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Cen­tre de Neu­ro­physique, Phys­i­olo­gie et Patholo­gie — CNRS UMR 8119
Uni­ver­sité Paris Descartes
45 Rue des Saints Pères
75270 Paris Cedex 06
France

Fax : +33 (0) 1 42 86 20 80

Dr. Daniel ZYTNICKI

Research direc­tor, DR-CNRS
Spinal phys­i­ol­o­gy and patho­phys­i­ol­o­gy

daniel.zytnicki@-Code to remove to avoid SPAM-parisdescartes.fr
+33 1 42 86 22 85, room H345A

In the past years we studied :

The presynaptic inhibition of Ib afferents from tendon organs during contraction

We demon­strat­ed that dur­ing con­trac­tion of ankle exten­sors the dif­fer­ent neu­ronal tar­gets of Ib affer­ents do not get the same infor­ma­tion : for some tar­gets the mes­sage is fil­tered out by presy­nap­tic inhi­bi­tion (Zyt­nic­ki et al. 1990) where­as oth­er tar­gets receive an unfil­tered infor­ma­tion (Zyt­nic­ki et al. 1995). Numer­ous axo-axon­ic con­tacts (the mor­pho­log­i­cal sub­strate of presy­nap­tic inhi­bi­tion) impinge on Ib col­lat­er­als, main­ly on the ter­mi­nal branch­es (Lam­otte d’Incamps et al. 1998a). Some of them are active dur­ing con­trac­tion as indi­cat­ed by intra-axon­al record­ings of pri­ma­ry affer­ent depo­lar­iza­tions (PADs) (Lafleur et al. 1992). Numer­i­cal sim­u­la­tions of a com­part­men­tal mod­el of Ib col­lat­er­al sug­gest that PAD is like­ly to be by itself respon­si­ble for presy­nap­tic inhi­bi­tion (Lam­otte d’Incamps et al. 1998b). The elec­tro­ton­ic struc­ture of Ib col­lat­er­als and the dis­tri­b­u­tion of axo-axon­ic con­tacts on ter­mi­nal branch­es account for the spa­tial pro­cess­ing of Ib infor­ma­tion by presy­nap­tic inhi­bi­tion (Lam­otte d’Incamps et al. 1999).

Meth­ods : in vivo intra­cel­lu­lar record­ings of lum­bar motoneu­rons and neu­rons of the dor­sal spino-cere­bel­lar tract dur­ing mus­cle con­trac­tion, intra-axon­al record­ing dur­ing con­trac­tion of iden­ti­fied Ib affer­ent, intra-axon­al labelling of Ib affer­ent, immuno­his­to­chem­istry, con­fo­cal microscopy, com­part­men­tal mod­el­ing of myeli­nat­ed fiber

The positive feedback elicited on homonymous motoneurons by proprioceptive input during contraction

We demon­strat­ed that pro­pri­o­cep­tive inputs elicit­ed by iso­met­ric con­trac­tions of pretib­ial flex­ors induce exci­ta­to­ry poten­tials (pos­i­tive feed­back) in homony­mous motoneu­rons. This pos­i­tive feed­back is due to the pas­sive mechan­i­cal acti­va­tion of spin­dle pri­ma­ry end­ings and to the lack of Ib inhi­bi­tion (Brizzi et al. 2002). Con­trac­tion of Per­oneus bre­vis elic­its a sim­i­lar feed­back in per­oneal motoneu­rons (Kouchtir et al. 1995). In that case spin­dle acti­va­tion is facil­i­tat­ed by the action of squelet­to-fusimo­tor axons. Mechan­i­cal acti­va­tion of foot cuta­neous recep­tors has com­plex actions on per­oneal motoneu­rons (Per­ri­er et al. 2000a) and can con­trol the effi­ca­cy of the con­trac­tion-induced pos­i­tive feed­back (Per­ri­er et al. 2000b).

Meth­ods : in vivo intra­cel­lu­lar record­ings of motoneu­rons

Recent work using the dynamic clamp method in vivo :

Increas­ing by 50 to 100% the input con­duc­tance of a lum­bar motoneu­ron does not change the slope of the cur­rent — fre­quen­cy rela­tion­ship (I-f curve). Shunt­ing inhi­bi­tion shifts the I-f curve as would a hyper­po­lar­iz­ing cur­rent. The shift is pro­por­tion­al to the con­duc­tance added at the soma with the dynam­ic clamp and depends on an intrin­sic prop­er­ty of the motoneu­ron, its shunt poten­tial. This quan­ti­ty indi­cates how sen­si­tive is the motoneu­ron to shunt­ing inhi­bi­tion (Brizzi et al. sub­mit­ted).

Publications de Daniel Zytnicki