Culture of Neurospheres Derived from the Neurogenic Niches in Adult Prairie Voles

Neurospheres are primary cell aggregates that comprise neural stem cells and progenitor cells. These 3D structures are an excellent tool to determine the ...

Universidad Nacional Autónoma de México

We have previously shown that sexual behavior induces a reward state, as evaluated by conditioned place preference (CPP), only when males or females are able to control the rate of sexual interaction. In the present experiment, we evaluated if male rats that are repeatedly tested in a situation in which they are not able to control the sexual interaction eventually develop CPP. Three groups of sexually naïve male rats were used. One group never mated. A second group was tested once a week for 10 consecutive weeks in a chamber in which they controlled the rate of the sexual interaction. The third group was mated for the same number of weeks in a chamber in which the female, but not the male, controlled mating. The three groups were then tested for CPP. Only the group able to control the sexual interaction developed CPP. The group that had no control over the rate of the sexual interaction did not develop CPP even after 10 tests in which they consistently displayed sexual behavior. These results suggest that an estrous female and/or sexual behavior are powerful incentives that maintain mating even if the rewarding properties of the incentive are reduced.

Sexual experience and conditioned place preference in male rats.

Estrous female rats pace their coital contacts to control the rate of cervical/vaginal stimulation. Females that receive at least 10 paced intromissions develop a reward state, evaluated by conditioned place preference (CPP), whereas females that do not pace their coital contacts do not develop CPP. We asked if the blockade of androgen receptors could modify the number of intromissions needed during paced mating to develop CPP. Pregnant females received daily injections of the androgen receptor antagonist flutamide from day 12 of pregnancy until pups were born. When adults, females exposed prenatally to flutamide or vehicle were ovariectomized and hormonally primed to evaluate if paced and non-paced mating induced CPP. The prenatal flutamide treatment did not affect the capacity of females to develop CPP to a systemic morphine injection. Flutamide-treated females that paced their sexual contacts developed CPP with fewer intromissions than control females. No effect on conditioning was observed when females were not allowed to pace their sexual contacts. The results suggest the existence of a threshold of cervical/vaginal stimulation that correlates with the induction of a reward state and that this threshold can be reduced by prenatal blockade of androgen receptors.

Prenatal blockade of androgen receptors reduces the number of intromissions needed to induce conditioned place preference after paced mating in female rats.

The serotonin 1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) produces a drastic facilitation of ejaculation characterized by a significant reduction in the number of pre-ejaculatory intromissions and a shortening of ejaculation latency. In the present study, the authors evaluated whether this facilitation of ejaculation can induce a reward state assessed by conditioned place preference. Males treated with 0.1 or 1.0 mg/kg of 8-OH-DPAT showed a clear facilitation of ejaculation but did not develop conditioned place preference. These results clearly indicate that the pharmacological facilitation of ejaculation and the reduction of the number of intromissions does not necessarily make sex rewarding.

Facilitation of ejaculation induced by 8-OH-DPAT does not produce conditioned place preference in male rats.

Paced mating reduces the aversive properties and increases the positive characteristics of mating, inducing a reward state. Pacing is able to induce conditioned place preference (CPP), whereas nonpaced mating does not. The authors hypothesized that the aversive properties of mating are caused by androgens from adjacent males or from the mother during fetal life. To test whether aromatization of androgens induces the aversive properties of mating, female rats were treated perinatally with 1,4,6-androstatriene-3, 17-dione (ATD) to inhibit aromatization. When adults, these females were ovariectomized and hormonally primed to evaluate CPP after paced and nonpaced mating. During paced mating, control females showed higher return latencies after ejaculation, whereas ATD-treated females did not show a similar increase. In CPP tests, both paced and nonpaced mating induced a reward state in ATD-treated females, whereas only paced mating induced a reward state in control females. These results show that the perinatal inhibition of aromatization enhances the rewarding properties of mating, suggesting that estradiol induced the aversive properties of mating and/or modified the perinatal organization of the neuronal pathways in females.

Perinatal inhibition of aromatization enhances the reward value of sex.

