Different olfactory system deficits affect the antigonadal action of light deprivation differently in male rats

Twenty-eight day-old male rats were subjected to: Blinding-olfactory bulbectomy, Blinding-peripheral anosmia, Blinding-accessory olfactory bulbectomy and Blinding-sham olfactory operation. A set of rats remained intact. Six weeks later, their pituitary-gonads-accessory sex organs were studied. Bulbectomy as well as peripheral anosmia exaggerated the antigonadal effects of blindness, while the accessory olfactory system impairment did not. It is suggested that olfactory bulbectomy potentiation of the antigonadal effects of light deprivation is due to a lack of sensory function rather than to bulbectomy itself and that the accessory olfactory system which is involved in the priming pheromonal effects does not play any role in the inhibition of the antigonadal effects of blindness.     

Calcium-binding proteins: differential expression in the rat olfactory cortex after neonatal olfactory bulbectomy

Calbindin, parvalbumin, and calretinin, members of EF-hand calcium-binding proteins, play important roles in buffering intracellular calcium ions. These proteins are localized in distinct populations of cells in the olfactory bulb (the primary sensory relay in the olfactory system) and its major synaptic target, the primary olfactory cortex (POC). In the present study, the postnatal expression of these calcium-binding proteins in layer III of POC was quantitatively examined 30 days after neonatal bulbectomy, a manipulation known to cause cell death and neurotransmitter changes. The numbers of both calbindin and parvalbumin-immunoreactive profiles showed significant increases (68% and 163%, respectively), while calretinin-immunoreactive profiles exhibited a 46% reduction. The data demonstrate that the expression of these calcium-binding proteins is regulated in part by the afferent input from the olfactory bulb. Furthermore, the resultant increase in calbindin and parvalbumin expression may provide neuroprotective support necessitated by possible alterations in intracellular calcium ions and other neurochemical factors that accompany neonatal bulb removal.     

Calcium‐binding proteins: Differential expression in the rat olfactory cortex after neonatal olfactory bulbectomy

Calbindin, parvalbumin, and calretinin, members of EF‐hand calcium‐binding proteins, play important roles in buffering intracellular calcium ions. These proteins are localized in distinct populations of cells in the olfactory bulb (the primary sensory relay in the olfactory system) and its major synaptic target, the primary olfactory cortex (POC). In the present study, the postnatal expression of these calcium‐binding proteins in layer III of POC was quantitatively examined 30 days after neonatal bulbectomy, a manipulation known to cause cell death and neurotransmitter changes. The numbers of both calbindin and parvalbumin‐immunoreactive profiles showed significant increases (68% and 163%, respectively), while calretinin‐immunoreactive profiles exhibited a 46% reduction. The data demonstrate that the expression of these calcium‐binding proteins is regulated in part by the afferent input from the olfactory bulb. Furthermore, the resultant increase in calbindin and parvalbumin expression may provide neuroprotective support necessitated by possible alterations in intracellular calcium ions and other neurochemical factors that accompany neonatal bulb removal. © 1999 John Wiley & Sons, Inc. J Neurobiol 39: 207–217, 1999     

The contribution of the olfactory and tactile modalities to the nipple-search behaviour of newborn rabbits

By performing uni- and bilateral olfactory bulb lesions and uni- and bilateral transsections of the infraorbital branches of the trigeminal nerves in 2-day-old rabbits, it could be shown that: Both the olfactory and tactile modalities are essential for the successful performance of nipple-search behaviour. While bilateral bulbectomy completely eliminates searching, and hence suckling, unilateral bulbectomy has relatively little effect. Bilateral denervation of the muzzle does not eliminate searching, but pups are unable to suckle as they fail to show the mouth-opening component necessary for nipple attachment. In contrast to unilateral bulbectomy, unilateral denervation of the muzzle results in a lateralization of head movements during searching, nipple grasping and nipple release.     

