Sex steroid levels in Porichthys notatus, a fish with alternative reproductive tactics, and a review of the hormonal bases for male dimorphism among teleost fishes.

Plasma levels of 11-ketotestosterone, 11-beta-OH-testosterone, testosterone, and 17-beta-estradiol were measured in reproductive Porichthys notatus, a teleost fish with two male morphs and alternative reproductive tactics. The two male types had contrasting androgen profiles. 11-Ketotestosterone was the predominant androgen in the Type I male morph which acoustically courts females, excavates nests, and guards eggs. Yet testosterone was predominant in the plasma of the Type II male morph which neither courts females nor nests, but instead parasitizes Type I males with sneak or satellite spawning tactics. The Type I-Type II male divergence in reproductive tactics and androgen levels is paralleled by dimorphisms in the vocal system, in body size, and in relative testis size. A review of endocrine data from six different species with male dimorphism shows consistent differences between morphotypes and a striking pattern: 11-ketotestosterone levels are uniformly elevated in each "courting male" morphotype relative to its "noncourting" conspecific. This cross-species pattern may reflect the behavioral, gonadal, or morphological differences which characterize the two morphotypes. At this point, the morphological interpretation is favored.

Androgen effects on vocal muscle structure in a teleost fish with inter- and intra-sexual dimorphism.

The plainfin midshipman fish Porichthys notatus has both inter- and intra-sexual dimorphism in the sound-producing (vocal or sonic) muscles attached to the swimbladder wall. The "Type I" and "Type II" male morphs differ in that dramatic structural changes related to sexual maturity occur in the mass, the area of mitochondria-filled sarcoplasm, and the myofiber number of the sonic muscles of Type I males, but not in those of Type II males (nor of females). Androgen implantation for 9 weeks markedly increased the relative sonic muscle size in juvenile males, juvenile females, and Type II males, whereas estradiol or cholesterol treatment did not. The principal androgen effect on myofiber structure was an increase in the area of mitochondria-filled sarcoplasm. The ratio of sarcoplasm area to myofibril area (Sr/Mf) increased by 1.4- to 2-fold in myofibers of all androgen-treated groups, with the greatest structural change occurring in juvenile males. When androgen implants were removed from juvenile males, the muscle mass and Sr/Mf ratio reverted toward the unimplanted juvenile phenotype. Total fiber number in sonic muscle increased significantly in juvenile males following androgen implantation but did not detectably change in juvenile females or Type II males. These results suggest: 1) sonic muscle in Porichthys notatus is an androgen target tissue, 2) fiber structure and fiber number are androgen-sensitive features, and 3) there exist sex- and morph-specific patterns of sonic muscle responsiveness to androgen implants.

The ontogeny of inter- and intrasexual vocal muscle dimorphisms in a sound-producing fish.

This study documents the development of inter- and intrasexual dimorphisms in the vocal ('sonic') muscles of the swimbladder in the plainfin midshipman fish, Porichthys notatus. Midshipman have two male reproductive morphs, Types I and II. Only Type I males build nests and generate mate calls to attract females; Type II males sneak or satellite spawn. Vocal muscles in the mate-calling Type I males were 25-fold larger in absolute size (sixfold larger when scaled to body size) compared with females or non-calling Type II males. Dimorphisms in muscle mass were correlated with dimorphisms in fiber number and diameter. Only nascent Type I males experienced a pre-maturational, fourfold increase of fiber number followed by a rapid, fivefold increase in fiber cross-sectional area at sexual maturity. Also specific to Type I males was a striking change in cell structure: the ratio of sarcoplasm to myofibril area increased fivefold. By contrast, Type II males and females matured without showing any of these changes in sonic muscle--the trajectories which described juvenile growth continued to hold through maturity and adulthood. The results indicate distinct, non-sequential, ontogenetic trajectories for Type I and Type II males. The origin of the Type II male morphotype is described as paedomorphosis by progenesis: size distributions of free-living animals suggest that Type II males can mature precocially as one-year-old fish, whereas Type I males defer reproduction until they are at least two years of age.

4-Thia-trans-2-alkenoyl-CoA derivatives: properties and enzymatic reactions.

