Effect of destruction of midbrain raphe nuclei on the behavioral effects of dopaminergic substances and I-tryptophan

In experiments on male albino rats, after electrolytic lesions of dorsal and median mesencephalic raphe nuclei, l-DOPA and apomorphine did not exert their stimulating effect on aggressiveness and emotional reactivity, seen in control false-operated animals. The inhibitory effect of haloperidol on emotional reactivity increased after raphectomy. The stereotype behaviour elicited by dopaminergic agents and their effects on exploratory motor activity were not changed by raphectomy. It is assumed that the effects of dopamino-potentiating agents on emotional reactivity are partly mediated by their influence on serotonergic system.     

Antagonism between L-DOPA and apomorphine in their effects on rat behavior

The effect of simultaneous injections of apomorphine and l-DOPA on stereotypy, aggressiveness, on the exploratory motor activity, the threshold of emotional reactivity and aggressiveness elicited by painful electrical stimulation was studied in experiments on male albino rats. When injected separately, in control experiments, both compounds had similar effects on the exploratory-motor activity and the emotional behaviour, but when injected simultaneously in various doses a distinct antagonism between l-DOPA and apomorphine, according to all the behaviour tests, was noted (a decrease of sterotypy, aggressiveness and emotional reactivity). Against the background of l-DOPA apomorphine (5 mg/kg) increased the dopamine content in the forebrain and in the diencephalon even more. It is suggested that the increased level of the functionally active mediator suppressed the activity of postsynaptic receptors sensitive to it.     

Effects of chronically elevated intake of sweet solutions on sexual behavior of male rats

Three experiments were conducted on the sexual behavior of gonadally intact and castrated male Sabra rats. Half of the animals drank water during the course of the experiment and half were offered sweet solutions, the assumption being that sweet gustatory stimulation elevates the level of central endogenous opioid peptides in rats. The effects on sexual behavior of the following drugs were explored: the opiate receptor blocker naloxone (5 mg/kg, sc), the serotonin precursor 5-hydroxytryptophan (5-HTP) (20 mg/kg, sc), the serotonin antagonist methysergide (1 mg/kg, sc), and naloxone in combination with methysergide. Naloxone, whether administered alone or in combination with methysergide, impaired sexual performance in castrated male rats, and in gonadally intact rats maintained on sweet solutions. Methysergide elevated sexual behavior in all groups, whereas 5-HTP tended to suppress such behavior. The results support the hypothesis that endogenous opiates play a role in the expression of male sexual behavior in rats. While subtle in intact animals this role may become crucial following the disruption of sex hormone supply. Serotonergic influence on male sexual behavior is inhibitory.     

Localization of serotonin in the hypothalamus and the mesencephalon of the guinea-pig

Summary The distribution of serotonin in the hypothalamus and the mesencephalon of guinea-pigs pretreated with both pargyline and L-tryptophan was investigated immunohistochemically using monoclonal antibodies to 5-HT. 5-HT-positive fibers and varicosities appeared distributed throughout the hypothalamus. Some areas showed a greater density of immunoreactivity: the suprachiasmatic nucleus, the region of the supraoptic crest, the area of the medial forebrain bundle, the ventral part of the nucleus ventromedialis, the median eminence and the ventral part of the mammillary bodies. 5-HT nerve fibers were also scattered in the posterior lobe of the pituitary. An extensive supraependymal plexus of immunoreactive axons was observed in most ventricular regions. No 5-HT positive cell bodies were present in the hypothalamus of the guinea-pig under our experimental conditions, whereas an intense serotonin immunoreactivity was detected in perikarya of the brain stem. 5-HT cell bodies were found predominantly in the raphe region including the nucleus raphe dorsalis and raphe medianus, nucleus interpeduncularis, reticular formation and dorsal area of the medial lemniscus.     

