Bulb Removal Research Articles

The Olfactory Bulbs Tonically Inhibit Serum Gonadotropin and Prolactin Levels in Male Hamsters on Long or Short Photoperiod

Abstract Bilateral removal of the olfactory bulbs (BX) inhibits the testicular regression associated with maintenance of golden hamsters on short photoperiod (10L:14D). The present study was done to examine the reproductive endocrine changes following BX of hamsters, to test whether BX increases gonadotropin secretion by enhancing the rate of metabolism of peripheral testosterone, and to determine whether BX inhibits the response to photoperiod by blocking chemosensory signals from conspecifics. BX resulted in a marked increase in tonic serum gonadotropin levels in pre-pubertal (23 days old) and adult hamsters maintained on long photoperiod (14L:10D). Maintenance on 10L14D inhibited gonadotropin secretion in BX hamsters, but this only reduced the previously elevated levels to those of the sham group on stimulatory photoperiod, and the testes therefore remained large. BX hamsters on 10L:14D had a higher post-castration increase in serum luteinizing hormone than sham-operated hamsters. Following testosterone replacement (20 mm Silastic capsules), BX animals had lower serum testosterone and higher serum follicle- stimulating hormone levels than the sham group. BX hamsters had a shorter mean half-time for disappearance of testosterone from serum following removal of the capsule, but some animals in the sham group also metabolized testosterone rapidly. Isolation in cages receiving air filtered to remove pheromonal type molecules did not affect the rate or degree of testicular regression in response to short days. We conclude that the olfactory bulbs tonically inhibit gonadotropin release in golden hamsters on long or short photoperiod. The olfactory bulbs may facilitate the negative feedback of testosterone and may inhibit testosterone metabolism, but there were also steroid-independent effects. The influence of the olfactory bulbs on the hamsters' response to short days is apparently not related to chemosensory information from other hamsters.

The Olfactory Bulbs Enhance Reproductive Hormone Secretion in Male Rats on Long or Short Photoperiod

Abstract Unlike seasonally breeding species such as the Syrian hamster, Sprague-Dawley laboratory rats do not normally respond to short photoperiod (6L18D) with reproductive regression. However, removal of the olfactory bulbs (BX) unmasks a photoperiodic response in pre-pubertal rats so that blinding or short photoperiod results in an inhibition of reproductive hormone secretion and/or a delay in pubertal development. This is apparently mediated by pineal melatonin which inhibits gonadotropin and/or prolactin secretion, but the mechanism by which BX facilitates the response to photoperiod is not clear. Experiment I was performed to determine serum levels of reproductive hormones at frequent intervals following BX and/or maintenance on short days. Twenty-three-day old male rats were BX or underwent sham BX (SH). They were thereafter maintained on a 14L:10D (long photoperiod) or 6L:18D photoperiod for the duration of the study. At 6 weeks following surgery, BX rats on either photoperiod had smaller testes than the SH groups. At week 8, the BX group on 6L:18D had smaller testes than the other three groups. There were transient reductions in serum luteinizing hormone and follicle-stimulating hormone in the BX rats on short photoperiod, but there were prolonged effects of BX decreasing prolactin levels in rats on long or short photoperiod. In SH rats, testosterone was elevated for weeks 6 through 10 of the study, and BX blocked this increase. Experiment II was performed to determine whether BX alters testosterone feedback on gonadotropin secretion. Twenty-three-day old male rats were BX or underwent SH operation and were then returned to a room on 14L10D. Six to 8 weeks later, all animals were castrated and placed on 6L18D or returned to 14L:10D. Eight weeks following castration, the rats were implanted with Silastic capsules containing 0, 10, 20 or 40mm testosterone. The post-castration increase in serum luteinizing hormone and follicle-stimulating hormone was lower in the BX than SH rats. In long photoperiod, serum luteinizing hormone and follicle-stimulating hormone were often lower in the BX rats receiving no testosterone replacement or lower doses of testosterone than in the SH group receiving similar capsules. Maintenance on short photoperiod increased the responsiveness to testosterone so that even the rats receiving low doses of testosterone had very low luteinizing hormone and follicle-stimulating hormone levels whether they were SH or BX. In summary, BX rats on long or short photoperiod had lower serum prolactin and testosterone levels than the comparable SH group and BX inhibited the post-castration increase in gonadotropin secretion. The data therefore suggest that the olfactory bulbs tonically enhance reproductive hormone secretion (especially around the time of pubertal development).