4-Thiaacyl-CoA analogues, in which the 4-methylene group is replaced by a thioether sulfur atom, represent new chromophoric substrates of acyl-CoA dehydrogenases and oxidase. The corresponding 4-thia-trans-2-enoyl-CoA products exhibit a strong new absorption band (extinction coefficient 22 mM-1 cm-1) that is red shifted from 312 to 338 nm upon binding to the medium-chain acyl-CoA dehydrogenase. 4-Thiaoctanoyl-CoA reduces the dehydrogenase several-fold slower than octanoyl-CoA, although in turnover it is dehydrogenated 1.5-fold faster. The redox potential of 4-thia analogues is some 30 mV more negative than that of their unsubstituted counterparts. 4-Thia-trans-2-enoyl-CoA derivatives are slowly hydrated by enoyl-CoA hydratase (EC 4.2.1.17) to the corresponding thiohemiacetal which fragments nonenzymatically to 1 equiv each of malonylsemialdehyde-CoA and alkanethiol. This fragmentation reaction might explain the release of methanethiol during the transamination pathway of methionine degradation. 4-Oxaoctanoyl-CoA is a much poorer substrate and kinetic reductant of acyl-CoA dehydrogenase and oxidase than the 4-thia analogue. The corresponding enoyl-CoA product is also fragmented by the hydratase, yielding butanol and malonylsemialdehyde-CoA. Thus, 4-heterosubstituted acyl-CoA derivatives provide new tools for the study of beta-oxidation enzymes.

Cholinergic neurons in the brain of a teleost fish (Porichthys notatus) located with a monoclonal antibody to choline acetyltransferase.

A monoclonal antibody (Ab8) to choline acetyltransferase (ChAT) was used to locate structures showing ChAT-like immunoreactivity (ChAT-IR) in the brain of a teleost fish, the midshipman (Porichthys notatus). ChAT is the synthetic enzyme for acetylcholine found in neurons using that neurotransmitter; thus ChAT-IR may be interpreted as indicating putative cholinergic activity. Robust staining is seen in all cranial nerve motor nuclei. In addition, the brainstem of Porichthys is distinguished by two other expansive ChAT-IR zones: a sonic motor nucleus, which innervates swimbladder "drum" muscles, and an octavolateralis efferent nucleus, which innervates acoustic, vestibular, and lateral line end organs. Scattered labeled cells are found in several cranial sensory nuclei--the vagal lobe, and the main and descending trigeminal nuclei. ChAT-IR cells form restricted subpopulations in other noncranial nerve nuclei, including the granule cell layer of the cerebellum; superior, medial, and inferior divisions of the reticular formation; the stratum periventriculare of the midbrain's optic tectum; and the nucleus isthmi in the midbrain tegmentum. In the telencephalon, a dense population of ChAT-IR cells is found in the ventral nucleus of area ventralis; terminals and fine fibers are found in the dorsal, medial, and central nuclei of area dorsalis. Together, the data represent the first complete report of ChAT-IR cell bodies in the brain of any nonmammal with the monoclonal antibody Ab8, which has already been extensively used on a variety of vertebrate brains. The results are thus discussed from a comparative viewpoint, considering reports of ChAT-IR in different taxa.

The reductive half-reaction in Acyl-CoA dehydrogenase from pig kidney: studies with thiaoctanoyl-CoA and oxaoctanoyl-CoA analogues.

Thia- and oxaoctanoyl-CoA derivatives (substituted at the C-3 and C-4 positions) have been synthesized to prove the reductive half-reaction in the medium-chain acyl-CoA dehydrogenase from pig kidney. 3-Thiaoctanoyl-CoA binds to this flavoenzyme, forming an intense, stable, long-wavelength band (at 804 nm; extinction coefficient = 8.7 mM-1 cm-1 at pH 7.6). The intensity of this band increases about 20% from pH 6.0 to pH 8.8. This long-wavelength species probably represents a charge-transfer complex between bound acyl enolate as the donor and oxidized flavin adenine dinucleotide as the acceptor. Thus, the enzyme catalyzes alpha-proton exchange, and no long-wavelength bands are seen with 3-thiaoctyl-CoA (where the carbonyl moiety is replaced by a methylene group). 3-Oxaoctanoyl-CoA binds comparatively weakly to the dehydrogenase, with a long-wavelength band at 780 nm which is both less intense and less stable than the corresponding thia analogue. These data suggest that the enzyme can accomplish alpha-proton abstraction from certain weakly acidic acyl-CoA derivatives, without concerted transfer of a hydride equivalent to the flavin. 4-Thiaoctanoyl-CoA is dehydrogenated in the standard assay 1.5-fold faster than octanoyl-CoA. Titrations of the medium-chain dehydrogenase with the 4-thia derivative resemble those obtained with octanoyl-CoA, except for the contribution of the strongly absorbing 4-thia-trans-2-octenoyl-CoA product. The corresponding 4-oxa analogue is a much poorer substrate (10% of the rate shown by octanoyl-CoA) but again effects substantially complete reduction of the flavin chromophore in the dehydrogenase.(ABSTRACT TRUNCATED AT 250 WORDS)