Foteos Macrides

Efferents and centrifugal afferents of the main and accessory olfactory bulbs in the hamster

Abstract The efferents and centrifugal afferents of the hamster olfactory bulbs were studied using orthograde and retrograde tracing techniques. Following injections of tritiated amino acids which were restricted to the main olfactory bulb (MOB), autoradiographic grains were observed ipsilaterally over layer IA of the entire anterior olfactory nucleus (AON), the ventral portion of the hippocampal rudiment (HR), the entire prepyriform cortex and olfactory tubercle, the anterior and posterolateral cortical amygdaloid nuclei and the lateral entorhinal cortex. An ipsilateral projection to the nucleus of the lateral olfactory tract (nLOT) was also indicated. No subcortical or contralateral projections were observed. Amino acid injections into the accessory olfactory bulb (AOB) revealed ipsilateral projections to the superficial plexiform layer of the medial and posteromedial cortical amygdaloid nuclei and to the bed nucleus of the accessory olfactory tract (nAOT) and the bed nucleus of the stria terminalis (nST). Following injections of HRP which were restricted to the MOB, contralateral HRP-positive neurons were found predominantly in pars externa and to a lesser extent in the other subdivisions of the AON. Centrifugal projections to the MOB were identified ipsilaterally from the entire AON, the ventral portion of the HR, the anterior portion of the prepyriform cortex, and the nLOT. No labelled neurons were found in the olfactory tubercle, the anterior and posterolateral cortical amygdaloid nuclei or the entorhinal cortex. Centrifugal projections to the MOB were also identified from subcortical structures of the ipsilateral basal forebrain and from midline structures of the midbrain. Labelling occurred in the fusiform neurons of the diagonal band near the medial base of the forebrain at the level of caudal olfactory tubercle. Heavy labelling was seen in a distinct group of large, predominantly multipolar neurons (magnocellular preoptic area) that continued from the level of caudal olfactory tubercle to the level of the nLOT. This band of HRP-positive neurons could be followed more caudally to a position dorsal and medial to the nLOT near the lateral margin of the lateral anterior hypothalamic area. The midbrain projections to the MOB originated in the dorsal and median raphe nuclei. After injections of HRP into the AOB, centrifugal projections were identified from the nAOT and the posteromedial cortical amygdaloid nucleus. In addition, isolated neurons were labelled in the medial cortical amygdaloid nucleus but no labelled neurons were found in the nST. These results support the notion of two anatomically distinct olfactory systems and demonstrate two previously unreported pathways through which the limbic system may modulate sensory processing in the olfactory bulb.

Laminar distributions of interneurons in the main olfactory bulb of the adult hamster

Abstract The laminar distributions of intemeurons in the hamster olfactory bulb were studied with rapid Golgi techniques. Eight morphologically distinct classes of intemeurons were characterized according to their somal locations and their dendritic and axonal properties. Two of these classes, Blanes and Golgi cells, had somata restricted to the deeper layers of the bulb and were not observed more superficially than the mitral body layer (MBL). Their dendrites and axons were predominantly situated within the granule cell layer (GRL) and internal plexiform layer (IPL) but occassionally could be traced as superficially as the deeper portion of the external plexiform layer (EPL). Neither their dendrites nor their axons were oriented consistently with respect to the layers of the bulb. Blanes cells had numerous dendritic spines whereas Golgi cells were relatively spine-poor. Two other classes had somata that were restricted to the IPL and MBL, and had dendrites that exhibited clear orientations with respect to these layers. One class, horizontal cells, had dendrites that ran tangentially within the IPL and MBL. The other class, Cajal cells, had radially oriented dendrites that extended peripherally into the superficial region of the EPL and centrally for greater distances into the GRL. Both classes had axons that projected superficially into the EPL. The granule cells in our material were similar to those described in other species. The sixth class of intemeurons was designated as Van Gehuchten cells. The somata of Van Gehuchten cells were restricted to the EPL and MBL. Their processes branched elaborately within the EPL and MBL but were not oriented consistently with respect to these layers. It is unclear from our material whether these cells bear axons or whether they are amacrine intemeurons. Another class, superficial short axon cells, had somata that were predominantly located at the boundary between the EPL and the glomerular layer (GL) but could also be found throughout the periglomerular region and the superficial half of the EPL. These cells had dendritic and axonal processes that extended predominantly into the GL and appeared to branch around and between individual glomeruli. The eighth class, periglomerular cells, had somata located throughout the GL. Most of these cells gave rise to one dendritic trunk that arborized within a single glomerulus. Occassionally a second, less elaborate dendritic process emerged from the main trunk or from the soma and extended into the periglomerular space or encroached upon an adjacent glomerulus. However, we did not find any periglomerular cells with extensive dendritic arbors in more than one glomerulus. These distributions are discussed in relation to the notion that olfactory bulb interneurons may be assigned to two functional groups associated with two distinct levels of integration.

