[Olfaction in depressive disorders: Issues and perspectives]

Research on sensorial interactions with psychiatric diseases and particularly with the depressive syndrome has mainly focused on visual or auditory processes and much less on olfaction. The depressive illness is one of the most frequent psychiatric diagnoses in the community, with approximately one in five women and one in eight men experiencing a major depressive episode during their lifetime. Although genetic, epigenetic, neuroanatomical, neurochemical, neuroendocrinological and neuroimmunological changes can be detected during depression, the etiology of depression remains partly unclear. The current explanatory models are based on two main factors, i.e. pharmacological dysfunctions and stress effects. In this way and because of strong connections between olfactory pathways and cerebral areas implied in mood regulation and emotions (i.e. the limbic system and prefrontal areas), the interactions between olfaction and depression could constitute a relevant way of research at three different levels. First, olfactory dysfunction observed in depression could serve the diagnosis and contribute to a better understanding of mechanisms implied in thymic pathologies. Published papers show a decrease of olfactory sensitivity in major depression which does not occur in bipolar or saisonal depression. Second, it has been shown that olfactory deficits could induce depressive symptoms. In this context, an animal model (olfactory bulbectomized rat) reinforces the hypothesis of the important role of olfaction in depression based on neuroanatomical and neurochemical observations. Third, several publications have demonstrated that odors can positively impact the depressive mood. Thus, a remediation by odors in depression appears to be a promising way. From several decades, the olfaction/depression interactions have been covered by a broad literature. Thus, the present review will not propose an exhaustive examination but aims to point out the most recently published papers and highlight their contributions to the understanding of olfactory processes implied in depression.

Pheromone-induced odor learning modifies Fos expression in the newborn rabbit brain

Associative learning contributes crucially to adjust the behavior of neonates to the permanently changing environment. In the European rabbit, the mammary pheromone (MP) excreted in milk triggers sucking behavior in newborns, and additionally promotes very rapid learning of initially neutral odor cues. Such stimuli become then as active as the MP itself to elicit the orocephalic motor responses involved in suckling. In this context, the rabbit is an interesting model to address the question of brain circuits early engaged by learning and memory. Here, we evaluated the brain activation (olfactory bulb and central regions) induced in 4-day-old pups by an odorant (ethyl acetoacetate, EAA) after single pairing with the MP and its subsequent acquired ability to elicit sucking-related behavior (conditioned group) or after mere exposure to EAA alone (unconditioned group). The brain-wide mapping of c-Fos expression was used to compare neural activation patterns in both groups. Evidence of high immunostaining to odorant EAA occurred in the mitral+granule cells layer of the main olfactory bulb in pups previously exposed to EAA in association with the MP. These pups also showed higher expression of Fos in the piriform cortex, the hypothalamic lateral preoptic area and the amygdala (cortical and basal nuclei). Thus, MP-induced odor learning induces rapid brain modifications in rabbit neonates. The cerebral framework supporting the acquisition appears however different compared to the circuit involved in the processing of the MP itself.

Brain processing of the mammary pheromone in newborn rabbits

Chemosignals strongly contribute to social interactions in mammals, including mother-young relationships. In the European rabbit, a volatile compound emitted by lactating females in milk, the 2-methylbut-2-enal, has been isolated. Carrying the properties of a pheromone, in particular the spontaneous ability to release critical sucking-related movements in newborns, it has been called the mammary pheromone (MP). Lesion of the vomeronasal organ and preliminary 2-deoxyglucose data suggested that the MP could be processed by the main olfactory system. However, the neuronal substrate that sustains the MP-induced response of neonates remained unknown. Here, we evaluated Fos expression in 4-day-old-rabbits exposed to the MP (in comparison with control neonates exposed to non-relevant odorant, no odorant or unmanipulated pups) both at the level of the olfactory bulb and central brain regions. Evidence of high and widespread Fos immunoreactivity in the main olfactory bulb appear in MP pups while the accessory olfactory bulb exhibits a negligible staining. However, no obvious bulbar pattern of Fos expression is observed, when in contrast a certain pattern emerges with the neutral odorant. Compared to this latter, the MP exposure increases Fos expression in the anterior piriform cortex, the organum vasculosum of the lamina terminalis and the habenula, with a tendency in the lateral preoptic region. For the first time, a pheromone essential for mother-young interaction is thus highlighted for its processing by the main olfactory system, the whole olfactory bulb, and by brain regions involved in osmoregulation, thirst and motivation-guided motor responses.