Olfactory bulb removal: Effects on sexual behavior and partner-preference in male rats

Control and bilaterally bulbectomized male rats were tested in an arena where the male could choose to spend time with (and mate with) a sexually receptive female, a nonreceptive female, or be in a neutral compartment. Control males mated with, and showed a strong preference for, sexually receptive females. Bulbectomy virtually eliminated mating. In addition, bulbectomized males showed no preference for a receptive female over a nonreceptive female, and spent their time equally between the receptive female, the nonreceptive female, and the neutral compartment. Effects of bulbectomy on preference and copulation could be consequences of a severely impaired ability to smell—the perception of odors may be essential for sexual arousal, or the absence of preference and copulation after bulbectomy might reflect a deficit in the male's ability to make odor-dependent classification of conspecifics as appropriate sexual partners. Or the behavioral effects of bulbectomy might reflect a disruption of tonic input to the forebrain that has little or nothing to do with the sensory impairment that follows bulb removal. But whatever the reason, in partner-preference tests bulbectomized males show a striking indifference to the sexual status of females, and it seems likely that the failure to mate is causally linked to this effect of surgery.

Inhibitory effects of centrally and peripherally induced anosmia on mounting behavior in the female rat

Adult ovariectomized female rats received a testosterone-propionate (TP)-filled silastic implant and were tested for mounting behavior seven days later. Exposure to estrous female urine but not to urine from ovariectomized females increased the number of TP-treated females that displayed mounting behavior. Olfactory bulb removal on its own and peripheral anosmia induced by intranasal ZnSO 4 application impaired mounting behavior. These results are discussed with respect to the effects of anosmia on copulatory behavior in the male.

Olfactory bulb transplantation into the olfactory bulb of neonatal rats

Embryonic olfactory bulbs (E14–E18) were homotopically transplanted into neonatal rats (P1–P5) after partial or total bulb removal. After different survival times, the animals were sacrificed and their brains processed for histological and immunohistological observations. The growing sensory axons randomly formed glomeruli within the transplanted tissue which often acquired a typical laminar organization. Myelinated fibers connecting the transplant with the telencephalon were clearly identified in one animal. Thus, the present study has shown that olfactory bulb transplants were able to differentiate, mature and establish relationship with both the periphery and the brain.

Lordosis behavior in intact male rats: Effects of hormonal treatment and/or manipulation of the olfactory system

The aim of this study was to investigate the olfactory mechanisms regulating the display of lordosis behavior in intact Wistar male rats bred in our colony. Gonadally intact males show a low capacity to respond by lordosis to male mounts and were insensitive to manipulations of the olfactory system (exposure to the odor of male urine or accessory bulb removal (AOBR)) which have been previously shown to facilitate the display of lordosis behavior in orchidectomized animals primed with ovarian hormones. Treatment with either estradiol benzoate (EB) or EB and progesterone (P) consecutively did not render these gonadally intact animals sensitive to the effects of AOBR. By contrast exposure to male urine was capable of facilitating the display of lordosis behavior in intact male rats given EB + P consecutively. These results are discussed in the light of previous findings showing that (1) two inhibitory structures, the accessory olfactory bulb and the septal and preoptic areas, are involved in the control of lordosis behavior in the male rat; (2) the effects of olfactory cues on the display of lordosis behavior are dependent on the action of both EB and P in orchidectomized animals.

Plasticity-related binding of GABA and muscarinic receptor sites in piriform cortex of rat: An autoradiographic study

