Olfactory contribution to Fos expression during mating in inexperienced male hamsters

Male hamsters are very dependent on chemosensory cues for normal mating behavior. We have previously reported that central, vomeronasal pathways are intensely and selectively activated during mating or pheromonal stimulation. The contribution of main olfactory sensory input to the patterns of c-fos activation was investigated in this study. Sexually inexperienced male hamsters were either made anosmic by intranasal infusion of zinc sulfate or remained intact. Fos protein immunoreactivity was analyzed in main olfactory and vomeronasal pathways of the zinc sulfate-treated, anosmic animals after mating with receptive females for 45 min, and compared with Fos patterns seen in intact mating animals, some of which have been described in a previous publication. The zinc sulfate-treated anosmic males described here all mated when given access to receptive females. Whether mated or unstimulated, anosmic males had little or no Fos expression in main olfactory pathways; significantly less even than in unstimulated intact animals. Mating did not increase Fos expression in main olfactory pathways of intact animals over that of unstimulated intact controls. However, Fos expression in central vomeronasal pathways was significantly higher in mating anosmic males, as in intact males, compared with appropriate non-mating controls. Fos expression was significantly different between intact and zinc sulfate-treated anosmic mating males in only one area studied. The rostral anterior medial amygdala, known to receive a small olfactory terminal field, had significantly lower Fos expression in zinc sulfate-treated anosmic males that mated when compared with intact-mating animals. Thus, functional main olfactory input to the rostral vomeronasal amygdala can be demonstrated but does not appear to be critical for mating behavior in previously inexperienced male hamsters with intact vomeronasal organs. Other main olfactory input appears to have a negligible contribution to Fos-patterns in such animals.      

Sexual behavior in male rodents

The hormonal factors and neural circuitry that control copulation are similar across rodent species, although there are differences in specific behavior patterns. Both estradiol (E) and dihydrotestosterone (DHT) contribute to the activation of mating, although E is more important for copulation and DHT for genital reflexes. Hormonal activation of the medial preoptic area (MPOA) is most effective, although implants in the medial amygdala (MeA) can also stimulate mounting in castrates. Chemosensory inputs from the main and accessory olfactory systems are the most important stimuli for mating in rodents, especially in hamsters, although genitosensory input also contributes. Dopamine agonists facilitate sexual behavior, and serotonin (5-HT) is generally inhibitory, though certain 5-HT receptor subtypes facilitate erection or ejaculation. Norepinephrine agonists and opiates have dose-dependent effects, with low doses facilitating and high doses inhibiting behavior.     

Evidence that olfactory bulbectomy does not influence testicular regression in golden hamsters on short photoperiod by altering pineal melatonin production

Summary A recent study has shown that olfactory bulbectomy (BX) will prevent reproductive regression associated with short photoperiod in male golden hamsters. The results of experiments reported in this paper show that bulbectomized hamsters on long or short photoperiod still show a large nocturnal elevation in pineal melatonin production and that BX inhibits the reproductive regression induced by exogenous melatonin in pinealectomized hamsters. The data therefore indicate that BX does not inhibit short photoperiod induced testicular regression by altering melatonin secretion.     

Serial copulatory behavior of male hamsters and rats

The copulatory behavior of mammalian males is generally characterized by the male's repeated approaches to and mounting of the female. The mounting behavior can lead to intromission, and after several intromissions, an ejaculation occurs. Following ejaculation, the male refrains from sexual activity for a period of time, the so-called "post-ejaculatory interval (PEI)". Most mammals will return to copulate again. Both male hamsters and rats were used and each animal performed five series of copulations with a proestrous female. From the 1st to 5th series of copulations the hamsters showed a shorter PEI than the rats. In addition, the PEI of the hamsters showed no change after each ejaculation, while the rats gradually showed a significantly increased PEI during the five series of copulations.     