Correlation between olfactory bulb volume and olfactory function in children and adolescents

The olfactory bulb (OB) is considered to be the most important relay station in odor processing. The present study aimed to investigate the volumetric development of the human bulb and the olfactory function during childhood and youth. Furthermore, the present study aimed to investigate a possible correlation between OB volume and specific olfactory functions including odor threshold, odor discrimination and odor identification. A total of 87 subjects (46 boys, 41 girls), aged 1-17 years (mean age 8 years), participated in this study. None of them reported olfactory dysfunction or had signs of a dysfunctional sense of smell. Whenever possible, participants received a volumetric scan of the brain and lateralized olfactory tests. Volumetric measurements of the right and left OB were taken by manual segmentation of the coronal slices through the OB. Significant correlations between OB volumes and olfactory function were observed. Both, OB volumes and olfactory function increased with age, although the correlation between structure and function was not mediated by the subjects' age. In conclusion, for the first time, the present study showed a correlation between OB volume and olfactory functions in children.

Subliminal fear priming potentiates negative facial reactions to food pictures in women with anorexia nervosa

BACKGROUND

To investigate hedonic reactivity and the influence of unconscious emotional processes on the low sensitivity to positive reinforcement of food in anorexia nervosa (AN).

METHOD

AN and healthy women were exposed to palatable food pictures just after a subliminal exposure to facial expressions (happy, disgust, fear and neutral faces), either while fasting or after a standardized meal (hunger versus satiety). Both implicit [facial electromyographic (EMG) activity from zygomatic and corrugator muscles, skin conductance, heart rate, and videotaped facial behavior] and explicit (self-reported pleasure and desire) measures of affective processes were recorded.

RESULTS

In contrast to healthy women, the AN patients did not display objective and subjective indices of pleasure to food pictures when they were in the hunger states. Pleasure to food cues (liking) was more affected than the desire to eat (wanting) in AN patients. Subliminal 'fear faces' increased corrugator muscle reactivity to food stimuli in fasting AN patients, as compared to controls.

CONCLUSIONS

The results suggest that unconscious fear cues increase the negative appraisal of alimentary stimuli in AN patients and thus contribute to decreased energy intake.

Metacognition in action: the importance of implementation intentions

When people furnish their goal intentions ("I intend to attain the goal x!") with implementation intentions ("I will initiate the goal-directed response y when situation z arises!"), the initiation of goal-directed responses becomes automatized. As this type of automaticity stems from a single act of will, it is referred to as strategic automaticity. We report various studies demonstrating that strategic automaticity leads to immediate and efficient responding, which does not need a conscious intent. In addition, the situational cues specified in implementation intentions seem to be easily detected and readily attended to. Further research indicates that the strategic automaticity induced by implementation intentions also helps resist temptations and fight bad habits. Following Nelson's (1996; Nelson & Narens, 1994) model of metacognition, we suggest that goal intentions and, in particular, implementation intentions are important components of the metacognitive control of action geared toward its initiation, continuation, and termination.

Salivary cortisol and aggression in a population-based longitudinal study of adolescent males

Chronic antisocial behaviour in youth has been associated with cortisol, a measure of stress reactivity. However, some studies have found low cortisol levels, while others have found elevated cortisol levels. The present study compared variously defined aggressive subgroups for differences in salivary cortisol. A population-based sample of boys was followed longitudinally from childhood to adolescence. Assessments of different forms of antisocial behaviour were obtained from various informants at several points in time, and cortisol was collected at age 13. Higher cortisol levels were found in boys with conduct disorder (CD) than in boys without CD. In addition, boys with an aggressive form of CD had higher cortisol levels than boys who showed a covert form of CD. Furthermore, reactive aggression was strongly correlated with elevated cortisol. Adolescent boys with chronic reactive aggression and those who scored high on aggressive CD symptoms seem to have a more active hypothalamic-pituitary-adrenal system.

Behavioural, growth and immune consequences of early weaning in one-week-old large-white piglets

Genetic improvement in sows' prolificity is limited by their milk capacities, which do not allow all piglets to survive or grow normally. This experiment compared the behaviour, growth and immune responses of piglets that were weaned early at 6 days of age (EW) vs. control Large White piglets' (C) suckled by their mothers. Behaviour of 9 litters of 5 to 8 piglets in each group were observed from d5 to d20. All piglets were weighed from birth to d74. Three piglets from each group were slaughtered on d36 for immunological analysis. Until they began to eat dry food, EW piglets walked and vocalised more than C piglets. After that time, when resting, they were less often lying down and more frequently in contact with littermates under the heater. Aggressive behaviour and belly-nosing were more frequent. They displayed a more marked growth check after weaning than did C piglets until 28 days of age. In EW piglets, at 36 days of age, there was a higher density of T- and B-lymphocytes in the gut epithelium and lamina propria, fespectively, in relation to the size of lymphoid follicles of Peyer's patches. The results indicate great behavioural adaptation capacities of very early-weaned piglets, together with earlier maturation of their gut immune system.