This study has used the recently developed in vitro quantitative autoradiographic technique to examine the effects of olfactory bulb (OB) removal on receptor-binding sites in the deafferented piriform cortex (PC) of the rat. The γ-aminobutyric acid-benzodiazepine receptor (GABA-BZR)- and muscarinic cholinergic receptor (MChR)-binding sites in layer I of PC were localized using [ 3H]flunitrazepam and [ 3H]quinuclidinyl benzilate as ligands, respectively. From the resultant autoradiograms the optical densities were measured using a Drexel-DUMAS image analysis system. The densities of BZR and MChR-binding sites were markedly increased in the PC ipsilateral to the lesion as compared to the contralateral side in those subjects that were operated in adulthood (Postnatal Day 100, PN 100). Comparisons between the unoperated and PN 100 operated animals also showed significant increases in the deafferented PC. In the animals operated on the day of birth (PN 0) no significant differences were seen between the operated and the contralateral PC. The difference between the PN 0 deafferented PC and the unoperated controls shows a slight decrease in BZR density in the former group; however, in case of the MChR there is a slight increase on the side of the lesion. These results demonstrate that deafferentation of PC by OB removal appears to modulate both the BZR-binding sites that are coupled with the GABA-A receptor complex and the MChR-binding sites. The results also suggest the possibility of a role for these neurotransmitter receptor-binding sites in plasticity following deafferentation.

Recovery of olfactory behavior following removal of accessory olfactory bulb in adult rat

It has been shown that male rats demonstrate a preference for the odor of the female rat. This preference has been suggested to be a function of the accessory olfactory pathway. Thus, changes in preference of the male rat for the odor of the female were examined following accessory olfactory bulb (AOB) removal. Preference decreased to about 30% of that seen in the intact rat during the 10 days following AOB removal. Thereafter, it increased gradually over one month survival time up to approximately 70% of the level demonstrated by the intact rat. The rats whole main olfactory bulb and AOB were removed did not show any recovery at any survival time. The time course of the behavioral recovery after AOB removal was compared with the time course of the recovery of synaptic density which was observed in the medial amygdaloid nucleus after AOB removal 12. The relationship between functional recovery and reorganization of synaptic connections is discussed.

Bilateral transection of the lateral olfactory tract but not removal of the vomeronasal organs inhibits short-photoperiod-induced testicular regression in golden hamster

It is now known that removal of the olfactory bulbs increases basal gonadotropin secretion and prevents short-photoperiod-induced testicular regression in Syrian hamsters. The experiments described in the present paper were an attempt to determine which neuronal systems associated with the olfactory bulbs are responsible for this influence on the reproductive neuroendocrine axis. In the first experiment, removal of the vomeronasal organ failed to influence gonadotropin secretion or testes weight in hamsters on long or short photoperiod, suggesting that the vomeronasal-accessory olfactory pathway is not individually responsible for the effect of the olfactory bulbs on gonadotropin secretion. In the second experiment, bilateral transection of the lateral olfactory tracts (LOT) did prevent short-photoperiod-induced testicular regression and the associated decrease in gonadotropin secretion. Since the nervus terminalis is confined to the surface of the medical olfactory bulb pathway, the results of LOT transection indicate that the nervus terminalis, which itself contains gonadotropin releasing hormone, does not mediate the influence of the olfactory bulbs on gonadotropin secretion. These results further suggest that the olfactory bulb influence on gonadotropin secretion is due to neural connections to the pyriform cortex, entorhinal cortex or amygdala.

Olfaction directs skilled forelimb reaching in the rat

Rats were trained to reach for food pellets, which varied in size from 20 to 300 mg, from one of 21 locations on a shelf located just outside a test cage. After a barrier was lifted, giving access to a food pellet, latency to contact the food was timed, number of reaches to contact the food were counted, the distance of each misplaced reach from the food was measured and the success or failure of each attempt was noted. Control rats walked along the front of the cage sniffing to locate the food. Once they located a food pellet, they inserted their nose between the bars of the cage, sniffed the food for one to three respiratory cycles, raised their snout slightly, and then inserted a forepaw to grasp the food. They seldom required more than three reaches to contact the food and on about half of all trials they were successful in grasping the food. They were more successful in grasping medium-sized food pellets. Performance was unchanged on all measures after vision was occluded with eye patches. Following olfactory bulb removal, however, the rats no longer sniffed to locate the food or sniffed the food prior to initiating a reach. Rather they systematically moved along the length of the cage inserting their snout between the bars at each possible food location and without sniffing reached for the food 'as if blind'. Latency, number of reaches to contact the food and the distance of misplaced reaches increased whereas success rate remained unchanged. Substantial additional impairments were not produced when the bulbectomized rats were given visual occlusion. The study demonstrates that rats locate food and direct reaching using olfaction. The results are discussed in terms of the sensory control of skilled limb use and their relevance to the evolution of the sensory guidance of limb use.

