Worm Breeder's Gazette 11(1): 62

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Functions of the GREENs: Slippery Pharynxes and Serotonin

Leon Avery

In my initial survey of the pharyngeal neurons, I classified them 
into three groups: M4, MC, and the 12 remaining anatomical types of 
pharyngeal neurons, which I call the GREENs.  None of the individual 
GREEN neuron types is necessary for superficially normal pumping, but 
when all 12 are killed, pumping becomes very abnormal.  I have 
recently made some progress in figuring out what they are doing.  
During normal pumping, bacteria move posterior in the pharynx when 
the muscles contract, and are held where they are when the muscles 
relax again, so that they are efficiently transported towards the 
intestine.  When all the GREENs were killed, the pharynx appeared to 
become slippery: bacteria slid anterior as well as posterior.  When 
bacteria were abundant, the lumen of a GREEN pharynx became distended 
with them, and they were ground up and passed to the intestine only 
slowly.  Seymour et al (J Zool 201: 527) showed by microcinematography 
that in normal pumping the contraction and relaxation of the corpus 
muscles are not precisely simultaneous along its length: both begin at 
the front.  They proposed this has a function in trapping bacteria in 
the pharynx.  I suspect that in the absence of the GREENs this fine 
timing goes awry, and as a result bacteria are not held back by the 
relaxing pharyngeal muscles.  
The GREEN neuron I understand best at present is M3.  When M3 was 
killed, there was a subtle abnormality in pumping: the contractions 
lasted longer.  Conversely, when all the GREENs except M3 were killed, 
contractions were very brief.  Thus M3 hastens pharyngeal muscle 
relaxation during a pump, and is opposed by some other(s) of the 
GREENs.  I5 is probably (one of) the GREEN(s) that opposes M3, since 
pumps became briefer when I5 alone was killed.  When both M3 and I5 
were killed, pumps were long, just as when M3 alone was killed, 
suggesting I5 may exert its effects on pump length via M3.  In fact, 
I5 does synapse on M3.  There was also a new effect when both M3 and 
I5 were killed: the isthmus became slippery.  The timing of anterior 
isthmus contraction was abnormal in M3-I5 worms: it contracted just 
after the corpus contraction, instead of simultaneously with it, and 
remained contracted longer.  
M3 is also important for corpus function.  In fact, when all the 
GREENs except M3 were killed, the corpus was not slippery.  Other 
GREENs important for normal corpus function are I2, I6, M1, and 
possibly I4.  M5 may also be important for isthmus function.  However, 
I have not worked out the details for any of these.  
I have also learned something about GREEN function in a completely 
different way.  I discovered previously that imipramine stimulates 
pumping in wild-type worms, but not in mutants that have reduced 
levels of serotonin (WBG 10(2): 39).  The only serotonergic neuron in 
the pharynx is NSM, and the only pharyngeal neurons connected to the 
extrapharyngeal nervous system are I1 and M1.  I therefore killed NSM, 
I1, and M1, thinking to remove any serotonin from the pharynx, and to 
sever its communication with extrapharyngeal serotonergic neurons that 
might be stimulating pumping.  Sure enough, imipramine did not 
stimulate pumping in I1- M1- NSM- worms.  I have not yet tested 
whether it is necessary to kill all three to get the effect.