Sadayuki F. Takagi

Centrifugal influence on olfactory bulb activity in the rabbit.

(1) Regions which exert centrifugal influences on the olfactory bulb activity were studied by applying systematic stimulation to various areas of the ipsilateral telencephalon in the rabbit. By delivering electric stimuli to the anterior commissure (AC), the deep lying structures in the projection areas of the lateral olfactory tract (LOT) and the medial forebrain bundle situated between the lateral hypothalamic area and the lateral preoptic area, negative field potentials were evoked in the granule cell layer (GCL) of the bulb. (2) Intracellular recordings from the mitral cells and the GCL neurons in the olfactory bulb were performed in order to clarify the modes of the centrifugal influences on the olfactory bulb neurons. (3) EPSPs were recorded in the GCL neurons by stimulation of the deep-lying structure of the prepiriform cortex as well as by stimulation of the AC. The onset time and duration of the EPSPs corresponded well to those of the negative field potentials in the GCL. Thus, it was suggested that these negative potentials were caused by the EPSPs of the number of granule cells. (4) In almost all of the mitral cells, IPSPs were recorded by stimulation of the AC and the deep-lying structures of the LOT projection areas. The onsets of the IPSPs were found with delays of several milliseconds from those of the negative field potentials in the GCL. (5) It was postulated that the excitation of the centrifugal system mainly exerts a depressive influence on the activity of the mitral cell, and that the GCL neuron (presumably the granule cell) seems to be an inhibitory interneuron interpolated between the extrinsic fibers from the telencephalon and the mitral cell.

Studies on the olfactory nervous system of the old world monkey

From the results of our electrophysiological and HRP studies in the old world monkey, multiple olfactory pathways have been clarified. The old world monkey has two neocortical olfactory areas, but no functional vomeronasal system. The response patterns to odors in various olfactory areas have also been studied. On the other hand, in the rabbit (Onoda and Iino, 1980) and dog (Onoda et al., 1981, 1982), which do have active vomeronasal systems, only one neocortical olfactory area was found. This important difference had already been indicated in three previous papers in which Takagi (1979, 1980, 1981) theorized that mammals can be divided into two groups according to their olfactory nervous mechanisms. One group includes old world monkeys, higher primates and man, and the other new world monkeys and lower mammals.

Axonal projection of anterior olfactory nuclear neurons to the olfactory bulb bilaterally

Abstract The axonal projection of anterior olfactory nuclear (AON) neurons to the ipsilateral and contralateral olfactory bulbs and to the prepiriform cortex was analyzed electrophysiologically in the rabbit. Of 117 AON neurons which sent their axons to the anterior commissure, 46 cells (39%) and 55 cells (47%) were activated antidromically by ipsilateral and contralateral olfactory bulb stimulation, respectively, and 22 AON neurons (19%) were activated antidromically from both. The mean axonal conduction velocity of the AON neurons was 2.8 m/s in the AON—anterior commissure axonal segment, 1.6 m/s in the AON—contralateral offactory bulb segment, and 1.0 m/s in the AON—ipsilateral bulb segment. These results and the collision tests between the antidromically evoked spikes indicate that a number of AON neurons send their axons to the contralateral olfactory bulb via the anterior commissure and that the same neurons send thin axon collaterals to the ipsilateral bulb. These axonal projections are significant in relation to the synaptic influences of these axons upon olfactory bulb neurons.

Modulation by prostaglandin D2 of mitral cell responses to odor stimulation in rabbit olfactory bulb

Recent work in our laboratory has demonstrated that prostaglandin (PG) D2 and the enzyme activities for its biosynthesis and inactivation are highly concentrated in the olfactory bulb and that the mitral cell layer of the bulb is enriched with PGD2-binding protein. We therefore investigated the role of PGD2 in the processing of odor signals in the rabbit olfactory bulb by an electrophysiological technique. Iontophoretic (-100 nA, 20 s), intra-arterial (0.0125-0.1 mg/kg) and intravenous (i.v., 0.05-0.3 mg/kg) administration of PGD2 enhanced and prolonged the responses of mitral cells to some of the olfactory stimuli tested. The extent and duration of granule cell inhibition of mitral cells were assessed by recording field potential responses in the bulb to paired lateral olfactory tract volleys. The i.v. administration of indomethacin or diclophenac, both of which are inhibitors of PG biosynthesis, resulted in prolongation of the granule cell inhibition of mitral cells without any significant change of the conditioning amplitudes. It also caused the reduction of the spike responses of mitral cells to olfactory stimuli. After treatment with indomethacin, the i.v. administration of PGD2 (1 mg/kg) rapidly reduced the duration of the granule cell inhibition of mitral cells. These results indicate that PGD2 plays a modulatory role in the mitral cell responses to odor stimuli by suppressing the inhibitory synaptic inputs from granule cells to mitral cells.

Olfactory Frontal Cortex and Multiple Olfactory Processing in Primates

When we (Tanabe et al., 1974) began our studies on the brain mechanism of olfaction in our laboratory, we found that an olfactory projection area in the neocortex had not been studied physiologically and had been entirely unknown until Allen’s pioneer work (1940, 1943) appeared. In ablation and electrophysiological experiments on dogs, Allen found that the ventrolateral portion of the frontal lobe is related to olfaction, but his study was fragmentary. We thus faced many important but unresolved problems regarding olfactory nervous pathways.

