Abstract: Previous workers had identified the vomeronasal organ, on anatomical evidence, as an accessory olfactory organ, present in most terrestrial vertebrates. Lesion experiments had demonstrated its importance in sexual behaviour in the hamster. Howevever, the sequestered position of the vomeronasal receptor epithelium within the organ raised questions concerning the access of olfactory stimuli. Using electrophysiological and pharmacological methods we have now demonstrated the following. 1. A pumping mechanism exists, powered by vasomotor movements, which can suck stimulus substances into the vonmeronasal organ. 2. A mechanism also exists for the active expulsion of the contents of the vomeronasal organ. 3. These mechanisms are activated by fibres running in the nasopalatine nerve. 4. The suction mechanism is controlled by sympathetic, probably adrenergic, fibres from the superior cervical sympathetic ganglion. Control of the expulsion mechanism has not been definitely established but does not appear to be sympathetic. 5. The vomeronasal organ can be adequately stimulated by activation of the pumping mechanism in the presence of odour. 6. Odour responses of single units in the accessory olfactory bulb have been recorded for the first time. 7. The time course of neuronal response in the accessory olfactory bulb is more rapid than predicted by many authors. The response is sufficiently fast that the vomeronasal system cannot be ruled out as a possible sensory pathway in many odour related behaviours. Possible modes of action of the pumping mechanism in awake animals are discussed.

Abstract: The onset of maternal responsiveness by virgin female rats to foster pups was observed after (i) complete vomeronasal nerve cuts, (ii) partial olfactory bulb cuts, or (iii) the combined procedures. Although both vomeronasal nerve cuts and olfactory bulb cuts resulted in a more rapid onset of maternal care, relative to control animals with sham operations, animals sustaining the loss of both sources of olfactory input exhibited the shortest response latency. These findings are discussed in terms of the probable distinct functions of the two olfactory systems in the control of maternal behavior in the rat.

Abstract: Electroantennogram responses of Colorado beetles were recorded to 53 plant volatiles including isomers. The system of antennal olfactory receptors is selective, even at high dpses several compounds cause fairly small responses. Diminishing the concentration to a moderate stimulus strength reduces the number of perceptible chemicals. Distinct electroantennogram responses are obtained to a group of closely related components, namely the general green leaf volatiles trans-2-hexen-I-ol, cis-3-hexenI-ol, hexanol-I, trans-2-hexenal, hexanal and cis-3-hexenyl-acetate, and to isomers such as trans-3hexen-l-ol and cis-2-hexen-l-ol. The threshold concentration of the most effective compound, trans2-hexen-l-ol is 1.2 x 10 ~ molecules per ml of air. The antennal olfactory receptors of the Colorado beetle are sensitively tuned to the perception of these general green leaf volatiles. As olfactory receptors of a number of phytophagous insects have been reported to respond to these components, this volatile complex probably plays a part in the host selection behaviour of various phytophagous insects. In host selection behaviour, sensory systems of phytophagous insects face a wide diversity of information from the environment. The sensory systems can cope with this excess of information, excluding irrelevant parts, and in this way limiting the input to beneficial elements (Dethier, 1971). As in all insect chemoreceptors, the antennal olfactory receptors are primary neurons lacking synaptic connections until they enter the central nervous system (Kaissling, 1971). The selected input to the brain can be directly analysed by making use of electrophysiological techniques. The electroantennogram method (EAG; Schneider, 1957) records the responses of antennal olfactory receptors to volatile compounds. In principle, this should segregate irrelevant chemicals from the volatiles which are potentially beneficial to the particular insect species. It reflects the summation of receptor potentials of the individual olfactory neurons in the antenna (Boeckh et al., 1965), and thus indicates the sensitivity of the main olfactory system. The EAG has been a vital tool in the analyses of sex pheromones (see e.g. Roelofs & Comeau, 1971). However, this method has been scarcely employed as a bioassay of host plant volatiles (see Simpson, 1976). Initial olfactory orientation directs the adult Colorado beetle Leptinotarsa decemlineata Say, towards solanaceous plant species (Visser & Nielsen, 1977). The

Abstract: 1. Using a cortical cup technique, the release of seven endogenous amino acids from the isolated rat olfactory cortex slice has been monitored. 2. Electrical stimulation of the lateral olfactory tract at a frequency of 4 min−1 was accompanied by a significant increase in the release of aspartate, GABA and taurine; the release of GABA and aspartate but not that of taurine was Ca2+-dependent. 3. Chronic unilateral bulbectomy was accompanied by a specific, significant fall in the aspartate content of the olfactory cortex which reached a maximum 5 days after surgery and persisted for at least a further 5 days. Electrical stimulation of the lateral olfactory tract of such preparations did not release any of the amino acids under investigation. 4. When slices from the unoperated side were exposed to solutions containing 25 m M-K+ or stimulated with electrodes placed directly on the cortex enclosed by the cup there was a Ca2+-dependent release of aspartate and GABA accompanied by a Ca2+-independent release of taurine. Following chronic bulbectomy, these procedures failed to evoke significant release of aspartate whereas the characteristics of GABA and taurine release were unaltered. 5. It is concluded that aspartate may be the excitatory transmitter of some of the terminals of the lateral olfactory tract fibres and that GABA may be a transmitter at some inhibitory synapses of the rat olfactory cortex.

