On the scent of sexual attraction

A study in the current issue of BMC Biology has identified a mouse major urinary protein as a pheromone that attracts female mice to male urine marks and induces a learned attraction to the volatile urinary odor of the producer. See research article http://www.biomedcentral.com/1741-7007/8/7

Attraction to sexual pheromones and associated odorants in female mice involves activation of the reward system and basolateral amygdala

Adult female mice are innately attracted to non-volatile pheromones contained in male-soiled bedding. In contrast, male-derived volatiles become attractive if associated with non-volatile attractive pheromones, which act as unconditioned stimulus in a case of Pavlovian associative learning. In this work, we study the chemoinvestigatory behaviour of female mice towards volatile and non-volatile chemicals contained in male-soiled bedding, in combination with the analysis of c-fos expression induced by such a behaviour to clarify: (i) which chemosensory systems are involved in the detection of the primary attractive non-volatile pheromone and of the secondarily attractive volatiles; (ii) where in the brain male-derived non-volatile and volatile stimuli are associated to induce conditioned attraction for the latter; and (iii) whether investigation of these stimuli activates the cerebral reward system (mesocorticolimbic system including the prefrontal cortex and amygdala), which would support the view that sexual pheromones are reinforcing. The results indicate that non-volatile pheromones stimulate the vomeronasal system, whereas air-borne volatiles activate only the olfactory system. Thus, the acquired preference for male-derived volatiles reveals an olfactory-vomeronasal associative learning. Moreover, the reward system is differentially activated by the primary pheromones and secondarily attractive odorants. Exploring the primary attractive pheromone activates the basolateral amygdala and the shell of nucleus accumbens but neither the ventral tegmental area nor the orbitofrontal cortex. In contrast, exploring the secondarily attractive male-derived odorants involves activation of a circuit that includes the basolateral amygdala, prefrontal cortex and ventral tegmental area. Therefore, the basolateral amygdala stands out as the key centre for vomeronasal-olfactory associative learning

Attraction to male pheromones and sexual behaviour show different regulatory mechanisms in female mice

In rodents, female sexual behaviour is under hormonal control. The attraction females show for male-derived nonvolatile chemicals (pheromones) can be regarded as the first step of this behaviour, but it is unknown whether this attraction is also modulated by sexual steroids. To test this possibility, ovariectomized adult female mice with no experience of chemical signals from adult males were randomly assigned to four groups that received oil (control), progesterone, estradiol (E) or estradiol+progesterone (E+P) injections, respectively. Females were then tested for their attraction to male-soiled bedding and, subsequently, for their proceptive behaviour when confronted to adult males. Females showed attraction to male-soiled bedding irrespective of the hormonal treatment, whereas only those females treated with E or E+P showed proceptive behaviour. Therefore, in contrast to proceptive and copulatory behaviour, the female attraction to male pheromones is independent of sexual steroids, thus indicating that those parts of the vomeronasal system involved in this attraction do not respond to steroids. In summary, sexual behaviour in female mice can be seen as a two-step process. First, females are attracted by male pheromones, a process which is independent of their hormonal status. After encountering the males, females show proceptive behaviour only in estrous, when fertilization is more likely. The attraction exerted by male sexual pheromones promotes female autostimulation that might ensure anticipatory endocrine changes leading to ovulation by the time of sexual intercourse

Understanding the basic circuitry of the cerebral hemispheres: the case of lizards and its implications in the evolution of the telencephalon

The organization of the cerebral hemispheres of mammals is characterized by corticostriatal glutamatergic projections and striatopallidal GABAergic ones, plus the descending projections of the pallium and subpallium to extratelencephalic targets. The present review of the available neuroanatomical data on the forebrain of lizards suggests that the telencephalon of reptiles also follows this basic pattern of connectivity. In addition, we show that this basic circuitry includes a pallido-cortical projection, therefore forming a cortico-striato-pallido-cortical circuit. The analysis of this circuitry for the medial, dorsal, lateral, and ventral pallial divisions in reptiles and mammals leads to the following conclusions: (1) The medial and dorsal cortices of lizards together appear to be equivalent to the medial pallium of mammals. (2) The projection from the lacertilian dorsal cortex to the striatum proper resembles the subiculo-striatal projection of mammals, rather than the isocortical projection to the caudatus-putamen. (3) Most of the dorsal striatum of reptiles is engaged in the corticostriatal circuit corresponding to the ventral pallium (the anterior dorsal ventricular ridge), and therefore, it is not equivalent to the mammalian caudatus-putamen, which is involved in the circuit of the dorsal pallium. (4) The main and accessory olfactory bulbs also follow this pattern of connections

Attractive properties of sexual pheromones in mice: Innate or learned?

It is generally assumed that chemical signals (sexual pheromones) constitute the primary stimulus for sexual attraction in many mammals. However, it is unclear whether these pheromones are volatile or nonvolatile and which sensory systems are involved in their detection (vomeronasal and/or olfactory). Moreover, it has been demonstrated that experience influences the behavioral response to sexual pheromones and the sensory systems implicated. In order to clarify this issue, the attractive properties of volatile and nonvolatile components of the male-soiled bedding have been analyzed in female mice that had no previous experience with adult male-derived chemical signals (chemically naı̈ve females) using two-choice preference tests. The results indicate that some nonvolatile male-derived substances exert an innate attraction to females, but volatiles derived from male-soiled bedding do not attract chemically naı̈ve females. Therefore, the primary attractive sexual pheromone includes a nonvolatile compound (e.g. major urinary proteins, MUPs). On the other hand, male-derived volatiles become attractive to females because of repeated exposure to male-soiled bedding. This represents a Pavlovian-like associative learning in which previously neutral volatiles (very likely odorants) acquire attractive properties by association with the nonvolatile, innately attractive pheromone(s). These findings indicate that not only the sexual but also the ‘chemical’ experience (previous experience with sexual pheromones) has to be taken into account to interpret the role of chemicals as releaser or primer pheromones. The sensory systems involved in the detection of these stimuli and the neural basis of the odor–pheromone association are discussed

Neural Correlates of Phrase Rhythm: An EEG Study of Bipartite vs. Rondo Sonata Form

This paper introduces the neural correlates of phrase rhythm. In short, phrase rhythm is the rhythmic aspect of phrase construction and the relationships between phrases. For the sake of establishing the neural correlates, a musical experiment has been designed to induce music-evoked stimuli related to phrase rhythm. Brain activity is monitored through electroencephalography (EEG) by using a brain–computer interface. The power spectral value of each EEG channel is estimated to obtain how power variance distributes as a function of frequency. Our experiment shows statistical differences in theta and alpha bands in the phrase rhythm variations of two classical sonatas, one in bipartite form and the other in rondo form