Receptive field structure in the visual cortex: does selective stimulation induce plasticity?

Sensory areas of adult cerebral cortex can reorganize in response to long-term alterations in patterns of afferent signals. This long-term plasticity is thought to play a crucial role in recovery from injury and in some forms of learning. However, the degree to which sensory representations in primary cortical areas depend on short-term (i.e., minute to minute) stimulus variations remains unclear. A traditional view is that each neuron in the mature cortex has a fixed receptive field structure. An alternative view, with fundamentally different implications for understanding cortical function, is that each cell's receptive field is highly malleable, changing according to the recent history of the sensory environment. Consistent with the latter view, it has been reported that selective stimulation of regions surrounding the receptive field induces a dramatic short-term increase in receptive field size for neurons in the visual cortex [Pettet, M. W. & Gilbert, C. D. (1992) Proc. Natl. Acad. Sci. USA 89, 8366-8370]. In contrast, we report here that there is no change in either the size or the internal structure of the receptive field following several minutes of surround stimulation. However, for some cells, overall responsiveness increases. These results suggest that dynamic alterations of receptive field structure do not underlie short-term plasticity in the mature primary visual cortex. However, some degree of short-term adaptability could be mediated by changes in responsiveness.

Stimulation of mouse mammary tumor virus superantigen expression by an intragenic enhancer.

The mechanisms regulating expression of mouse mammary tumor virus (MMTV)-encoded superantigens from the viral sag gene are largely unknown, due to problems with detection and quantification of these low-abundance proteins. To study the expression and regulation of the MMTV sag gene, we have developed a sensitive and quantitative reporter gene assay based on a recombinant superantigen-human placental alkaline phosphatase fusion protein. High sag-reporter expression in Ba/F3, an early B-lymphoid cell line, depends on enhancers in either of the viral long terminal repeats (LTRs) and is largely independent of promoters in the 5' LTR. The same enhancer region is also required for general expression of MMTV genes from the 5' LTR. The enhancer was mapped to a 548-bp fragment of the MMTV LTR lying within sag and shown to be sufficient to stimulate expression from a heterologous simian virus 40 promoter. No enhancer activity of the MMTV LTR was observed in XC sarcoma cells, which are permissive for MMTV. Our results demonstrate a major role for this enhancer in MMTV gene expression in early B-lymphoid cells.

Tonic stimulation of renin gene expression by nitric oxide is counteracted by tonic inhibition through angiotensin II.

This study was designed to examine the possible involvement of prostaglandins and nitric oxide (NO) in the renin stimulatory effect of angiotensin II (AngII) antagonists. To this end, plasma renin activities (PRAs) and renal renin mRNA levels were assayed in rats that were treated with the Ang-converting enzyme inhibitor ramipril or with the AngII AT1-receptor antagonist losartan. Ramipril and losartan increased PRA values from 7.5 +/- 1.6 to 86 +/- 6 and 78 +/- 22 ng of AngI per h per ml and renin mRNA levels from 112 +/- 9% to 391 +/- 20% and 317 +/- 10%, respectively. Inhibition of prostaglandin formation with indomethacin did not influence basal or ramipril-affected PRA. Basal renin mRNA levels also were unchanged by indomethacin, while increases in renin mRNA levels after ramipril treatment were slightly reduced by indomethacin. Inhibition of NO synthase by nitro-L-arginine methyl ester (L-NAME) reduced PRA values to 3.2 +/- 0.9, 34 +/- 13, and 12.1 +/- 2.7 ng of AngI per h per ml in control, ramipril-treated, and losartan-treated animals, respectively. Renin mRNA levels were reduced to 77 +/- 14% under basal conditions and ramipril- and losartan-induced increases in renin mRNA levels were completely blunted after addition of L-NAME. The AngII antagonists, furthermore, induced an upstream recruitment of renin-expressing cells in the renal afferent arterioles, which was also blunted by L-NAME. These findings suggest that renin mRNA levels are tonically increased by NO and that the action of NO is counteracted by AngII.

Synergy between T-cell immunity and inhibition of paracrine stimulation causes tumor rejection.

During tumor progression, variants may arise that grow more vigorously. The fate of such variants depends upon the balance between aggressiveness of the variant and the strength of the host immunity. Although enhancing host immunity to cancer is a logical objective, eliminating host factors necessary for aggressive growth of the variant should also be considered. The present study illustrates this concept in the model of a spontaneously occurring, progressively growing variant of an ultraviolet light-induced tumor. The variant produces chemotactic factors that attract host leukocytes and is stimulated in vitro by defined growth factors that can be produced or induced by leukocytes. This study also shows that CD8+ T-cell immunity reduces the rate of tumor growth; however, the variant continues to grow and kills the host. Treatment with a monoclonal anti-granulocyte antibody that counteracts the infiltration of the tumor cell inoculum by non-T-cell leukocytes did not interfere with the CD8+ T-cell-mediated immune response but resulted in rejection of the tumor challenge, indicating a synergy between CD8+ T-cell-mediated immunity and the inhibition of paracrine stimulation.

Stimulation of human monocytes with macrophage colony-stimulating factor induces a Grb2-mediated association of the focal adhesion kinase pp125FAK and dynamin.

