J.W. Resink

Pimozide modulates the luteinizing hormone-releasing hormone effect on gonadotrophin release in the African catfish, Clarias lazera

In the African catfish the effect of (i) the dopamine antagonist pimozide (PIM), (ii) a luteinizing hormone-releasing hormone analog (LH-RHa), and (iii) a combination of these substances on gonadotrophin (GTH) release and on ovulation was investigated. PIM alone increased plasma GTH levels in juvenile catfish but was ineffective in mature animals. LH-RHa increased plasma GTH levels in both juvenile and mature catfish and within 12 hr after the injection a high rate of ovulation (80%) was observed. PIM potentiated the LH-RHa effect on GTH release and ovulation. It was concluded that dopamine does not effect the GTH release directly, but modulates the effect of endogenous and exogenous gonadotrophin-releasing hormone.

Steroid glucuronides of the seminal vesicle as olfactory stimuli in African catfish, Clarias gariepinus

Abstract Electrical responses were obtained from the olfactory epithelium (electro-olfactogram, EOG) and from the olfactory tract of female African catfish. The EOG response of females to holding water of males depends on the presence and the size of the males seminal vesicle. Male catfish thus appeared to release odorants originating from the seminal vesicle. The fluid from this exocrine gland is a highly stimulatory odorant because it contains steroid glucuronides. Higher levels of steroid glucuronides in the seminal vesicle fluid of feral spawning males makes the fluid more potent as an olfactory stimulus, whereas removal of the glucuronides diminished the response. Ovulation did not affect the sensitivity to these complex mixtures of glucuronides in the seminal vesicle fluid. The olfactory epithelium of females also responded to solutions of individual synthetic steroid glucuronides. Of the glucuronides tested, 5β-pregnane-3α,17α-diol-20-one-3α-glucuronide was the most potent odorant. It had a detection threshold of approximately 10 −11 M . Thresholds for the other glucuronides ranged between 10 −9 and 10 −6 M . The present data demonstrate the importance of seminal vesicle steroid glucuronides as olfactory cues.

The seminal vesicle of the African catfish, Clarias gariepinus

SummaryThe seminal vesicle of the African catfish, Clarias gariepinus, consists of 36–44 fingerlike lobes built up of tubules in which a fluid is secreted containing acid polysaccharides, acid-, neutral- and basic proteins, and phospholipids. In this fluid sperm cells are stored. The seminal vesicle fluid immobilizes the sperm cells. After ejaculation, it prolongs the period of sperm activity. The seminal vesicle fluid is secreted by the epithelium lining the tubules. The tubules in the proximal part of the lobes are predominantly lined by a simple cylindrical and those of the distal part by a simple squamous epithelium. These epithelial cells contain enzymes involved in energy-liberating processes, the enzyme activites being proportional to the height of the cells. Interstitial cells between the tubules have enzyme-histochemical and ultrastructural features indicative of steroid biosynthesis. Similar characteristics are found in testicular interstitial cells. The most rostral seminal vesicle lobes and the most caudal testicular efferent tubules form a network of tubules that opens at the point where the paired parts of the sperm ducts fuse with each other. The tubules of most seminal vesicle lobes, however, form a complex system that fuses with the unpaired part of the sperm duct.

The chemical nature of sex attracting pheromones from the seminal vesicle of the African catfish, Clarias gariepinus

Abstract In attraction tests, ovulated female African catfish, Clarias gariepinus , were attracted by the administration of 2.0 ml/l seminal vesicle fluid to the aquarium water. Lower doses (0.1 and 0.5 ml/l) were ineffective, and a high concentration (8.0 ml/l) seemed to have a repulsive effect. After fractionation of the fluid, an isolated steroid conjugate fraction appeared to contain the attractant. No other stimuli beyond this fraction were required to attract groups of female catfish after ovulation. Other constituents of the fluid such as polysaccharides, proteins, phospholipids and steroids failed to attract the females. GCMS analysis of the steroid conjugate fraction revealed the presence of eight different steroid glucuronides. After removal of these steroid glucuronides, the steroid conjugate fraction lost its attractive effect. A mixture of seven available synthetic steroid glucuronides was composed according to the quantitative results of the GCMS analysis. This mixture appeared to have a powerful dose-dependent attractive effect on ovulated females. It is concluded that a combination of various steroid glucuronides, present in seminal vesicle fluid, functions as a sex attractant, bringing male and female African catfish together shortly before spawning.

