Yasuhiro Takashima

Orbital cortex neuronal responses during an odor-based conditioned associative task in rats

Neuronal activity in the rat orbital cortex during discrimination of various odors [five volatile organic compounds (acetophenone, isoamyl acetate, cyclohexanone, p-cymene and 1,8-cineole), and food- and cosmetic-related odorants (black pepper, cheese, rose and perfume)] and other conditioned sensory stimuli (tones, light and air puff) was recorded and compared with behavioral responses to the same odors (black pepper, cheese, rose and perfume). In a neurophysiological study, the rats were trained to lick a spout that protruded close to its mouth to obtain sucrose or intracranial self-stimulation reward after presentation of conditioned stimuli. Of 150 orbital cortex neurons recorded during the task, 65 responded to one or more types of sensory stimuli. Of these, 73.8% (48/65) responded during presentation of an odor. Although the mean breadth of responsiveness (entropy) of the olfactory neurons based on the responses to five volatile organic compounds and air (control) was rather high (0.795), these stimuli were well discriminated in an odor space resulting from multidimensional scaling using Pearsons correlation coefficients between the stimuli. In a behavioral study, a rat was housed in an equilateral octagonal cage, with free access to food and choice among eight levers, four of which elicited only water (no odor, controls), and four of which elicited both water and one of four odors (black pepper, cheese, rose or perfume). Lever presses for each odor and control were counted. Distributions of these five stimuli (four odors and air) in an odor space derived from the multidimensional scaling using Pearsons correlation coefficients based on behavioral responses were very similar to those based on neuronal responses to the same five stimuli. Furthermore, Pearsons correlation coefficients between the same five stimuli based on the neuronal responses and those based on behavioral responses were significantly correlated. The results demonstrated a pivotal role of the rat orbital cortex in olfactory sensory processing and suggest that the orbital cortex is important in the manifestation of various motivated behaviors of the animals, including odor-guided motivational behaviors (odor preference).

Characteristics of rat lateral hypothalamic neuron responses to smell and taste in emotional behavior

Single unit activity in the lateral hypothalamus (LHA) of the rat was recorded while the animal learned to discriminate cue signals. Normally preferred potables (glucose, orange, or grape solution) or intracranial self-stimulation (ICSS) were used as rewards. Electric shock or tail pinch were used as aversive stimuli. The same behavior, licking, was the response required to either obtain the rewarding stimuli or avoid the aversive ones. For positive reinforcement a rat was rewarded with fluid or ICSS upon licking a spout presented in front of its mouth. In negative reinforcement experiments, an aversive stimulus, electric shock or tail pinch, was applied if the rat did not lick the spout. Solutions having smell only, taste only, or smell-plus-taste, were prepared from oranges or grape extract. Of 392 neurons analyzed, 256 responded differentially to rewarding and aversive stimuli, and 138 of these were tested with the 3 different solutions. Similar LHA neural responses occurred during actual drinking of the 3 kinds of solutions, as well as on recognition of the cue signal. Responses to smell only had shorter latency than responses to taste only. Neural activity in response to solutions that could be both smelled and tasted was the sum of activity in response to taste-only solutions plus that in response to smell-only solutions. Cue signal responses were rapidly acquired, usually within 2-5 trials, for both taste-only and smell-only solutions. The results indicate the integration of both taste and olfactory information by the same LHA neurons, and these neurons are involved in cue signal learning. Present results of LHA neuronal responses to taste and smell suggest that the intensity of gustation and olfaction may add together to enhance instinctive hedonic sensations. These neurons are involved in the formation of stimulus-reinforcement association in learning, and in elicitation of conditioned emotional responses.

Suitability of the odor stick identification test for the japanese in patients suffering from olfactory Disturbance

We studied the suitability of the Odor Stick Identification Test for the Japanese (OSIT-J) in patients suffering from olfactory disturbance. In 120 patients with olfactory disturbance (age range 12-85 years) there were statistically significant correlations between the odor identification rate on the OSIT-J, the results of the Japanese standardized olfactory test (T&T olfactometry) and subjective symptom scores. In every patient treated for olfactory disturbance, the OSIT-J reflected the grade of recovery from the olfactory disturbance as determined by means of T&T olfactometry. The odor identification rate on the OSIT-J also correlated significantly with the results of the i.v. Alinamin test. Regarding the rate of correct recognition of odors on the OSIT-J, menthol and curry odors were recognized with a high rate and orange and wood odors with a low rate. Although the OSIT-J includes 13 kinds of odorants, the number of odorants used can be reduced to a minimum of 5 as the results obtained with this reduced form of the OSIT-J also correlated with the results of T&T olfactometry and the subjective symptom scores as well as with the results obtained with the 13-odorant OSIT-J. We conclude that the OSIT-J is suitable not only as a screening test for olfactory disturbance but also for practical use in clinical otorhinolaryngology.

Rat preference for food-related odors

Preferences for food-related odors and the effects of fasting on those preferences were investigated during rat bar pressing for brief odor presentation. A rat was housed in an equilateral octagonal cage and had free access to food and water, except during fasting. Among 8 food-related odor substances (black pepper, cheese, coffee, milk, nut, peppermint, plum and orange), black pepper, milk and coffee were most preferred, and cheese was least preferred, but even the bar pressing rate for cheese was above the operant level. This data indicates that all 8 odors were preferred by rats, although there were different degrees of preference in individual animals. Fasting substantially increased the rate of bar pressing for odors and changed the odors preferences. This result was probably due to increased search for food and water. Since bar pressing was reinforced by nothing other than odor presentation, the results reveal inherent odor preferences of rats.

Changes in Detection Thresholds of Androstenol and Pentalide During the Menstrual Cycle

Fluctuations in women’s sensory sensitivity, feelings, and behavior during the menstrual cycle have been suggested. Most studies of olfactory sensitivity have suggested increased sensitivity during the ovulatory phase [1,2,3]. However, several reports have noted a secondary peak during the luteal phase [1] and some have reported no changes during the menstrual cycle [3]. The physiological mechanisms for these responses related to each phase are not fully understood. Some authors have suggested that changes in olfactory sensitivity might be due to peripheral mechanisms that limit the access of odorant molecules to olfactory receptors [2], while others have indicated that these changes might be directly related to the central nervous system, which is affected by sexual hormones [3]. The possible involvement of human pheromones is very interesting. Androstenol and androstenone, which have musk-like odors, occur both in urine and as a product of the apocrine glands in humans and are secreted more by men than by women. Although these pheromones are implicated in the sexual behavior of the boar, their effects on humans are not well known. Some studies [3] have suggested that there is no relationship between the menstrual cycle and olfactory sensitivity for non-human odors, but that sensitivity does change for particular human odors, such as that of androstenone.