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Olfaction is vitally important to animals in all environments and is used to identify food, habitat, conspecifics and predators. Some odors, like pheromones or the pungent smell of spoiled foods, can trigger pre-existing behavioral responses that appear to require no learning. Most odors, however, are only attended to as a result of prior experience. It is believed that different types of odors are processed in different olfactory pathways in the forebrain. This thesis examines the relationship between innate and learned olfactory behaviors and the anatomy of the neural pathways that underlie them, using the zebrafish olfactory system as a model. I first characterized an appetitive olfactory behavior, which is displayed promptly by zebrafish when they encounter amino acid odors. A similar appetitive behavior can also be learned by the fish for another, initially neutral odorant, if it is repeatedly paired with food rewards. Zebrafish can therefore respond to, and learn to respond to certain odors. I then conducted an in-depth anatomical analysis of the structure and distribution of glomeruli in the zebrafish olfactory system. Glomeruli are spheroidal synaptic aggregates that organize and shape olfactory information that arrives in the brain. Throughout the development of zebrafish, I identified two distinct populations of glomeruli. One population consisted of 25 individually identifiable, anatomically stereotypic glomeruli that closely resembled specialized glomeruli in mammals and insects. These glomeruli were already formed during embryonic development and persisted in remarkably stable configurations throughout later developmental stages. I hypothesize that the 25 individually identifiable glomeruli constitute stable olfactory pathways (i.e., for innate olfactory behaviors). Most glomeruli, however, were anatomically variable and displayed different distributions within coarsely circumscribed regions in the zebrafish olfactory bulbs. The development of these glomeruli could be modified by sensory experience, suggesting that they may comprise plastic olfactory pathways that subserve the establishment of learned olfactory behaviors. Collectively my results show that innate and learned olfactory behaviors may indeed be represented in different olfactory pathways, and that these types of pathways may be located in both main and accessory olfactory systems.

Using an operant-olfactometer, the long term learning and memory, executive function, olfactory sensitivity, and working memory of the 5XFAD mouse model of Alzheimer’s disease was assessed. Six month old male and female 5XFAD and wildtype mice were tested. No deficits were found on an olfactory discrimination task or a reversal learning task. Female and transgenic mice performed better than male and wildtype mice on the higher odour concentrations, but not the lower concentrations, of the sensitivity task, suggesting differences in learning rate or maximum performance on the task, but not olfactory detection. This study demonstrated for the first time that mice are able to learn an olfactory delayed matching to sample task with delays up to 30 seconds long. Female mice showed higher levels of performance on the matching to sample task than male mice, indicative of better working memory.

Can our sense of smell influence our ability to self-regulate? The following thesis examined whether or not olfactory cues could influence a cognitive measure of self-regulation, and whether this effect would be moderated by goals. Further, it was proposed that emotion would mediate the relationship between scents and self-regulation. A total of 127 participants took part in the study. Magazine covers were used to prime either health or indulgence goals and participants were exposed to either an appetitive scent (baking cookies) or a non-appetitive scent (lavender) with the aim of creating emotional conflict. Self-regulation was measured by performance on a Stroop task. Goals were found to interact with scent type in order to yield differing impacts on self-regulation, however, the predicted mediating effects of emotion were unsupported. / None

The study of feeding behavior, and in particular the study of subjective hedonic experience and objective measures of motivation, are central to understanding how appetite regulation can be compromised in certain individuals. Furthermore, with an integrated picture of physiological and behavioral changes that can occur as a result of energy deprivation what emerges is a better understanding of how palatable food can disrupt attempts at regulating body weight at lower levels of body energy stores. In Article I, the genetic association study examining a potential role for a dopamine-related polymorphism in weight loss, it was shown that contrary to the main hypothesis there was no association between TaqIA polymorphism and the amount of body weight loss. In Article II, it was shown that palatability and olfaction ratings increased as a result of a 24 hour fast and females demonstrated larger improvements in overall olfactory performance. Initial body weight was positively related to improved odor detection threshold and total odour score (TDI). Using the same population sample as Article II, Article III highlights that higher sensitivity to reward and disinhibition scores correlated with responding for palatable snack food stimuli in the relative-reinforcing value of food (RRV) task, further indicating that RRV has strong ties with impulsivity. There was a demonstrable lack of negative alliesthesia under the fasted condition where, after a 75% increase in ad libitum energy intake (EI) relative to the fed condition, this greater amount of food consumed was still rated as being more palatable than the lesser amounts consumed under the fed condition. In Article IV it was shown that an equicaloric (-25%) energy deficit by diet alone was a greater challenge to appetite regulation and resulted in greater compensatory increases in EI than deprivation by exercise alone. Independent of deprivation modality there were significant improvements in odour threshold scores. TDI score increased only under diet alone; furthermore, the noted increase in mean TDI score was positively related to increased ad libitum EI. The picture that emerges is that, acutely, a complete fast has more pronounced effects on appetite and ad libitum EI than dieting alone, which in turn had greater effects than exercise alone or controls. Also, TDI improved under all three methods of energy deprivation, but moreso under conditions of deprivation by diet alone.

