Long-Term Synaptic Plasticity in Rat Barrel Cortex.

Rats generate sweeping whisker movements in order to explore their environments and identify objects. In somatosensory pathways, neuronal activity is modulated by the frequency of whisker vibration. However, the potential role of rhythmic neuronal activity in the cerebral processing of sensory signals and its mechanism remain unclear. Here, we showed that rhythmic vibrissal stimulation with short duration in anesthetized rats resulted in an increase or decrease in the amplitude of somatosensory-evoked potentials (SEPs) in the contralateral barrel cortex. The plastic change of the SEPs was frequency dependent and long lasting. The long-lasting enhancement of the vibrissa-to-cortex evoked response was side- but not barrel-specific. Local application of dl-2-amino-5-phosphonopentanoic acid into the barrel cortex revealed that this vibrissa-to-cortex long-term plasticity in adult rats was N-methyl-d-aspartate receptor-dependent. Most interestingly, whisker trimming through postnatal day (P)1-7 but not P29-35 impaired the long-term plasticity induced by 100 Hz vibrissal stimulation. The short period of rhythmic vibrissal stimulation did not induce long-lasting plasticity of field potentials in the thalamus. In conclusion, our results suggest that natural rhythmic whisker activity modifies sensory information processing in cerebral cortex, providing further insight into sensory perception.

Astrocyte-restricted disruption of connexin-43 impairs neuronal plasticity in mouse barrel cortex.

There is intensive gap-junctional coupling between glial processes, but their significance in sensory functions remains unknown. Connexin-43 (Cx43), a major component of astrocytic gap-junction channels, is abundantly expressed in astrocytes. To investigate the role of Cx43-mediated gap junctions between astrocytes in sensory functions, we generated Cx43 knockout (KO) mice with a mouse line carrying loxP sites flanking exon 2 of the Cx43 gene and the transgenic line expressing Cre recombinase under control of the glial fibrillary acidic protein promoter, which exhibited a significant loss of Cx43 in astrocytes in the barrel cortex. Although Cx43 expression between the astrocytes measured by immunohistochemistry was virtually abolished in Cx43 KO mice, they had normal architecture in the barrel cortex but the intensity of cytochrome oxide histochemistry decreased significantly. In vivo electrophysiological analysis revealed that the long-term potentiation of the vibrissal evoked responses in the barrel cortex evoked by high-frequency rhythmic vibrissal stimuli (100 Hz, 1 s) was abolished in Cx43 KO mice. Current source density analysis also revealed that astrocytic Cx43 was important to the flow of excitation within the laminar connections in barrel cortex. Behavioral tests showed that the ability of Cx43 KO mice to sense the environment with their whiskers decreased. Even so, the jump-stand experiment showed that they could still discriminate rough from smooth surfaces. Our findings suggest that Cx43-mediated gap-junctional coupling between astrocytes is important in the neuron-glia interactions required for whisker-related sensory functions and plasticity.

Glial modulation of vibrissal sensory processing in rats.

Interactions between neurons and glial cells in the brain have important roles in brain functions such as development and plasticity of neural circuits or functions. Glial cells are much more actively involved in brain functions than previously thought. Here, we used vibrissal stimuli to induce sensoryevoked responses and multiunit spikes in the contralateral barrel cortex in a rat model. Local application of the gliotoxin DL-alpha-aminoadipate (AA) revealed that glial cells were involved in the sensoryevoked responses. The increases in the amplitude of somatosensory-evoked potential (SEP) and multiunit sensory-evoked spike rates in barrel cortex after AA injection were dramatic. Immunohistochemical staining of brain lipid binding protein (BLBP) and NeuN showed AA decreased cell number of astrocytes but not neurons in the barrel cortex. In conclusion, our results suggested an important role for astrocyte metabolism in normal synaptic activities.

[Role of astrocytes in sensory processing in central nervous system].

There are two types of cells in the central nervous systems (CNS) of mammals-neurons and glia. The structure and function of neurons have been thoroughly studied; while the role of glia in information processing has not been systematically studied because they cannot produce action potentials like neuron. During the past decades, glial cells were considered to play a supportive role in CNS instead of information processing. Recently, a variety of studies suggest that glial cells are actively involved in the regulation of brain function associated with neurons. Glial cells, especially astrocytes play important roles in different sensory processing. In the present article, we review the role of astrocytes in sensory processing in the CNS.

[Effect of whisker trimming on behavior and barrel cortex of rat].

OBJECTIVE: To investigate the change of behavior, as well as the plasticity of somatosensory cortex after whisker trimming. METHODS: SD rats were divided into 4 groups. Group A is the normal control group; group B: bilateral vibrissotomy on the second postnatal day; group C: unilateral right vibrissotomy on the second postnatal day; group D: right unilateral whisker trimmed during 1-5 days after birth, and leave untreated after the 5th postnatal day. Their body weight, length of the left D2 whiskers was measured on the 30th postnatal day. At the same time, the changes of their behavior (including the slit-detection test, the home exploring behavior and thigmotaxis test) were also recorded on the 30th postnatal day. Cytochrome oxydase histochemistry (CO reaction)was applied to study the development and arrangement of barrel cortex. RESULTS: In the slit-detection test, control rats could find and get into the right slit very quickly. The rats in group B could get into the slit only if their noses touched the slit. The rats in group C couldn't identify the slit by right face, but if they turned their body and touched the slit with the left whiskers, they could get into the slit very quickly. The behavior of rats in group D was similar to that in group C. The time spent for finding out the right slit of the rats in group A, B, C was obviously longer than that of group A (P < 0.01, P < 0.05, P < 0.01). In the exploring behavior and thigmotaxis test, the time for left thigmotaxis, right thigmotaxis and total thigmotaxis of rats in group B was longer than that of control animals. The time for right thigmotaxis of group C was significantly shorter than that of group A (P < 0.05). Both the weight of the rats and the length of left D2 whiskers of rats in all the four groups had no significant difference. CO reaction showed that the barrels became smaller, the septum was not clear, the arrangement of the barrels was not tidy in the mice whose right whiskers were trimmed from 2-30 days after birth. CONCLUSION: Deafferentation doesn't change the body weight and length of the whiskers left. But the stimulation of whiskers is important for rodent especially in thigmotaxis and exploring behavior. Deafferentation can also induce the plastic change of barrel cortex.