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Within a 4-hr period after parturition, the ewe learns the odor of her lamb that will allow later recognition of her offspring from alien lamb. This study investigated the importance of the activation of olfactory bulb (OB) beta-noradrenergic receptors in establishing this olfactory memory. Pregnant ewes (n = 24) were cannulated bilaterally in the OB. Two days before parturition, OB were perfused continuously (10 microliters/hr) with either a solution containing the selective beta-noradrenergic antagonist propranolol (10(-3) M) or vehicle. The results showed that, although 8 of 9 control ewes were still able to bond selectively to their lambs, only 7 of 15 propranolol-treated animals were able to bond (p = .04). These results suggest that activation of beta-noradrenergic receptors in the OB during the period surrounding parturition is required to establish olfactory recognition of the lamb.

The olfactory bulb (OB) of the rat receives an extrinsic innervation from the most anterior part of the basal forebrain cholinergic complex. The effect of microiontophoretically applied acetylcholine (ACh) on OB unit activity was studied in 16 adult male rats. A total of 80 units was recorded and in 50% of the cases the cell layer where the recording was done was clearly identified. The results provide evidence for a particularly high level of sensitivity to ACh in the outer glomerular layer (73%). Both inhibitory and excitatory responses were found. These results are in agreement with histological studies indicating that this layer presents the highest density of cholinergic terminals. As a whole, present knowledge suggests the existence of a strong cholinergic control of the olfactory input at the level of the first synapse in the system.

This study investigated a possible participation of the centrifugal serotonergic (5-HT) innervation of the olfactory bulb (OB) in the control of the multiunit mitral cell responsiveness in behaving rats. A bilateral injection of 5,6-dihydroxytryptamine solution (5,6-DHT) into the OB induced in this structure an average 70% reduction in the level of endogenous serotonin. Control and treated animals were habituated to eat a single 2 h daily meal. Recording sessions were performed either after a 22 h fasting period or just after the meal. The summated multiunit mitral cell activity and vigilance state parameters were recorded in the absence of and during repeated stimulation by puffs of food odour and isoamyl acetate. The results showed that the 5,6-DHT treatment did not modify significantly previously established centrifugal controls exerted at the OB level: (1) the selective enhancement of the mitral cell responsiveness to food odour occurring in waking food-deprived animals; (2) the inhibition of the olfactory input during slow wave sleep. However, the considered 5-HT projections could mediate some inhibitory influence on mitral cell activity during wakefulness only. Finally, the 5-HT innervation of the OB did not seem to be involved in basic mechanisms of olfactory recognition.

Food deprived control rats presented the following characteristics: (1) in a two-choice behavioral test, the animals explored significantly more the side of the cage odorized by a food odor (FO) than the non odorized one; (2) FO presentations in slow wave sleep (SWS) aroused them significantly more often than in a food satiated condition; (3) during wakefulness, the multiunit mitral cell responsiveness towards FO was selectively enhanced. The same 3 parameters have also been tested in animals where projections of one olfactory bulb were completely sectioned, or intact either in the medial or in the lateral part of one peduncle; the other olfactory peduncle was completely severed. The results showed that waking rats needed both medial and lateral projection pathways to perform normally in the food odor detection task, and to display the normal mitral cell excitability. However, in SWS, one medial pathway at least was needed to mediate normal rates of neocortical arousal in response to FO stimulations. The results are considered in terms of functional complementarity/redundance of the medial and lateral olfactory pathways.

The centrifugal control exerted by different arousal states on the rat olfactory bulb was investigated. The olfactory tubercle was unilaterally coagulated with either 1 mA or 3 mA current. The vigilance state parameters and multiunit mitral cell activity were recorded in freely moving rats, stimulated either by their usual food odor or by isoamyl acetate, in a hungry or a satiated state. In each animal, a unilateral lesion affected resting activity and the relative proportion of positive (excitatory) and negative (inhibitory) responses in the same way in both olfactory bulbs; these effects were proportional to the extent of the lesion. In wakefulness, a nutritional modulation of the bulb responses for food odor existed in spite of a slight decrease in the general arousal level. In slow wave sleep (SWS), when compared to a control group, the rats with lesions showed an increase of neocortical desynchronization induced by olfactory stimulation, and a large decrease of mitral cell excitability. Inhibition of the olfactory input, which normally develops during SWS, could involve mainly mesencephalic neurons reaching the olfactory tubercle and the bulb via the ventral part of the medial forebrain bundle.

Ascending noradrenergic projections from locus coeruleus reaching the rat olfactory bulb (OB) synapse onto gamma-aminobutyric acid (GABA)-ergic interneurons. We tested the hypothesis that these interneurons could locally modulate noradrenaline (NA) release. On superfused OB slices, GABA (10, 100 and 1000 microM) enhanced potassium-evoked release of newly accumulated [3H]NA. This raises the possibility that GABAergic interneurons could establish a functional link between olfactory deutoneuron activity and NA release in the rat OB.

