Biology Reference
In-Depth Information
The extensive colocalization of NOS and GAL in the floor suggests that both
neurochemical markers can act as inhibitory neuromodulators/neurotransmitters.
The inhibitory role of NO on the muscle cells of the RG of bovines has been clearly
demonstrated by Barahona et al. (
1998
) and may be supported by the lack of SP
coexpression in nitrergic neurons in the present study. In fact, analogous to what has
been observed in the GITs of many other mammals, it is plausible to hypothesize
that SP has an excitatory role; furthermore, both acetylcholine and SP evoke
contractions of isolated ruminal smooth muscle (Vassileva et al.
1978
). The excit-
atory effect of SP has also been hypothesized by Pfannkuche et al. (
2003
) who
found extensive colocalization of SP and acetylcholine in the RG of sheep, and
whose contractile effects on the reticulum have been reported by Wong and
McLeay (
1988
). In the present study, we rarely found neurons expressing CALB,
CGRP, or IB4. Consequently, we can hypothesize that the sensory fibers of the RG
may have an extrinsic origin coming from the spinal ganglia, in which both CGRP
and NF neurons have been shown to project into the sheep duodenum and ileum
(Mazzoni et al.
2010
) or from the distal vagal ganglia or from primary sensory
neurons located in other districts of the FS. Alternatively, it is tempting to speculate
that, in the RG, intrinsic primary neurons, through which the enteric reflex is
initiated, express unknown specific neurotransmitters, different from what has
been observed in other regions of the same species.
References
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€