The effect of forelimb deafferentation in early postnatal ontogeny on the development of synaptic transmission in the hippocampus]

Hippocampal slices from 15-20-day-old Wistar rats were used to study the development of some features of synaptic transmission in hippocampus and the influence of partial limitation of the sensory inflow in the early ontogeny of this transmission. The dynamics of population spike changes was observed in the CA1 hippocampal field in response to stimulation of Schaffer collaterals. The early ontogenetic limitation of the sensory inflow was accomplished by cutting n. medianus on the 13th day. Between the 15th and 20th days, the dynamics of the population spike amplitude increase in the control and experimental animals was similar, however, the response amplitude of the control rats remained higher than in the experimental animals throughout the whole period of observation. It is suggested that the partial limitation of sensory inflow from a forelimb at the early stages of the ontogeny alters the formation of synaptic transmission in hippocampus.     

Prostate response to prolactin in sexually active male rats

Background  

The prostate is a key gland in the sexual physiology of male mammals. Its sensitivity to steroid hormones is widely known, but its response to prolactin is still poorly known. Previous studies have shown a correlation between sexual behaviour, prolactin release and prostate physiology. Thus, here we used the sexual behaviour of male rats as a model for studying this correlation. Hence, we developed experimental paradigms to determine the influence of prolactin on sexual behaviour and prostate organization of male rats.     

Compensation in behavioral disorders in rats receiving 5,7-DHT neonatally and by transplantation of embryonic raphe nucleus tissue

In 62 male Wistar rats the influence was studied of the transplanted embryonal tissue of raphe nuclei (NR) on the mechanisms of compensation of disturbances of exploratory activity, sensory attention, learning and emotional reactivity induced by neonatal injection of 5,7-DHT. In histochemical studies by Falk-Hillarp method the presence of yellow fluorescence confirmed the specificity of transplanted 5-HT neurones. It is found that NR transplantation causes in animals after 3 months recovery of orienting reaction to sensory stimuli, reduces rats reactivity in the open field, restores the ability to discrimination of emotionally positive influence, disturbed by neonatal injection of 5,7-DHT. The obtained data show the possibility of compensation of behaviour disturbances caused by chronic deprivation of 5-HT system activity by transplantation in the neocortex parenchyma of the embryonal tissue, containing serotoninergic neurones.     

The prediction of resistance to emotional stress based on the individual testing of behavior

On the basis of the elaborated experimental model for testing of emotional interaction of animals individual typification of behaviour was established according to which all experimental male rats of August line were subdivided into groups: I--rats manifesting behaviour of avoidance, "victims" of electrocutaneous stimulation; II--without definite behaviour with respect to the "victim" rat; III--rats, preferring the behaviour determining electrocutaneous stimulation of the "victim" rat. All typified animals were subjected to emotional stress with the use of the elaborated experimental model of aggressive-conflict behaviour. Stability against emotional stress of each group of animals was studied. Significant differences were established of stability degree to emotional stress of the rats of three groups manifesting different types of behavioural reaction in conditions of emotional interaction. The most stable were rats of the I group, the least--of the III group; rats of the II group were in the middle position. Typification on the basis of testing of emotional interaction of animals allows to prognosticate individual stability against emotional stress.     

Évaluation des effets prosexuels des extraits de Bridelia ferruginea chez le rat mâle naïf