The ability to control or pace the sexual interaction has important physiological and behavioral consequences for the female rat. Paced mating favors reproduction and induces a positive affective state as revealed by conditioned place preference (CPP). In the present experiment we evaluated: 1) If paced mating induces CPP in naturally cycling females; 2) If females developed a positive affective state if they paced the sexual interaction through a 1- or a 3-hole pacing chamber; 3) If females that mate with the same male without pacing the sexual interaction develop CPP. In the first experiment intact females were divided in 4 different groups; 2 paced the sexual interaction until receiving 1 or 3 ejaculations; the other 2 groups mated, without pacing the sexual interaction, until receiving 1 or 3 ejaculations. Only the group that paced the sexual interaction until receiving 3 ejaculations developed a positive affective state. In experiments 2 and 3 hormonally treated ovariectomized females were used. In experiment 2 females were allowed to pace the sexual interaction through a 1- or a 3-hole pacing chamber: A clear positive affective state was induced in both testing conditions. Finally, in experiment 3 females did not develop CPP for non-paced sex despite the fact that they mated with the same male in the conditioning sessions. These results demonstrate that the pattern of vaginocervical stimulation that the females received by engaging in approach and avoidance behaviors to pace the sexual interaction can induce a positive affective state in naturally cycling females. They also confirm the existence of a threshold of vaginocervical stimulation for paced mating to induce CPP in female rats.

Hormonal and testing conditions for the induction of conditioned place preference by paced mating.

The present experiment was designed to determine if intromissions alone could induce a reward state as evaluated by conditioned place preference (CPP). We also compared the rewarding properties of one ejaculation and a morphine injection. We evaluated if intromissions alone could induce CPP in males with one or three ejaculations as previous sexual experience. Different groups of males were allowed to display 5, 10, and 15 intromissions or an ejaculation with a sexually receptive female before being placed in the originally non-preferred compartment of a CPP cage. On alternate days they were placed in the preferred compartment. The groups that displayed 5 or 10 intromissions did not modify their original preference, regardless of whether they had experienced 1 or 3 ejaculations before the conditioning procedure. The groups that had experienced 1 ejaculations that were allowed to display 15 intromissions or one ejaculation modified their original preference indicating the induction of a reward state. These results suggest that male rats displaying sexual behavior require a minimum amount of stimulation, 15 intromissions or an ejaculation, in order for sex to be sufficiently rewarding to induce CPP. In a separate experiment we evaluated if a morphine injection (1mg/kg) has the same reward value that one ejaculation in male rats has. Two groups of sexually active males were used, in one group ejaculation was paired with the initially non-preferred compartment and morphine administration was paired with the initially preferred compartment. In the other group morphine injection was paired with the non-preferred compartment and ejaculation with the preferred compartment. None of the groups changed their originally preferred compartment suggesting that morphine and one ejaculation have the same reward value in male rats.

Reward value of intromissions and morphine in male rats evaluated by conditioned place preference.

An important number of Sprague-Dawley males selected by strict inbreeding process for their high spontaneous yawing frequency (HY) fail to copulate after repeated exposure to receptive females. These HY males that fail to mate are called non-copulators (HYNC). The causes of this behavioral deficit are still unknown. The aim of the present study was to make a detailed behavioral characterization of these animals by evaluating: their partner preference between a sexually receptive female as opposed to a sexually active male; their ability to detect food related odors and their preference for sexually relevant chemosensory cues between bedding from estrous females, bedding from sexually active males and clean bedding. We also evaluated whether these males had alterations in motor function using a rotarod or in their general reward system mediated by opioids by injecting them with 1mg/kg of morphine to evaluate if they develop conditioned place preference (CPP). At the end of these behavioral tests, we measured their plasmatic levels of testosterone (T). Together, these results will contribute to elucidate the causes of their deficient copulatory performance. Both HYNC and HY copulators (HYC) males showed a clear preference for receptive females as opposed to sexually active males. As well, both groups of animals had a similar ability to detect food related odors. HYC males had a clear preference for estrous female odors as opposed to male or clean bedding, but HYNC males spend the same amount of time sniffing estrous, anestrous, male and clean bedding. In both, HYC and HYNC, morphine induced CPP suggesting that in these males the reward system is functional. No differences were found in motor coordination or in T levels between HY and HYNC males. The behavioral deficit in HYNC male rats cannot be explained by an alteration in: partner preference, food related odor recognition, motor coordination, general reward system, or differences in plasmatic levels of T. However, HYNC males present clear deficits in recognizing sexually relevant odors. These results could, at least in part, explain the deficient execution of copulatory pattern in HYNC males.

Behavioral characterization of non-copulating male rats with high spontaneous yawning frequency rate.

The ovarian hormones estrogen and progesterone are required for the complete display of sexual behavior in female rats. Paced mating produces a reward state in intact cycling and ovariectomized (OVX), hormonally primed females as evaluated by the conditioned place preference (CPP) paradigm. Most of the studies that have evaluated CPP induced by paced mating in OVX females have used relatively high doses of estradiol benzoate (EB). In the present study we determined if different doses of EB, combined with progesterone (P), could induce CPP after paced mating. For this purpose OVX female rats were divided in five groups that received one of different doses of estradiol benzoate (5, 2.5, 1.25 or 0.625 μg estradiol+0.5mg of progesterone) before being allowed to pace the sexual interaction and conditioned in a CPP paradigm. We found that the lowest dose of EB used (0.625 μg) significantly reduced the lordosis quotient and the lordosis coefficient. Even though these females paced the sexual interaction, they didn't change its original preference, suggesting that sexual interaction did not induce a positive affective, reward state. Females allowed to pace the sexual interaction with higher doses of EB developed CPP after paced mating. These results indicate that a threshold of estradiol is required for paced mating to induce CPP.