Ultrastructure of synaptic remodeling in piriform cortex of adult rats after neonatal olfactory bulb removal: an immunocytochemical study.

The purpose of this investigation was to study possible remodeling in synaptic structures of the piriform cortex (PC) of adult rats following neonatal deafferentation by removal of the olfactory bulb (OB) at birth. Emphasis was placed on possible qualitative changes in the ultrastructure and immunocytochemical localization of cholecystokinin (CCK, a possible excitatory neurotransmitter or modulator) and glutamic acid decarboxylase (GAD, precursor enzyme to the inhibitory transmitter GABA) in axons, terminals, and synaptic complexes. Light microscopic results in normal adult material show that GAD-positive terminals form a dense band subjacent to the lateral olfactory tract (LOT), become less dense in deeper Ib, and are rare in layer II. Following deafferentation, GAD-positive terminals appear denser and more homogeneously distributed throughout layer I and are also more prevalent in layer II. Ultrastructural results of normals and controls indicate GAD-positive terminals normally contain pleomorphic or flattened vesicles and form symmetric contacts onto dendritic shafts and branches throughout layer I. In deafferented layer I not only do there appear to be greater numbers of symmetric GAD-positive contacts, but in contrast to normals, asymmetric contacts mainly onto spines are now present. Light microscopic results from deafferented material also show an apparent proliferation with spread or sprouting of CCK-positive fibers or axonlike structures mainly into layer Ia, whereas these fibers are normally observed only in the LOT and are generally few in number. Also in normals the few CCK-positive terminals in the area subjacent to the LOT contain flattened or pleomorphic vesicles and form symmetric contacts. Deafferentation results in CCK-positive terminals throughout layer I with a greater frequency of synaptic contacts which now also include a few asymmetric contacts onto spines. The findings clearly show modifications in synaptic patterns of immunocytochemical-labeled terminals that might be compatible with the process of atypical reinnervation of deafferented postsynaptic sites and possible ingrowth of new axons.

Brain output dysregulation induced by olfactory bulbectomy: an approximation in the rat of major depressive disorder in humans?

Mounting evidence indicates that the emotional, cognitive, neurovegetative and behavioral symptoms of patients with major depressive disorder are due to abnormal neurochemical substrates in the brain. Although the specific neurochemical abnormalities responsible have not been identified, the presenting symptoms of major depression are consistent with a disruption of normal neural communications between the limbic system and hypothalamus. Following removal of the olfactory bulbs, rats display a syndrome of behavioral deficits that also reflect a disruption of the limbic-hypothalamic axis. Moreover, the bulbectomy induced deficits are selectively reduced by the chronic administration of the same drugs that alleviate the symptoms of depression when given chronically to the patients. In addition to this pharmacological similarity, there are also numerous behavioral parallels between bulbectomized rats and major depression patients. The bulbectomized rat provides a good model in which to study antidepressant drugs and also may provide neurochemical and neuroanatomical data that are relevant to understanding the biological substrates of emotion and the causes of depression in humans.

Memory deficit in passive-avoidance learning in bulbectomized Long-Evans hooded rats

Male and female Long-Evans hooded rats were subjected to either olfactory bulb damage or control surgery. Olfactory bulb removal resulted in increased mouse killing, increased irritability to handling, and increased open-field activity. In acquisition trials on a modified passive-avoidance apparatus, control animals habituated rapidly to the apparatus, while OB rats showed little evidence for habituation. All controls showed 24-hour retention of shock on the last acquisition trial, while OB rats showed the typical retention deficit, despite being given a behavioral alternative to withholding a response. The P-A deficit in OB rats appears to be a learning/memory deficit, not the result of heightened activity.