Knowledge about the use and behavioural relevance of the different senses in the South American Coati is limited. The aim of the present study was therefore to investigate the use of the sense of smell in this species. Twenty-five captive coatis were observed at the zoo of La Paz for a total of 120 hours to collect data on olfactory-related behaviors. The coatis frequently performed behaviors in response to the detection of odors such as sniffing on the ground, on objects, on food, on conspecifics, or in the air. In contrast, they did not display many odor depositing behaviors such as urinating, defecating, or scent-marking. The most frequently performed olfactory-related behavior was “sniffing on ground” which accounted for an average of 40 % of all recorded behaviors. In general, both adult males and non-males (here defined as adult females, as well as sub-adults and juveniles of both sexes) performed olfactory-related behaviors at similar frequencies. However, a few frequency differences for certain behaviors were found in the morning and in the afternoon, and in food or no food conditions, respectively. When food was present, for example, the coatis spent less time on olfactory-related foraging behaviors like “sniffing on ground” and “nose-digging” compared to when food was not present. The finding that scent-marking was rare in this captive group, indicates little need for territorial marking or communication of reproductive state under these circumstances. Findings from this study support the idea that Nasua nasua use their sense of smell in a variety of different contexts, and further studies are needed to extend the results.

Doctor of Philosophy (PhD) / Abstract Olfactory tasks are used very often with laboratory animals in studies of the neurobiology of learning and memory. Rats and mice are extremely sensitive in their detection and discrimination of odours, learn olfactory tasks rapidly, and can display higher order cognitive functions in olfactory tasks. This cognitive capacity may rival the ability of primates to learn analogous tasks with visual cues and most likely reflects strong anatomical connections between the olfactory bulbs and higher brain regions such as the piriform cortex, orbitofrontal cortex and hippocampus. The current thesis explored olfactory discrimination learning and performance in rats and had two principal aims. The first part of the thesis was oriented around odour masking phenomena in rats: the ability of one odour in a mixture to suppress detection of a second odour in that mixture. A specialized behavioural paradigm was developed to allow the study of odour masking in the rat. The second part of the thesis was pharmacological and determined whether the acquisition, reversal and performance of olfactory discriminations, and analogous auditory discriminations, are affected by two commonly used classes of drugs (benzodiazepines and cannabinoids). Together, these studies attempt to gain a better understanding of the nature of olfactory discrimination learning in rats, by using both psychophysical and pharmacological approaches, and to develop behavioural paradigms which may be used in future psychophysical and pharmacological studies. Following an introduction and review of olfactory and auditory studies in rat (Chapter 1), odour masking phenomena were studied in Chapter 2. The aliphatic aldehydes butanal (C4) and heptanal (C7) were used in the study. Aldehydes were of interest as this class of odorants abound in nature and may be important for rodents’ species-specific communication. Thirsty rats were initially trained to discriminate C4 and C7 in the olfactometer, using a go/no-go olfactory discrimination task. This involved rats learning to nose poke in an odour port and to lick a tube for a water reward on presentation of the rewarded component S+, while withholding licking at the tube when the other, unrewarded, aldehyde (S-) was presented. Odour mixtures (C4C7 or C7C4) were then introduced into the task as an additional non-rewarded condition (mixture S-). The concentration of the non-rewarded aldehyde in the mixture was then systematically decreased, while the concentration of the rewarded aldehyde was kept constant. When the non-rewarded aldehyde reached a critical low level in the mixture, rats started to make responses to the non-rewarded mixture (false alarms) showing that the S+ odour was suppressing the S- odour in the mixture, so the mixture was being responded to in the same manner as the S+ odour presented alone. Results also showed asymmetric suppression in the mixture condition, such that butanal suppressed detection of heptanal at a much lower concentration than vice versa. A second experiment demonstrated that