Projections and neurochemical coding of motor neurones to the circular andlongitudinal muscle of the guinea pig gastric corpus

The present study identified projection and neurochemical coding patterns o f intrinsic circular (CMN) and longitudinal muscle motor neurones (LMN) in the guinea pig stomach by using the retrograde tracer DiI (1,1'-didodecyl-3 ,3,3',3'-tetramethylindocarbocya nine perchlorate) in combination with the immunohistochemical demonstration of choline acetyltransferase (ChAT), enke phalin (ENK), neuropeptide Y (NPY), nitric oxide synthase (NOS) and substan ce P (SP). Populations of LMN and CMN had similar neurochemical coding and a clear polarity of projection. Taking all DiI-labeled cell bodies as 100%, ascending pathways exhibited the coding ChAT/- (CMN:14.7%/LMN:18.3%), ChAT /ENK (15.7%/10.1%), ChAT/SP/+/-ENK (19.2%/16.4%), or ChAT/NPY (4.4%/7.6%); descending pathways had the coding NOS/- (13.8%/16.9%), NOS/NPY (9.9%/17%), NOS/ENK (4.4%/1.2%) or NOS/NPY/ENK (13.0%/5.5%). The relative contribution s of these populations were not different between CMN and LMN. However, tar get-specific projection patterns were revealed: most LMN (82%) had longitud inal whereas most CMN (58%) had circumferential projection preferences. The results indicate that gastric circular and longitudinal muscle layers are innervated by ascending excitatory and descending inhibitory pathways in th e myenteric plexus. The projection patterns of CMN and LMN were different a nd followed the orientation of the muscle layers. It is suggested that the specific muscle motor pathways in the gastric myenteric plexus coordinate t he reflex-mediated phasic and tonic activity of gastric muscle layers.