Reproductive effects of olfactory bulbectomy in the Syrian hamster

The effects of olfactory bulbectomy on circulating gonadotropin, prolactin and testosterone levels and on the testicular and pituitary responses to shortening of day length were studied in Syrian hamsters. Adult animals maintained on a 14L:10D cycle were sham-operated or sustained bilateral radical olfactory bulbectomies by aspiration to remove the main and accessory olfactory bulbs and the adjacent regions of the anterior olfactory nucleus. They were then maintained either on the long photoperiod or housed on a 10L:14D cycle. Testicular length was measured at weekly intervals over a 5-mo period. Sham-operated controls exhibited the normal pattern of testicular regression and eventual recrudescence on the short photoperiod. Testicular regression was significantly reduced in bulbectomized animals. Many of these animals showed no regression; others exhibited a reduced degree and/or shortened duration of regression. Serum levels of follicle-stimulating hormone (FSH) were substantially elevated in bulbectomized males maintained in long days. Their serum levels of luteinizing hormone (LH), prolactin and testosterone remained within the range for shams on long photoperiod. In short days, the bulbectomized animals showed the normal, pronounced decline in circulating prolactin levels. Serum FSH and LH levels also showed substantial declines, but the FSH levels were not reduced below the range for controls in long days, and the decline in LH levels was not as great as that for controls in short days.(ABSTRACT TRUNCATED AT 250 WORDS)     

Development of paleocortical projections through the anterior commissure of hamsters adopts progressive, not regressive, strategies

The perinatal development of anterior commissure projections was studied in hamsters by use of carbocyanine crystals implanted either into the commissure or into the ventrolateral prosencephalon. The earliest fascicles of growing commissural fibers had reached the midline on day 14 of gestation (E14). On E15, these fibers had entered the opposite hemisphere and reached the borders of their target regions. No waiting period was observed, since on E16 axons were already collateralizing into most targets. On P1, labelled cells were seen in all regions projecting through the anterior commissure in adults, namely, the anterior olfactory nucleus, olfactory tubercle, piriform cortex, nucleus of the lateral olfactory tract, bed nucleus of the stria terminalis, insular, perirhinal, entorhinal, and temporal cortices, as well as the amygdaloid complex. No evidence of topographical exuberance was detected. Counts of labelled neurons showed that the number of commissural cells increased gradually after birth. It is concluded that the development of paleocortical connections through the anterior commissure employs progressive strategies, lacking the regressive phenomena that are characteristic of the neocortical projections through the corpus callosum.     

Development of palecortical projections through the anterior commissure of hamsters adopts progressive,not regressive,strategies

The perinatal development of anterior commissure projections was studied in hamsters by use of carbocyanine crystals implanted either into the commissure or into the ventrolateral prosencephalon. The earliest fascicles of growing commissural fibers had reached the midline on day 14 of gestation (E14). On E15, these fibers had entered the opposite hemisphere and reached the borders of their target regions. No waiting period was observed, since on E16 axons were already collateralizing into most targets. On P1, labelled cells were seen in all regions projecting through the anterior commissure in adults, namely, the anterior olfactory nucleus, olfactory tubercle, piriform cortex, nucleus of the lateral olfactory tract, bed nucleus of the stria terminalis, insular, perirhinal, entorhinal, and temporal cortices, as well as the amygdaloid complex. No evidence of topographical exuberance was detected. Counts of labelled neurons showed that the number of commissural cells increased gradually after birth. It is concluded that the development of paleocortical connections through the anterior commissure employs progressive strategies, lacking the regressive phenomena that are characteristic of the neocortical projections through the corpus callosum.     