when both butanal and heptanal were present in a binary mixture at the same concentration (10-6 volume %), rats responded to the mixture as if only butanal was present. Our findings are in agreement with human studies showing component interactions in binary mixtures of aldehydes. The molecular feature of carbon chain length appears to be a critical factor in determining the outcome of interactions between aldehydes at peripheral olfactory receptors, with smaller chain aldehydes better able to compete for receptor occupancy. Subsequent chapters explored the effects of two classes of commonly used drugs - benzodiazepines and cannabinoids - on olfactory and auditory discrimination in rats. Animal models such as the radial arm maze, Morris water maze and object recognition test are routinely used to test adverse and facilitatory effects of drugs on cognition in rodents. However, comparatively few pharmacological studies employ olfactory or auditory go/no-go paradigms. Thus, an important part of the present thesis was to assess the viability of using such paradigms in detecting pharmacological effects, and to identify whether such effects may be modality specific (i.e. whether a drug has a greater effect on olfactory or auditory tasks). In Chapter 3, the effects of benzodiazepines on olfactory discrimination tasks were explored. Rats were injected with the benzodiazepine drugs midazolam or diazepam and tested on discrimination tasks involving either the auditory and olfactory modality. Results showed that midazolam (0.5–2 mg/kg sc) did not affect the performance of a well-learned two-odour olfactory discrimination task, and moderately facilitated the performance of a go/no-go auditory discrimination task. On the contrary, midazolam (1 mg/kg) impaired the acquisition of a novel go/no-go olfactory discrimination task, as well as the reversal of a previously well-learned olfactory discrimination. However, midazolam did not affect the acquisition or reversal of an equivalent auditory discrimination task. The olfactory bulb and the piriform cortex are intimately involved in associative learning and behavioural aspects of olfactory performance, and have high concentrations of benzodiazepine receptors. These may therefore be possible neural substrates for the disruptive effects of benzodiazepines on olfactory learning. Findings from Chapter 4 indicated that the prototypical cannabinoid agonist delta-9-tetrahydrocanabinol (Δ9 THC) (0.3, 1 and 3 mg/kg) impairs auditory discrimination performance, but had no effect on equivalent olfactory discriminations. This is in marked contrast to the effects of benzodiazepines. Residual effects were observed, such that auditory discrimination performance was still impaired on the day following Δ9 THC administration. Delta-9-tetrahydrocanabinol effects were prevented by co-administration of the cannabinoid antagonist rimonabant (3 mg/kg). In addition, the anandamide hydrolysis inhibitor URB597 (0.1 and 0.3 mg/kg), which boosts levels of endogenous cannabinoids in the synapse, also impaired auditory discrimination performance, and this effect was also reversed by rimonabant. This study also assessed the effects of Δ9 THC (0.3, 1 and 3 mg/kg) and URB597 (0.1 and 0.3 mg/kg) on acquisition and reversal of novel olfactory discriminations. Results showed that Δ9 THC impairs olfactory reversal learning without affecting acquisition of the original discrimination. It is argued that this reversal deficit may be part of a wider capacity for cannabinoids to impair cognitive flexibility. The final Chapter (General Discussion) discusses the relevance and implications of the combined findings. The results add significantly to our current understanding of perceptual, learning and memory processes involving the olfactory modality in rats. With respect to olfactory perception, this thesis introduced a new behavioural paradigm, which can be used to assess component suppression in mixtures, and may be of use in future psychophysical studies involving rodents or other species. With respect to learning and memory, the thesis provides novel information on the disruptive effects of benzodiazepines and cannabinoids on olfactory and auditory tasks. It is concluded that go/no-go olfactory and auditory discrimination tasks in rats can provide a useful platform for assessing the disruptive and modality-specific effects of drugs on learning, performance and cognitive flexibility. Future studies might expand the range of drugs tested on these paradigms and might consider chronic as well as acute drug effects.

Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 4 uppsatser.

Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniversitet, 2004. / Härtill 4 uppsatser.