Radoslav K. Andjus

Rapid Naloxone-Induced Alterations of Androgen Variables in the Growing Male Rat

Contrary to earlier views on the inability of naloxone to affect androgen variables by way of general circulation, systemically applied naloxone (2.5 mg/kg body weight, single i.p. or i.v. injection) has been shown to rapidly induce (within an hour) a significant fall (-35.7% on the average) of the concentration of serum androgen (testosterone and dihydrotestosterone; (T + DHT) in peripubertal rats (51-58 days old). Such a response to the opiate antagonist was absent, however, in low-androgen prepubertal animals (37-44 days old) and in those among peripubertal rats which still showed subcritical initial levels of androgen in circulation (less than 1.5 ng/ml; experiments with repeated blood sampling in catheterized animals). In peripubertal rats naloxone was also shown to induce a significant decrease (-36%) in basal in vitro androgen production by testes removed 15 or 30 min following the intraperitoneal administration of the opiate antagonist. Such an inhibitory effect on basal steroidogenesis has not been observed in control multiple-dose experiments in which incubated testes from naloxone-naive rats have been directly challenged with naloxone; on the contrary, enhancing direct effects were recorded, but only with the highest concentration of naloxone tested (10(-4) M). The possibility thus remains open that indirect inhibitory effects of injected naloxone may be operational in intact animals. Hypoprolactinemia, known to interfere in an age-dependent manner with the responsiveness of Leyding cells to luteinizing hormone (LH), may be of particular relevance.(ABSTRACT TRUNCATED AT 250 WORDS)

Electroretinographic evaluation of spectral sensitivity in yellow and silver eels (Anguilla anguilla)

Although differences in visual pigments between developmental stages of the European eel are well known, the expected differences in spectral sensitivity have not been demonstrated at the electrophysiological level. In fact, one past electroretinographic study led to the conclusion that in eels there is no change in scotopic sensitivity, with increasing sexual maturity. In the present experiments, electroretinograms (ERGs) were recorded from in situ eyecups of immobilized eels Anguilla anguilla (L.) caught in coastal running waters. It was shown that the ERG b-wave is as good an indicator of spectral sensitivity as the unmasked late receptor potential (LRP) which directly reflects the responsiveness of photoreceptors. Complete spectral-sensitivity curves, based on b-wave thresholds and on thresholds of LRP subsequently isolated by means of sodium iodate, have been obtained in the same eel. Using fitted amplitude-log intensity functions for threshold calculation, and two models for computer-assisted fitting of spectral-sensitivity curves, significant differences in lambda max were found between yellow and silver developmental stages of the eel, identified by ocular index measurements.

Some Components of Hibernation Rhythms

Abstract: At low ambient temperatures some small mammals drastically reduce their body temperature and enter a state of dormancy known as hibernation. They exhibit endogenous rhythms of heterothermy/homeothermy and body mass fluctuations with the period close to one year. At high ambient temperature only body mass cycling is expressed for almost one year as well. The effect of temperature on circannual periods of some biological rhythms in different hibernators in free‐running conditions as well as the circaseptal character of the intrahibernation rhythm of periodic arousals are reviewed.

Effects of short-term and long-term hyperprolactinemia on the developmental pattern of androgen and LH levels in the immature male rat.

Developmental patterns of serum levels of androgens and of the luteinizing hormone (LH) were studied comparatively in: i) long-term hyperprolactinemic (LT) immature male rats bearing ectopic pituitary grafts since the age of 21 days and examined at weekly intervals thereafter; and ii) in short-term hyperprolactinemic (ST) males grafted at several postnatal intervals and sacrificed 7 days postoperatively. In both ST and LT rats serum LH was markedly reduced, but only during the early prepubertal period (30 to 37days), characterized in normal rats by conspicuously high LH levels. During the next pubertal phase of development (51 to 58 days), normally characterized by a steep rise of serum androgens in the presence of relatively low LH, the androgen surge was significantly attenuated in LT, but not in ST animals. This suggests that elevated PRL, if maintained long enough prior to the pubertal age, may significantly attenuate or delay the intensified secretion of androgens characteristic of puberty, presumably by suppressing the intensive prepubertal LH secretion. In LT rats the testicular growth was moderately retarded, but the growth of the dorsal prostate was enhanced, suggesting a PRL-induced increase of responsiveness to androgen.

Photopic Vision in Eels: Evidences of Color Discrimination

Abstract: Several classes of second‐order retinal neurons have been studied electrophysiologically in European eel (Anguilla anguilla) from two different localities, Lake Seliger in Russia and the coastal waters of the Adriatic Sea in Montenegro. The majority of L‐horizontal cells (68 explored) had both rod and cone inputs, an uncommon phenomenon among teleosts. Pronounced color‐opponent properties, often taken as pointing to the capacity of color vision, were identified in one amacrine cell, apparently of the “blue/yellow” (or /blue/green”) type. Microspectrophotometric measurements revealed two different spectral classes of cones with absorption maxima at about 525 and 434 nm. The existence of green‐sensitive and blue‐sensitive cone units was thus revealed by both electrophysiological and microspectrophotometric techniques.