This study investigated the role of the noradrenergic (NA) and the serotoninergic (5-HT) centrifugal fibers on the olfactory bulb (OB). For this purpose, behavioral responses largely depending on olfactory information were measured in rats after discrete bilateral injections into the OB with either 6-hydroxydopamine (6-OHDA) or 5,6-dihydroxytryptamine (5,6-DHT) solutions. The evaluation of the level of endogenous 5-HT in the OB was measured by high performance liquid chromatography. The NA fibers appeared lesioned after the 6-OHDA treatment only, whereas the 5-HT level was significantly reduced in 5,6-DHT treated bulbs only (34% of the control value). The animals were fed on usual stock-diet (S) and had the choice between S and a novel food (V) on neophobia test, and again on the following day after aversive conditioning (0.9 mEq/kg LiCl i.p.). The behavioral results showed that the drug administrations were followed by a significant effect in one case only: the intake of V was significantly enhanced in 6-OHDA treated animals during neophobia test. Thus, neophobia was reduced by 6-OHDA. The data are interpreted as follows: (1) the lesion of the bulbar NA or 5-HT fibers does not induce total anosmia; and (2) the NA innervation of the OB could play a role in the modulation of behavioral responses to biological odorants.

Previous studies have shown that the olfactory bulb (OB) responsiveness was selectively enhanced towards food odor in free-moving hungry rats. this modulation of the olfactory input depended on the action of centrifugal fibers. The present study investigated the possible involvement of the noradrenergic (NA) projections from the locus coeruleus to the OB in this adaptative control of the OB excitability. After plugging of the olfactory lumen, 17 rats received discrete injections of 6-hydroxydopamine solution (10 micrograms of the salt; 40 nmol free base) into one OB (6-OHDA bulb) and the vehicle into the contralateral side (control bulb); 10 sham operated rats received intrabulbar isotonic saline solution injected bilaterally (sham bulbs). In the 12 6-OHDA bulbs with the noradrenaline content significantly reduced, the mean dopamine and noradrenaline levels were, respectively, 90% and 34% of the control values. One week after treatment, the average irritability score was significantly higher in the 6-OHDA treated animals than in the sham-operated ones. The main electrophysiological effect of the treatment was to amplify the selective enhancement of OB responsiveness to food odor normally occurring in hungry animals; this effect was restricted to the 6-OHDA bulbs. The results discussed considering the possible involvement of NA fibers in selective attention to odors at the OB level.

The combined modulating effects of the general level of arousal and specific hunger arousal on the olfactory bulb responses were investigated in the rat. Vigilance state parameters and multi-unit mitral cell activity were recorded in freely moving animals stimulated by control odours and by their usual food odour, either in the hungry or the satiated state. The nutritionally modulated bulb responses towards food odour were observed only for high arousal level (wakefulness). In rapid eye movement sleep (REMS), no olfactory response occurred. In slow wave sleep (SWS), one observed either a high bulb responsiveness to stimuli with neocortical arousal, or a general inexcitability. Each odorous stimulus in SWS elicited a higher neocortical arousal rate in the hungry than in the satiated state, as did food odour compared with control odours in both nutritional states. In SWS, a progressive alteration of the nutritionally modulated responses occurred at first at the bulb level and later for inner structures. Rats fed 2 h a day displayed a reversed circadian sleep-waking cycle and a lower SWS proportion compared with rats fed ad libitum. The hunger arousal could quantitatively and qualitatively modulate the activity of structures regulating the sleep-waking pattern.

During the past five years, 127 newborn infants with marked anoxia, severe cardiac failure or respiratory problems secondary to a cardiac lesion were operated upon at l'Hôpital Ste-Justine, Montreal, Quebec.Infants in cardiorespiratory distress from a cardiac lesion for which the surgical treatment is well established, such as complicated coarctation of the aorta, were either cured or improved in 78% of cases. The fatal outcome following medical treatment of patients suffering from lesions for which the surgical treatment is not yet well established, e.g. interruption of the aortic arch, led us to operate upon these infants with the hope of salvaging some of them despite the high surgical risk.The decision to operate was usually based on clinical grounds; however, cine-angiocardiography was at times required to establish the exact diagnosis. Light anesthesia was essential to the success of the operation. Postoperative care was facilitated by a team of nurses well experienced in the treatment of newborn subjects with heart lesions. Fluids were administered in a minimum quantity of 700 c.c./m.(2) for 24 hours, and potassium was the only electrolyte added to the replacement fluids. Respiratory problems were reduced to a minimum by active physiotherapy. However, intubation with aspiration of tracheobronchial secretions was carried out when necessary.