Effects of Exposure to Vaginal Odor and Receptive Females on Plasma Testosterone in the Male Hamster

Changes in plasma testosterone (T) levels following the placement of a receptive female into a male’s cage and after exposure to the odor of vaginal discharge in the absence of a female were studied i

Temporal relationships between hippocampal slow waves and exploratory sniffing in hamsters

Temporal relationships between inhalation, vibrissal protraction, and hippocampal slow wave activity during exploratory sniffing were studied in freely moving hamsters. Subjects exhibited stereotyped sniffing bouts during which respiration rates routinely were faster than 5 Hz, and inhalations were accompanied by protractions of the mystacial vibrissae. Sniffing invariably was accompanied by rhythmical slow wave activity (RSA) in the dorsal hippocampus. During presentations of various odorants, RSA generally appeared prior to the commencement of sniffing and continued for several minutes beyond the cessation of sniffing bouts. Sniffing and RSA rates were similar, but rarely identical for the full duration of a bout. Bouts typically contained more than 15 sniffs and occasionally consisted of more than 200 successive sniff cycles. During the course of bouts, sniffing and RSA often assumed identical repetition rates for periods of four to ten successive sniff cycles. These recurring periods of entrainment generally were preceded by brief accelerations or decelerations in sniffing rate, or a skipped inhalation cycle or vibrissae twitch. Except for such single skips, inhalation and vibrissal protraction were coordinated regardless of whether the sniffing and limbic rhythms were entrained. For individual subjects, there appeared to be preferred temporal relationships between inhalation cycles and hippocampal waves during entrainments. Analyses of 3000–11,000 sniff cycles and 6000–12,000 slow waves per subject indicated that the repetition rates for hippocampal waves were not altered during sniffing, and that each subject consistently exhibited a preferred temporal relationship between sniffing and RSA in the presence of different odorants. It is suggested that the limbic rhythm does exert a modulating or facilitating influence on the sniffing rhythm but does not directly drive it, and that recurring entrainments with a similar temporal relationship may provide a basis for correlating odorinduced changes in the timing of olfactory unit activity relative to rhythmic unit activity in the limbic system.

The spatial organization of the peripheral olfactory system of the hamster. part I: Receptor neuron projections to the main olfactory bulb

The spatial organization of projections from olfactory receptor neurons to the main olfactory bulb (MOB) was studied in hamsters by using fluorescent stilbene isothiocyanates as retrograde tracers. Injections confined to small sectors of the MOB produce labeling of receptor neurons that is more restricted circumferentially (i.e., with respect to the medial-lateral and dorsal-ventral axes) than longitudinally (i.e., with respect to the rostral-caudal axis) along the mucosal sheet. This restricted labeling is also discontinuous, giving an initial impression that the peripheral input is only crudely organized with respect to the medial-lateral and dorsal-ventral axes of the nasal cavity. However, from analyses of serial sections, it is apparent that each set of mucosal segments shares convergent projections to a circumferential quadrant of the MOB with other segments that are positioned around a common domain of the nasal cavity airspace. The primary afferent projections to the MOB, thus, are organized rhinotopically (i.e., with respect to the three-dimensional position of receptor neurons in olfactory space) rather than mucosotopically.

Male hamster copulatory responses to a high molecular weight fraction of vaginal discharge: Effects of vomeronasal organ removal

The importance of the vomeronasal (accessory olfactory) system for the copulatory responses of male hamsters to a high molecular weight fraction (HMF) of vaginal discharge was assessed in animals that had their vomeronasal organs (VNO) removed. These organs were extirpated bilaterally using an oral approach through the palate so as to eliminate the peripheral afferents to the accessory olfactory bulb (AOB) with minimal or no damage to the main olfactory system. The selective peripheral deafferentation procedure was verified by applying horseradish peroxidase intranasally following intraperitoneal injections of epinephrine to facilitate the vomeronasal pumping mechanism that draws fluids into the VNO. Heavy, bilateral anterograde labeling was evident in the olfactory nerve afferents within the main olfactory bulb of males that had their VNO removed and of animals that received sham surgery. Sham-operated males also had heavy, bilateral labeling in the vomeronasal nerve afferents within the AOB, whereas no such labeling occurred among animals with bilateral removal of the VNO. In sham-operated animals, both the HMF and the unfractionated discharge significantly increased the incidence of intromission attempts toward anesthetized males (surrogate females) whose hindquarters were scented with these stimuli. The unfractionated discharge also produced a significant elevation of overt copulatory behavior in males with selective peripheral deafferentation of the vomeronasal system, whereas the HMF did not facilitate copulatory behavior in these animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Responses of the male golden hamster to vaginal secretion and dimethyl disulfide: attraction versus sexual behavior.

