Summary
Injection of picrotoxin solutions into the pericardium of lobsters,Homarus americanus, to produce final, estimated blood concentrations of between 8×10−8M and 4.5×10−6M led to disruption of the normal motor output to the scaphognathite. The phase separation of the starts of the bursts in the D1 and D2 muscles (Young, 1975) was reduced on the average by 49%; that of L1 and L2 muscles by 16%. The durations of the D1 and L1 bursts increased by 94% and 48% respectively. The phase separation between the starts of the levator and depressor portions of the cycle was not altered. Whilst rhythmic activity persisted ventilatory rates were depressed, and reversals and ventilatory pauses continued to occur. The rate of reversals and their pattern were not greatly altered. Inexplicably, tonic, synchronous spikes occurred in all four groups of muscles, levator and depressor, during periods of severe disruption. It was concluded that in spite of this, the observations supported the proposals of Young (1975) that (a) recruitment of the D2 and L2 bursts normally is delayed partly by inhibition from D1 and L1 units respectively, and (b) termination of D1 and L1 bursts results normally from inhibition due to activity in D2 and L2 units respectively. The findings also indicated that the synaptic mechanism determining timing within the depressor and levator sessions differs fundamentally from that operating between sessions. One mechanism may be based on picrotoxin-sensitive, and the other on picrotoxin-insensitive inhibition.
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Abbreviations
- GABA :
-
gamma-aminobutyric acid
- SG :
-
scaphognathite
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Young, R.E., Wilkens, J.L. & Dodd, C. Pharmacological dissection of a neural pattern generator. J. Comp. Physiol. 139, 1–10 (1980). https://doi.org/10.1007/BF00666189
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DOI: https://doi.org/10.1007/BF00666189