PUTATIVE TRANSMITTERS IN DENERVATED OLFACTORY CORTEX

Olfactory bulb removal and the consequent degeneration of the lateral olfactory tract led to a selective change in putative synaptic transmitters of the denervated olfactory cortex of guinea-pigs. Nine days after bulbectomy there was a significant decrease in content of aspartate (31%) and glutamate (20%) in olfactory cortex but no change in neocortex. The content of GABA, alanine and ACh in olfactory cortex was unchanged (± 3 per cent of control). The content of 5-HT, dopamine, NE and glycine was increased by 10-18 per cent. The decrease in aspartate and glutamate content of the olfactory cortex after bulbectomy suggests that these two amino acids have a high concentration in fibres of the lateral olfactory tract. This tissue may prove to be useful in determining the possible role of these acidic amino acids in neuronal function.     

Olfactory bulbectomy modifies photic entrainment and circadian rhythms of body temperature and locomotor activity in a nocturnal primate

Studies on rodents have emphasized that removal of the olfactory bulbs modulates circadian rhythmicity. Using telemetric recordings of both body temperature (Tb) and locomotor activity (LA) in a male nocturnal primate, the gray mouse lemur, the authors investigated the effects of olfactory bulbectomy on (1) the circadian periods of Tb and LA in constant dim light condition, and (2) photic re-entrainment rates of circadian rhythms following 6-h phase shifts of entrained light-dark cycle (LD 12:12). Under free-running condition, bulbectomized males had significantly shorter circadian periods of Tb and LA rhythms than those of control males. However, the profiles of Tb rhythms, characterized by a phase of hypothermia at the beginning of the subjective day, and Tb parameters were not modified by olfactory bulbectomy. Under a light-dark cycle, olfactory bulbectomy significantly modified the expression of daily hypothermia, especially by an increase in the latency to reach minimal daily Tb, suggesting a delayed response to induction of daily hypothermia by light onset. Reentrainment rates following both a 6-h phase advance and a 6-h phase delay of entrained LD were also delayed in bulbectomized males. Olfactory bulbectomy led to significant fragmentation of locomotor activity and increased locomotor activity levels during the resting period. The shortening of circadian periods in bulbectomized males could partly explain the delayed responses to photic stimuli since in control males, the longer the circadian period, the better the response to light entrainment. This experiment shows for the 1st time that olfactory bulbs can markedly modify the circadian system in a primate.     

Plasma prolactin in relation to changes in oestrous cyclicity following olfactory bulbectomy in post-pubertal pigs

Prolactin was determined by radioimmunoassay in the peripheral plasma of five post-pubertal Large White gilts before and after olfactory bulbectomy. In the oestrous cycle before bulbectomy and in cycles after bulbectomy, the highest concentrations of prolactin were found during the period from the late luteal phase to oestrus. Throughout the prolonged summer anoestrus which occurred after bulbectomy, the amounts of prolactin were similar to base-line quantities found during the oestrous cycle between Days 3 and 12. These results differ from those found for the seasonally breeding European wild sow where high prolactin levels are associated with a summer anoestrus.     

Role of olfaction in food preference as evaluated in an animal model.

Food preference in individual animals is regulated by brain activity. Two murine model systems for investigating food preference were developed by focusing on fruit juices. In a home-cage, two-bottle test, the volume of apple juice consumed was found to be much larger than that of orange juice. In a two-nozzle "Drinkometer" test, by which each mouse was kept in a 38 cm (W) x 32 cm (D) cage and each drinking event was recorded by an electronic "Drinkometer" device, it was again found that the mice preferred drinking apple juice to orange juice. To elucidate the role of olfaction in this food preference, mice were subjected to an olfactory bulbectomy to remove the olfaction capability. In the home-cage two-bottle test, the preference for apple juice over orange juice was apparent even after the olfactory bulbectomy, indicating that olfaction was not essential for the formation of food preference behavior. In contrast, in the two-nozzle "Drinkometer" test, the preference for apple juice over orange juice was found to be abrogated by this surgery, implying the involvement of olfaction-based memory on food preference behavior.     

Effects of bilateral olfactory bulbectomy on the anterior pituitary corticotropic cell activity in male rats.

