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Molecular mechanisms of dendritic spine development and maintenance

100%

Sala C., Cambianica I., Rossi F.

Acta Neurobiologiae Experimentalis

2008

vol. 68

issue 2

289-304

The large majority of excitatory synapses are located on dendritic spines which are discrete membrane protrusions present on neuronal dendrites. Interestingly the highly heterogeneous morphology of dendritic spines is thought to be the morphological basis for synaptic plasticity associated to learning and memory formation. Indeed dendritic spines structure is regulated by molecular mechanisms that are fine tuned and adjusted according to level and direction of synaptic activity, development, specific brain region, and different experimental behavioral conditions. This supports the idea that reciprocal changes between the structure and function of spines impact both local and global integration of signals within dendrites. An increasing number of proteins have been found to be morphogens for dendritic spines and provided new insights into the molecular mechanisms regulating spine formation and morphology. Thus determining the mechanisms that regulate spine formation and morphology is essential for understanding the cellular changes that underlie learning and memory in normal and pathological conditions.

Changes of motor unit contractile output during repeated activity

88%

Lochynski D., Celichowski J., Korman P., Raglewska P.

Acta Neurobiologiae Experimentalis

2007

vol. 67

issue 1

23-33

The aim of the study was to evaluate changes in the motor unit output and to determine changes in the optimal stimulation frequency (i.e., giving the maximal output per one pulse) during prolonged contractile activity when, successively, potentiation of force and fatigue developed. The influence of these phenomena was studied on three types of motor units: fast fatigable (FF), fast resistant (FR) and slow (S) in the rat medial gastrocnemius muscle. The motor units were isolated by a method of splitting of L5 ventral root into very thin bundles of axons which were electrically stimulated 10 times with repeated series of 10 trains of stimuli at duration of 500 ms and progressively increasing (1?150 Hz) frequency. The initial (the first series of stimulating trains), potentiated (the second series), as well as fatigued (the tenths series) force recordings were compared. The motor unit output was expressed as the area under the force-time record in response to one stimulus measured at a plateau phase of the tetanic force. The stimulation frequency when the force-time area per one pulse was maximal was accepted as the optimal frequency. In fast motor units, the maximal contractile output increased with potentiation and was reduced with fatigue, and the optimal frequency decreased and increased, respectively. Nevertheless, the fusion degrees of the optimal tetanic contractions were similar in initial state, potentiation and fatigue independently of the changes in force. The applied stimulation protocol had almost no influence on the mechanical activity of slow motor units. The study highlights the physiological importance of force potentiation induced by preceding contractile activity for the economy of motor performance. The observed changes of the optimal stimulation frequency are consistent with the known changes in the motor unit firing rates during voluntary activity when the two phenomena develop.

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2 Acta Neurobiologiae Experimentalis

1 2008

1 2007

1 Cambianica I.

1 Celichowski J.

1 Korman P.

1 Lochynski D.

1 Raglewska P.

1 Rossi F.

1 Sala C.

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Molecular mechanisms of dendritic spine development and maintenance

Changes of motor unit contractile output during repeated activity