Behavioural and neurochemical responses of male and female chicks to cat odour

Primary Cultures of Olfactory Neurons from the Avian Olfactory Epithelium

The culture of the olfactory epithelium has been a useful model for the study of neurogenesis since olfactory neurons regenerate continuously throughout the adult lifespan. Structurally and functionally mature olfactory neurons are generated in vitro from non-neuronal precursors in a process that resembles the in vivo counterparts. This chapter describes a technique for culture of olfactory neurons from the avian olfactory epithelium of embryonic chickens; this enables the controlled laboratory study of a critical sensory system that is unstudied in this major vertebrate class. The techniques described here are broadly applicable to other endothermic vertebrate species.

The effect of age on vigilance: a longitudinal study with a precocial species

Vigilance allows prey species to detect predators before it is too late to escape. While the adaptive value of vigilance has become clearer over the years, developmental questions have attracted little attention. I explored the effect of age and group size on vigilance in a precocial species, the domestic fowl (Gallus gallus domesticus). I recorded vigilance in groups of various sizes in juveniles and one year later in adults. Vigilance decreased with group size in juveniles and to a lesser extent in adults. Juveniles tested alone showed longer feeding and vigilance bouts than adults reflecting their inexperience with predation threats and more rapid satiation, respectively. Adults in larger groups were more vigilant reflecting the need to monitor aggressive conspecifics in addition to predators. Gradual acquisition of information about risk posed by predators and conspecifics and feeding constraints influenced the expression of vigilance as a function of age in this species.

Embryonic exposure of chicken chicks (Gallus gallus domesticus) leads to heightened sensitivities towards the exposed scent

In chickens, food consumption can be altered by exposing the chicks to scents as embryos. We exposed eggs to an orange-scented food additive in the final days of incubation. Following hatching, we tested these exposed chicks’ ability to detect this scent at a variety of concentrations. We found that orange-exposed chicks responded to an orange-scented solution at lower concentrations than control chicks. This sensitization may allow chicks to be more effective at locating acceptable food items but requires further testing to determine its significance. Orange-exposed and control chicks were also tested with the scent of raspberry. Orange-exposed chicks responded to the raspberry presentation significantly more than the control chicks did, suggesting that the embryonic exposure to orange may have influenced how the chicks responded towards another fruity smell. This result suggests that chicks may be learning general characteristics of exposed scents while in the egg, though this needs further research.

The underestimated role of olfaction in avian reproduction?

Until the second half of the 20th century, it was broadly accepted that most birds are microsmatic if not anosmic and unable to detect and use olfactory information. Exceptions were eventually conceded for species like procellariiforms, vultures or kiwis that detect their food at least in part based on olfactory signals. During the past 20-30 years, many publications have appeared indicating that this view is definitely erroneous. We briefly review here anatomical, electrophysiological and behavioral data demonstrating that birds in general possess a functional olfactory system and are able to use olfactory information in a variety of ethological contexts, including reproduction. Recent work also indicates that brain activation induced by sexual interactions with a female is significantly affected by olfactory deprivation in Japanese quail. Brain activation was measured via immunocytochemical detection of the protein product of the immediate early gene c-fos. Changes observed concerned two brain areas that play a key role in the control of male sexual behavior, the medial preoptic nucleus and the bed nucleus of the stria terminalis therefore suggesting a potential role of olfaction in the control of reproduction. The widespread idea that birds are anosmic or microsmatic is thus not supported by the available experimental data and presumably originates in our anthropomorphic view that leads us to think that birds do not smell because they have a rigid beak and nostrils and do not obviously sniff. Experimental analysis of this phenomenon is thus warranted and should lead to a significant change in our understanding of avian biology.

The peripheral olfactory system of the domestic chicken: physiology and development

Olfaction is a ubiquitous sensory system found in all terrestrial vertebrates. Birds use olfaction for several important activities such as feeding and mating; thus, understanding bird biology would also require the systematic study olfaction. In addition, the olfactory system has several unique features that are useful for the study of nervous system function and development, including a large multigene family for olfactory receptor expression, peripheral neurons that regenerate, and a complex system for sensory innervation of the olfactory bulb. We focused on physiological, anatomical and behavioral approaches to study the chick olfactory neurons and the olfactory bulb. Chick olfactory neurons displayed some properties similar to those found in mature neurons of other vertebrate species, and other properties that were unique. Since information from these neurons is initially processed in the olfactory bulb, we also conducted preliminary studies on the developmental timeline of this structure and showed that glomerular structures are organized in ovo during a critical time period, during which embryonic chicks can form behavioral associations with odorants introduced in ovo. Lastly, we have shown that chick olfactory neurons can grow and mature in vitro, allowing their use in cell culture studies. These results collectively demonstrate some of the features of the olfactory system that are common to all vertebrates, and some that are unique to birds. These highlight the potential for the use of the physiology and development of the olfactory system as a model system for avian brain neurobiology.