Musculinization and defeminization induced in female hamsters by neonatal treatment with estradiol, RU-2858, and nafoxidine

Newborn female hamsters were treated with 0.1 or 1.0 ng of estradiol benzoate (EB), with 1.0 ng–2.0 μg of the synthetic estrogen RU-2858, or with 0.1 or 0.5 μg of the antiestrogen nafoxidine. When adult the animals were treated with EB and progesterone and tested for the display of lordosis and with testosterone propionate and tested for the display of mounting behavior. The EB doses used failed to alter sexual differentiation. RU-2858 masculinized and defeminized in a dose-dependent manner being most effective when given neonatally as two divided doses. Nafoxidine inhibited lordosis without enhancing mounting behavior. The findings support the hypothesis that estrogens may be involved in the normal sexual differentiation process.     

Masculinization and defeminization induced in female hamsters by neonatal treatment with estradiol, RU-2858, and nafoxidine

Newborn female hamsters were treated with 0.1 or 1.0 ng of estradiol benzoate (EB), with 1.0 ng–2.0 μg of the synthetic estrogen RU-2858, or with 0.1 or 0.5 μg of the antiestrogen nafoxidine. When adult the animals were treated with EB and progesterone and tested for the display of lordosis and with testosterone propionate and tested for the display of mounting behavior. The EB doses used failed to alter sexual differentiation. RU-2858 masculinized and defeminized in a dose-dependent manner being most effective when given neonatally as two divided doses. Nafoxidine inhibited lordosis without enhancing mounting behavior. The findings support the hypothesis that estrogens may be involved in the normal sexual differentiation process.     

Differential sensitivity of mounting and lordosis control systems to early androgen treatment in male and female hamsters.

The effects of early testosterone propionate (TP) treatment on the adult sexual behavior of hamsters were investigated in two experiments. In Expt. I, male and female pups were injected with oil vehicle or 1, 5, 10, 50, 100, or 250 μg of TP 24 hr after birth. In Expt. II, males and females received either oil or 10 μg of TP on the day of birth (Day 1), Day 3, Day 5, Day 7, or Day 9. At 70 days of age all animals were gonadectomized and 10 days later tested for lordosis behavior after estrogen and progesterone priming. One week after the test for female behavior all females began receiving 500 μg of TP each day and were tested for mounting and intromission behavior three times at 10 day intervals. Lordosis behavior was inhibited by as little as 5 μg of TP given 24 hr after birth. In males this dose produced the maximal effect, but in females increasing dosages resulted in a proportional decrease in lordosis duration. One μg of TP neonatally facilitated later mounting and intromission behavior in females and 250 μg of TP was no more effective than 1 μg. Lordosis duration was inhibited in females by 10 μg of TP on either Day 1 or 3, however, mounts and intromissions were facilitated by TP treatment on Day 1, 3, 5 or 7. These experiments demonstrate that the mechanisms mediating masculine behavior are more sensitive to neonatal TP treatment than are the mechanisms mediating lordosis behavior.     

Hamsters Use Predator Odors as Indirect Cues of Predation Risk

Golden hamsters (Mesocricetus auratus) use olfactory cues to assess traits of conspecifics such as kinship, individual identity, and reproductive status. The environment, however, is full of a wide variety of other olfactory information such as signals emitted by some of the hamster’s primary predators. Given this, we hypothesized that hamsters use odors from predators as an indirect sign of increased predation risk in the environment. In addition, based on data that show that wild hamsters are diurnal while laboratory hamsters are nocturnal, we hypothesized that if golden hamsters did respond to the predator odors, perceived predator risk might influence daily activity patterns in hamsters. We tested male and female hamsters over 5 d with scent gland secretion from domestic ferrets (Mustela putorius furo) and compared their behavior to that observed when they were exposed to a clean arena. In response to the predator odor, subjects significantly decreased the amount of time active outside of their burrow, returned to their burrow more quickly, and spent less time near the predator odor than the clean control stimulus. These results strongly support our hypothesis that hamsters, like other species of small mammals, avoid predator odors. The results did not, however, support our second hypothesis that exposure to predator odors during the dark phase of the light cycle would elicit a switch to a more diurnal pattern of activity. More work is needed to understand how environmental cues and internal mechanisms interact to shape activity patterns.     