Olfactory bulb removal decreases androgen receptor binding in amygdala and hypothalamus and disrupts masculine sexual behavior

In these experiments we examined the relationship between olfactory bulb removal, limbic system androgen receptor binding and male copulatory behavior. Sexually experienced male rats were castrated, and implanted with two 10 mm testosterone-filled silastic capsules. Animals then underwent either bilateral olfactory bulb removal (BOB) or sham surgery (Sham). Beginning 1–2 days post-operatively both BOB and Sham operates were given 4 tests for male copulation on alternate days. Less than 40% of BOB males ejaculated. In contrast, 80–100% of sham operates continued to ejaculate throughout the 4 postoperative tests. Cell nuclear androgen receptor binding was assessed in amygdala, hypothalamus, preoptic area and septum 1–2 and 8–9 days after either bulbectomy or sham surgery. We found that olfactory bulbectomy significantly reduces androgen receptor binding in amygdala and hypothalamus. The reduction in androgen receptor binding in amygdala occurs within 1–2 days following olfactory bulb removal and is correlated with the disruption of ejaculatory activity. These data suggest that the neuromodulation by olfactory bulb input to androgen-concentrating neurons in the amygdala and hypothalamus is necessary for effective copulation in male rats.

Role of central α 2-adrenoceptors on the development of muricidal behavior in olfactory bulbectomized rats: Effect of α 2-adrenoceptor antagonists

Upon surgical removal of olfactory bulbs, by the 8th to 10th day after the surgery muricidal behavior has been demonstrated in 75.4% of rats. In the homogenates of forebrain obtained from rats demonstrating muricidal behavior, levels of noradrenaline, 5-hydroxytryptamine and their metabolites (i.e., 3-methoxy-4-hydroxyphenylglycol sulfate and 5-hydroxyindoleacetic acid) were not changed. However, the fractional turnover rate of noradrenaline in the forebrain of the olfactory bulbectomized rats was significantly decreased without alterations in the metabolism of 5-hydroxytryptamine when compared to that of the sham rats. The muricidal behavior and the aggressiveness were suppressed by antagonists of α 2- adrenoceptors (yohimbine, idazoxan and rauwolscine), but not by the α 1- adrenoceptor antagonist (corynanthine). Furthermore, upon administration of yohimbine or idazoxan to rats demonstrating the muricidal behavior, the level of noradrenaline in the homogenates of forebrain was decreased while that of 3-methoxy-4-hydroxyphenylglycol sulfate was increased. The maximum binding capacity (B max) of [ 3H]yohimbine to the forebrain membranes obtained from the olfactory bulbectomized rats was significantly higher than that from the sham rats without demonstrating any differences in dissociation constants (K d) between the two brain membranes. Based on these results, it was suggested that olfactory bulbectomy has caused some functional changes in central α 2- adrenoceptors .

A new immunization procedure for obtention of anti-leucine-enkephalin antibodies: Part II. Effects of Olfactory Bulb Removal on pro-enkephalin related peptides in rat brain

Bilateral Olfactory Bulb Removal (OBR) induced both complex behavioral alterations and a decrease of many neurotransmitter levels. We studied brain levels of the pro-enkephalin related peptides 45 days after OBR. Opioid levels were studied using three different highly specific antisera exhibiting very high affinities in radioimmunoassays in striatum, hypothalamus, hypophysis, brain stem and cortex. Methionine enkephalin levels increase significantly in striatum (42%), hypophysis (94%) and hypothalamus (25%) and non-significantly in the other areas. Leucine-enkephalin levels tended to increase in all dissected structures but a significant increase only occured in striatum (42%). Octapeptide levels (Methionine-enkephalin-Arg-Gly-Leu) significantly increase in striatum (22%) and decrease in hypophysis (97%) and in brain stem (76%). All these results are partially consistent with the decrease of opiate binding described previously after OBR and suggest a complex imbalance in neurotransmitters after such a sensorial deprivation. It is suggested that the modifications of enkephalinergic neurotransmission might be related to the stressful state induced by OBR.

Age-dependent cell death in the olfactory cortex: lack of transneuronal degeneration in neonates.

