1. The effects of blocking gamma-aminobutyric acid- and glycine-mediated synaptic transmission by bicuculline and strychnine on the neonatal rat isolated spinal cord were investigated by intracellular recording from motoneurons with the use of current-clamp and voltage-clamp techniques and by extracellular recording from homologous ventral roots of the L5 segment. 2. Bicuculline per se evoked irregular bursts of motoneuron membrane potential, often comprising individual events fused together. Strychnine alone did not elicit spontaneous bursting in the large majority of preparations. Simultaneous application of bicuculline and strychnine consistently induced regular rhythmic bursts (frequency approximately 2 per min, duration approximately 7 s), comprising a rapid depolarization followed by large-amplitude oscillations. 3. Burst frequency, duration, and intraburst oscillation time course were independent of motoneuron membrane potential. Burst and oscillation amplitude decreased with membrane depolarization and, under voltage-clamp conditions, inverted polarity near 0 mV. 4. The regular bursts produced by bicuculline and strychnine were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione, tetrodotoxin, or Cd2+. 5. N-methyl-D-aspartate antagonists [R-5-aminophosphonovalerate or 3-((RS)-2-carboxypiperazine-4-yl)-propyl-1-phosphonate (CPP)] reversibly blocked or slowed down bursting induced by bicuculline and strychnine. Addition of cyclothiazide to the bicuculline and strychnine solution increased bursting frequency while preserving the regular burst structure; under these conditions bursts became insensitive to CPP. 6. In the presence of bicuculline and strychnine, 5-hydroxytryptamine (5-HT) increased burst frequency and decreased burst duration in a dose-dependent fashion. 7. In the presence of bicuculline and strychnine, L5 ventral roots developed synchronous rhythmic activity with a time course similar to that recorded from individual motoneurons. The rhythmic activity was accelerated by 5-HT on both roots, in accordance with observations on single motoneurons. 8. Rhythmic bursts thus appear to result from large, synchronous synaptic events generated by a network modulated by 5-HT and highly sensitive to variations in efficacy of glutamatergic synaptic transmission. These results show that in the rat spinal cord highly patterned motor output can occur despite block of inhibition.

Spontaneous rhythmic bursts induced by pharmacological block of inhibition in lumbar motoneurons of the neonatal rat spinal cord / Bracci, E.; Ballerini, L.; Nistri, A.. - In: JOURNAL OF NEUROPHYSIOLOGY. - ISSN 0022-3077. - 75:2(1996), pp. 640-647. [10.1152/jn.1996.75.2.640]

Spontaneous rhythmic bursts induced by pharmacological block of inhibition in lumbar motoneurons of the neonatal rat spinal cord.

Ballerini, L.;Nistri, A.
1996

Abstract

1. The effects of blocking gamma-aminobutyric acid- and glycine-mediated synaptic transmission by bicuculline and strychnine on the neonatal rat isolated spinal cord were investigated by intracellular recording from motoneurons with the use of current-clamp and voltage-clamp techniques and by extracellular recording from homologous ventral roots of the L5 segment. 2. Bicuculline per se evoked irregular bursts of motoneuron membrane potential, often comprising individual events fused together. Strychnine alone did not elicit spontaneous bursting in the large majority of preparations. Simultaneous application of bicuculline and strychnine consistently induced regular rhythmic bursts (frequency approximately 2 per min, duration approximately 7 s), comprising a rapid depolarization followed by large-amplitude oscillations. 3. Burst frequency, duration, and intraburst oscillation time course were independent of motoneuron membrane potential. Burst and oscillation amplitude decreased with membrane depolarization and, under voltage-clamp conditions, inverted polarity near 0 mV. 4. The regular bursts produced by bicuculline and strychnine were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione, tetrodotoxin, or Cd2+. 5. N-methyl-D-aspartate antagonists [R-5-aminophosphonovalerate or 3-((RS)-2-carboxypiperazine-4-yl)-propyl-1-phosphonate (CPP)] reversibly blocked or slowed down bursting induced by bicuculline and strychnine. Addition of cyclothiazide to the bicuculline and strychnine solution increased bursting frequency while preserving the regular burst structure; under these conditions bursts became insensitive to CPP. 6. In the presence of bicuculline and strychnine, 5-hydroxytryptamine (5-HT) increased burst frequency and decreased burst duration in a dose-dependent fashion. 7. In the presence of bicuculline and strychnine, L5 ventral roots developed synchronous rhythmic activity with a time course similar to that recorded from individual motoneurons. The rhythmic activity was accelerated by 5-HT on both roots, in accordance with observations on single motoneurons. 8. Rhythmic bursts thus appear to result from large, synchronous synaptic events generated by a network modulated by 5-HT and highly sensitive to variations in efficacy of glutamatergic synaptic transmission. These results show that in the rat spinal cord highly patterned motor output can occur despite block of inhibition.
75
2
640
647
Bracci, E.; Ballerini, L.; Nistri, A.
File in questo prodotto:
File Dimensione Formato  
1996_J Neurophysiol.pdf

non disponibili

Tipologia: Versione Editoriale (PDF)
Licenza: Non specificato
Dimensione 2.03 MB
Formato Adobe PDF
2.03 MB Adobe PDF   Visualizza/Apri   Richiedi una copia

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/20.500.11767/13927
Citazioni
  • ???jsp.display-item.citation.pmc??? 31
  • Scopus 132
  • ???jsp.display-item.citation.isi??? 127
social impact