Bertil Borg

LHRH-immunoreactive cells in the brain of the three-spined stickleback, Gasterosteus aculeatus L. (Gasterosteidae)

SummaryCells immunoreactive with an anti-LHRH serum were visualized in the brain of the three-spined stickleback, Gasterosteus aculeatus, by means of the PAP technique. Positive cells were found in a periventricular position in the nucleus praeopticus pars magnocellularis, the nucleus dorsomedialis thalami, the nucleus ventromedialis thalami, the nucleus periventricularis posterior, and in the periventricular dorsomedian tegmentum. These cells were frequently observed to contact the CSF.

Serotonin and opsin immunoreactivities in the developing pineal organ of the three-spined stickleback, Gasterosteus aculeatus L.

Summary5-hydroxytryptamine (5-HT, serotonin)- and opsin-immunoreactive sites were studied in the developing pineal complex of the stickleback, Gasterosteus aculeatus L., by use of light-microscopic indirect immunoperoxidase techniques.5-HT immunoreactivity first occurs in the pineal organ at the age of 80 h after fertilization and appears to be localized in cells of the photoreceptor type. The outer segments of a few pineal photosensory cells exhibit opsin immunoreactivity at the age of 84 h after fertilization. The number of cells seems to increase until the pineal organ is completely developed. The increase in the number of 5-HT immunoreactive perikarya runs parallel in time to that of the opsinimmunoreactive outer segments. The cells of the parapineal organ show neither opsin nor 5-HT immunoreactivity. The retina of the embryonic stickleback does not display opsin immunoreactivity until after hatching, which takes place about 144 h after fertilization.These results suggest, in the three-spined stickleback, an earlier light-perception capacity for the developing pineal organ than for the retina.

The pineal complex of the three-spined stickleback, Gasterosteus aculeatus L.

SummaryThe pineal complex of the three-spined stickleback (Gasterosteus aculeatus L.) was investigated by light and electron microscopy, as well as fluorescence histochemistry for demonstration of catecholamines and indolamines. The pineal complex of the stickleback consists of a pineal organ and a small parapineal organ situated on the left side of the pineal stalk. The pineal organ, including the entire stalk, is comprised mainly of ependymal-type interstitial cells and photoreceptor cells with well-developed outer segments. Both unmyelinated and myelinated nerve fibres are present in the pineal organ. Nerve tracts from the stalk enter the habenular and posterior commissures. A small bundle of nerve fibres connects the parapineal organ and the left habenular body. The presence of indolamines (5-HTP, 5-HT) was demonstrated in cell bodies of both the pineal body and the pineal stalk, and catecholaminergic nerve fibres surround the pineal complex.

Extraretinal photoreception involved in photoperiodic effects on reproduction in male three-spined sticklebacks, Gasterosteus aculeatus

Abstract Unoperated and blinded male three-spined sticklebacks were subjected to different photoperiods (light:dark (LD) 8:16 and 16:8 hr) and high temperature for 30 days in winter. Secondary sexual characters developed in both unoperated and blinded males in LD 16:8, but not in LD 8:16. Photoperiodic effects on spermatogenesis were also found in both blinded and intact males. Thus, extraretinal photoreception is involved in photoperiodic effects on reproduction in this species.

Effects of methyltestosterone on spermatogenesis and secondary sexual characters in the three-spined stickleback (Gasterosteus aculeatus L.)

Abstract Methyltestosterone administered via the water (35 μ/liter) at the end of the breeding season prevented involution of secondary sexual characters (high kidney epithelium) and prevented initiation of spermatogenesis in male three-spined sticklebacks. In control males regression of kidney and initiation of spermatogenesis were strongly correlated.

Stimulatory effects of methyltestosterone on pituitary gonadotropic cells and testes leydig cells of the three-spined stickleback, Gasterosteus aculeatus L., in Winter ☆

Male three-spined sticklebacks were kept for a month in short photoperiod at ca. 20 degrees in winter. During this period methyltestosterone (MT), dissolved in the water (35 micrograms/liter), stimulated the appearance of breeding colors and kidney hypertrophy, characters which were both absent in the controls. MT furthermore prevented the onset of spermatogenesis. The gonadotropic cells of the MT-treated fish contained significantly more dilated endoplasmic reticulum and less granules than those of the controls. The nuclei of the testes Leydig cells were enlarged after treatment with MT. These findings suggest the existence of a positive feedback of androgen on the gonadal-pituitary axis of the male stickleback in winter.

Ontogenetic development of the pineal organ, parapineal organ, and retina of the three-spined stickleback, Gasterosteus aculeatus L. (Teleostei)

SummaryThe ontogenetic developments of the pineal organ, parapineal organ, and retina were studied by the use of light and electron microscopy in embryos and fry of the teleost, Gasterosteus aculeatus, from 60 to 168 h after fertilization. Sixty to 66 h after fertilization, the primordium of the pineal complex is discernible in the diencephalic roofplate; the parapineal anlage is located rostral to the pineal anlage. Photoreceptor cells endowed with outer segments are present in the embryonic pineal organ already after 72 h, whereas outer segments of retinal photoreceptors could not be demonstrated before 144 h (hatching occurs between 120–144 h). Furthermore, neuropil formations with synaptic specializations are present in the rostral part of the pineal organ 108 h after fertilization. At 72 h, the embryonic parapineal parenchyma is already differentiated into parapinealocytes, which give rise to the parapineal tract, and glia-resembling elements. Although parapinealocytes carry cilia (9 × 2 + 0), only a single outer segment of the photoreceptor type could be demonstrated in the parapineal organ of one adult stickleback. Photoreceptors present in the pineal organ of unhatched embryos are hardly involved in visual functions, but may already at this early developmental stage serve as photoneuroendocrine transducers.

Diurnal variation of 5-hydroxytryptamine content in the pineal organ of the yellow eel (Anguilla anguilla (L.))

Abstract For determination of the amount of 5-hydroxytryptamine (5-HT) in the pineal organ and serum of the yellow eel, single or pooled pineal organs and blood were sampled and investigated using high-performance liquid chromatography with electrochemical detection. The eels were kept under a strict light regime of LD 12:12 for 5 weeks prior to commencement of the investigation. The peak level of 5-HT content in the pineal organ was found at the dark-to-light transition, whereas the lowest content was recorded in the middle of the light phase and at the light-to-dark transition. A relatively high 5-HT content was also present in the middle of the dark phase. The serum content of 5-HT, however, showed no such pronounced diel fluctuation.