Adult olfactory cortical neurons in layer IIa undergo fulminant transneuronal degeneration after removal of afferent olfactory bulb fibers (Price, '76, Neurosci Abst. 2:161; Heimer and Kalil, '78, J. Comp. Neurol. 178:559-609). This provides an unusual example of dependence of a mature population of neurons on axonal input. In order to investigate whether similar transneuronal degeneration occurs in immature animals, a series of rats were subjected to unilateral olfactory bulb removal at various ages during the first 3 postnatal weeks. The brains were examined for degeneration after short survivals by use of the de Olmos cupric silver method, which selectively stains degenerating neurons. In addition, animals with long survivals were examined with the HRP retrograde tracing method, in order to determine if cells that survive the acute effects of deafferentation develop normal patterns of connections. Young neurons are more resistant to the effects of olfactory bulb removal than more mature neurons. There was little degeneration of cortical neurons after bulb ablation during the first 2 postnatal weeks. Although layer IIa does not become distinct from layer IIb in these experimental animals, cells that have connections normally characteristic of the cells of layer IIa, and are situated at the superficial edge of layer II, were identified with the HRP method. The severity of transneuronal degeneration increases and becomes adultlike between the second and third postnatal weeks. This increase in transneuronal degeneration is temporally associated with a progressive reduction in axonal sprouting following deafferentation during the first 3 postnatal weeks, as described in the companion paper (Friedman and Price, '86). Thus, axon sprouting may "protect" the immature IIa neurons from the effects of removal of the fibers from the olfactory bulb. A period of normal cell death has also been identified in olfactory cortex by the use of the de Olmos cupric silver method. This cellular degeneration is much less severe and has a different time course and laminar distribution than the transneuronal degeneration produced by olfactory bulb ablation in adults. Although normal cell death appears to be potentiated by removal of the olfactory bulb on postnatal day 1, it is clearly a different process from the transneuronal reaction.

Accessory olfactory bulb lesions and lordosis behavior in the male rat feminized with ovarian hormones

Orchidectomized rats were given estrogen and progesterone and tested for feminine behavior in the presence of a mounting male after accessory olfactory bulb removal (AOBR). Complete AOBR caused a rise in the number of estrogen-progesterone-treated male rats responding by lordosis behavior to male mounts as compared to controls and sham-operated animals. By contrast, LQ scores did not appear to differ in these three groups of animals. The results are discussed in terms of involvement of the main and the accessory olfactory systems in the regulation of feminine behavior in the male rat.

The effects of fluoxetine and zimeldine on the behavior of olfactory bulbectomized rats

Previous work has shown that subchronic administration of antidepressant drugs can reverse the behavioral and physiological changes produced by removal of the olfactory bulbs of rats. It has also been reported that acute administration of drugs believed to enhance serotonergic transmission can improve passive avoidance performance in bulbectomized rats. In order to follow up this observation the effects of the serotonin reuptake inhibitor, fluoxetine, were studied in bulbectomized and control rats. Fluoxetine produced a dose-related improvement in the passive avoidance behavior of bulbectomized rats in a step-down task and in a Y-maze. The effect of fluoxetine on step-down avoidance was blocked by metergoline and was also shown by zimeldine, another inhibitor of serotonin reuptake. However, in tests of active avoidance responding in a shuttle box and exploratory locomotion, fluoxetine produced similar disruptions of behavior in both bulbectomized and control animals. Thus, the effects of fluoxetine on the behavior of bulbectomized rats are dependent upon the behavioral test.

Olfactory environment and early mating behavior in the cyclic female rat

The objectives of this study were to examine the effects of olfactory cues from the male and of olfactory bulb removal on early mating behavior in sexually inexperienced diestrous female rats primed with estrogen. Four-day cyclic rats isolated from the male were given either 2.5 μg or 10 μg estradiol benzoate (EB) and presented to stimulated males in the late afternoon of diestrus 2 between 18:00 and 19:00 for a 10 min sexual behavioral session. Dose-dependent effects of estrogen were observed since 10 μg EB significantly increased the proportion of females displaying early mating as compared with those given 2.5 μg EB. Olfactory bulb removal prior to estrogen treatment caused a rise in the number of females which mated early with respect to the non bulbectomized controls. Exposing the females to bedding soiled with male urine on diestrus 2 at 10:00 did not affect early mating behavior. By contrast the olfactory stimuli became efficient when 2.5 μg EB treated females were given 10 μg progesterone (P) by the time of exposure to male urine. The results were discussed with respect to the role played by the olfactory system in the control of lordosis behavior throughout estrous cycle in female rats. P was concluded to be involved in the perception of the olfactory signals from the male which facilitate early mating behavior in diestrous female rats.