Worm Breeder's Gazette 9(2): 53

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.

Immunocytochemical and Autoradiographic Studies of Putative Gabanergic Neurons in Ascaris

J. Guastella, C.D. Johnson, and A.O.W. Stretton

Previous studies reported from this laboratory, using a wholemount 
immunocytochemical technique, indicate that a physiologically 
identified set of inhibitory motorneurons in Ascaris (the ventral and 
dorsal inhibitors) stain intensely with an antiserum prepared against 
the neurotransmitter gamma-aminobutyric acid (GABA) (WBG, vol.  8(2), 
p.  33).  We have also observed staining of four neurons located at 
the anterior margin of the nerve ring which are probably analogous to 
the RME neurons (V,D,L,R) in C.  elegans  as well as staining in a 
variable number of other neurons in the head.  We are now extending 
these immunocytochemical studies to sectioned material which, together 
with an analysis of H-GABA uptake, gives us a more complete view of 
GABA-related mechanisms in Ascaris.Staining of nerve cord sections 
with the GABA antiserum reveals a cluster of immunoreactive neuronal 
profiles in both the ventral and dorsal cords.  The position of these 
neurites within the cords strongly suggests that they represent the 
processes of the inhibitory motorneurons.  Staining of profiles on the 
side of the cord containing the excitatory motorneurons is not seen.  
In addition, none of the ventral cord interneurons stain with this 
antiserum, indicating that, if there are inhibitory interneurons in 
the ventral cord, they are probably not GABAnergic.  A single stained 
profile, located just below the excitatory cluster, is seen in the 
ventral cord, and a single stained profile, located at the base of the 
dorsal cord, are also observed.  Based on comparisons between 
sectioned material and wholemounts, we believe that these profiles 
represent the ventral and dorsal processes of RMEV and RMED, 
As autoradiographic analysis of specimens incubated with 0.5uM H-
GABA shows that several neurons in the head are labeled, among them 
the RME cells, suggesting that these neurons possess an active uptake 
mechanism for this neurotransmitter.  In the ventral and dorsal nerve 
cords, single processes, whose position and morphology suggest that 
they are the nerve cord processes of RMEV and RMED, are also labeled.  
However, the inhibitory motorneurons, which stain so intensely with 
the GABA antiserum, are not labeled with H-GABA.  Heavy labeling of 
muscle (both cephalic and somatic) is also seen, but the functional 
significance of this is unknown.
Thus, there appear to be at least two classes of nematode neurons 
with GABA-related markers: one class, which possesses a GABA-like 
immunoreactive substance as well as an uptake system for GABA (e.g., 
the RME cells); and a second class which possesses a GABA-like 
immunoreactive substance, but which lacks an uptake system for GABA (e.
g., the inhibitory motorneurons).  It is interesting to note that GABA 
uptake, a marker traditionally used by mammalian neuroanatomists to 
visualize neurons thought to use GABA as a neurotransmitter, does not 
result in the labeling of a class of physiologically identified 
inhibitory neurons in the nematode.