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Abstract
Alternative nutrient sources to fishmeal for fish feed, such as insect meals, represent a promising sustainable supply. However, the consequences for fish digestive function have not been exhaustively investigated. In the present study we evaluated the effect of partial fishmeal substitution with 10% Hermetia illucens (Hi10) larvae meal on the neuromuscular function of proximal and distal intestine in gilthead sea bream. In animals fed with insect meal, weight and growth parameters were similar to controls fed with conventional fishmeal. In addition, no anomalies in intestinal gross morphology and no overt signs of inflammation were observed. The gastrointestinal transit was significantly reduced in Hi10 fed animals. In the proximal and distal intestine longitudinal muscle, Hi10 feeding downregulated the excitatory cholinergic and serotoninergic transmission. Sodium nitroprusside-induced inhibitory relaxations increased in the proximal intestine and decreased in the distal intestine after Hi10 meal. Changes in the excitatory and inhibitory components of peristalsis were associated with adaptive changes in the chemical coding of both proximal and distal intestine myenteric plexus. However, these neuromuscular function alterations were not associated with considerable variations in morphometric growth parameters, suggesting that 10% Hi meal may represent a tolerable alternative protein source for gilthead sea bream diets.
Highlights
Abbreviations H&E Hematoxylin-eosin LMMP Longitudinal muscle myenteric plexus neuronal nitric oxide synthases (nNOS) Neuronal nitric oxide synthases 5-HT Serotonin ChAT Cholineacetyltransferase substance P (SP) Substance P geometric center (GC) Geometric center CCh Carbachol EFS Electric field stimulation TTX Tetrodotoxin nonadrenergic non-cholinergic (NANC) Non-adrenergic non-cholinergic NO Nitric oxide sodium nitroprusside (SNP) Sodium nitroprusside enteric nervous system (ENS) Enteric nervous system ACh Acetylcholine FCR Food conversion ratio SGR Specific growth rate
In particular we could demonstrate the presence of the most important enteric neurotransmitters such as acetylcholine (ACh), substance P (SP), serotonin (5HT) and nitric oxide (NO) in different myenteric neuron populations, which showed the morphological characteristics of excitatory and inhibitory motor neurons, ascending and descending interneurons and primary sensory neurons involved in the peristaltic reflex[6,8]
Upon gross visual inspection of gilthead sea bream, no major differences in the proximal and distal intestine obtained from control fishmeal-fed fish (CTRL) and fish fed with the Hermetia illucens 10% meal (Hi10) were observed between the two experimental groups
Summary
Abbreviations H&E Hematoxylin-eosin LMMP Longitudinal muscle myenteric plexus nNOS Neuronal nitric oxide synthases 5-HT Serotonin ChAT Cholineacetyltransferase SP Substance P GC Geometric center CCh Carbachol EFS Electric field stimulation TTX Tetrodotoxin NANC Non-adrenergic non-cholinergic NO Nitric oxide SNP Sodium nitroprusside ENS Enteric nervous system ACh Acetylcholine FCR Food conversion ratio SGR Specific growth rate. Since changes in nutrient composition in the intestinal lumen may induce both short- and long-term changes in myenteric neurotransmitter expression, excitability, and viability, impacting gastrointestinal transit[10,11], we aimed in this study to investigate possible adaptive changes in the neuromuscular component of the proximal and distal intestine of gilthead sea bream fed either with control fishmeal diet or with a diet containing 10% of Hermetia illucens larva meal To this end, we evaluated the excitatory and inhibitory responses of the longitudinal muscle by means of in vitro organ bath assays. We evaluated whether substituting conventional normal fishmeal with insect meal could modify the distribution and abundance of ACh-, SP-, 5HT-, and NO-containing neurons in the myenteric plexus of the proximal and distal intestine of adult gilthead sea bream as well as the efficiency of the gastrointestinal transit in vivo
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