Bilateral olfactory bulbectomy (OB) has drastic biochemical and behavioral effects and is often associated with an increase in plasma corticosterone concentrations. This experiment examined the effects of OB on adrenocorticotropin (ACTH) and corticosterone release under basal and stress conditions and on proopiomelanocortin (POMC) gene expression. Bulbectomy potentiated hypophysal ACTH and adrenal corticosterone release induced by ether stress but had no effect on ACTH release under basal conditions, despite a significant increase of circulating corticosterone. POMC gene expression was stronger (+60%) in OB rats than in sham-operated rats. These results suggest that olfactory bulbectomy substantially altered the negative feed-back exerted by glucocorticoids on anterior pituitary corticotropic cells in the male rat.     

Fluoro Jade-B Detection of Dying Cells in the SVZ and RMS of Adult Rats After Bilateral Olfactory Bulbectomy

A novel fluorochrome, Fluoro-Jade B, was used to detect dying precursor cells in the subventricular zone (SVZ) and rostral migratory stream (RMS) of adult rats after bilateral olfactory bulbectomy and in control intact rats. The animals in experimental group were left to survive 3 days and from 3 till 16 months after surgical procedure. 1. In the control animals, Fluoro-Jade B positive cells were visible in the SVZ and within the whole extent of the RMS. The number of Fluoro-Jade B positive cells increased in the elbow in comparison to the rest parts of the RMS. 2. In the experimental animals surviving either 3 days or from 3 till 16 months after bilateral olfactory bulbectomy, Fluoro-Jade B positive cells displayed the similar pattern of distribution as in the control animals. However, some quantitative differences in the labeled cells number along the rostral migratory pathway appeared. 3. The average number of degenerating cells within the control SVZ and RMS was 26.24+/- 0.686. In bulbectomized animals, regardless of survival time, an insignificant increase of Fluoro-Jade B positive cells number occurred. We can conclude that dying of precursor cells is a physiological process running within the SVZ/RMS in both control and experimental animals. Moreover, this physiological process is not influenced by survival period after bilateral olfactory bulbectomy. Our results demonstrate Fluoro-Jade B as a useful marker of dying cells.     

Olfactory bulbectomy blocks mating-induced ovulation in musk shrews (Suncus murinus)

In many species, reproductive function can be modified by olfactory inputs. We employed bilateral olfactory bulbectomy (BULBX) to examine the effects of disruption of olfactory inputs on mating behavior and ovulation in female musk shrews. On several measures, sexual behavior was delayed in BULBX females compared to controls. When females were mated on five consecutive days, the majority of unoperated and sham-operated (SHAM) shrews ovulated; only one female subjected to BULBX ovulated. Administration of GnRH induced ovulation in the majority of females. We performed immunocytochemistry to assess the effects of bulbectomy on mating-induced responses of the neural GnRH system. In BULBX and SHAM females, the numbers of cells containing proGnRH immunoreactivity in the medial septum (MS)/diagonal band (DB) were significantly elevated 1 h after mating. Bulbectomy increased the numbers of GnRH-immunoreactive peptide-containing cells in the preoptic area, but it reduced neuron numbers in the MS/DB, as compared with those in SHAM controls. In addition, the GnRH-immunoreactive fiber area in the median eminence was greater in BULBX than in SHAM females. In sum, female musk shrews can display receptivity and engage in copulation without olfactory inputs. However, the olfactory system is essential for mating-induced ovulation.     

Effect of Lesions of the Olfactory Bulb on the Levels of Amino Acids and Related Enzymes in the Olfactory Cortex of the Guinea Pig

Abstract: Olfactory bulb removal and consequential degeneration of the lateral olfactory tract led to a decreasein the levels of glutaminase and malate dehydrogenase inthe ipsilateral olfactory cortex. These changes in enzyme activity may account for the well established decrease inthe levels of aspartate and glutamate in the olfactory cortex following ipsilateral bulbectomy. The level of glutamine synthetase, a glial marker enzyme, was slightly-increased while the activities of glutamate decarboxylase, glutamate dehydrogenase, and glutamate oxaloacetic transaminase were unchanged.     