Neuroendocrine consequences of very early weaning in swine

An experiment was conducted to investigate the consequences of very early weaning of piglets on neuroendocrine variables and growth. Sixty piglets from eight litters were either weaned on Postnatal Day 6 (early weaning, or EW piglets) or left with their dam until normal weaning at Day 28 (control piglets, or C). At Days 5, 7, 11, 14, and 19, urine was collected between 7:00 and 8:00 a.m. for the measurement of catecholamines, glucocorticoids, and creatinine. Compared with C, EW piglets displayed a transient increase in urinary cortisol on the day following separation from their dam (Day 7) (P<.05). Urinary norepinephrine (NE) was three times lower in EW compared to C piglets from Day 7 until Day 14 (P<.01) but there was no difference between the two groups on Day 19. Urinary epinephrine (EPI) did not differ between C and EW piglets on the day after weaning. Thereafter, EW piglets displayed a three times drop in urinary EPI as compared to C piglets until the end of the period (P<.01). Weaning induced an immediate reduction in food intake and growth rate and at Day 28, the body weight of EW piglets was 1.60 kg lower than that of C piglets (P<.0001). In conclusion, weaning of 6-day-old piglets results in a marked and prolonged suppression of the release of catecholamines. This result likely reflects physiological responses to insufficient energy intake after weaning, as reflected also by changes in thermoregulatory behavior. The transient increase in cortisol excretion in weanlings may be caused by both emotional distress and acute food deprivation.

Microsatellite variation in cassava (Manihot esculenta, Euphorbiaceae) and its wild relatives: further evidence for a southern Amazonian origin of domestication

Genetic variation at five microsatellite loci was used to investigate the evolutionary and geographical origins of cassava (Manihot esculenta subsp. esculenta) and the population structure of cassava's wild relatives. Two hundred and twelve individuals were sampled, representing 20 crop accessions, 27 populations of cassava's closest wild relative (M. esculenta subsp. flabellifolia), and six populations of a potentially hybridizing species (M. pruinosa). Seventy-three alleles were observed across all loci and populations. These data indicate the following on cassava's origin: (1) genetic variation in the crop is a subset of that found in the wild M. esculenta subspecies, suggesting that cassava is derived solely from its conspecific wild relative. (2) Phenetic analyses group cassava with wild populations from the southern border of the Amazon basin, indicating this region as the likely site of domestication. (3) Manihot pruinosa, while closely related to M. esculenta (and possibly hybridizing with it where sympatric), is probably not a progenitor of the crop. Genetic differentiation among the wild populations is moderately high (F:(ST) = 0.42, rho(ST) = 0.54). This differentiation has probably arisen primarily through random genetic drift (rather than mutation) following recent population divergence.

Human foetuses learn odours from their pregnant mother's diet

Olfactory responsiveness was assessed in 24 neonates born to mothers who had or had not consumed anise flavour during pregnancy. Both groups of infants were followed-up for behavioural markers of attraction and aversion when exposed to anise odour and a control odour immediately after birth and on day 4. Infants born to anise-consuming mothers evinced a stable preference for anise odour over this period, whereas those born to anise non-consuming mothers displayed aversion or neutral responses. This study provides the first clear evidence that through their diet human mothers influence the hedonic polarity of their neonates' initial olfactory responses. The findings have potential implications for the early mother-to-infant transmission of chemosensory information relative to food and addictive products.

Role of mother-young interactions in the survival of offspring in domestic mammals

The defining characteristic of mammals is that females nurse and care for their young; without this, the neonate has no chance to survive. Studies on wild and domestic species show that the neonatal period is the most critical step in the lifetime of a mammal. This review compares three well-studied species (the rabbit, pig and sheep) that differ in their parental strategies and in the problems that neonates have to overcome. As a general trend, mother-young interactions vary according to the maturity of the newborn, and the size of the litter. Neonatal survival relies to a great extent on an environment that is ecologically appropriate for the developmental stage of the neonate, and on optimum interactions with the mother. Adaptive maternal care supposes that the mother provides the basic needs of the neonate: warmth (in pigs and rabbits) or shelter, food, water and immunological protection (via colostrum) and, in some instances, protection from predators and other conspecifics. A major risk facing all neonates, other than the birth process itself, is inadequate colostrum intake owing to delayed suckling or competition with siblings, which leads to starvation, hypothermia or even crushing, as has been observed in pigs.