Behaviorial effects of a synthetic mixture of aliphatic acids in rhesus monkeys (Macaca mulatta).

The stimulation of sexual behavior by a synthetic mixture of volatile aliphatic acids (acetic, propanoic, methylpropanoic, butanoic, methylbutanoic, methylpentanoic) was studied in male rhesus monkeys. Twelve intact adult males and 12 long-ovariectomized adult females were used in 24 paired combinations (541 tests each of 1 hr). A mixture of authentic acids similar to that found in the vaginal secretions of estrogenized females was applied to the sexual skin area of ovariectomized females immediately before tests with males. There was marked between-pair variability during the application of both control and test substances. However, using rigorous behavioral criteria, there was a well-marked stimulation either of male mounting attempts or of ejaculations in 12 of 24 pairs involving 9 of 12 males. Three males responded with both female partners, three responded with neither female partner, and six responded with one partner only. In the responding pairs, there were highly significant increases in mounting attempts and ejaculations, an effect that could be attributed only to treatment. We conclude, therefore, that these aliphatic acids (copulins), which act via olfactory pathways, have communicatory significance in rhesus monkeys.     

The causation of two scent-marking behaviour patterns in female hamsters (Mesocricetus auratus)

Social, olfactory, and oestrous cycle influences on the frequency of flank-marking and vaginal marking were studied in female hamsters. Vaginal marking was more frequent in the presence of males or their odours than females or their odours. Vaginal marking frequency was greatest the day before oestrus (day 4), intermediate on days 2 and 3, and zero on the oestrous day. The probable sexual advertisement functions of vaginal marking were discussed. In contrast, flank-marking by females was stimulated more by other female odours than by male odours. The frequency of flank-marking was elevated by agonistic encounters and was reduced by sexual encounters. Flank-marking seems to have functions related to functions of aggression among hamsters.     

Behavioral effects of a synthetic mixture of aliphatic acids in rhesus monkeys (Macaca mulatta)

The stimulation of sexual behavior by a synthetic mixture of volatile aliphatic acids (acetic, propanoic, methylpropanoic, butanoic, methylbutanoic, methylpentanoic) was studied in male rhesus monkeys. Twelve intact adult males and 12 long-ovariectomized adult females were used in 24 paired combinations (541 tests each of 1 hr). A mixture of authentic acids similar to that found in the vaginal secretions of estrogenized females was applied to the sexual skin area of ovariectomized females immediately before tests with males. There was marked between-pair variability during the application of both control and test substances. However, using rigorous behavioral criteria, there was a well-marked stimulation either of male mounting attempts or of ejaculations in 12 of 24 pairs involving 9 of 12 males. Three males responded with both female partners, three responded with neither female partner, and six responded with one partner only. In the responding pairs, there were highly significant increases in mounting attempts and ejaculations, an effect that could be attributed only to treatment. We conclude, therefore, that these aliphatic acids (copulins), which act via olfactory pathways, have communicatory significance in rhesus monkeys.     

Lesion of the Olfactory Epithelium Accelerates Prion Neuroinvasion and Disease Onset when Prion Replication Is Restricted to Neurons

Natural prion diseases of ruminants are moderately contagious and while the gastrointestinal tract is the primary site of prion agent entry, other mucosae may be entry sites in a subset of infections. In the current study we examined prion neuroinvasion and disease induction following disruption of the olfactory epithelium in the nasal mucosa since this site contains environmentally exposed olfactory sensory neurons that project directly into the central nervous system. Here we provide evidence for accelerated prion neuroinvasion and clinical onset from the olfactory mucosa after disruption and regeneration of the olfactory epithelium and when prion replication is restricted to neurons. In transgenic mice with neuron restricted replication of prions, there was a reduction in survival when the olfactory epithelium was disrupted prior to intranasal inoculation and there was >25% decrease in the prion incubation period. In a second model, the neurotropic DY strain of transmissible mink encephalopathy was not pathogenic in hamsters by the nasal route, but 50% of animals exhibited brain infection and/or disease when the olfactory epithelium was disrupted prior to intranasal inoculation. A time course analysis of prion deposition in the brain following loss of the olfactory epithelium in models of neuron-restricted prion replication suggests that neuroinvasion from the olfactory mucosa is via the olfactory nerve or brain stem associated cranial nerves. We propose that induction of neurogenesis after damage to the olfactory epithelium can lead to prion infection of immature olfactory sensory neurons and accelerate prion spread to the brain.     