Abstract: The pigeon olfactory nerve has been sectioned to explore the course of retrograde degeneration of the sensory neurons’ perikarya, which are located in the olfactory neuroepithelium. Both light- and el

Abstract: The development of the olfactory organ in the rainbow fish, Nematocentris maccullochi, was studied using scanning and transmission electron microscopy; it was compared with the developmental process in other teleosts, especially in the closely related atherinids and cyprinodonts. The formation of the nares parallels that in atherinids, salmonids, cyprinids and heterosomats, but differs from that found in cyprinodonts. Another ontogenetic feature in which the olfactory organs of the rainbow fish and also of atherinids differ from those of cyprinodonts, is the occurrence of transitory kinociliary cells which disappear during the postlarval period. The divergent evolutionary pathways are discussed with reference to experimental investigations. During development, ciliated and microvillous receptor cell types occur. At the primary larval stage ciliated receptor neurons are exclusively present. At a later stage the microvillous type develops and becomes equal in frequency. Thus, the microvillous receptor represents a separate type of olfactory neuron and is not a progenitor of the ciliated receptor cell.

Abstract: 1 Potential changes between the pial and cut surfaces of slices of guinea-pig olfactory cortex in vitro produced by gamma-aminobutyric acid (GABA) were recorded with extracellular electrodes 2 GABA, superfused over the pial surface (01 to 10 mM), produced a pial-negative potential deflection, accompanied by inhibition of the postsynaptic response to lateral olfactory tract (LOT) stimulation 3 This effect was replicated by the following compounds (potency relative to GABA = 1, in brackets): 3-aminopropanesulphonic acid (53), epsilon-aminovaleric acid (007), beta-alanine (007), beta-amino-nibutyric acid 005), epsilon-aminocaproic acid, alpha-amino-isobutyric acid, L-leucine (less than 002) 4 L-Glutamate (1 to 10 mM) produced a very large surface negative shift, with relatively less synaptic inhibition Glycine (1 to 10 mM) produced less surface negatively, accompanied by synaptic inhibition 5 Responses to GABA were antagonized more effectively than those to glycine by bicuculline (3 to 30 micrometer) and picrotoxin (1 to 30 micrometer) Strychnine (1 to 10 micrometer) incompletely inhibited responses to glycine 6 It is concluded that, while the locus within the slice of these effects is uncertain, the preparation may be useful for testing the interaction of drugs with cerebral GABA receptors

Abstract: 1. Potential changes were recorded from the lateral olfactory tract in slices of rat olfactory cortex in vitro at room temperature. 2. Superfused gamma-aminobutyric acid (GABA) usually produced dose-related depolarization of the lateral olfactory tract. Muscimol and 3-aminopropanesulphonic acid appeared more potent depolarizing agents than GABA, and glycine and taurine appeared less potent. Carbachol and glutamate were virtually ineffective. 3. The GABA responses were at least partially Cl- dependent. 4. (+)-Bicuculline and higher concentrations of strychnine antagonized the GABA but not the glycine-induced depolarizations. Paradoxically, responses to high doses of GABA were sometimes potentiated by both bicuculline and strychnine. 5. It is suggested that GABA receptors could occur as widely on nerve terminals as they do postsynaptically in the CNS, where GABA could be involved in the modulation of transmitter output.

Abstract: Carnosine has been applied by microiontophoresis to identified neurones in the olfactory bulb of the rat from solutions of different pH. Although mainly without effect when compared with conventional excitatory and inhibitory amino acids, the dipeptide tended to be depressive when ejected as a cation and excitant when ejected as an anion. The results obtained are not in favour of this substance being an excitatory transmitter in the primary olfactory pathway.