Attraction of newborn rabbits to abdominal odors of adult conspecifics differing in sex and physiological state

The present study aimed at assessing the ability of newborn rabbits (1-3 days) to detect and discriminate abdominal odors emitted by adult conspecifics varying in sex and physiological state. Pups were submitted to a two-choice test exclusively based on olfaction, which permitted exposure to conspecifics either during successive or simultaneous presentations. Their orientation toward either of the two stimuli was timed. These behavioral assays revealed that (a) pups display attraction to odors of the abdomen of nonlactating, nonpregnant females and males when pitted against a control stimulus; (b) pups preferred the odor of nonlactating, nonpregnant females when simultaneously presented with the odor of a male; (c) all sexually mature females (virgin, pregnant, or lactating) were attractive to pups; (d) the odor of lactating females was preferred to the odor of either nonlactating, nonpregnant or pregnant females. Thus, from the first day after birth, newborn rabbits are able to olfactorily discriminate conspecifics from cues emitted at the abdominal level and display the strongest attraction to lactating females.

Immediate postnatal sucking in the rabbit: its influence on pup survival and growth

This study was aimed at characterising the impact of immediate postnatal sucking on pup survival and development. The interactive effects of postnatal success with the day 0 weight of pups, the nest-access regimen (controlled or free) or parity of females was investigated. Pups (n = 900) were categorised according to their initial ingestion of colostrum. In primiparous does: (1) pup mortality between d0-d10 was higher for unsuccessful than for successful early suckers; (2) lighter d0-weight reduced survival for unsuccessful but not for successful pups; (3) free nest-access of females annihilated the survival advantage fostered by the initial sucking success. In secondiparous does, these impacts waned. Finally, whatever the does' parity, only d0-weight influenced pup weight-gain between d0-21. Thus, pup survival seemed to depend (at least in primiparae) on their ability to suck right after birth, and to display a pattern of energy saving without being disturbed by the females' nest entries.

Olfactory alliesthesia in human neonates: prandial state and stimulus familiarity modulate facial and autonomic responses to milk odors

This study examines the effects of a shift in the motivational state (from hunger to satiety) of human neonates on their behavioral and autonomic responsiveness to artificial and food-related odors as a function of stimulus familiarity. In Experiment 1, videotaped facial movements and autonomic (respiration rate: RR, heart rate: HR) responses to five olfactory stimuli (familiar regular formula, unfamiliar regular formula, protein hydrolysate formula, vanillin, control) are recorded in 3-day-old neonates (n = 14) during episodes of irregular sleep. The infants are tested on average 50 min. before and after bottle feeding. RR discriminates the odor stimuli from the control stimulus, indicating clear olfactory detection. Furthermore, neonates react with higher HR change only when exposed to their familiar formula milk during the postprandial condition. The measurement of facial movements with the Baby-Facial Action Coding System indicates that disgust and aversive actions are more often evoked by the odor of regular formulas (familiar or unfamiliar) than by the other olfactory stimuli during the postprandial condition. In Experiment 2, untrained adult observers, presented with the videotapes of the infants' facial responses to the odors, are able to decode differential hedonic signals from the sender faces as a function of the infants' motivational states. The present findings are in line with the concept of olfactory alliesthesia as defined in adults.

Psychobiological consequences of two different weaning methods in sheep

Weaning is associated with a break in the mother-infant contact. In sheep, under natural conditions, the rupture of the social bond is progressive. In contrast, weaning imposed by breeders may result in psychobiological disturbances. The aim of this experiment was to measure the behavioural, hormonal and immune consequences of two types of sudden weaning: total separation (TS) and partial separation (PS), in 42 Ile-de-France ewes and their 60 lambs. TS animals (lambs and ewes) vocalized less frequently and for a shorter period of time than did the PS animals. Neither the plasmatic cortisol level in lambs nor the humoral response of dams and young were modified by the two weaning methods. In contrast, the excretion of coccidial oocysts increased significantly after weaning in TS lambs only and the growth rate of TS females was lower than that of the other lambs. These results suggest that these methods of rupture of mother-young social contact have only limited negative consequences on both partners in sheep, contrary to primates and rodents.