The attractiveness of dimethyl disulfide, a presumptive pheromone in hamster vaginal secretion, was comparable to that of whole secretion when these odorants were presented to males in the absence of other stimuli associated with hamsters. Dimethyl disulfide was significantly less effective than whole secretion in attracting male hamsters away from the anterior body regions of other, anesthetized males. In contrast to whole secretion, dimethyl disulfide did not promote intromission attempts by male hamsters toward anesthetized males. Dimethyl disulfide may function to attract males into the vicinity of females or may be a general attractant not specific to females, and additional compounds may be responsible for the ability of vaginal secretion to facilitate overt sexual behavior. The attraction of sexually naive males to the secretion from estrous females was comparable to their attraction after mating experience, but recent copulatory experience significantly increased the ability of estrous secretion to promote intromission attempts. Vaginal secretion from lactating females was comparable to that from nulliparous, estrous females in its attractiveness to adult males and in its ability to facilitate overt sexual behavior. The maternal odors to which male hamsters are exposed during neonatal life may include those which will attract and sexually excite them in adulthood.

Chemical studies of hamster vaginal discharge: male behavioral responses to a high molecular weight fraction require physical contact

This report describes the isolation and behavioral testing in normal male hamsters of a high molecular weight fraction (HMF) of vaginal discharge which accounts for much of the aphrodisiac activity in the discharge. The HMF encompasses a group of proteins which elute as a relatively narrow, major peak upon agarose gel filtration of estrous vaginal discharge. The crude fraction from gel filtration retains a variety of volatiles including sulfur-containing compounds which we have previously found to account for much of the initial attraction of males to the female but which do not, themselves, facilitate overt copulatory behavior. Procedures for markedly reducing the presence of such volatiles to yield the HMF are described. In behavioral assays using anesthetized males as surrogate females, scenting the hindquarters of the surrogates with the HMF elicits intense genital investigation by experimental males, although this effect on investigatory behavior is not as dramatic as that of the unfractionated vaginal discharge. Like the unfractionated discharge, the HMF significantly increases the incidence of intromission attempts toward scented surrogates. To assess whether physical contact with the HMF is required for behavioral activity, as would be expected if the active material is proteinaceous, series of preference tests were performed using vanillin as a competing stimulus under conditions in which physical contact with the stimuli either was possible or was prevented. The unfractionated discharge was preferred in both conditions, whereas significant preferences for the HMF were exhibited only if it could be contacted by the snout of experimental males. The active material in the HMF thus appears to be of extremely low volatility, at least prior to physical contact with it by the male.

Olfactory bulbectomy impairs the rat's radial-maze behavior ☆

Previous studies had shown that transection of the lateral olfactory tracts and lesions of the septohippocampal system were similar in the deficits they engendered in nest building and food piling or hoarding by hamsters. The present investigation asked whether olfactory lesions would also produce deficits in radial-maze behavior like those associated with septo-hippocampal lesions. Radical olfactory bulbectomy led to a marked deterioration in preoperatively trained behavior in an 8-arm radial maze. The behavioral changes resembled those resulting from septo-hippocampal lesions in three ways: (1) There were fewer choices of adjacent arms and more choices of more distant arms. (2) Choice accuracy as a function of successive choices within a trial declined more rapidly. (3) The probability of repeating choice sequences was abnormally high. Earlier studies had shown that the rat does not require olfactory cues to perform efficiently in radial mazes. It therefore seems likely that the deficits described here resulted from the disruption of interconnections between the olfactory and septo-hippocampal systems rather than from the loss of olfactory sensitivity.

Responses of the male golden hamster to mixtures of odorants identified from vaginal discharge.

A series of aliphatic acids and alcohols was isolated and identified from hamster vaginal discharge. These materials along with a previously identified hamster attractant pheromone, dimethyl disulfide, were assayed in amounts characteristic of a single female collection for their ability to attract normal males and to promote copulatory behavior toward female surrogates. Estrous hamster vaginal discharge attracted normal males and stimulated copulatory attempts toward scented surrogates. Male copulatory behavior was unmodified by: dimethyl disulfide, the aliphatic acids, the aliphatic alcohols or a grand mixture of all these identified components of vaginal discharge. Therefore there must be some, as yet unidentified, material in vaginal discharge which induces normal males to engage in copulatory behavior. Neither the acids nor the alcohols when presented as mixtures had significant effects on male attraction. The attractiveness of a grand mixture of dimethyl disulfide and the series of aliphatic acids and alcohols was comparable to the attractiveness of dimethyl disulfide alone. Thus, the presence of small amounts of dimethyl disulfide can account for much of the ability of whole vaginal discharge to attract males to the odor source even when this compound is assayed in the presence of large amounts of inactive biological odorants.