Search

Mechanical and visual stimulation lasting for fractions of seconds to few seconds induce inTenebrio molitor at larval stage coordinate motor responses. Such movements are oscillatory in nature, their frequency is about 0.1 Hz and this value is largely independent from the intensity of the stimulus, their amplitude is proportional to it.

Plasma and testicular testosterone concentrations in the frog, Rana esculenta, were studied by radioimmunoassay and showed similar seasonal fluctuations. The increase in testicular androgen during November preceded that occurring in the plasma by 2 months. Pituitary products and gonadotrophin releasing hormone, and the responsiveness of the testis to these substances play an important role in determining the hormone profile.J. Endocr.(1984) 102, 387–392

The authors report the profiles of luteinizing hormone (LH), estradiol (E2), progesterone (P) and androstenedione (A) in some female pigs with altered plasma hormonal levels. Twenty cycles are described and 19 out of them are characterized by low plasma P in luteal phase of different etiology, at least as measured by hormone concentrations. The following disorders are observed: a) possible impairement of follicular maturation; b) impaired LH secretion in presence of too high E2; c) low LH base-line values; d) inadequate luteal phase; e) short luteal phase; f) heat disorders. An attempt is made to correlate the altered hormonal profiles with the high rate of summer conception failure in sows.

Plasma progesterone levels were determined three days after weaning in 151 sows Landrace x Large White. Furthermore, the influence of bromocriptine (Parlodel®, Sandoz) was studied on the resumption of ovarian activity in 19 sows during the hot season. An increased progesterone base-line level was shown during the June-July-August period as compared with May and September-October. No correlation was found between progesterone levels and the percentage of sows which returned to estrus 10 days after weaning except when progesterone levels reached and exceeded 0.9 ng/ml; in this case, no sow resumed ovarian activity in normal time. Bromocriptine treatment had no influence on the resumption of ovarian activity, suggesting that prolactin is not involved in the lack of estrus after weaning. An influence of environmental factors is also suggested.

In mammals endorphinergic systems have been shown to modulate reproductive processes and β-endorphin (β-EP) has been found to influence sexual functions, acting at the hypothalamus-pituitary-gonadal axis level. Using immunocytochemical and in vitrostudies, evidence for a diffuse pro-opiomelanocortin-related opioid system in the lizard Podarcis s. siculawas produced. In the testis, β-EP immunoreactivity showed seasonal variation, being most pronounced in the interstitial cells of sexually quiescent lizards (December). Reverse-phase high-performance liquid chromatography, coupled with radioimmunoassay and immunocytochemistry, showed that β-EP and acetyl β-EP increased during December, while their concentrations were low during April, when the highest testicular activity occurred.Using in vivostudies, it was found that naltrexone treatment, blocking pituitary opioid receptor, increased androgen levels in the plasma and in the testis. It was also found with in vitrostudies that the endogenous opioid system inhibits gonadotrophin release and therefore androgen production by the testis.The data reported here provide evidence for the physiological role played by opioid peptides at the pituitary level to regulate the seasonal reproductive activity of the lizard Podarcis s. sicula.Journal of Endocrinology(1994) 143,565–571

The sperm-releasing activity of a gonadotropin releasing hormone (GnRH) agonist, Buserelin (GnRH*) and hypophysis homogenate (PD) preparations was studied in intact and hypophysectomized (PDX) frogs,Rana esculenta. In addition, human chorion gonadotropin (hCG) was tested in PDX animals, and GnRH antagonist (GnRHA) treatments were carried out in intact and PDX animals, in combination with the hormonal injections. GnRH*or PD treatments were able to elicit spermiation in intact and PDX animals. While GnRH*, injected 24 h later, was again effective in inducing spermiation in intact animals, this was not the case in PDX frogs. GnRHA counteracted GnRH*effects in intact frogs. Moreover, in PDX animals GnRHA injections counteracted the spermreleasing activity induced by hCG or GnRH*, but failed to inhibit sperm-releasing activity induced by PD homogenate.

An anatomical investigation has been carried out on the third optic ganglion of the fly, Musca domestica. Two systems of giant units, the dendritic arborizations of which are arranged orthogonally relative to each other, dominate the neuropile of this ganglion. The elements of the two systems have been reconstructed using a graphical procedure based on histological sections. One system branches predominantly in the dorsoventral direction, the other one in the anterior-posterior direction. Both systems of the giant units have a twin system composed of elements smaller in diameter and strictly parallel to the main units. The two systems have been termed the Vertical and Horizontal Systems.

Summary.Ile-de-France ewes had high plasma progesterone concentrations during early summer–late winter. Gentile-di-Puglia ewes had high progesterone values during the winter–spring–summer period but during autumn progesterone values were very low and oestrous behaviour was not displayed. The comparison with Ile-de-France ewes indicates that a phase shift occurs in the annual ovarian activity in ewes of the Gentile-di-Puglia breed.Keywords:season; progesterone; photoperiod; ovarian activity; ewes

A review of the literature on insect receptors shows that they have always been considered permanent structures where changes are not expected to occur during the life of the imago. This work shows that in Tenebrio molitor adults the receptors on the antennae continue to grow. Their diameter and length were measured, using the SEM (Scanning Electron Microscope). A method was developed for optical correction leading to a considerable improvement in accuracy of measurement. Finally, a hypothesis on growth and its effects on behavior is advanced.

In intact frogs, both GnRHA and L-dopa were able to increase testicular and plasma androgen levels and to induce spermiation. The dopamine antagonist pimozide inhibited both the effects of L-dopa but not those of GnRHa. Hypophysectomy reduced androgen levels, but spermiation was still induced by both GnRHa and L-dopa, suggesting that these agents can directly influence the testis through a route not involving the pars distalis. Again, pimozide antagonised spermiation induced by L-dopa but not that induced by GnRHa.

The present data show that experimentally-controlled environmental variables (light and temperature) can alter circulating androgen levels in the male green frog,Rana esculenta, treated in different phases of the testicular cycle.

The presence and activity of brain, pituitary and testicular β-endorphin (β-EP)-like material have been studied in the frog, Rana esculenta, using reverse-phase high-pressure liquid chromatography, coupled with radioimmunoassay and immunocytochemistry. In-vivo and in-vitro treatments with naltrexone were carried out to assess the putative physiological activity of opioid peptides.β(1–31) and (1–27), together with their acetylated forms, have been identified in brain, pituitary and testis. In particular, β-EP(1–31) concentrations peaked during July in the brain and pituitary, whilst in testes maximum concentrations were found in April and November. β-EP immunoreactivity was present in the brain within the nucleus preopticus and nucleus infundibularis ventralis while positive fibres in the retrochiasmatic regions projected to the median eminence. In the testis, interstitial cells, canaliculi of the efferent system, spermatogonia and spermatocytes showed positive immunostaining for β-EP. In intact animals, naltrexone treatment increased plasma and testicular androgen levels and this effect was confirmed in in-vitro incubations of minced testes. Naltrexone also induced a significant increase in germ cell degeneration.Our results indicated that an opioid system modulates the hypothalamus-pituitary-gonadal axis in the frog, Rana esculentaand, for the first time, we have shown that the testicular activity of a non-mammalian species may be regulated by opiates locally.Journal of Endocrinology(1993) 137,49–57