Differential effects of two estrogen antagonists on the development of masculine and feminine sexual behavior in hamsters

To determine whether nonsteroidal antiestrogens can be used to investigate the role of aromatization in behavioral masculinization and defeminization, newborn male and female hamsters were administered 0.5 or 5.0 μg of the antiestrogens nafoxidine or tamoxifen on postnatal Days 1 and 2. Other females received 1.0 μg of the synthetic estrogen RU-2858 (RU) alone or in combination with 0.5 or 5.0 μg of nafoxidine or tamoxifen. All animals were tested for the display of masculine and feminine sexual behaviors in adulthood. Nafoxidine, tamoxifen, and RU all reduced lordosis behavior in adult females, indicating that the antiestrogens probably have some estrogenic properties. Nafoxidine had no effect on male mating behavior in female hamsters when given alone; when given to male hamsters or female hamsters receiving a partially masculinizing dose of RU, this compound effectively reduced the frequencies of masculine sexual behaviors (mounts and intromissions) displayed by the treated animals. However, nafoxidine-treated males had the same mating efficiency (ME = intromissions/ mounts) as control males. Tamoxifen, in contrast, facilitated the display of mounting behavior in females when given alone or in combination with RU. Male hamsters receiving 5.0 μg of tamoxifen had high mount frequencies and slightly reduced intromission frequencies, but their ME scores were only half of control levels. Thus nafoxidine itself simultaneously promoted defeminization and antagonized masculinization while tamoxifen appeared to facilitate both processes. The data support the hypothesis that estrogens derived via aromatization from androgens play an important role in both masculinization and defeminization, at least in hamsters. The differential effects of tamoxifen and nafoxidine suggest that these and other antiestrogens might serve as useful tools for dissociating and independently examining these two components of the sexual differentiation process.     

Estrogen plus androgen induced mounting in adult female hamsters

This study demonstrated that the combined administration of estrogens and androgens activates the display of mounting by female hamsters. Forty-nine ovariectomized hamsters were injected daily with either estradiol benzoate (EB, N = 8); dihydrotestosterone propionate (DHTP, N = 7); testosterone propionate (TP, N = 6); androstenedione (AD, N = 9); EB plus DHTP (N = 10); or estrone plus DHTP (E₁ + DHTP, N = 9). All androgens were administered at a dose of 1 mg per day for the first 24 days and at a dose of 2 mg per day for the last 14 days. The EB dose was 6 μg per day and the E₁ dose was 100 μg per day. Females were tested for male behavior once a week starting on Day 10 of injections and for female behavior on Day 39.One hundred percent of EB + DHTP treated females; 67% of the E₁ + DHTP treated females; 55% of the AD treated females; 33% of the TP treated females; 29% of the DHTP treated females; and none of the EB treated females mounted during at least one test. Only one of the E₁ + DHTP treated females showed the intromission pattern; otherwise most females which mounted displayed the intromission pattern. The median number of days preceding the onset of mounting ranged from 21 to 31 days and did not differ among treatment groups.     

