Martin P. Schreibman

Vitellogenin-induced pathology in male summer flounder (Paralichthys dentatus)

Male summer flounder (Paralichthys dentatus) were given two injections (initially and 2 weeks later) of 17beta-estradiol (E2) totaling 0.2 (2 x 0.1), 2.0 (2 x 1.0) or 20.0 (2 x 10.0) mg E2/kg body weight. Blood and tissue samples were collected 4, 6 and 8 weeks after the initial injection in the (2 x 0.1) mg/kg treatment, 4, 6, 8, and 15 weeks after the first injection in the (2 x 1.0) mg/kg treatment and at 4 weeks only in the (2 x 10.0) mg/kg treatment. Five of the 12 fish injected twice with 10.0 mg/kg were moribund before the first sampling period. Circulating levels of vitellogenin (VTG) in the blood of all E2-injected fish from all treatments were comparable with those concentrations found in the blood of wild male carp (Cyprinus carpio) and walleye (Stezostedion vitreum) previously collected near a sewage treatment plant (0.1-10.0 mg VTG/ml plasma). Excessive hyalin material accumulated in the livers, kidneys and testes of the treated fish. A portion of that material was identified as VTG by immunohistochemistry. The accumulation of VTG, and possibly other estrogen-inducible proteins, resulted in hepatocyte hypertrophy, disruption of spermatogenesis, and obstruction or rupture of renal glomeruli.

Endocrine control of freshwater tolerance in teleosts.

The teleosts Xiphophorus maculatus, Xiphophorus hellerii, Xiphophorus milleri , and Xiphophorus variatus xiphidium are native to freshwater streams. Following hypophysectomy their ability to survive in fresh water is abolished and they must be maintained in 1/3 sea water. When hypophysectomized fish are returned to fresh water they succumb within 16 days. The mean survival time of these fish in fresh water is: X. maculatus , 8.7 days; X. hellerii , 8.6 days; X. milleri , 5.5 days; X. v. xiphidium , 4.3 days. Fish in osmotic shock, when returned to dilute sea water, generally show gradual recovery. Injections of saline, neurohypophysial hormones (vasopressin and oxytocin), growth hormone, TSH, and ACTH failed to maintain hypophysectomized X. maculatus in fresh water. Only prolactin (ovine) was effective. Platyfish, injected with 10 μ g of prolactin per gram weight of fish, survived the duration of hormone administration. However, following the withdrawal of hormone, all completely hypophysectomized fish died within 16 days. Prolactin in quantities of less than 1.0 μ g is totally unsuccessful in promoting freshwater survival of fish without their pituitary glands. Compared with uninjected controls, the administration of saline or ineffective hormones considerably shortens the mean survival time of hypophysectomized fish in fresh water. In a few fish, hypophysial tissue in amounts sufficient to support them in fresh water, regenerated in four to six weeks. In some of these individuals the glands regenerated without connection to the hypothalamus.

Immunocytochemical localization of serotonin in the brain and pituitary gland of the platyfish, Xiphophorus maculatus

SummaryImmunoreactive serotonin (ir-5HT) containing cells were localized in the brain and pituitary gland of the platyfish by use of immunoperoxidase procedures. In the brain, ir-neurons were found lining the wall of the third ventricle and in its lateral and posterior recesses. More caudally, ir-perikarya were found in the valvular portion of the cerebellum and in the raphe region. Ir-5HT was also localized within the pineal gland in fish that had been sacrificed before 1:00 p.m. Within the pituitary gland, ir-5HT was localized in periodic acid Schiff-positive cells of the pars intermedia of all fish while, in only a few animals, less intense immunoreactivity was also present in gonadotrops of the caudal pars distalis.

Histology and histochemistry of the testis and ovary of the platyfish, Xiphophorus maculatus, from birth to sexual maturity

SummaryThe gonads of 3-day- to 7-month-old male and female platyfish (Xiphophorus maculatus) were examined for the presence of Δ5-3β-hydroxysteroid dehydrogenase (3β-HSD) and glucose-6-phosphate dehydrogenase (G6PD) by histochemical means. In 3-day-old males a positive response for both enzymes is localized in the Leydig cells. With subsequent testicular development, these cells increase in number and display greater activity at the periphery of the testis and around the efferent ducts. In 3-day-old females 3β-HSD and G6PD are localized in the stromal cells of the ovary. These cells increase in number and activity as the animals become sexually mature. Sertoli cells, efferent duct epithelium, and ovarian granulosa cells are negative at all stages of development examined. Our findings suggest that the gonads of neonatal fish possess the potential for steroidogenesis. The role played by sexsteroid hormones in the maturation of the brain-pituitary-gonad axis is discussed.