Abstract: The olfactory organs of 6 rainbow fish species were studied, and were compared with those of closely related cyprinodonts. It has been found that, in contrast to cyprinodonts, the olfactory mucosa of rainbow fish is more conspicuously thrown up into folds. Their arrangement in parallel is considered a relatively primitive character of the organ. Electron microscopic investigations on Nematocentris maccullochi have shown that the sensory epithelium consists of basal, supporting, and two types of receptor cells, ciliated and microvillous. As in cyprinodonts the receptor cell cilia exhibit a basic 9 + 0 microtubular pattern. In Nematocentris the frequency of receptor cells, between 200,000 and 250,000 per mm2, is lower than in cyprinodonts. It may be suggested that the lower density is compensated for by enlargement of the sensory area due to the folding. In addition to broad-surfaced dendritic membrane appositions found in both Nematocentris and cyprinodonts, contacts by means of dendritic spines are found only in the rainbow fish. The olfactory supporting cells of the latter are distinguished from those in cyprinodonts by more prominent lateral interdigitations, centrioles, and the higher number of vesicles associated with extensive Golgi complexes.

Abstract: Finkenzeller (1966) and Allison and Goff (1967), in studying the olfactory system, succeeded in finding olfactory evoked potentials (OEPs) on the intact skull of awake humans. Partly due to the technical difficulties associated with olfactory stimulation, however, there has been little subsequent progress in this area.

Abstract: The anatomical structure of the olfactory organs, nerve tracts and brain was described in Silurus glanis. The changes connected with aging were considered. The olfactory lamellae are thin and tightly set in a rosette. In the 1 year old individuals there are 48...51 lamellae in a single rosette. This number increases gradually with age and in the 9...10 year old welses reaches 150. The surface area of the lamellae of a single rosette also indicates an increase: in the 1 year old specimen it equals 117 mm2, while in the adult individual (5...6 year old)--1040 mm2. This is due to the increase in both the size of each lamella and the number of the lamellae. The obtained results are discussed with regard to other author's data. It has been found that the dynamics of the increase of the surface area of the olfactory epithelium in fish are closely related to the way of life and not to the systematic affiliation of the species.

Abstract: Following olfactory bulbectomy (BULBX), ovariectomized female rats show enhanced behavioral sensitivity to estradiol benzoate (EB) as measured by an index of sexual receptivity, lordosis responding. We have proposed previously that alterations in EB sensitivity which also are produced by septal destruction reflect disruptions of gamma-aminobutyric acid (GABA) inhibitory feedback on dopamine (DA) cell bodies in the midbrain, which may be inhibitory to the expression of lordosis. Since the olfactory system as well as the septum receives mesolimbic DA projections, in the present study we examined the effects of EB given to bulbectomized and sham-operated rats on tyrosine hydroxylase (TH) activity in the olfactory tubercle (OT), nucleus accumbens septi and corpus striatum. Glutamic acid decarboxylase (GAD) activity was measured in the ventral tegmental region (VTR) and the substantia nigra (SN). Rats received 2 μg EB/day for 3 days and were tested on Day 4 in a 20 mount behavioral test. Ten bulbectomized rats demonstrating enhanced behavioral sensitivity to EB and all sham-operated rats (N = 10) were selected for further study. Five rats in each group received 0.05 ml oil/day X 3 (BULBX-oil, SHAM-oil), and five received 2 μg EB/day X 3 (BULBX-EB, SHAM-EB). Rats were sacrificed on Day 4. Subsequent assays revealed a bulbectomy-dependent decrease in TH activity in the striatum, and a lesion plus EB-dependent decrease in TH activity in the OT. GAD activity was slightly but significantly suppressed in the VTR in the SHAM-EB group relative to that in the SHAM-oil group. Rats of the BULBX-EB group failed to exhibit decreased GAD activity. Thus, bulbectomy may result in enhanced behavioral sensitivity to EB due to disruptions in GABA-DA interactions, which are similar to those observed following septal destruction and which result in diminished behaviorally inhibitory DA tone.

Abstract: Evidence presented here suggests that glomerulus formation within the olfactory bulb of the rat, which is mostly a postnatal event, is directed by the olfactory nerve rather than by the influences of mitral and tufted cells

Abstract: 1. By counting the axons per micron 2 on electronmicrographs of cross-sectioned olfactory nerves and multiplying this number by the area of the cross-sectioned nerves, the number of olfactory receptors was determined in 4 breeds of domestic pigeons including homing pigeons. 2. The total number of olfactory receptors varied between 3.0 and 7.4 . 10(6). It significantly depended on the body size of the pigeons. There was no evidence for differences in the number of olfactory receptors between the breeds independent of body size. 3. No differences in the relative size of the olfactory bulbs could be detected between the breeds. 4. The ultrastructure of the olfactory epithelium was basically similar to that of other birds. The covering mucus layer was revealed to be a secretion product of both the olfactory glands of Bowman and the olfactory supporting cells. No differences were observed in the ultrastructure of the olfactory region between the four breeds investigated.