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Showing 5 results for Somatosensory Cortex


Volume 1, Issue 1 (4-1997)
Abstract

The results of psychophysical studies suggest that displacement velocity may contribute significantly to the sensation of subcortical somatosensory neurons. The cortical correlates of these phenomena, however, are not known. In the present study the responses of rapidly adapting (RA) neurons in the forelimb region of cat primary somatosensory cortex (SI) to controlled displacement of skin and hair was studied. The cortical RA neurons were grouped according to their response patterns to constant-velocity ramp stimuli. Firing frequency, spontaneous activity, receptive field organization, and cortical laminar location of the RA neurons were studied and compared between the groups. There was a continuum in the response pattern of RA neurons to constant -velocity displacement. In one extent of the continuum, (G1IF1, n = 16) neurons typically responded to constant-velocity ramp stimuli with 1-3 impulses at the beginning of the ramp they had little or no spontaneous activity and responded only to fast stimuli. In the other extent of the continuum, (G2IF2, n = 15) neurons responded throughout the ramp and sometimes during the initial phase of sustained stimuli. These neurons usually had higher spontaneous activities than G1IF1 neurons and responded to relatively slower stimuli. Gint/Fint (n = 18) neurons fell between the two types: they had an initial brief response which was sometimes followed, after a period of low or no activity, by a discharge towards the end of the ramp. Nine neurons had response patterns suggesting the existence of either convergence between these types or input from other types of mechanoreceptors. The average and instantaneous firing frequency of the majority of RA neurons increased as the ramp velocity was increased. The variation in the firing frequency of G2IF2 RA neurons had the widest range of firing frequencies and, in average, generated higher firing frequencies to both low and high displacement velocities. Coefficients of regression lines for linear, logarithmic and power functions were not significantly different among RA types. No correlation was found between cortical laminar location and RA types.

Volume 3, Issue 2 (11-1999)
Abstract

  Although each subdivision of primary somatosensory cortex (SI) receives dense input from the thalamus, but the exact location and type of information that the fibers convey have not been identified yet. In the present study, the exact source of thalamocortical fibers to areas 2 and 3b was investigated using tract-tracing techniques. Following injection of tracer into area 3b, labeled neurons were only found in the VPL. However, labeled neurons were found in VPL and PoM as well as in LP following tracer injection into area 2. Also less densely labeled neurons were found in CLN, VA, and VL. There were no significant differences in the size of area l-labeled neurons following injection of tracer into areas 3b and/or 2 of VPL. These results indicate that area 2 is involved in the processing of tactile information related to sensorimotor coordination and planning as well as in pain perception.


Ali Shamsizadeh, Vahid Sheibani, Yaghoub Fathollahi, Mohammad Javan, Javad Mirnajafi-Zadeh, Mohammad Reza Afarinesh,
Volume 11, Issue 2 (8-2007)
Abstract

Previous studies have shown that the receptive field properties, spontaneous activity and spatio-temporal interactions of low-threshold mechanical somatosensory cells in the barrel cortex are influenced by C-fibers. In this study, we examined the effect of C-fiber depletion on response properties of barrel cortex neurons following experience dependent plasticity. Methods: In this study, exteracellular single unit recording was performed on 154 barrel cortex neurons in 70 male Wistar rats (38-41days old). For depleting of C-fibers, neonatal rats received an intra-peritoneal injection of capsaicin solution (50 mg/kg) on the first neonatal day. For induction of experience dependent plasticity, all whiskers but D2 on the left muzzle, were plucked from first neonatal day. Neuronal ON and OFF responses were recorded in right barrel cortex following principal whisker (PW) and its caudal adjacent whisker (AW) deflection. Results: Whisker plucking increased PW–evoked ON responses both in capsaicin and vehicle treated rats (all P<0.05). In vehicle treated rats, AW-evoked ON responses were decreased in plucked animals (P< 0.05). Of particular interest, in capsaicin treated rats, AW-evoked ON responses were not decreased in plucked animals. Analyzing OFF responses showed similar result to ON responses. Conclusion: These findings indicate that c-fibers can modulate neuronal response properties following experience dependent plasticity in layer IV of barrel cortex.
Hashem Haghdoost Yazdi, Mohamad Reza Esmaili, Mohamad Sophiabadi, Christian Stricker,
Volume 11, Issue 2 (8-2007)
Abstract

Introduction: Neurons in layer II and III of the somatosensory cortex in rats show high frequency (33 ± 13 Hz) of miniature excitatory postsynaptic currents (mEPSCs) that their rates and amplitudes are independent of sodium channels. There are some changes in these currents in neurodegenerative and psychological disorders. Regarding to well known roles of the neuromodulatory brain systems in these disorders, study the effects of these systems on the miniature currents provides data to understand more precisely pathogenesis of this disorders. Because cortical neurons receive very dense noradrenergic innervations, we examined effects of noradrenergic system on these currents. Methods: Whole cell patch clamp recordings were made on pyramidal neurons of the barrel cortex from brain slices that continuously superfused with artificial cerebrospinal fluid (ACSF) containing tetrodotoxin, sodium channel blocker and picrotoxin, blocker of the GABA receptors. Results: Application of noradrenalin significantly increased frequency and decreased amplitude of the mEPSCs. Using specific agonists and antagonists of the noradrenergic system, it was determined that the effects are mostly mediated by α1 receptor. Conclusion: Our results showed that noradrenergic system controls sodium channel independent synaptic transmission which can be of importance in regulation and induction of many physiological and pathophysiological conditions.
Vahid Sheibani, Somaye Arabzadeh, Mohamadreza Afarineshkhaki, Ali Shamsizadeh, Hossein Aminizadeh, Saeed Azizolahi,
Volume 11, Issue 4 (1-2008)
Abstract

Introduction: Barrel cortex of rats is a part of somatosensory cortex, which receives information from facial whiskers. Vibrisectomy by sensory deprivation leads to some changes in the barrel cortex, which have been known as experience dependent plasticity. On the other hand, Norepinephrine (NE) and locus coeruleus, which is the main source of NE, influenced response properties of cortical barrel neurons. In this study, the effect of NE depleted and sensory deprivation on induction of experience dependent plasticity was investigated. Materials and methods: In this study sixty wistar rats (250±25gr) were used. Rats were divided into four groups: 1.Control group (Intact). 2. NE depleted group in which Norepinephrine was selectively depleted by IP injection of DSP4. 3. Sensory deprivation group that all whiskers (except the whisker D2) on the left side were trimmed every other day. 4. NE depleted + sensory deprivation group. By using extracellular single unit recordings, the excitatory (magnitude and latency) and initiatory (Conditioning Test Ratio, CTR index) receptive fields of barrel cortical neurons were calculated. Results: Sensory deprivation led to an increase both in the response magnitude to principle whisker deflection (spared whisker) and in the CTR. In NE depleted + sensory deprivation group, the response magnitude and CTR index were the same as control group. Conclusion: The result showed that experience dependent plasticity has a facilitating effect on excitatory receptive field while decreasing the inhibitory circuits in the brain. When NE content of the brain was depleted before sensory deprivation, these changes were not seen. We conclude that NE depletion inhibits the plastic changes in the response properties of neurons following sensory deprivation.

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