Increased Level of β-Amyloid in the Brain of Bulbectomized Mice

Six weeks after bilateral olfactory bulbectomy, a peptide with molecular weight of 4 kD was revealed in extracts of the neocortex and hippocampus from mice. Using monoclonal antibodies 4G8, this peptide was identified as beta-amyloid. Its level was significantly higher in the bulbectomized animals than in sham-operated mice. The bulbectomized mice displayed sharp impairment in spatial memory when tested in the Morris water maze. The results suggest that bulbectomy initiates in the brain a pathological process similar to human Alzheimer's disease in location, biochemistry, and behavioral manifestations.     

The Response of Ornithine Decarboxylase During Neuronal Degeneration and Regeneration in Olfactory Epithelium

Mature olfactory neurons are continually replaced from a population of progenitor cells. Olfactory nerve section, bulbectomy, or treatment with certain chemicals induces degeneration of olfactory neurons followed in some cases by regeneration. Ornithine decarboxylase (ODC) activity was measured in mouse olfactory tissues as an indicator of cellular regeneration. ODC activity in olfactory tissue (0.2–0.4 nmol/mg protein/h) is 10-30 times higher than in a variety of other cerebral tissues. Within 3 h after unilateral olfactory nerve section, ODC activity in the epithelium declines to 50% of control followed by a slow return to basal activity by 6 days. In the same animals, ODC activity increases severalfold in bulb (1 day) with a gradual decline to normal (9 days). Except for an early transient increase, the effects of unilateral bulbectomy on epithelial ODC activity are similar to those seen after nerve section. The changes in ODC activity following intranasal irrigation with 10 mm -colchicine also closely mimic those seen after nerve section. The effects of intranasal irrigation on ODC activity with 0.5% Triton X-100 or 0.17 m -ZnSO₄ are more complex. Thus, when the mature neuronal population is degenerating after surgery or chemical treatments, ODC activity decreases in the epithelium. The subsequent increase of ODC activity prior to reconstitution of the mature neuronal population probably reflects the regeneration mechanism of the olfactory epithelium. The increase of ODC activity in the olfactory bulb after nerve section is best interpreted as a cellular injury response. These alterations in ODC activity in olfactory tissues after chemical and surgical treatments constitute the earliest biochemical events observed in these tissues in response to cellular damage.     

The development of standard stimulus animals for mouse (Mus musculus) aggression testing by means of olfactory bulbectomy

The usual round-robin technique employed in aggression testing with mice has several major deficiencies. A set of specifications is given for the ideal standard stimulus mouse, which would overcome these deficiencies. In a series of seven experiments, we found that the technique of bilateral olfactory bulbectomy yielded stimulus animals which very closely approximated our ideal. Bulbectomized mice would elicit attack behaviour from normal males, would almost never initiate an attack themselves, rarely fought back when attacked, and were very homogeneous in their capability to release attack behaviour. These findings were obtained whether the mice were tested within a few days after bulbectomy or 40 days afterwards.     

The Ginkgo biloba extract modulates the balance between proliferation and differentiation in the olfactory epithelium of adult mice following bulbectomy.

Abstract - The adult olfactory receptor neurons (ORNs), located in the olfactory epithelium (OE) are permanently renewed thanks to neuronal progenitors present in the deep part of the OE, the globose basal cells (GBCs). Following the ablation of their synaptic target, the olfactory bulb (OB), ORNs degenerate by apoptosis and a wave of neurogenesis, including proliferation of GBCs and neuronal differentiation of their progeny, restores the olfactory function. The Ginkgo biloba extract (EGb 761) (Beaufour Ipsen, France) was administered to adult mice at the doses of 50 or 100 mg/kg, following bilateral bulbectomy and its effects on the expression of PCNA, reflecting the number of proliferating GBCs and on growth associated protein 43 (GAP-43), expressed by differentiating neurons were measured by Western blotting. PCNA expression peaked 9 days post-bulbectomy in untreated animals, but 7 days post-lesion in EGb 761-treated animals. A simultaneous reduction in GAP-43 expression suggested that EGb 761 may temporarily favor the proliferation of GBCs rather than their entry into the differentiation pathway. Probably as a consequence of the earlier onset of the neurogenetic response to bulbectomy, neuronal differentiation was enhanced in the OE, 3 weeks post-bulbectomy. These data suggest that EGb 761 may have beneficial effects upon neurogenesis in the OE through changing the balance between proliferation and differentiation.     