The stem barks and the leaves from Bridelia ferruginea (BF, Euphorbiaceae), a medicinal plant, are used in traditional medicine for the treatment of several ailments including male impotency. The present study was aimed at investigating the effects of the dried stem bark of BF on the sexual behaviour of normal and castrated sexually inexperienced male Wistar rats. Animals were orally administered with 100 mg/kg of either the aqueous or the ethanol extracts of BF whilst the neutral control group received in the same way 10 ml/kg of distilled water. The positive control group was treated with a subcutaneous injection of testosterone propionate (20 mg/kg/day/3days) prior to the experiment. The sexual behaviour of all rats was monitored on days 0, 1 and 7 by measuring frequencies of penile erection, mount, intromission and ejaculation. In a separate group of normal sexually inexperienced rats, the pro-sexual effects induced by a single dose of the aqueous extract (100 mg/kg) were measured after pre-treatment with either haloperidol (10 mg/kg), atropine (10 mg/kg) or L-omega-nitro-arginine methyl ester (Lω-NAME, 10 mg/kg). Results obtained showed a significant influence of the duration of treatment on the frequencies of penile erection, mount and intromission of both normal and castrated rats. An increase in all sexual performance parameters was observed when compared to respective controls. The intromission frequency of normal animals was significantly increased (P < 0.05–0.01) on day 1 of treatment and the effect was more expressed in rats receiving the aqueous extract. In castrated animals, a statistical increase was noticed on day 7 for rats treated with testosterone. The sexual effects induced by the aqueous extract of BF were completely abolished after pre-treatment of rats with atropine or haloperidol while pre-administration of Lω-NAME did not produce any significant effects. Flavonoids and sterols revealed in the aqueous and ethanolic extracts from the barks of BF may account for the enhancement of sexual activity in naive rats which could be expressed through dopaminergic and/or cholinergic receptor(s). Results of this work also give value to the traditional use of the plant for the improvement of male sexual behaviour.     

Androgen-dependent fighting behaviour in male mice

The influence of testosterone propionate, 17 alpha-methyl-testosterone and cyproterone acetate on isolation induced fighting behaviour of mice was studied in a simple testing procedure. Decreased aggressiveness has been established in mature, sexual experienced and isolated male mice both following castration and administration of the antiandrogen cyproterone acetate, respectively. Replacement therapy with testosterone propionate s.c. and 17 alpha-methyl-testosterone p.o. has been shown to restore the decreased level of aggresiveness after castration.     

Sexual Behaviour following Castration in Experienced and Inexperienced Male Rabbits

Sexual activity declines after castration in all mammalian species studied (Beach 1948, Beach and Pauker 1949, Beach 1970, Grunt and Young 1953, Michael and Wilson 1974, Phoenix, Slob and Goy 1973, Rosenblatt and Aronson 1958). The rate of decline of sexual behaviour is generally slower than that of the function of the accessory sexual glands. Two factors have been suggested to contribute to the maintenance of sexual behaviour for some time after castration: secretion of androgen from the adrenal cortex and sexual experience. However, adrenalectomy does not seem to influence post-castrational behaviour in hamsters (Warren and Aronson 1956), dogs (Schwartz and Beach 1954), rats (Bloch and Davidson 1968), mice (Burge and Edwards 1971), and cats (Cooper and Aronson 1958), and the degree of sexual experience appears to be of little importance for the postcastrational behaviour of rats (Bloch and Davidson 1968, Rabedeau and Whalen 1959) and dogs (Hart 1968). But male cats with sexual experience continue to mate after castration for a considerably longer period than inexperienced cats (Rosenblatt and Aronson 1958). Some experienced animals were able to achieve insertion at the 10th week after castration, whereas none of the inexperienced animals did so after the first week. In conclusion, the importance of experience seems to vary between species, whereas the adrenal androgens are of doubtful significance for postcastrational behaviour. We have casually observed that castrated rabbits retain their sexual vigour longer if they are given extensive precastrational experience. The importance of experience has now been studied systematically in animals of mixed strains generally used in the laboratory. As a comparison, we studied the postcastrational behaviour in some New Zealand White rabbits with extensive sexual experience.     

Change in certain forms of aggressive behavior and the concentration of monoamines in the brain during selection of wild rats for taming

Norway rats have been selected during 20 generations by the absence of aggressive reaction to man (tamed rats). From 7 up to 20th generations of selection, different forms of aggressive behaviour (reaction to glove, intermale, shock-induced aggression and predatory aggression) were studied, and the level of noradrenaline, serotonin and its metabolite 5-hydroxyindoleacetic acid was determined in the brain. In the absence of aggressive reaction to glove in tamed rats, the shock-induced aggression considerably decreased while the predatory aggressiveness (mouse-killing behaviour) and intermale aggressiveness did not change. Beginning from 15-16th generation of selection, a higher level of the 5-hydroxyindoleacetic acid in the hypothalamus was established, in the 20th generation an increased content of serotonin was revealed in the hypothalamus and the midbrain. In some generations of selection an increased level of noradrenaline in the hypothalamus in comparison to wild rats was observed. A conclusion is made that the selection of animals by taming unequally influences different kinds of aggressiveness and is accompanied by inherited consolidated reorganization of the monoamine brain systems.     