Behavioral correlates of olfactory and trigeminal gaseous stimulation in chickens, Gallus domesticus

Despite growing evidence of avian olfactory abilities, there are few reports of behavioral correlates of chemosensory stimulation in birds. The present study aimed to determine how the behavioral responses of hens to selected gases might be affected by input from different chemosensory systems. We also hoped to relate electrophysiological thresholds previously measured in our laboratory to behavioral evidence of perception. Immediate behavioral responses to ascending series of short (7 s) pulses of olfactory (hydrogen sulphide), trigeminal (carbon dioxide) and combining (ammonia) gaseous stimulants were measured in 12 partially restrained adult hens (Gallus domesticus) using a purpose built gas delivery system. The concentration ranges applied matched those used in our previous electrophysiological studies of olfactory bulb responses. Consistent and specific behavioral responses were observed in response to stimulation with each gas. While significant increases in mandibulation (a distinctive rapid bout of bill movements), interruption of ongoing behavior, orientation to the end of the stimulus, and struggling were seen during stimulation with all three gases, orientation towards the stimulus occurred only in response to the olfactory stimulants, ammonia and hydrogen sulphide. The only gas to elicit significant avoidance was hydrogen sulphide, while gasping and headshaking were elevated in response to stimulation with carbon dioxide. Approximate threshold values for some types of behavior related reasonably well to receptor thresholds determined electrophysiologically, but perception may have occurred at lower concentrations without overt behavioral consequences. The diversity of the behavioral responses observed supports the notion that the gases selectively stimulated different sensory pathways.

A tangerine-scented social odour in a monogamous seabird

Social odours, conspecific chemical signals, have been demonstrated in every class of vertebrate except birds. The apparent absence is surprising, as every bird examined has a functional olfactory system and many produce odours. The crested auklet (Aethia cristatella), a monogamous seabird, exhibits a distinctive tangerine-like scent closely associated with courtship. Using T-maze experiments, we tested whether auklets preferred conspecific odours and whether they distinguished between different types of scent, two prerequisites of chemical communication. Crested auklets exhibited: (i) an attraction to conspecific feather odour; (ii) a preference for two chemical components of feather scent (cis-4-decenal and octanal), which we identified as seasonally elevated; and (iii) differential responses to odours, as indicated by a preference for auklet odour, an aversion to mammalian musk, but no significant response to banana essence (amyl acetate). Our results suggest that crested auklets detect plumage odour and preferentially orientate towards this stimulus. The striking and well-described courtship display that involves the scented neck region, the 'ruff sniff', provides a conspicuous behavioural mechanism for odour transmission and the potential for scent assessment during sexual selection. Although the importance and full social function of chemical signals are just beginning to be understood in birds, including crested auklets, social odours promise to reveal a largely unexplored and possibly widespread means of avian communication.

Norepinephrine, epinephrine and MHPG levels in chick brain development

In this study we determined the norepinephrine (NE), epinephrine and methoxy-hydroxy-phenyl-glycol (MHPG) levels in dissected chick telencephalon, diencephalon/mesencephalon and cerebellum in a number of stages from the late embryonic period (E16, E17, E18 and E19) and post-hatching period (P1, P2, P3, P4, P5, P15 and P30) using HPLC coupled with a coulometric detection system. A mobile phase which permits the detection of NE, epinephrine and MHPG simultaneously is also described. During development, NE levels increase dramatically after hatching in all brain structures studied and are not correlated in the same period with an increase in the MHPG/NE ratio. The values obtained for epinephrine and MHPG were significantly lower than the NE values in all the structures and stages studied. Our results support the notion of a specific role for NE during the first days after hatching.

Fluvoxamine treatment of mixed anxiety and depression: evidence for serotonergically mediated anxiolysis

Although increasing evidence suggests that selective serotonin reuptake inhibitor (SSRI) treatment may be effective for anxiety in addition to depression, SSRI anxiolysis has not been definitively related to the inhibition of serotonin (5-HT) transport. The gene that encodes for the human serotonin transporter (5-HTT) expresses its protein in neurons and in blood platelets, and both tissues respond to transport inhibition similarly in response to SSRI treatment. This study examined the relationship between the change in the 5-HTT's apparent affinity for 5-HT and the anxiolytic response in a group of 18 fluvoxamine-treated patients meeting Structured Clinical Interview for DSM-IV criteria for both generalized anxiety disorder and major depression. Significant decreases were found in both Hamilton anxiety and Hamilton depression scores over a 2-month treatment period. Robust increases were found in the apparent affinity constant (Km) for platelet 5-HT transport with treatment, and the increases covaried significantly with the decrease in anxiety (F = 4.97, p < 0.03). The pretreatment 5-HTT Km significantly correlated with the improvement in depression scores (r = 0.53, p < 0.03), consistent with the Hypothesis of Initial Conditions. These results suggest that the therapeutic effect of SSRI treatment can be linked to the magnitude and time-course of 5-HT transport inhibition effected with fluvoxamine, a drug that seems to have an antianxiety effect of the same magnitude as its effect on depression.