Olfactory function in the human fetus: evidence from selective neonatal responsiveness to the odor of amniotic fluid

This study was aimed at characterizing the level of specificity of the human newborn's response to an odor experienced in utero. Three groups of breast-fed infants and 3 groups of bottle-fed infants were examined on Postnatal Day 3 for their differential head-turning response when exposed to paired-choice tests contrasting the odors of either familiar (f) amniotic fluid (AF) or nonfamiliar (nf) AF or either of these AF odors and a control (C) stimulus. In fAF versus nfAF tests, the infants oriented preferentially to the odor of fAF, regardless of their feeding regimen (i.e., of their postnatal reexposure to AF-like cues in maternal milk). The fAF or nfAF versus C tests showed that this response pattern was caused by a true positive orientation toward fAF and not by avoidance from nfAF odor. This highly selective neonatal response to fAF odor is consistent with the hypothesis that the human fetus can detect and store the unique chemosensory information available in the prenatal environment and that this information becomes coupled with positive control of behavior.

What sounds reach fetuses: biological and nonbiological modeling of the transmission of pure tones

In utero transmission of external and maternal sounds has been studied in pregnant women and in an animal model of human species, the sheep. These works, especially the most recent ones, suggest that local and environmental factors interfere in such a way that signals are attenuated in a complex manner as frequency increases. The present work investigated whether a plain rubber sphere which was filled with water could be considered as a reliable nonbiological model in a study describing the characteristics of sound transmission. A sweeping pure tone, presented externally, was measured inside the rubber sphere using a high signal-to-noise ratio experimental hydrophone. A paradigmatic three components curve was observed between 100 and 20,000 Hz. In the first component of the curve (low to midfrequencies between 100 and 1,000 Hz), the intensity of the inside signal remained stable. The second component of the curve was composed of higher frequencies with the inside pressure falling gradually, demonstrating attenuation of the external signal. The third component of the curve appeared above a critical frequency, the value of which depended on several model and environment parameters. In this component, a series of rapid peaks and drops of the inside high frequency pressure was observed, indicating the presence of resonance systems. Analyses were carried out on the effects of several acoustical parameters, including: the size of the sphere, the location of the hydrophone in the sphere, the distance between the signal source and the hydrophone, the location of the external reference microphone, and the acoustical structure of the environment. These parameters allowed for the definition of their respective roles in the in-utero transmission of external sounds. These data were then compared with measurements performed within a biological model--ewes--under close acoustical settings. The comparisons confirmed the validity of the measurements, suggesting that the model may be useful in studies of sound transmission in utero.

Maternal and paternal perception of individual odor signatures in human amniotic fluid--potential role in early bonding?

Both human mothers and fathers are able to discriminate the odors of 2 samples of amniotic fluid (AF), one from their own newborn infant and one from an unrelated infant. Moreover, both parents are able to accurately identify the odor of the AF from their own infant. They report qualitative similarity descriptions of their infant's AF odor to the odor of the actual newborn infant and to the odor of the mother, especially at the end of gestation. These data indicate that human AF carries individualized odor properties, the roles of which in the initiation of parent-infant interactions are hypothesized.

Bottle-fed neonates prefer an odor experienced in utero to an odor experienced postnatally in the feeding context

The head-orientation response of 2- and 4-day-old bottle-feeding neonates was studied in paired-choice odor tests. Three tests were conducted at Days 2 and 4 after birth to assess the development of the relative response between two salient odors from the prenatal and postnatal environments: (a) amniotic fluid (AF) versus formula milk (FM), (b) FM versus control stimulus (distilled water), and (c) AF versus control stimulus. At both ages, AF and FM elicited positive orientation when presented simultaneously with the control stimulus, indicating that both odors were detectable and attractive to the infants. However, when AF and FM were presented concurrently, the infants expressed significantly longer orientation response toward AF odor than toward FM odor at the age of 2 and 4 days. Within the first 4 days of life, bottle-feeders thus display olfactory preference for a prenatal substrate over a postnatal substrate to which they were recurrently exposed in the feeding situation.