Different doses of estradiol benzoate induce conditioned place preference after paced mating.

In rodents, sexual behavior depends on the adequate detection of sexually relevant stimuli. The olfactory bulb (OB) is a region of the adult mammalian brain undergoing constant cell renewal by continuous integration of new granular and periglomerular neurons in the accessory (AOB) and main (MOB) olfactory bulbs. The proliferation, migration, survival, maturation, and integration of these new cells to the OB depend on the stimulus that the subjects received. We have previously shown that 15 days after females control (paced) the sexual interaction an increase in the number of cells is observed in the AOB. No changes are observed in the number of cells when females are not allowed to control the sexual interaction. In the present study we investigated if in male rats sexual behavior increases the number of new cells in the OB. Male rats were divided in five groups: (1) males that did not receive any sexual stimulation, (2) males that were exposed to female odors, (3) males that mated for 1 h and could not pace their sexual interaction, (4) males that paced their sexual interaction and ejaculated one time and (5) males that paced their sexual interaction and ejaculated three times. All males received three injections of the DNA synthesis marker bromodeoxyuridine at 1h intervals, starting 1 h before the beginning of the behavioral test. Fifteen days later, males were sacrificed and the brains were processed to identify new cells and to evaluate if they differentiated into neurons. The number of newborn cells increased in the granular cell layer (GrCL; also known as the internal cell layer) of the AOB in males that ejaculated one or three times controlling (paced) the rate of the sexual interaction. Some of these new cells were identified as neurons. In contrast, no significant differences were found in the mitral cell layer (also known as the external cell layer) and glomerular cell layer (GlCL) of the AOB. In addition, no significant differences were found between groups in the MOB in any of the layers analyzed. Our results indicate that sexual behavior in male rats increases neurogenesis in the GrCL of the AOB when they control the rate of the sexual interaction.

Sexual activity increases the number of newborn cells in the accessory olfactory bulb of male rats.

Sexual receptivity in female rodents induced by the sequential injection of estrogen and progesterone is followed by a period in which females do not respond behaviorally to a second administration of progesterone (P); this is known as sequential inhibition. It has been proposed that the induction of sequential inhibition by progesterone in rats depends on down regulation of the progesterone receptor (PR) in brain areas involved in the expression of female sexual receptivity. P is rapidly metabolized to a variety of 5α- or 5β-ring A-reduced progestins (RPrg). These RPrg have little or no affinity for the PR. They stimulate sexual receptivity (lordosis) more potently than P itself in estrogen-primed rats and do not induce sequential inhibition. The purpose of the current study was to test the role of the PR in the facilitation of lordosis and sequential inhibition induced by P and the following RPrg: 5α-pregnandione (5α-DHP), 5α,3β-pregnanolone (5α,3β-Pgl), 5β-pregnanedione (5β-DHP), and 5β,3α-pregnanolone (5β,3α-Pgl) in ovariectomized (ovx) female mice primed with estradiol benzoate. The RPrg were tested in C57BL/6 mice and in a strain lacking the progesterone receptor expression (PRKO). Our results show that both facilitation and sequential inhibition of lordosis induced by progesterone require the presence of the progesterone receptor. Interestingly, some RPrg facilitate lordosis but do not induce sequential inhibition in female mice. Sexual receptivity induced by RPrg does not require the progesterone receptor. Thus, RPrg induce sexual receptivity, but they probably exert their effects through a different cellular mechanism that does not involve the progesterone receptor. (PsycINFO Database Record

Participation of progesterone receptors in facilitation and sequential inhibition of lordosis response induced by ring A-reduced progesterone metabolites in female mice.

Francisco Camacho

Departamento de Neurobiología Conductual y Cognitiva,
Instituto de Neurobiología,
Departamento de Neurobiología Conductual y Cognitiva, Instituto de Neurobiología

Universidad Nacional Autónoma de México

Culture of Neurospheres Derived from the Neurogenic Niches in Adult Prairie Voles

Francisco Camacho

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Universidad Nacional Autónoma de México

Culture of Neurospheres Derived from the Neurogenic Niches in Adult Prairie Voles

Departamento de Neurobiología Conductual y Cognitiva,
Instituto de Neurobiología,
Departamento de Neurobiología Conductual y Cognitiva, Instituto de Neurobiología