Functional significance of the co-localization of taste buds and teeth in the pharyngeal jaws of the largemouth bass, Micropterus salmoides.

Studies of feeding behavior in the largemouth bass, Micropterus salmoides, revealed that live goldfish or artificial food balls are ingested in three discrete steps: inhalation of the food into the oral cavity, passage through the pharyngeal cavity, and swallowing. Food balls with or without a feeding stimulant were inhaled with equal frequency; thus, vision was clearly the major sense affecting inhalation. However, food balls with defined concentrations of a feeding stimulant were swallowed in a dose-dependent manner, whereas food balls without a feeding stimulant were promptly expelled. Thus, gustation played a major role in stimulating swallowing. Videotaped observations of feeding behavior suggested that both food processing and gustation occur in the pharynx and take place before the swallowing of either goldfish or food balls. The well-developed pharyngeal jaws of largemouth bass consist of six major pads of caniform teeth in the upper pharynx and two pads in the lower pharynx. Scanning electron microscopy showed that taste buds were abundant around most of these pharyngeal teeth. Histological sections prepared from all pharyngeal pads revealed that both elevated and flattened taste buds occur with the teeth. The morphology of these taste buds was typical of that described in other teleosts. Neuronal profiles, visualized with an HNK-1 monoclonal antibody, were observed entering each taste bud. The antibody also selectively stained a group of one to four putative sensory cells in each taste bud and the distal processes of these cells in the receptor area. The co-localization of teeth and taste buds on the pharyngeal jaws indicates that food processing and gustation both occur there, and that together these processes determine whether a potential food item is swallowed.

Steroidogenesis in Fundulus heteroclitus V.: purification, characterization, and metabolism of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one by intact follicles and its role in oocyte maturation.

In vitro steroidogenesis of ovarian follicles incubated with radioactive precursors or a Fundulus heteroclitus pituitary extract (FPE) was investigated. Steroids were extracted from both the medium and follicular tissue and fractionated by liquid or thin-layer chromatography. A similar pattern of steroid metabolites was obtained with either [14C]pregnenolone or [14C]progesterone as exogenous precursor. Several metabolites comigrated with known reference steroids and thus were tentatively identified. Some have been previously reported to induce germinal vesicle breakdown (GVBD) in this and other species, particularly 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (DHP). [3H]DHP added to intact follicles or denuded oocytes was also extensively metabolized. All the DHP metabolites produced by the intact follicle were tested for biological activity. Three of the metabolites were almost as effective inducers of GVBD as DHP itself, and two were tentatively identified as 5 alpha-pregnan-3 alpha,17 alpha,20 beta-triol and 5 alpha-pregnan-3 beta,17 alpha,20 beta-triol. However, DHP was the most potent and the quickest inducer of GVBD, indicating that its maturational action is not due to metabolic conversion to a more active form. In addition, we found two very active fractions after HPLC analysis of steroid extracts from FPE-stimulated follicles: one that corresponded to and was further identified (mass spectroscopy) as DHP and a second tentatively identified as the DHP metabolite 5 alpha-pregnan-3 beta,17 alpha,20 beta-triol. This study provides strong evidence that DHP plays the major role as a maturation inducing-steroid in F. heteroclitus, even though DHP is not the only active steroid produced by maturing follicles.

Biosynthesis and physiological role of homarine in marine shrimp.

Glycine, which contributes 2 carbon atoms and the nitrogen for the biosynthesis of homarine by homogenates of shrimp muscle, reacts metabolically with succinyl coenzyme A to form N-succinylglycine. The latter product is effectively converted by such homogenates to homarine, and it is concluded that N-succinylglycine is on the main pathway of this biosynthetic series of reactions and provides all of the required atoms in homarine, except for the N-methyl carbon. A possible pathway for the complete biosynthesis of homarine is described. Evidence is presented that homarine acts as a transmethylating agent in shrimp muscle homogenates and is capable of transferring its N-methyl group to form mono-, di-, and trimethylamines, trimethylamine oxide, choline, and betaine. In this process, homarine loses its methyl groups to form picolinic acid, and, conversely, picolinic acid can be methylated to yield homarine. It is speculated that homarine is not only a "methyl" donor but may serve as a reservoir of methyl groups in crustacea.

Biosynthesis in vitro of homarine and pyridine carboxylic acids in marine shrimp.

Minces and homogenates of muscle obtained from the marine shrimp Penaeus duorarum are capable of synthesizing homarine from [14C]glycine. Glycine carbon atoms are incorporated into homarine but not significantly into picolinate or quinolinate. [2-14C]Acetate is readily incorporated into quinolinate in the in vitro system but only slightly into homarine and not at all into picolinate. Quinolinic acid is rapidly methylated to N-methyl quinolinate which is not decarboxylated to form homarine. Procedures have been developed for the satisfactory separation of N-methyl quinolinate from homarine.