A histological and histochemical study of the oesophagus and oesogaster ofthe Senegal sole, Solea senegalensis

A histological and histochemical study was performed in the buccal cavity a nd papillae, which were around the teeth, as well as in the oesophagus and oesogaster of the Senegal sole, Solea senegalensis adult specimens. The oesophagus and oesogaster were made up of four distinct layers: mucosa, submucosa, muscular and serous. Two morphological types of epithelial cell s were distinguishable in the oesophageal mucosa: the more numerous type ce lls possessed an electron-dense cytoplasm, whereas the Cytoplasm was electr on-clear in the other cells. Mucus-secreting cells were the dominant featur e of the epithelium throughout the oesophagus. These goblet cells were fill ed with numerous mucous droplets of low electron-density. The oesophagus wa s devoid of taste buds. In the oesogaster mucosa, three types of cells were distinguished: dark, ro dlet and light epithelial cells. Dark epithelial cells showed different cha racteristics from that in the oesophagus: the nucleus was irregular with an electron-dense hyaloplasm, the cytoplasm had a scarce smooth and granular endoplasmic reticulum; a Golgi apparatus consisted of four parallel cistern ae, dense granules without membrane, lysosomes and numerous mitochondria. T he rodlet cells were elongated, contained rod-like structures and were surr ounded by an electron-dense capsule-like structure. The bulk of the rodlet cell was composed of up to 20 extended rodlet units. Light epithelial cells of the oesogaster had the same characteristics as those observed in the oe sophagus and contained numerous mitochondria with a dense matrix, abundant smooth endoplasmic reticulum and numerous vesicles. In the goblet cells of the papillae, sulfomucin was recognised, since they showed alcianophilia (alcian blue pH 1.0 and 0.5). These cells were negativ e to protein reaction (bromophenol blue) and contained -S-S- and SH groups. Enzymatic activities (alkaline phosphatase, acid phosphatase, ATPase (pH 7 .2 and 9.4) and lipid reactions were negative in the goblet cells of the bu ccal cavity. Epithelial cells of oesophagus contained a weak presence of acid and neutra l mucopolysaccharides. Oesophageal goblet cells contained carboxylated, sul phated (weakly and strongly ionised) mucosubstances and sialic acid. Most g oblet cells did not contain proteins and presented disulphide (-S-S-) and s ulphydril (-SH) groups. Proteins in general, and in particular those rich i n lysine, tyrosine and arginine were present in the epithelium, lamina prop ria, submucosa and muscular layer of the oesophagus. Lipids in general and phospholipids were observed in the oesophageal epithe lium while unsaturated. acid and neutral lipids were not observed. The lami na propria and submucosa contained a weak presence of phospholipids and uns aturated lipids. Acid phosphatase and ATPase (pH 7.2) activities were obser ved in the lamina propria, submucosa and muscular regions, while ATPase (pH 9.2) activity was weak in these areas. ATPase activity (pH 7.2 and 9.5) wa s very weak in the epithelium. Oesophageal goblet cells were negative to li pid and enzymatic reactions.