Plasticity in primary somatosensory cortex resulting from environmentally enriched stimulation and sensory discrimination training

We studied primary-somatosensory cortical plasticity due to selective stimulation of the sensory periphery by two procedures of active exploration in adult rats. Subjects, left with only three adjacent whiskers, were trained in a roughness discrimination task or maintained in a tactile enriched environment. Either training or enrichment produced 3-fold increases in the barrel cortex areas of behaviorally-engaged whisker representations, in their zones of overlap. While the overall areas of representation expanded dramatically, the domains of exclusive principal whisker responses were virtually identical in enriched vs normal rats and were significantly smaller than either group in roughness discrimination-trained rats. When animals were trained or exposed to enriched environments with the three whiskers arrayed in an are or row, very equivalent overlaps in representations were recorded across their greatly-enlarged whisker representation zones. This equivalence in distortion in these behavioral preparations is in contradistinction to the normal rat, where overlap is strongly biased only along rows, probably reflecting the establishment of different relations with the neighboring cortical columns. Overall, plasticity phenomena are argued to be consistent with the predictions of competitive Hebbian network plasticity.

Non-homogeneous spatial configuration of vibrissae cortical representation in layer IV of the barrel somatosensory cortex

In the present experiments we studied exclusive and overlapping cortical representational areas of the vibrissae in layer IV cells, across the entire barrel subfield of the rat somatosensory cortex, looking for evidences that would challenge the present assumptions of homogeneity and symmetry among cortical columns in this sensorial system. Our main findings were that in layer IV of the rat barrel cortex: A) Size of vibrissae cortical representational areas (X=0.4174mm²; SD=0.025) was not homo geneous, vibrissae in dorsal rows (A-B) had significantly smaller areas than those in ventral rows (D-E), a pattern that repeated itself in arcs 1-4. B) This difference arises from vibrissal representational overlap, and not from variations in exclusive zones, which are surprisingly homogeneous in size across the barrel cortex (X=0.079mm²; SD=0.0075); C) The extent of overlapping cortical areas varied systematically, with intra-row overlapping areas having a predominant bias (71.4 percent of total overlapping) independent of area sizes. Accordingly, vibrissae shared receptive fields with an average of 1.15 vibrissae in the same row and 0.38 in the same are. Barrel cortex has been viewed operationally as a conglomerate of essentially homogenous cortical columns that interact equivalently in the are and row dimensions. Our simple but global cortical reconstructions show that this predominant view should be revised. We postulate that the vibrissae/barrels spatial disposition in rows and ares has a relevant functional meaning, related to different sensory capabilities.

Padronização das técnicas de secção do nervo facial e de avaliação da mímica facial em ratos / Standardization of techniques used in facial nerve section and facial movement evaluation in rats

OBJETIVOS: Padronização da técnica de secção do nervo facial extratemporal em ratos e elaboração de uma escala de avaliação da mímica facial desses animais antes e após essa secção. TIPO DE ESTUDO: Experimental. MÉTODO: Vinte ratos Wistar foram anestesiados com xilasina e ketamina e submetidos à secção do nervo facial próximo à sua emergência pelo forame mastóideo na pele. Todos os animais foram avaliados. Foram observados: fechamento ocular, reflexo de piscamento, movimentação e posicionamento das vibrissas, e foi elaborada uma escala de avaliação e graduação destes parâmetros. RESULTADOS: O tronco do nervo facial foi encontrado entre a margem tendinosa do músculo clavotrapézio e a cartilagem auricular. O tronco foi seccionado proximal à sua saída pelo forame mastóideo e os cotos foram suturados com nylon 9-0. Foi elaborada uma escala de avaliação e graduação da mímica facial independente para olho e vibrissa e a somatória dos parâmetros, como forma de avaliar a face paralisada. A ausência de piscamento e de fechamento ocular recebeu valor 1; a presença de contração do músculo orbicular, sem reflexo de piscamento, valor 2; fechamento ocular de 50 por cento através de reflexo de piscamento, valor 3, o fechamento de 75 por cento, valor 4. A presença de reflexo de piscamento com fechamento ocular completo recebeu valor 5. A ausência de movimento e posição posterior das vibrissas recebeu pontuação 1; tremor leve e posição posterior, pontuação 2; tremor maior e posição posterior, pontuação 3 e movimento normal com posição posterior, pontuação 4. A movimentação simétrica das vibrissas, com posição anterior recebeu pontuação 5. CONCLUSÃO: O rato apresenta anatomia que permite fácil acesso ao nervo facial extratemporal, possibilitando secção e sutura desse nervo de forma padronizada. Também foi possível estabelecer uma escala de avaliação e graduação da mímica facial dos ratos com paralisia facial a partir da observação clínica desses animais.

AIM: standardization of the technique to section the extratemporal facial nerve in rats and creation of a scale to evaluate facial movements in these animals before and after surgery. STUDY DESIGN: Experimental. METHOD: twenty Wistar rats were anesthetized with ketamine xylazine and submitted to sectioning of the facial nerve near its emergence through the mastoid foramen. Eye closure and blinking reflex, vibrissae movement and positioning were observed in all animals and a scale to evaluate these parameters was then created. RESULTS: The facial nerve trunk was found between the tendinous margin of the clavotrapezius muscle and the auricular cartilage. The trunk was proximally sectioned as it exits the mastoid foramen and the stumps were sutured with a 9-0-nylon thread. An evaluation and graduation scale of facial movements, independent for eye and vibrissae, was elaborated, together with a sum of the parameters, as a means to evaluate facial palsy. Absence of eye blinking and closure scored 1; the presence of orbicular muscle contraction, without blinking reflex, scored 2; 50 percent of eye closure through blinking reflex, scored 3, 75 percent of closure scored 4. The presence of complete eye closure and blinking reflex scored 5. The absence of movement and posterior position of the vibrissae scored 1; slight shivering and posterior position scored 2; greater shivering and posterior position, scored 3 and normal movement with posterior position, scored 4; symmetrical movement of he vibrissae, with anterior position, scored 5. CONCLUSION: The rat anatomy allows easy access to the extratemporal facial nerve, allowing its sectioning and standardized suture. It was also possible to establish an evaluation and graduation scale of the rat facial movements with facial palsy based on the clinical observation of these animals.