Neonatal responsiveness to the odor of amniotic and lacteal fluids: a test of perinatal chemosensory continuity

The head-orientation response of 2- and 4-day-old breast-feeding neonates was studied in paired-choice odor tests. Three tests were conducted on day 2 (amniotic fluid [AF] versus Colostrum; AF versus Control; Colostrum versus Control) and on day 4 (AF versus Milk; AF versus Control; Milk versus Control). At 2 days, both AF and Colostrum elicited positive orientation when presented simultaneously with the control stimulus, indicating that both odors were detectable to the infants. However, no differential responses were noted when AF and colostrum were presented concurrently, suggesting that both of these substrates were treated as similar sensorily and/or hedonically. On day 4, the odors of AF and transitional milk elicited attraction responses when presented in competition with a control stimulus. When the odor of milk was presented simultaneously with the odor of AF, the former elicited longer head orientation. Thus, within the first 4 days of life olfactory selectivity changes from a null preference between cues carried in AF and in colostrum to a positive preference for cues carried in postamniotic odors, that is, breast milk. An additional experiment indicated that 3-day-old neonates orient longer toward the odor of their own AF than toward the odor of alien AF, showing that prenatal odors elicit selective responding for some time after birth. Altogether these results were interpreted as supporting the hypotheses that prenatal experience might influence the earliest odor preferences in the breast-feeding human neonate and that these preferences rapidly evolve according to postnatal experience.

Cholecystokinin receptors mediate the development of a preference for the mother by newly born lambs

The aim of this study was to investigate the effect of selective cholecystokinin (CCK) antagonists on the development of a preference for the mother by newly born lambs. At birth lambs received an injection of the CCK-A antagonist devazepide (0.01 or 0.1 mg/kg), the CCK-B antagonist PD135158 (0.01 or 0.1 mg/kg), or saline for the controls (1 ml/kg). No major side effects were observed in the first 4 postnatal hours except that lambs receiving PD135158 displayed more exploratory behavior towards the maternal body than lambs from the other groups. When tested in a 2-choice test situation at 24 hr of age, lambs treated with PD135158 or saline spent significantly more time near their dams than near the alien ewes, whereas lambs treated with devazepide did not show any discrimination. The effect of devazepide persisted at 48 hr of age. The use of a CCK-A antagonist, but not a CCK-B antagonist, was concluded to prevent the formation of a preferential relationship between the lamb and its mother, most probably by impairing neonatal learning.

Rating and recognition of peers' personal odors by 9-year-old children: an exploratory study

Eighteen elementary school children assessed the pleasantness and perfumed aspect of familiar peers' odors, sampled through tee shirts worn without modification of hygienic habits. The participants were also requested to categorize the odors by sex and to recognize those of several target classmates varying in sex and socioemotional status (the participant's most preferred classmate vs. a mere acquaintance). The ratings of odors by familiar peers appeared consistent with those obtained from nonfamiliar peers and adults and varied according to the sex of wearer of the tee shirts. For the five categories of peers examined, as well as for the participants themselves, olfactory recognition was better than chance. Moreover, it was higher for the same-sex preferred peers than for the others only for the female perceivers. The results are discussed in terms of their behavioral relevance for peer relationships, focusing especially on (a) the relations between sex differences in odors and gender development and (b) the function of olfactory memory in the emotional regulation of friendships.

Cholecystokinin receptors mediate the development of a preference for the mother by newly born lambs

The aim of this study was to investigate the effect of selective cholecystokinin (CCK) antagonists on the development of a preference for the mother by newly born lambs. At birth lambs received an injection of the CCK-A antagonist devazepide (0.01 or 0.1 mg/kg), the CCK-B antagonist PD135158 (0.01 or 0.1 mg/kg), or saline for the controls (1 ml/kg). No major side effects were observed in the first 4 postnatal hours except that lambs receiving PD135158 displayed more exploratory behavior towards the maternal body than lambs from the other groups. When tested in a 2-choice test situation at 24 hr of age, lambs treated with PD135158 or saline spent significantly more time near their dams than near the alien ewes, whereas lambs treated with devazepide did not show any discrimination. The effect of devazepide persisted at 48 hr of age. The use of a CCK-A antagonist, but not a CCK-B antagonist, was concluded to prevent the formation of a preferential relationship between the lamb and its mother, most probably by impairing neonatal learning.

Orientation responses to biological odours in the human newborn. Initial pattern and postnatal plasticity

The initial pattern and development of odour preference was studied in infants simultaneously exposed to amniotic fluid (AF) and maternal lacteal secretion (L). Five groups of varying age (range: 1-5 days) and breast-feeding experience (range: 0-32 feeds) were studied. Before postnatal day 3, no evidence of differentiation of AF and L was apparent. After 3 days and 7-12 breast-feeding episodes, a significant preference for L arised. The initial stage (days 1-3) may reflect fetal acquisition of AF odour and sensory/motivational equivalence of AF and L odours. The second stage (days 4-5) may reflect the infants' perception of change in milk quality and increasing experience with milk. This sequential development attests to a high plasticity in the initial stage of human olfactory development.