The effect of bull seminal ribonuclease on reproductive organs and sexual behaviour in male rats

Wistar male rats received an intratesticular injection (at 114 and 265 days of age) of 3 mg of partially purified bull seminal ribonuclease (AS RNase) or saline. It was found that sexual behaviour (initiation of copulation as well as copulatory behavioural pattern) of experimental males was not changed, but the ability of these males to fertilize females was evidently suppressed. In addition to significantly lower weights of testes and epididymis, inhibition of seminiferous epithelium development (aspermatogenesis) associated with the absence of spermatozoa was determined in cauda epididymidis in experimental animals. However, Leydig cells remained without changes. Plasma testosterone levels of AS RNase treated males were not altered in comparison with the controls. Thus AS RNase specifically impaired spermatogenesis but did not influence androgen action and sexual behaviour.     

Steroid hormones as mediators of neural plasticity

Steroid and thyroid hormone receptors are expressed in the developing brain and persist throughout adult life. They mediate a variety of effects on the brain, ranging from developmental effects of thyroid hormone and the process of sexual differentiation to the cyclic changes during reproductive cycles in adult female animals. This review summarizes data from the author's laboratory on three topics: (1) actions of extradiol and progesterone on the ventromedial nucleus of the hypothalamus in adult female and male rats, showing both the cyclicity and the consequences of brain sexual differentiation; (2) actions of estradiol on the cholinergic neurons of the basal forebrain of the female and male rat, reflecting the plasticity of the adult cholinergic system as well as sex differences which are developmentally programmed; and (3) diverse actions of estrogens, thyroid hormone and glucocorticoids on the morphology of hippocampal neurons. The review concludes by discussing the interactions between "organizational" (i.e. developmental) effects and the "activational" effects of steroids on the mature nervous system in relation to the environmental control of brain gene expression.     

Corpus allatum function during sexual maturation of male Diploptera punctata

ABSTRACT. The effect of allatectomy on synthesis of accessory reproductive gland secretion, spermatophore production and sexual behaviour in male Diploptera punctata was investigated during the first 6 weeks of adult life. After allatectomy, synthesis of the secretion and production of spermatophores was slightly reduced relative to sham-operated animals (by 16%), but not relative to normal animals. However, sexual behaviour of the operated animals appeared normal. Thus, the corpora allata (CA) may not be necessary for the sexual functioning of male D.punctata. The synthesis of C₁₆ juvenile hormone (C₁₆ JH; JH III) by isolated pairs of CA from individual males was followed during this period and, at all times, the rate of synthesis was less than 8pmolh^-1 per pair, a rate similar to that observed in pregnant females. The significance of this continued synthesis of JH by male CA is unknown, although it may be related to the maintenance of general metabolic activities.     

Effect of various periods of social isolation of juvenile rats on the level of their intraspecies aggression at a sexually mature age

Isolation of male outbred white rats from the same age rats at 12-30 and 15-30 days of postnatal life increases their aggressiveness in pubertal age and causes a change of aggressive reactions spectrum towards the decrease of attacks and increase of threats in relation to intruders. These changes in the ontogenetic formation of rats aggressive behaviour are not compensated by the experience of rats social intercourse in the period 30-70th days. A hypothesis is made about the existence of sensitive period of rats aggressive behaviour formation with the approximate limits 15th-30th days of postnatal life during which under the influence of contacts with rats of the same age prerequisites are created for consolidation of various agonistic reactions in resultant act of mature aggression.     