An enhanced olfactory marker protein immunoreactivity in individual olfactory receptor neurons following olfactory bulbectomy may be related to increased neurogenesis

Olfactory marker protein (OMP) is a 19-kD acidic protein found throughout the cytoplasm of mature olfactory receptor neurons (ORNs). Its function remains unknown. Following olfactory bulbectomy, the proportion of ORNs mature enough to express OMP declines greatly. However, in the few remaining mature ORNs, it has been observed that the intensity of OMP immunoreactivity (IR) appears to increase over that of ORNs on the unoperated side. We have now investigated this phenomenon quantitatively in rats subjected to unilateral olfactory bulbectomy. Results show that at all postbulbectomy survival periods examined quantitatively (3 days to 6 months), a significant decrease (19–37%) occurs in the transmission of incident light through OMP(+)-ORNs in bulbectomized versus unoperated olfactory epithelium (OE). Further, we also observed a consistent side-to-side difference in OMP IR in control unoperated animals. Possible explanations for these observations and their relation to the still unknown function of OMP are discussed. To test the possibility that OMP might serve a mitogenic role in the OE, recombinant OMP was added to organotypic explant cultures of fetal olfactory mucosa. Addition of OMP resulted in a dose-dependent increase in the density of bromodeoxyuridine-positive cells in the cultures, with a 50% increase occurring at the plateau OMP concentration of 25 nM. © 1998 John Wiley & Sons, Inc. J Neurobiol 34: 377–390, 1998     

Comparison of the effects of anosmia induced by either peripheral lesion or bulbectomy upon the feeding pattern of the rat (author's transl)]

In order to support the contention that the feeding pattern seen after olfactory bulb removal is due to a sensory loss, the feeding pattern of rats was studied after a peripheral chemical lesion of the olfactory mucosa. A conditioned smell aversion procedure was used to assess the occurence and duration of anosmia after the topical application of zinc sulfate to the olfactory mucosa. It was found that the sensory deficit induced by the peripheral lesion lasted from four to six days. The occurrence of the disrupted feeding pattern in the peripherally lesioned rats coincided in time with the short period of anosmia. Thus, the disruption of the feeding pattern after bulbectomy and after lesions of the central olfactory pathways is clearly the result of anosmia and not of the loss of other non-sensory functions of the olfactory bulbs.     

Lack of fibulin-3 alters regenerative tissue responses in the primary olfactory pathway

The adult olfactory epithelium has maintained the ability to reconstitute its olfactory sensory neurons (OSNs) from a basal progenitor cell compartment. This allows for life-long turnover and replacement of receptor components as well as repair of the primary olfactory pathway in response to injury and environmental insults. The present study investigated whether fibulin-3, a glycoprotein in the extracellular matrix and binding partner of tissue inhibitor of metalloproteinases-3 (TIMP-3), plays a role in ongoing plasticity and regenerative events in the adult primary olfactory pathway. In wild-type control mice, fibulin-3 protein was detected on IB4⁺CD31⁺ blood vessels, nerve fascicles and the basement membrane underneath the olfactory epithelium. After target ablation (olfactory bulbectomy), fibulin-3 was also abundantly present in the central nervous system (CNS) scar tissue that occupied the bulbar cavity. Using two different lesion models, i.e. intranasal Triton X-100 lesion and olfactory bulbectomy, we show that fibulin-3 deficient (Efemp1^?/?) mice have impaired recovery of the olfactory epithelium after injury. Ten days post-injury, Efemp1^?/? mice showed altered basal stem/progenitor cell proliferation and increased overall numbers of mature (olfactory marker protein (OMP) -positive) versus immature OSNs. However, compromised regenerative capacity of the primary olfactory pathway in Efemp1^?/? mice was evidenced by reduced numbers of mature OSNs at the later time point of 42 days post-injury. In addition to these neural differences there were consistent changes in blood vessel structure in the olfactory lamina propria of Efemp1^?/? mice. Overall, these data suggest a role for fibulin-3 in tissue maintenance and regeneration in the adult olfactory pathway.