Facial and autonomic responses to biological and artificial olfactory stimuli in human neonates: re-examining early hedonic discrimination of odors

Responses of awake and asleep 3-day-old human neonates were recorded to the presentation of artificial (vanillin, butyric acid, formula milks) and biological (breast milk, amniotic fluid) odorants matched on subjective intensity and trigeminal dimensions. The responses included behavioral (facial and oral movements) and autonomic (respiration, differential skin temperature) measures. The neonates reacted with significant facial and respiratory changes to low concentrations of olfactory stimuli during the various behavioral states. The analysis of olfacto-facial configurations revealed that behavioral markers of disgust (nose wrinkling, upper lip raising) discriminated between some odors judged as being pleasant and unpleasant by adult raters (vanillin vs. butyric acid). However, although some early predisposition to process the affective significance of stimuli may be suggested, no convincing evidence was obtained that neonates discriminated the hedonic valence of odors within the same perceptual space as adults. Finally, neonates evinced a differential pattern of respiratory responding to the presentation of milk odors according to the mode of feeding (breast vs. bottle feeding), suggesting that early olfactory discrimination may be mediated by stimuli with high ecological salience.

Male testosterone linked to high social dominance but low physical aggression in early adolescence

BACKGROUND

The association of male pubertal testosterone with social dominance and physical aggression was studied in a population sample of boys followed from age 6 to 13 years to understand the origin of the links between violent behavior and gonadal hormones.

METHOD

Physical aggression was assessed from the end of kindergarten to the end of elementary school by teachers and peers (aged 6 to 12 years). Social dominance and testosterone levels were assessed at 13 years of age during a 1-day visit to a laboratory with four unfamiliar peers.

RESULTS

Boys perceived as socially dominant by unfamiliar peers were found to have concurrently higher levels of testosterone than boys perceived as less socially dominant. In contrast, boys who had a history of high physical aggression, from age 6 to 12, were found to have lower testosterone levels at age 13 compared with boys with no history of high physical aggression. The former were also failing in school and were unpopular with their peers.

CONCLUSIONS

Both concurrent and longitudinal analyses indicated that testosterone levels were positively associated with social success rather than with physical aggression. High testosterone levels in adolescent boys may thus be regarded as a marker of social success in a given context, rather than of social maladjustment as suggested in previous studies.

Fetal sensory competencies

A growing body of evidence is available about the functioning of fetal sensory systems during gestation. This article aims at reviewing data concerning (i) the presence of potential sensory stimulation in the fetal milieu, (ii) the sequential functional development of the sensory systems and (iii) physiological and behavioral responses of fetuses to various types of stimulation. Human data are compared with data collected in other mammalian species. Most studies have investigated auditory and chemosensory (olfactory and gustatory) responsiveness of the fetus in the second half of gestation. They demonstrate that (i) motor and heart rate responsiveness depends on gestational age and characteristics of stimulation; (ii) fetal sensory experience has short- and long-term effects at morphological, functional and behavioral levels (for example transnatal learning). The clinical consequences of the fetal sensory functioning are developed.

Gas chromatographic-mass spectrometric method to characterise the transfer of dietary odorous compounds into plasma and milk

The flavours contained in a mammalian mother's milk can exert a marked influence on her offspring's proximate suckling behaviour and later preferences. The aim of this study was to establish a reliable analytical procedure to characterise the mammary transfer of selected volatile constituents of maternal food from non-pregnant and recently parturient ewes. Six known volatile compounds, most representative of cumin aroma (alpha-pinene, gamma-terpinene, cuminaldehyde, p-cymene, limonene and cineole), were traced in the blood and milk of ewes fed with cumin seeds, using liquid-liquid extraction combined with gas chromatography-specific ion monitoring mass spectrometry. Among the six cumin odour markers, only one, p-cymene, was transferred in quantifiable amounts into the venous plasma. The other cumin markers could only be detected as traces corresponding to amounts lower that the limit of quantification. In milk, four of the cumin markers could be detected, and two of these were quantified.

Longitudinal patterns of heart rate and fighting behavior in 9- through 12-year-old boys

OBJECTIVE

To assess the temporal stability of heart rate and to examine its relationship with fighting behavior.

METHOD

Heart rate at ages 9 through 12 was compared to a composite measure of fighting behavior in three cohorts of low socioeconomic status boys (n = 138; two cohorts of boys who had been rated as having disruptive behavior problems in kindergarten and one normative cohort) while controlling for body size, pubertal status, and level of family adversity.