Influences of the paraventricular and suprachiasmatic nuclei and olfactory bulbs on melatonin responses in the golden hamster

Removal of the pineal, or denervation of this gland by superior cervical ganglionectomy, blocks testicular regression in golden hamsters exposed to short photoperiods. Aspiration of the olfactory bulbs or lesions of the suprachiasmatic or paraventricular nuclei of the hypothalamus (SCNx or PVNx) have similar effects. We have examined the effects of these operations on pineal melatonin content and gonadal responses to various patterns of exogenous melatonin in order to examine the roles played by the olfactory bulbs, the SCN, and the PVN in hamster photoperiodism. SCNx and PVNx significantly reduced pineal melatonin content throughout the dark phase, while bulbectomy did not significantly affect melatonin concentrations at the time of the nocturnal peak. Bulbectomy significantly delayed the nightly onset of locomotor activity in hamsters exposed to 14L:10D, but not that of animals housed in 10L:14D. Although bulbectomy reduced the gonadal response to one or three daily injections of melatonin, these individuals exhibited significant testicular regression in response to melatonin as long as injections fell in the evening. In contrast, destruction of the PVN rendered hamsters unresponsive to one daily melatonin injection, but equally responsive to three injections, regardless of the time of day at which these injections were given. Whereas exposure of bulbectomized hamsters to 30 weeks of short days made them refractory to subsequent melatonin challenge, PVNx hamsters remained sensitive to appropriately timed melatonin treatments regardless of their photoperiodic history. Many, but not all hamsters that experienced complete SCN lesions remained sensitive to three daily melatonin injections.(ABSTRACT TRUNCATED AT 250 WORDS)     

The nasal cavity is a route for prion infection in hamsters

Animals that naturally acquire the prion diseases have a well-developed olfactory sense that they utilize for a variety of basic behaviors. To assess the potential for the nasal cavity to serve as a point of entry for prion diseases, a small amount of prion-infected brain homogenate was placed inferior to the nostrils of hamsters, where it was immediately sniffed into the nasal cavity. Hamsters extra-nasally inoculated with the HY strain of transmissible mink encephalopathy (TME) agent had an incubation period that was not significantly different from per os inoculation of the same dose of the HY TME agent. However, the efficiency of the nasal route of inoculation was determined to be 10 to 100 times greater based on endpoint dilution analysis. Immunohistochemistry on tissues from hamsters killed at 2-week intervals after inoculation was used to identify the disease-associated form of the prion protein (PrP(d)) to determine the route of prion neuroinvasion. Nasal mucosa-associated lymphoid tissue and submandibular lymph nodes initially accumulated PrP(d) as early as 4 weeks postinfection. PrP(d) was first identified in cervical lymph nodes at 8 weeks, in the mesenteric lymph nodes, spleen, and Peyer's patches at 14 weeks, and in the tongue 20 weeks after inoculation. Surprisingly, there was no evidence of PrP(d) in olfactory epithelium or olfactory nerve fascicles at any time after inoculation. Therefore, the HY TME agent did not enter the central nervous system via the olfactory nerve; instead, PrP(d) accumulated in elements of the cranial lymphoreticular system prior to neuroinvasion.     

Mounting behavior and lordosis behavior in castrated male rats treated with testosterone propionate, or with estradiol benzoate or dihydrotestosterone in combination with testosterone propinonate.

Treatment of prepuberally castrated male rats with testosterone propionate (TP, 50, 200, 500, or 1000 μg for 30 days) in adulthood stimulated the display of both mounting behavior and lordosis behavior. No correlation between mounting and lordosis behavior could be detected at any TP dose level. Treatment of prepuberally castrated male rats with either 1 μg estradiol benzoate (EB) or 500 μg dihydrotestosterone (DHT) for 60 days stimulated the display of mounting behavior in three of eight and four of eight rats, respectively. Treatment with 200 μg TP for the last 30 days of rats receiving either EB or DHT for 60 days resulted in an abrupt onset on mounting behavior as compared to rats treated with oil for 60 days. These results show additive effects of EB or DHT and TP upon mounting behavior by male rats and are interpreted as a support for the suggestion that testosterone to estrogen as well as testosterone to DHT conversion may be involved in the mechanism whereby testosterone activates the mounting behavior of castrated rats.