Seasonal changes in steroid metabolism in the male reproductive organ-system of the African catfish, Clarias gariepinus

Steroid and steroid glucuronide synthesis in feral male African catfish was investigated in vitro by incubating testes with [3H]-pregnenolone and seminal vesicles with [3H]-androstenedione. In testes, the capacity to form progestins, androgens, especially 11-oxygenated ones, and steroid glucuronides increased enormously in the periods of full spermatogenesis and breeding, with 5β-pregnane-3α,17α,20α-triol and 5β-pregnane-3α,17α-diol-20-one glucuronide as the main polar products. In the same periods, seminal vesicles are able to form 11-oxygenated androgens from [3H]-androstenedione and show an increased capacity to form testosterone. Their ability to produce testosterone glucuronide is strongly enhanced in the period of full spermatogenesis and further increases in the breeding period. In this latter period, the capacity to form 5β-androstane-3α,17α-diol glucuronide is also stimulated. The function of the main steroids and steroid glucuronides is discussed, with special reference to the water-soluble compounds that may serve as sex pheromones.

Induction of gonadotropin release and ovulation by pheromones in the African catfish, Clarias gariepinus.

Abstract Ovulation experiments were carried out using mature female offspring of a cross between a female African catfish, Clarias gariepinus , from an established laboratory stock and a feral individual. Ovulation could successfully be induced in 67% of the females when they were held in the presence of a male and another ovulated female although visual and tactile stimuli could not be perceived due to compartmentalization in the aquaria by opaque perforated partitions. Successful ovulation (55%) was also obtained when ovarian fluid of an ovulated female was administered as a replacement of the ovulated female. However, experimental females with sectioned olfactory tracts did not respond. In addition, it was found that females exposed to ovarian fluid had increased plasma gonadotropin (GTH) levels. These ovulation responses were observed from March to May 1986, but not in December 1985 nor in June 1986. Experiments with the next generation of catfish led to a slight increase in plasma GTH levels, but not to ovulation induction. The importance of the nature of the offspring and the time of year for pheromonally induced GTH release and ovulation are discussed.

Quantitative enzyme histochemistry of steroid and glucuronide synthesis in testes and seminal vesicle, and its correlation to plasma gonadotropin level in Clarias gariepinus

In spawning Clarias gariepinus from the Hula Nature Reserve in Northern Israel, the mean value for the seminal vesicle somatic index (SVSI) had decreased as compared with that in prespawning fish, due to loss of seminal vesicle fluid. Mean gonadosomatic index (GSI), however, had increased, probably as a result of hydration, 3α-Hydroxysteroid dehydrogenase (3αHSD), 3βHSD and uridine diphosphoglucose dehydrogenase (UDPGD) reactions were demonstrated in interstitial cells of both testis and seminal vesicle. UDPGD reactions were also found in the epithelium of the seminal vesicle tubules. Quantitative determination of the enzyme reactions with a computerized image analysis system revealed that total activity of all three enzymes in interstitial cells of the seminal vesicle was distinctly stronger in spawning fish. Prespawning and spawning fish did not differ in total UDPGD activity in the epithelium lining the seminal vesicle tubules. In the testes of spawning fish, total 3βHSD activity was stronger and total UDPGD activity weaker than in prespawning fish, but total 3αHSD activity was not different. Plasma gonadotropin (GTH) levels in male catfish were low as compared with females. This level was significantly increased in spawning males and extremely high in ovulated female spawning fish. The findings point to marked changes in the production of steroids and glucuronides in the reproductive organ system during spawning, especially in the seminal vesicle. These changes are accompanied by elevated levels of circulating GTH.

Pheromone detection and olfactory pathways in the brain of the female African catfish, Clarias gariepinus

SummaryThe olfactory tract of the African catfish, Clarias gariepinus, consists of two tracts, the medial and lateral olfactory tract. Ovulated female catfish are attracted by male steroidal pheromones. Attraction tests with catfish in which the medial and lateral olfactory tract have been selectively lesioned show that the effects of these pheromones are mediated by the medial olfactory tract. The central connections of the medial and lateral olfactory tract have been studied by retro- and anterograde transport techniques using horseradish peroxidase as a tracer. Upon entering the forebrain, the medial olfactory tract innervates the posterior pars ventralis and pars supracommissuralis of the area ventralis telencephali and the nucleus preopticus periventricularis, the nucleus preopticus and the nucleus recessus posterioris. Application of horseradish peroxidase to the olfactory epithelium shows that part of the innervation of the area ventralis telencephali and the nucleus preopticus periventricularis can be attributed to the nervus terminalis, which appears to be embedded in the medial olfactory tract. The lateral olfactory tract sends projections to the same brain areas but also innervates the nucleus habenularis and a large terminal field in the area dorsalis telencephali pars lateralis ventralis. Furthermore, the medial olfactory tract carries numerous axons from groups of perikarya localized in the area dorsalis telencephali. Contralateral connections have been observed in the olfactory bulb, telencephalon, diencephalon and mesencephalon. It is suggested that processes of the medial olfactory tract innervating the preoptic region may influence the gonadotropin-releasing hormone system and in doing so may lead to behavioral and physiological changes related to spawning.