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Journal Article 2005; 26(4): 283-288 PubMed PMID: 16136014 Citation  Keywords:  Animals, Causalgia:physiopathology, Denervation, Electric Stimulation, Female, Male, Motor Cortex:physiology, Nociceptors:physiology, Pain Threshold:physiology, Rats, Rats, Long-Evans, Rhizotomy,.   

OBJECTIVES: The aim of the study was to describe the effect of motor cortex stimulation (MCS) on pain thresholds in deafferentated rats.

SETTINGS AND DESIGN: The effect of MCS was studied in 18 deafferentated and 14 intact laboratory rats, using a standardised plantar test and tail-flick latencies. Two inoxious stimulation electrodes were implanted subdurally over the cerebral cortex and a C5-Th1 dorsal root rhizotomy was performed on the left side. Pain thresholds were measured before and after cortical stimulation. The data were analysed with ANOVA for repeated measures.

RESULTS: MCS in intact animals evoked no changes in pain thresholds except for the contralateral forelimb, in which the pain threshold increased after MCS. Following deafferentation, pain thresholds increased in both plantar test and tail-flick in comparison to baseline values. When MCS was applied to the deafferentated animals, the pain thresholds returned to baseline levels. The effect of MCS disappeared within 24 hours.

MAIN FINDINGS: 1. MCS in intact animals evoked hypoesthesia in the corresponding contralateral forelimb; 2. deafferentation itself increased pain thresholds in the unaffected limbs; 3. under MCS, pain thresholds in deafferentated rats were not different from pre-dafferentation values; 4. the effect of MCS disappeared in 24 hours and oscillated.

CONCLUSIONS: Our results show a similar effect of the stimulation in man and experimental animals despite the differences in the organisation of the cerebral cortex. The use of laboratory animals is promising for further studies in the field of involved antalgic mechanisms of MCS....

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Journal Article 2005; 26(1): 25-28 PubMed PMID: 15726015 Citation  Keywords:  Aging:physiology, Animals, Animals, Newborn, Brachial Plexus:physiology, Electrophysiology, Entropy, Male, Neurons, Afferent:physiology, Pain:etiology, Rats, Rats, Wistar, Rhizotomy, Self Mutilation:etiology,.   

OBJECTIVES: The aim of the study was to describe the development of self-mutilation after extensive dorsal rhizotomy of the brachial plexus performed during early ontogeny in rats.

SETTINGS AND DESIGN: The rhizotomy was performed in three groups of rats according to the central nervous system maturation: infant, young, and adult. After the surgery the occurrence of self-mutilation behavior was compared. Rats from the infant group and non-mutilating deafferentated rats from the adult group underwent extracellular recordings from intralaminar thalamic neurons. Interspikes intervals of the records were compared by means of chaodynamic methods.

RESULTS: In the infant group self-mutilation did not develop at all. Among the young group self-mutilation developed in 40% of rats and consisted of superficial wounds in all cases. In adult self-mutilation appeared in 80% rats and consisted of both superficial wounds (75%) and amputation (25%). In the newborn group and the deafferentated adult group without any signs of self-mutilation means of the parameters were not significantly different and were significantly lower than those of intact adult rats.

MAIN FINDINGS: 1. Self-mutilation does not develop after the rhizotomy in the infant rats. 2. Neurons behave in chaotic way in adult as well as in young animals. 3. Chaodynamic parameters do not differ between infant and adult rats without any signs of self-mutilation.

CONCLUSIONS: The results suggest that development of self-mutilation behavior in rats strongly depends on the ontogenetical period of nervous system injury, and that mature nervous system is required for the development of described pathological behavior....

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Journal Article 2004; 25(6): 407-410 PubMed PMID: 15665800 Citation  Keywords:  Action Potentials, Animals, Entropy, Intralaminar Thalamic Nuclei:physiology, Male, Models, Neurological, Neuralgia:physiopathology, Nonlinear Dynamics, Rats, Rats, Wistar, Rhizotomy,.   

OBJECTIVES: A novel evaluative approach was used to determine single unit activities of non-bursting intralaminar thalamic nuclei under neuropathic pain state following dorsal rhizotomy.

SETTINGS AND DESIGN: Extensive dorsal rhizotomy at cervicothoracic level in rats was used as a model of central pain. After rhizotomy, rats were divided into two groups: rats without any signs of self-mutilation, and those presenting self-mutilation. Spontaneous single unit activities of neurons of intralaminar thalamic nuclei were recorded and interspike intervals (ISIs) of non-bursting cells were counted for both groups and compared with that of non-rhizotomized control rats. Chaodynamic methods were applied for the evaluation of the ISIs.

RESULTS: In control rats Lyapunov exponents, Shannon entropy and mutual information average values were significantly higher than those of rhizotomized rats without any signs of self-mutilation. Paradoxically, in animals presenting self-mutilation following rhizotomy the evaluated parameters were similar to those of controls. Further, Lyapunov exponents were positive values in all animals indicating chaotic pattern of the neuronal firing.

MAIN FINDINGS: 1. Neurons behave in chaotic way in all animals, 2. The most regular firing was found in non-mutilating rhizotomized animals, 3. Patterns of the firing in selfmutilating rats were similar to those in controls.

CONCLUSIONS: It is concluded that pain feeling is not executed neither by changes of chaotic dynamics of non-bursting intralaminar thalamic neurons. On the other hand, the paradoxical firing of the neurons under pathological brain matrix might participate in modification pain feeling....

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