. For Type A kinks, the original growth segment spatial orientation remains unchanged, there are no other changes in morphology or diameter, and growth continues. For Type B kinks, the spatial orientation of the original segment changes and it appears that the whisker bends over. Whiskers with Type B kinks show changes in morphology and diameter at the base, indicating grain boundary motion in the film, which eliminates the conditions suitable for long-term whisker growth. To estimate the errors in the whisker growth measurements, a technique is presented to correct for SEM projection effects. With this technique, the actual growth angles and lengths of a large number of whiskers were collected. It was found that most whiskers grow at moderate or shallow angles with respect to the surface; few straight whiskers grow nearly normal to the surface. In addition, there is no simple correlation between growth angles and lengths for whiskers observed over an approximate 2-year period.     

Chronic inhibition of NOS does not prevent plasticity of rat somatosensory (S1) cortex following deafferentation

Nitric oxide (NO) has been proposed as an intercellular messenger mediating postsynaptic to presynaptic information transfer in the induction of long-term potentiation. A number of studies support the possible involvement of NO in synaptic plasticity. NO may have a role in synaptogenesis and synaptic plasticity in developing rat brain and may play a fundamental part in the process of regeneration, plasticity, and retargeting of axons following injury. We examined the possible role of NO on plasticity in the rat first somatosensory cortex with [14C]2-deoxyglucose (2-DG) autoradiography in rats treated daily with l-nitroarginine (l-NA) following neonatal unilateral vibrissae deafferentation. After 6 weeks of l-NA treatment, the local cerebral glucose utilization (LCGU) and the spatial extent of the metabolic activation following stimulation of the spared whisker was measured. NOS catalytic activity exhibited significant inhibition throughout the treatment period. Vibrissae deafferentation produced a small but not statistically significant increase of LCGU in the vibrissa activated C3 barrel, and l-NA treatment did not alter the activation of LCGU in the deafferented cortex following whisker stimulation. Additionally, l-NA treatment did not alter the area of metabolic activation on either the non-deafferented side or the deafferented side. Deafferentation produced a 298% increase in the metabolic representation of the spared C3 barrel following stimulation in the saline treated animals, a 257% increase in the chronically l-NA treated animals, and a 256% increase in the short-term treated animals, all with respect to the response in the non-deafferented cortex. Metabolic plasticity in the barrel cortex was not attenuated by l-NA treatment. These results show that nitric oxide does not play a major role on developmental cortical plasticity induced by vibrissae deafferentation in the rat.