Effect of deafferentation of the forelimb on the postnatal development of the synaptic plasticity in the hippocampus

The postnatal development of LTP in CA1 area of hippocampus was studied in hippocampal slices from 13-20-day-old intact rats, after unilateral resection of n. medianus on the 13th day, and sham-operated animals. In slices from the intact rats prepared on the 15th-16th-day of postnatal development, the LTP magnitude and duration were significantly larger than in adult animals. Partial deafferentation eliminated this overshoot. However, a less pronounced increase in synaptic plasticity was observed in operated animals on the 17th day. The LTP suppression in the experimental animals may be explained by a decrease in the NMDA receptor activity due to enhanced synaptic activity in the hippocampus. We think that the limited sensory inflow from the partially deafferented forelimb to the hippocampus via the entorhinal cortex may be compensated by activation of other inputs from specific or/and nonspecific pathways. In contrast, the LTP magnitude and duration were significantly increased in slices from the sham-operated rats. This increase may be explained by a decline of synaptic activation of the hippocampus under anesthesia.     

Teratopsychogenetic effects apparently produced by nonphysiological neurotransmitter concentrations during brain differentiation.

In male rats treated with pargyline, reserpine or pyridostigmine during neonatal life significant permanent changes of sexual behaviour and conditioned learning behaviour were observed in juvenile and/or adult life. Male sexual activity and learning capacity were permanently decreased in neonatally pargyline- or reserpine-treated animals, but permanently increased in neonatally pyridostigmine-treated rats. These findings suggest that nonphysiological concentrations and/or turnover rates of neurotransmitters, if produced during a critical period of brain differentiation, are able to induce lifelond effective behavioural changes, i.e. teratopsychogenetic effects.     

The dehydroepiandrosterone sulfate influence on anxiety and depressive behaviour: participation of mu-opioid receptors

The dehydroepiandrosterone sulfate (DHEAS) influence on anxiety and depressive behaviour was studied in animals after chronic stress exposures. It is shown that DHEAS (30 mg/kg) reduced anxiety in submission (with increased level of stress-induced anxiety resulting from chronic (20-days) defeats in aggressive interactions) of male mice of CBA/Lac strain in the "partition" test and in the plus-maze test, whereas in the control--only in the plus-maze test. DHEAS injection (30 mg/kg) in male Wistar rats decreased depressive behaviour in the Porsolt test in control and multiple (shuttling on the laboratory scrambler for 18 days by 1 hour in day) stressed animals. NaItrexone (0.25 mg/kg in mice and 0.1 mg/kg in rats) blocked anxiolytic and antidepressant-like effects of DHEAS. The findings suggest that these DHEAS effects are mediated by mu-opioid receptors.     

Role of the serotoninergic system in the acceleration of sexual maturation in wild Norway rats selected for reduced aggressiveness toward humans

The role of the serotoninergic system in acceleration of the sexual development of domesticated rats (Rattus norvegicus) was assessed. The onset of age-related changes in hypothalamic serotonin during prepubertal period occurred earlier in domesticated than in aggressive male rats. Blockade of the serotoninergic system after p-chlorophenylalanine (PCPA) administration on days 40 and 44 delayed the development of the reproductive system in both aggressive and domesticated males. In 60-day-old rats treated with PCPA, levels of testosterone in plasma and the number of mature spermatozoa in epididymis were decreased compared to controls. At the same time, the administration of PCPA on days 30 and 34 did not modify basal testosterone secretion and other parameters in 60-day-old aggressive rats and produced a decrease similar to PCPA injections on days 40 and 44, although less pronounced, in the weights of testes in domesticated animals. Administration of 5-hydroxytryptophan (5-HTP), a precursor of serotonin synthesis, on days 30, 32, 34, 36 and 38 increased plasma testosterone levels and weights of the sex organs in 60-day-old domesticated males, but did not significantly affect the development of reproductive system in aggressive animals. These data indicate that serotonin stimulates sexual development of males during prepubertal period and this activating effect of serotonin occurs earlier in domesticated than in aggressive males. They also suggest that the acceleration in sexual maturation of domesticated rats could result from changes in the ontogenetic dynamic of hypothalamic serotonin induced by a selection for low aggressiveness towards man.