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. 1992 Oct;107(2):628–633. doi: 10.1111/j.1476-5381.1992.tb12794.x

The effect of centrally acting myorelaxants on NMDA receptor-mediated synaptic transmission in the immature rat spinal cord in vitro.

R J Siarey 1, S K Long 1, R H Evans 1
PMCID: PMC1907866  PMID: 1330190

Abstract

1. The effect of the myorelaxant drugs baclofen, diazepam and tizanidine have been compared on in vitro preparations of baby rat spinal cord and adult rat superior cervical ganglion. 2. Dorsal root-elicited long duration (time to half decay 9.71 +/- 0.29 s.e. mean, n = 31) ipsilateral ventral root reflexes (DR-VRP), measured as integrated area, of immature rat spinal cord preparations were abolished by RS-2-amino-5-phosphonopentanoate (AP5) (EC50 8.13 +/- 0.92 microM, n = 3). The initial short latency component of DR-VRP was resistant to AP5. 3. Baclofen abolished both components of the DR-VRP. Respective EC50 values for the AP5-insensitive and AP5-sensitive components were 237 +/- 68 nM (n +/- 7) and 57 +/- 10 nM (n = 7). These effects of baclofen were reversed by the GABAB antagonist, CGP35348. The apparent Kd values (16.7 +/- 6.4 microM, n = 3 and 14.3 +/- 3.9 microM, n = 6 respectively) for this reversal were not significantly different. 4. Tizanidine, clonidine and diazepam had no effect on the AP5-insensitive component of the DR-VRP. 5. The AP5-sensitive long duration component of the DR-VRP was depressed to respective maximal levels of 23.2 +/- 1.4% (n = 7), 18.8 +/- 3.8% (n = 4) and 47.6 +/- 1.6% (n = 5) of control (100%) levels by tizanidine (EC50 135 +/- 33 nM), clonidine (EC50 26.0 +/- 2.2 nM) and diazepam (EC25 114 +/- 12 nM, n = 4). The depressant effects of tizanidine and clonidine were reversed by idazoxan (1 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

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Selected References

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