Macrophage colony-stimulating factor (M-CSF) is required for the growth and differentiation of mononuclear phagocytes. In the present studies using human monocytes, we show that M-CSF induces interaction of the Grb2 adaptor protein with the focal adhesion kinase pp125FAK. The results demonstrate that tyrosine-phosphorylated pp125FAK directly interacts with the SH2 domain of Grb2. The findings indicate that a pYENV site at Tyr-925 in pp125FAK is responsible for this interaction. We also demonstrate that the Grb2-FAK complex associates with the GTPase dynamin. Dynamin interacts with the SH3 domains of Grb2 and exhibits M-CSF-dependent tyrosine phosphorylation in association with pp125FAK. These findings suggest that M-CSF-induced signaling involves independent Grb2-mediated pathways, one leading to Ras activation and another involving pp125FAK and a GTPase implicated in receptor internalization.

Towards Closed-loop Deep Brain Stimulation: Behavior Recognition from Human STN

Deep brain stimulation (DBS) provides significant therapeutic benefit for movement disorders such as Parkinson’s disease (PD). Current DBS devices lack real-time feedback (thus are open loop) and stimulation parameters are adjusted during scheduled visits with a clinician. A closed-loop DBS system may reduce power consumption and side effects by adjusting stimulation parameters based on patient’s behavior. Thus behavior detection is a major step in designing such systems. Various physiological signals can be used to recognize the behaviors. Subthalamic Nucleus (STN) Local field Potential (LFP) is a great candidate signal for the neural feedback, because it can be recorded from the stimulation lead and does not require additional sensors. This thesis proposes novel detection and classification techniques for behavior recognition based on deep brain LFP. Behavior detection from such signals is the vital step in developing the next generation of closed-loop DBS devices. LFP recordings from 13 subjects are utilized in this study to design and evaluate our method. Recordings were performed during the surgery and the subjects were asked to perform various behavioral tasks. Various techniques are used understand how the behaviors modulate the STN. One method studies the time-frequency patterns in the STN LFP during the tasks. Another method measures the temporal inter-hemispheric connectivity of the STN as well as the connectivity between STN and Pre-frontal Cortex (PFC). Experimental results demonstrate that different behaviors create different m odulation patterns in STN and it’s connectivity. We use these patterns as features to classify behaviors. A method for single trial recognition of the patient’s current task is proposed. This method uses wavelet coefficients as features and support vector machine (SVM) as the classifier for recognition of a selection of behaviors: speech, motor, and random. The proposed method is 82.4% accurate for the binary classification and 73.2% for classifying three tasks. As the next step, a practical behavior detection method which asynchronously detects behaviors is proposed. This method does not use any priori knowledge of behavior onsets and is capable of asynchronously detect the finger movements of PD patients. Our study indicates that there is a motor-modulated inter-hemispheric connectivity between LFP signals recorded bilaterally from STN. We utilize a non-linear regression method to measure this inter-hemispheric connectivity and to detect the finger movements. Our experimental results using STN LFP recorded from eight patients with PD demonstrate this is a promising approach for behavior detection and developing novel closed-loop DBS systems.

Effets de la stimulation magnétique transcrânienne dans la maladie de Parkinson avec déficits cognitifs légers

Beaucoup de patients atteints de la maladie de Parkinson (MP) peuvent souffrir de troubles cognitifs dès les étapes initiales de la maladie et jusqu’à 80% d’entre eux vont développer une démence. Des altérations fonctionnelles au niveau du cortex préfrontal dorsolatéral (CPFDL), possiblement en relation avec le noyau caudé, seraient à l’origine de certains de ces déficits cognitifs. Des résultats antérieurs de notre groupe ont montré une augmentation de l’activité et de la connectivité dans la boucle cortico-striatale cognitive suite à la stimulation magnétique transcrânienne (SMT) utilisant des paramètres « theta burst » intermittent (iTBS) sur le CPFDL gauche. Pour cette étude, 24 patients atteints de la MP avec des troubles cognitifs ont été séparées en 2 groupes : le groupe iTBS active (N=15) et le groupe sham (stimulation simulée, N=9). Une batterie neuropsychologique détaillée évaluant cinq domaines cognitifs (attention, fonctions exécutives, langage, mémoire et habiletés visuo-spatiales) a été administrée lors des jours 1, 8, 17 et 37. Le protocole iTBS a été appliqué sur le CPFDL gauche durant les jours 2, 4 et 7. Les scores z ont été calculés pour chaque domaine cognitif et pour la cognition globale. Les résultats ont montré une augmentation significative de la cognition globale jusqu’à 10 jours suivant l’iTBS active, particulièrement au niveau de l’attention, des fonctions exécutives et des habiletés visuo-spatiales. Cet effet sur la cognition globale n’est pas répliqué dans le groupe sham. Ces résultats suggèrent donc que l’iTBS peut moduler la performance cognitive chez les patients atteints de MP avec des déficits cognitifs.

Stimulation /

Mode of access: Internet.

Electronic Combat Stimulation Branch : Atlantic Ranges and Facilities, Naval Air Warfare Center Aircraft Division, Patuxent River, Maryland.

Mode of access: Internet.

Cumulative auditory effects resulting from multiple exposure to intense acoustic stimulation.

Pt. 1. Deafening effects of noise on the cat -- Pt. 2. Histological effects of intense sound on the inner ear.