Human olfactory communication of emotion

Nonhuman animals communicate their emotional states through changes in body odor. The study reported here suggests that this may be the same for humans. We collected underarm odors on gauze pads from 25 young women and men on two different occasions. On one occasion the donors were induced to feel happy by viewing an excerpt from a funny movie whereas on the other, separated by a day, they were induced to feel afraid by watching an excerpt from a frightening movie. One week later, 40 women and 37 men were asked to smell several different bottles, some of which contained underarm odor pads collected during the happy movie, some contained underarm odor pads collected during the frightening movie, whereas others contained unused pads (control odor). Each odor was identified on two separate tasks that involved identifying the odor from among three odors and identifying it again from among six odors. Data were the number of women and men who identified an odor correctly on both tasks. When asked to select which bottles contained "the odor of people when they are happy," women chose the correct bottles for both tasks significantly more often than chance. Men chose the bottle which contained the body odors collected when women (but not men) viewed the happy movie more often than would be expected by chance. When asked to select which bottles contained "the odor of people when they are afraid," women and men both chose the bottle that contained the body odors collected when men (but not women) viewed the frightening movie more often than would be expected by chance. The finding suggests that there is information in human body odors indicative of emotional state. This finding introduces new complexity in how humans perceive and interact.

Changes in olfactory responsiveness by the domestic chick after early exposure to odorants

There is increasing evidence that odorants are important in the formation of attachments by the domestic chick, Gallus gallus domesticus. We investigated whether early exposure to nonaversive odorants altered the responses of 1-day-old chicks to a number of odorants from naturalistic sources, including feathers and faeces of adult chickens, wood litter and food (chick starter mash). The odorants were delivered by dynamic olfactometry, in which air containing different concentrations of each odorant was presented separately to individually housed chicks together with a small, coloured bead at which they could peck. When tested with a faecal odorant, but not the other odorants, control chicks, incubated and reared under standard conditions, shook their heads more but their pecking responses did not vary for any of the odorants tested. Chicks that had been exposed to a moist-food odorant from embryonic day 20 to 18 h posthatching and tested with odorants from either moist or dry food pecked less than controls but shook their heads the same amount. Early exposure to the moist-food odorant did not affect responses to the odorants of feathers or faeces. Chicks apparently learn about their olfactory environment during the later part of incubation and in the early posthatching period and the memory formed alters behaviour on day 1 posthatching. Copyright 1999 The Association for the Study of Animal Behaviour.

Relative importance of odour and taste in the one-trial passive avoidance learning bead task

The relative importance of taste and odour cues in a one-trial passive avoidance learning (PAL) task was examined. One-day-old chicks were presented with a small bead and different combinations of the taste and odour of methyl anthranilate (MeA). The chicks had received three consecutive pretraining trials where they were presented with white, red, and blue beads. They were then trained with a red bead presented in one of four possible conditions: dry and unscented, with the odour but not the taste of MeA, with the bitter taste but not the odour of MeA (the chicks' nostrils were occluded with a wax preparation), or with the taste and odour of MeA. Recall was tested 10 min after training by presenting a red and then a blue bead with no odour or taste added. The number of pecks made at the bead and the number of bouts of head shaking during each of the trials were scored. During testing, chicks that were trained with the odour of MeA alone pecked less at a red bead than at a blue bead, compared with chicks trained with a dry and unscented bead, indicating that they discriminated between the training bead and a bead of a different colour. There was no significant difference between the discrimination ratio of chicks trained with the odour, taste, or taste and odour of MeA. These results demonstrate that chicks can perform PAL using taste and/or odour cues.

Recent developments in anxiety, stress, and depression

Recent research in the development, analysis, and pharmacology of animal tests of state anxiety is discussed, including the use of responses to predator odours, the role of learning in modifying the anxiety measured in the plus-maze, and the roles of cholinergic, NMDA, and dopaminergic systems. Developmental and genetic factors are considered with particular reference to the development of tests of trait anxiety. The roles of 5-HT1A receptors in anxiety, depression, impulsivitity, and agonistic behaviours are discussed. Recent studies on the impacts of stress on neurotransmitter, endocrine, and immune systems and the interactions between these systems are discussed, with particular emphasis on their contributions to the development of pathologic states relevant to anxiety and depression.