RESULTS

Heart rate showed moderate stability at 1- and 2-year intervals in two of the three cohorts. The composite fighting score was related to heart rate for 11-year-old boys in the normative cohort and 12-year-old boys in one of the disruptive cohorts.

CONCLUSION

These data support the conclusion that there is a relationship between heart rate and aggression even within a low socioeconomic status sample.

Facial responsiveness to odours in normal and pervasively developmentally disordered children

The facial responsiveness of 10 mutic children with pervasive developmental disorder (PDD) and 10 normal (N) children matched for sex and chronological age were covertly videotaped while presented with a set of odours contrasted in hedonic valence. Hedonic ratings of the stimuli were obtained both from the group of N subjects and a panel of adults. Two methods were used to measure facial responses in the same subjects. The first method consisted in an analysis of facial movements with the Facial Action Coding System. Results show that PDD and N subjects displayed distinct action units in response to unpleasant odours. PDD subjects typically displayed muscular actions indexing negative experience, while N subjects showed more smiles. With the second method, odour-elicited facial behaviour was rated by a panel of observers, who were asked to judge whether the subjects were exposed a pleasant, neutral or unpleasant smell. The facial responses to unpleasant odours were classified more accurately in PDD than in N subjects. These findings suggest a functional ability to sense the hedonics attached to odours, but a deficit of socialization of hedonic facial displays in developmentally disordered subjects.

Responsiveness to the odour of amniotic fluid in the human neonate

Two-day-old newborns were videotaped during a double-choice test contrasting the odours of their amniotic fluid (AF) and of a control stimulus. To control for early motor asymmetries, the lateral position of both stimuli was balanced both between and within subjects. On average, neonates oriented their nose for a significantly longer duration toward the odour of AF. Regardless of the nature of the stimulus, neonates also evinced a marked head-turning bias to the right side. The nature of the odour stimulus and side of presentation interacted so that infants turned their nose longer to the AF odour when it was presented from the right side. These data indicate that newborns can detect the AF odour, and that they remain attracted towards it for at least 2 days after birth.

Behavioural and cognitive characteristics of conduct disordered-hyperactive boys from age 6 to 11: a multiple informant perspective

Three subgroups of kindergarten boys (stable conduct disordered-hyperactive (SCDH), stable conduct disordered (SCD), stable non-deviant control (SC)) were defined and followed up three, four and five years later in primary school. Using assessments from multiple informants (teachers, mothers, peers, self), the results showed that SCDH boys were more hyperactive (i.e. overactive/inattentive) and displayed a greater diversity of conduct problems in school and home at follow-up compared to the other groups. These results and the fact that during early adolescence SCDH boys tend to develop a worse prognosis than SCD boys suggest that they should be distinguished.

Olfaction in utero: can the rodent model be generalized?

In this article we discuss five requirements that theoretically must be fulfilled for transnatal chemosensory learning to occur in three placental species, the rat, the sheep, and the human, viz. (1) minimum or partial maturity of nasal chemoreceptor systems, (2) efficient odorivector compounds in the fetal environment, (3) the ability to memorize chemosensory information across birth, (4) perinatal continuity in chemical signals, (5) neonatal ability to detect air-borne odorants previously experienced in the aquatic environment. A substantial body of data is reviewed for the rat, in which fetal chemosensation is now firmly established. The less studied ovine perinate also shows preliminary evidence of nasal chemoreception and of postnatal retention of prenatally experienced odorants. Concerning the human species, we discuss extensive anatomical data supporting nasochemoreception in utero, but as yet no direct or indirect functional demonstration is provided. Furthermore, the strongest evidence of odorivector compounds in amniotic fluid is from human data. The results presented allow generalization of chemosensory functioning in utero in the species considered.

Individual olfactory signatures as major determinants of early maternal discrimination in sheep

Responses of recently parturient ewes to their familiar versus separated (i.e., unfamiliar) twin lambs were observed in an attempt to elucidate further the characteristics of the phenotypic traits (signatures) mediating maternal recognition and bonding. Ewes responded more positively to their familiar lamb than to its twin that had been isolated at birth. Nonetheless, those same mothers also discriminated between their separated twin and unfamiliar alien lambs. Alien lambs elicited similar rejection behavior regardless of whether they had been housed with their own mother or in isolation prior to testing. Lambs appear to have individually distinct (olfactory) signatures; however, the signatures of twin siblings may be sufficiently similar to enable the mother to detect a resemblance. No evidence suggests that acquired maternal labels play a role in either the acceptance of the ewe's own lamb(s) or rejection of aliens.