The demonstration of neurophysin and arginine vasotocin by immunocytochemical methods in the brain and pituitary gland of the platyfish, Xiphophorus maculatus

Abstract We have used the unlabeled antibody peroxidase-antiperoxidase (PAP) immunocytochemical method to demonstrate that antisera generated against rat neurophysin (anti-rNP) and arginine vasotocin (anti-AVT) react with material in the pars parvocellularis and pars magnocellularis of the nucleus preopticus (NPO) and in the neurohypophysis of sexually mature platyfish ( Xiphophorus maculatus ). With anti-rNP and anti-AVT, long beaded axons were seen to extend between the NPO and the neurohypophysis. Neurophysin and arginine vasotocin are immunologically distinct entities as shown by control absorption procedures. The two appear to be elaborated and stored in similar locations and follow comparable routes of transport between the NPO and the pituitary gland.

Structural and functional links between olfactory and reproductive systems: puberty-related changes in olfactory epithelium

The structural and functional link between olfactory reproductive systems in male and female platyfish (Xiphophorus maculatus) is demonstrated by the connection of receptors in the nasal epithelium to a center in the brain that has a primary role in the development and functioning of the reproductive system. Profound morphological changes occur in the nasal epithelium, and LH-RH content increases in tracts of the olfactory lobe, at specific stages of sexual maturation and not according to chronological age. Our study provides new insight into the development of the mechanisms by which chemical environmental cues are received.

The Terminal Nerve of Sharks and Rays

The first notice of the terminal nerve ( T N ) was by Fritsch. Although he paid little attention to the structure, he drew it on a figure of the brain of the smooth dogfish shark, Mustelus, and referred to it as a supernumerary cranial nerve. The unique separation of the T N from the olfactory tract in elasmobranchs undoubtedly led to this observation. Locy later described the gross morphology of the T N in a variety of sharks and rays and carried out detailed developmental studies in Squalus. He characterized the T N as an independent nerve running from the rostra1 part of the telencephalic hemispheres to the olfactory epithelium (FIG. 1) and called it nervus terminalis because of its close relationship to the lamina terminalis. The unique features of the elasmobranch T N have also been used to advantage in recent studies on its

Continued reproductive potential in aging platyfish as demonstrated by the persistence of gonadotropin, luteinizing hormone releasing hormone and spermatogenesis

Male platyfish, Xiphophorus maculatus, ranging in age from 12 to 54 months (normal life span is 30 months), were examined for age-related changes in the distribution of immunoreactive gonadotropin (ir-GTH) and luteinizing hormone releasing hormone (ir-LHRH) in their pituitary glands, and for changes in the histology of their testes. Males sacrificed at 13 and 16 months of age served as controls. Immunocytochemical methods demonstrate that even in the oldest fish, some almost twice the average platyfish life span, ir-GTH and ir-LHRH are localized in the same pituitary cell types in the caudal pars distalis and pars intermedia as in younger sexually mature fish. The testes of old fish continue to contain all stages of spermatogenesis; however, there are age-related increases in the amount of intertubular connective tissue and the relative number of spermatozeugmata, and distortions in the organization of acini. Our observations indicate that GTH and LHRH production and spermatogenesis continue, and thus a potential for reproductive capability persists, in male platyfish up to the time of their death resulting from old age.

Sexually dimorphic, age-related changes in pituitary gonadotrop distribution

Sexually dimorphic, age-related changes occur in the distribution of pituitary gonadotrops in platyfish. In females, shortly after reaching sexual maturity, cells containing immunoreactive gonadotropin begin to appear among the prolactin cells of the rostral pars distalis and they become more numerous with advancing age. In males, if these cells do appear it is almost a year later and they are much fewer in number than in females. Evidence is presented which suggests that the gonadotropin containing cells in the rostral pars distalis are true gonadotrops rather than gonadotropin-secreting prolactin cells.

The effect of hypophysectomy on freshwater survial in teleosts of the order atheriniformes

Abstract Ten species of teleosts belonging to three families of Atheriniformes (Poeciliidae, Cyprinodontidae, Goodeidae) have been tested for their ability to survive in fresh water without a pituitary gland. The fish of the current report respond similarly to Atheriniformes previously investigated. Hypophysectomized fish enter into osmotic shock and generally die within three weeks when placed into fresh water but they will survive in dilute sea water (1.2% solution of commercial sea salts). Fish belonging to Poecilia survive for the shortest period. By comparison the mean survival time for Xiphophorus is longer and more variable. No correlation exists between the number of days hypophysectomized fish are held in one third sea water prior to testing and the length of time they survive in fresh water. This is also true for fish challenged a second time after recovering from osmotic shock. Presumably, osmotic difficulty commences upon exposure to fresh water but can be alleviated when fish are returned to dilute sea water. Five hypophysectomized fish survived in fresh water. Each of these exceptional animals had suffered brain damage during surgery. The significance of these observations is discussed as it is related to the natural habitat and salt tolerances of the fish studied.