Olfactory input to the lateral hypothalamus of the old world monkey

Responses of lateral hypothalamic neurons to 8 odors were studied in chronic unanesthetized old world monkeys (Macaca irus). Many neurons (54.5%) responded to a single odor only, and the number of neurons responding to 2, 3 and 4 odors decreased successively. No neuron responded to as many as 5 odors. Thus, the presence of olfactory input and a highly discriminative ability for odors were found in the lateral hypothalamic area (LHA). Neuronal responses to the same odors were also studied in the septum (Spt). In anesthetized old world monkeys, evoked potentials were recorded in the LHA and in areas of the Spt and the nucleus accumbens (Acc) during stimulation of the olfactory bulb (OB). When the Spt (and probably the Acc with it) was subsequently destroyed, OB-evoked potentials in the LHA disappeared. Next, by injecting horseradish peroxidase (HRP) into the LHA, an olfactory pathway to the LHA was examined. Labeled neurons were found mainly in the Spt and the Acc, and only partly in other areas. However, labeled neurons were scarcely found in the prepyriform (PPF)-entorhinal (ER) area or in the olfactory tubercle (OT). The present study thus shows that an olfactory pathway to the LHA passes through the Spt and probably also the Acc, but not through the PPF-ER areas nor through the OT in the old world monkey.

Monosynaptic and disynaptic activation of pyriform cortex neurons by synchronous lateral olfactory tract volleys in the rabbit.

To elucidate the organization of synaptic inputs to pyriform cortex neurons, intracellular and extracellular responses of single units were analyzed in urethane-anesthetized rabbits. The lateral olfactory tract (LOT) or the olfactory bulb (OB) was electrically stimulated. Intracellular recordings revealed two types of cells (type I and type II cells), according to the types of EPSP evoked by the LOT or OB shock. The EPSP in the type I cells had shorter latencies (0.0 to 0.9 ms) from the onset of the component 2 (C2) wave of the field potential (which signals the onset of the synaptic depolarization of the apical dendrites of the pyramidal cells in the PC), and that in the type II cells had longer latencies (1.0 to 6.0 ms). A conditioning LOT or OB shock did not suppress the testing EPSP in the type I cells, whereas the conditioning stimulation greatly suppressed the testing EPSP in most of the type II cells. Extracellular recordings from units responding synaptically to the LOT or OB shock revealed a group of units which had short latencies (0.7 to 1.9 ms) of spike discharges. Those units, which were likely to be the same cells as the type I cells, are believed to mediate excitatory synaptic inputs to the type II cells. On the basis of these results, we concluded that type I cells are monosynaptically activated by LOT volleys, whereas type II cells are activated di- or polysynaptically by way of a relay from type I cells. The type I cells were recorded in both the superficial and the deep parts of the pyriform cortex, although they were recorded more frequently in the superficial part. On the other hand, most of the type II cells were recorded in the deep part of the PC. These results support and extend the previous model, in which the monosynaptically activated superficial pyramidal cells give rise to excitatory inputs to other pyramidal cells and neurons in deep layers.

RESPONSES OF LATERAL HYPOTHALAMIC NEURONS TO ODOURS BEFORE AND DURING STOMACH DISTENSION IN UNANAESTHETIZED RABBITS

Publisher Summary There is much evidence that the lateral hypothalamic (LH) neurons receive olfactory inputs. Recent neuro-anatomical experiments have demonstrated that the origins of the fibers projecting to the LH neurons exist in several parts of the basal brain, such as the anterior olfactory nucleus, the olfactory tubercle, the amygdale, and the prepyriform cortex. Electro-physiological data also indicate the existence of these olfactory projections. This chapter describes a relationship between the behavior of LH neurons and the condition of the stomach. It discusses the study of the responses to the odors of LH neurons in unanesthetized rabbits. This was done through a preliminary operation performed under anesthesia. After the response patterns of all neurons to eight odors were examined, the rabbits stomach was inflated and any changes in their response patterns were sought. It is still entirely unknown where in the brain, the sensation of smell occurs. However, the finding that responses to odors of neurons in the feeding center become different, depending upon the condition of the stomach, indicates that the odors that are appetite-stimulating during the state of hunger become less and less attractive as the stomach is distended by food intake.

T&T Olfactometer for Standardized Olfactory Test and Its Uses

Today, most countries have standardized methods for testing vision and hearing. However, there are no set rules anywhere in the world for testing the olfactory sense, despite a growing need. To answer this need, an olfactory sense test has been developed, which uses a testing device called the T&T Olfactometer (Daiichi Yakuhin Sangyo, Tokyo, Japan). In 1975, a study group was set up with funding from the Ministry of Education and Cultural Affairs of Japan to formulate standards for testing the sense of smell. A further study group, under Professor Sadayuki Takagi of Gunma University, funded by the Ministry of Health and Welfare, was set up in the same year to research treatment for the impairment of the olfactory sense.

THE REPELLENT ACTION OF NARAMYSIN TO THE RAT

It is well known that naramysin, cyclohexiimid has a strong repellent action to the rat. It was intended to clarify which one of the two conceivable stimuli, the smell and the taste of the drug does a rat detest. It was concluded that the evasion of a rat to naramysin primarily originates in the taste of the drug, but once a rat experiences the detestable taste, it remembers the smell which works as a conditioning stimulus thereafter.