title: Postnatal maturation of the gastrointestinal tract: a functional and immunohistochemical study in the guinea-pig ileum at weaning.
abstract: Gastrointestinal motility is mainly controlled by the myenteric plexus. The longitudinal muscle-myenteric plexus (LMMP) preparation from the guinea-pig ileum is the best characterised adult gastrointestinal preparation; it has also been studied in old and neonatal animals, but not at weaning, when milk is substituted with the food typical of adult animals. We used LMMP preparations from weanling and adult guinea-pigs to study different functional parameters and immunohistochemically identified subpopulations of myenteric neurones, including the excitatory motor neurones to the longitudinal muscle (LM-EMN). Excitatory stimuli (low-frequency electrical stimulation, acetylcholine, substance P, and naloxone in morphine-tolerant preparations) produced similar responses in weanling and adult guinea-pigs. The endogenous cannabinoid anandamide, but not the synthetic cannabinoid agonist WIN 55,212-2 or the opioid morphine, inhibited the electrically stimulated twitches less efficaciously, and in vitro tolerance to morphine was also lower in weanling compared to adult animals. The packing densities of the calbindin-immunoreactive neurones (sensory neurones) and of neurones immunoreactive to both calretinin (CR) and neurofilament triplet protein (NFT; ascending interneurones) were slightly but significantly lower in weanling animals, whereas those of the neurones immunoreactive to CR but not NFT (LM-EMN) or immunoreactive to nitric oxide synthase (mainly inhibitory motor neurones) were comparable to the adult. Although guinea-pigs are relatively mature and can even ingest solid food at birth, their myenteric plexus is still not fully mature at the standard time of weaning. The nutritional, behavioural and environmental changes associated with weaning may be essential to attain full maturation of the myenteric plexus and gastrointestinal motility.
authors.affiliation: Departamento de Farmacología y Nutrición, Facultad de Ciencias de la Salud, Universidad Rey Juan Carlos, Spain. raquel.abalo@urjc.es
authors.forename: Raquel
authors.initials: R
authors.lastname: Abalo
authors.forename: Gema
authors.initials: G
authors.lastname: Vera
authors.forename: Antonio José
authors.initials: AJ
authors.lastname: Rivera
authors.forename: Ernesto
authors.initials: E
authors.lastname: Moro-Rodríguez
authors.forename: María Isabel
authors.initials: MI
authors.lastname: Martín-Fontelles
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology; D048588:Benzoxazines / Q000494:pharmacology; D064032:Calbindin 2; D064026:Calbindins; D018679:Cholinergic Agonists / Q000494:pharmacology; D004558:Electric Stimulation; D063388:Endocannabinoids; D005260:Female; D006168:Guinea Pigs; D007082:Ileum / Q000254:growth & development* / Q000294:innervation / Q000502:physiology; D007150:Immunohistochemistry; D009020:Morphine / Q000494:pharmacology; D009025:Morpholines / Q000494:pharmacology; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000294:innervation / Q000502:physiology; D009197:Myenteric Plexus / Q000187:drug effects / Q000254:growth & development* / Q000502:physiology; D009270:Naloxone / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D016900:Neurofilament Proteins / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D053284:Polyunsaturated Alkamides / Q000494:pharmacology; D043884:Receptor, Cannabinoid, CB1 / Q000819:agonists; D011957:Receptors, Opioid / Q000819:agonists; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D013373:Substance P / Q000494:pharmacology; D014886:Weaning
chemical_list: D001095:Arachidonic Acids; D048588:Benzoxazines; D064032:Calbindin 2; D064026:Calbindins; D018679:Cholinergic Agonists; D063388:Endocannabinoids; D009025:Morpholines; D009281:Naphthalenes; D009292:Narcotic Antagonists; D016900:Neurofilament Proteins; D053284:Polyunsaturated Alkamides; D043884:Receptor, Cannabinoid, CB1; D011957:Receptors, Opioid; D064030:S100 Calcium Binding Protein G; D013373:Substance P; D009270:Naloxone; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; D009020:Morphine; D000109:Acetylcholine; C078814:anandamide