Electrophysiological and spectral properties of second-order retinal neurons in the eel

Several classes of second-order neurons have been electrophysiologically explored in immature European eels (Anguilla anguilla) from two distant and ecologically different localities (in Russia and Yugoslavia). The majority of L-horizontal cells (58 explored) had both rod and cone inputs, an uncommon phenomenon among teleosts. Spectral sensitivity characteristics of a number of horizontal and bipolar cells indicated that yellow-sensitive and green-sensitive cones coexist in the retina of the European eel, and that rods and green-sensitive cones contain similar visual pigments. Pronounced color-opponent properties, often taken as the capacity of color vision, were identified in one amacrine cell, apparently of the B:Y (or B:G) type. Differences in retinal structure and responsiveness between eels from the two localities, presumably due to differences in local conditions for growth, were less important than between eels of the yellow and silver stage.

Brain Energetics and Tolerance to Anoxia in Deep Hypothermia

Abstract: The remarkable time‐resolution enhancement by deep lethargic hypothermia (15°C rectal temperature, “cold narcosis,”“anesthesia by internal cold”) of metabolic events in the rat brain after oxygen deprivation has been exploited to monitor metabolic changes by in vivo31P‐NMR. A correlation was established between the bioenergetic status of the brain and physiological descriptors of tolerance (survival and revival times) determined in parallel experiments with large series of animals. Spectral peak integrals were transformed into absolute concentrations by comparison to biochemically determined time series of data obtained in freeze‐trapping experiments conducted under identical conditions. Serial spectra were used to reconstruct the time‐course kinetics of intracellular brain pH and of concentration changes of inorganic phosphate, phosphocreatine, ATP, and ADP. Both the biochemical and NMR time series of data were simultaneously fitted by a set of exponential kinetic equations accounting for relationships imposed by the Lohmann and adenylate kinase reactions. Depletion profiles were then computed for a number of descriptors of brain energy status (energy charge, phosphorylation potential, total adenylate, and primary energy stores expressed as the sum of high‐energy phosphate‐bond equivalents). The results contribute to the understanding of the role of brain energetics in tolerance to oxygen deprivation.

Feeding habits of huchen Hucho hucho (Salmonidae) fry in the River Tresnjica, Yugoslavia

Abstract About 10000 huchen larvae, obtained by artificial spawning, were introduced on 28 May 1995 into the River Tresnjica, a tributary to the River Drina, using procedures applied routinely by local fishing associations. During next two months, only 33 fry were caught in the river. Nevertheless, valuable information has been obtained for the first time on young huchens in the Drina basin. The fry apparently selected slower or almost stagnant water habitats outside the main river course. The variability of prey organisms found in fry stomachs decreased with fry length. Larger and particularly motile prey, especially mayfly larvae, gradually dominated the fry diet. Also for the first time, we document homing instinct in huchens with mark‐recapture information: one out of the nine adults, tagged after spawning, was recaptured the following year at the same spawning site.

In vitro and in vivo thermal activation of steroid-receptor complexes from rats and ground squirrels (Spermophilus citellus)

Using 3H-labelled triamcinolone acetonide (3HTA, synthetic steroid hormone), it was shown that the in vitro time course kinetics of thermal activation of 3HTA-receptor complexes exhibited the same temperature dependence in liver cytosols prepared from hibernating ground squirrels (Spermophilus citellus) as in cytosols from the rat. When 3HTA was injected in vivo to animals hibernating with a body temperature of 3 degrees C, the activation and nuclear uptake of the in vivo formed steroid-receptor complexes proceeded at a slow rate, comparable to the one predicted by in vitro studies. In the hibernator, the results are not indicative of adaptive modifications at the level of thermal activation, but prove that steroid action does proceed at a temperature incompatible with hypothermic survival in the nonhibernator.

Mechanisms of Immediate Temperature Compensation: Experiments with Brain Synaptosomes from Rat and Ground Squirrel

Abstract: Glucose conversion by brain synaptosomes can be regarded as a special case of intrinsic kinetic properties of the enzyme substrate system. Temperature modulation of apparent Km for this process can be described with our kinetic model. Using experimental data and the kinetic model, the minimal Km value for glucose conversion in ground squirrel synaptosomes was found at the lower temperature (6.5°C), much lower than that for the rat (16.6°C). The inversion temperatures (Tmin) closely coincided with the lowest body temperatures from which the unassisted recovery from hypothermia was demonstrated in both species. This study indicated that thermal modulation of enzyme affinities may have an adaptive role in endotherms that is linked to their tolerance to hypothermia.