Bulb Removal Research Articles

The vomeronasal system, aggression, activity, and passive-avoidance learning in hooded rats

Muricidal behavior, irritability to handling, open-field activity, passive-avoidance learning, and weight change were measured in Long-Evans hooded rats after they had been subjected to olfactory bulb removal, cuts of the vomeronasal nerves, lateral olfactory bulb damage, or control operations. Bulbectomized animals displayed increases in irritability to handling, enhanced horizontal activity in the open field, and a deficit in passive-avoidance learning. Animals with lateral olfactory bulb lesions showed an increase in muricidal behavior. Although there were significant intragroup postoperative weight losses, there were no significant differences between groups. Damage to the vomeronasal system alone was not involved in any of the measured behaviors.

Increased estrogen receptor binding in amygdala correlates with facilitation of feminine sexual behavior induced by olfactory bulbectomy

In this experiment we tested the hypothesis that the potentiation of feminine sexual behavior following olfactory bulb removal in female rats would be associated with increased ovarian steroid receptor binding in brain. Ovariectomized adult female rats underwent either bilateral olfactory bulb removal (BOB) or a sham operation and were exposed to 100% estradiol (E 2) in silastic capsules for 4 or 6 h. Following behavior testing, either cell nuclear estrogen receptor levels were measured in amygdala, hypothalamus, preoptic area and pituitary, or cytosol progestin receptors levels were determined in cortex, preoptic area and hypothalamus. After 6 h E 2 exposure, BOB females showed increasing lordosis responding with increasing progesterone (P) doses, at levels significantly higher than those of sham-operated rats. After 4 h E 2 exposure bulbectomized rats showed both a facilitation of lordosis and elevated estrogen receptor levels in amygdala. Sham-operates showed neither response to the 4 h E 2 stimulus. For both BOB and sham groups, progestin receptors were induced after 6 h E 2 exposure, but were uninduced after 4 h E 2 exposure. Additional rats were exposed to 5% E 2 for 24 or 48 h, followed by P. Lordosis was potentiated in BOB rats at 24 h; sham-operates showed high levels of lordosis only after 48 h of 5% E 2 exposure. Proceptivity was enhanced in BOB rats after both 24 and 48h of 5% E 2 exposure. In contrast, proceptivity was rarely observed in sham-operates, or in either group after 4 or 6 h E 2 exposure. We propose that increased estrogen receptor binding in the amygdala may provide a biochemical basis for the increased estrogen sensitiity found in olfactory bulbectomized female rats.

Effect of lesions of the olfactory bulb on the levels of amino acids and related enzymes in the olfactory cortex of the guinea pig.

Olfactory bulb removal and consequential degeneration of the lateral olfactory tract led to a decrease in the levels of glutaminase and malate dehydrogenase in the ipsilateral olfactory cortex. These changes in enzyme activity may account for the well established decrease in the 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.

The vomeronasal organ: Primary role in mouse chemosensory gender recognition

Four experiments were conducted to determine the chemosensory modality that supports ultrasonic courtship vocalizations by male mice to females and to chemosignals from females. Both removal of the olfactory bulbs (Experiment 1) and removal of the vomeronasal organ (Experiments 2–4) produced similar deficits in the pattern of ultrasonic vocalizations elicited by conspecifics or their odors. Removal of the vomeronasal organ did not impair the ability to locate food buried under cage shavings. These results are consistent with the notion that the analysis of food related odors is subserved by olfaction and that vocalizations to sex chemosignals are elicited primarily by stimulation of the vomeronasal organ/accessory olfactory bulb. Removal of the vomeronasal organ did not induce seminal vesicle regression or lower plasma immunoreactive testosterone levels (Experiment 2) nor was an attempt to restore vocalizations with exogenous testosterone successful (Experiment 4). Thus the altered vocalization pattern following removal of the vomeronasal organ does not appear to arise as a motivational deficit mediated by androgens. Experiments 2 and 3 demonstrated that, in the absence of the vomeronasal organ, stimulation of other sensory systems can, to some extent, maintain the male's tendency to vocalize more to females or their odors than to males or their odors. However, this responsiveness to females may rely upon additional behavioral cues. Previous experience also plays a considerable role in the response to chemosensory gender cues by males who lack their vomeronasal organs. Removal of the vomeronasal organ prior to adult heterosexual encounters (Experiment 3) virtually eliminated the male's responsiveness to either anesthetized females or their chemosignals. Hence males require adult heterosexual experience with a functioning vomeronasal organ before other chemosensory systems acquire the ability to mediate gender recognition as measured by ultrasonic vocalizations.

Effect of ablation of the olfactory bulbs on the diet ingested by grazing sheep

The effect of removal of the olfactory bulbs on the diet ingested by oesophageal-fistulated sheep grazing five different sward types was examined. Six bulbectomised sheep were compared with a group of control sheep. The diet selected by the bulbectomised and control sheep on four of the five swards was similar. On the perennial ryegrass/white clover sward, the diet of the bulbectomised sheep had a significantly higher proportion of weed species than the diet of the control sheep. It was concluded that the role of olfaction in influencing the diet selected by the grazing sheep is a minor one.

Effect of removal of the olfactory bulbs on the estrous cycle of the mouse

The effects of removal of the olfactory bulbs on the estrous cycle and the weight of reproductive organs were examined in mice of the IVCS, ICR and C57BL/6 strains. Sham-operated and intact mice served as controls. Virgin female mice were surgically deprived of the olfactory bulbs at 8 weeks of age and caged individually in air-conditioned rooms with controlled lighting (14 hours of light, from 5 a. m. to 7 p. m., each day). Vaginal smears were observed daily. The animals were killed and their principal organs weighed at 6 weeks after the operation. The results obtained were as follows; 1) The olfactory bulb ablation prolonged the length of estrous cycle of mice of the ICR (6.0 days) and C57BL/6 (5.0 days) strains, but did not modify the cycle in those of the IVCS strain (4.0 days). 2) A decrease of ovarian weights by this operation was observed in the mice of the IVCS and ICR strains, but not C57BL/6 strain.

Studies on feminine sexual behavior in the male rat: Influence of olfactory stimuli

The aim of this study was to determine if the display of lordosis behavior in the male rat could be influenced by the olfactory environment. Unexperienced adult male rats were orchidectomized (ORCH). They were primed with 75 μg estradiol benzoate and 1 mg progesterone was injected at an interval of 39 hr following long-term (LT = 3 weeks) or short-term (SHT = 8 hr 30 min) exposure to the odor of male or female urine. For 10 min they were placed in the presence of a “stimulus” male of proven sexual vigor 9 hr 30 min ± 1 hr after progesterone injection. Both LT and SHT exposure to the odor of male urine caused a significant increase in the number of ORCH rats which showed lordosis response to male mounts compared to either the ORCH rats exposed to the odor of female urine or to the controls. Following complete olfactory bulb removal (COBR), no difference was observed in the occurrence of lordosis behavior between the ORCH rats whether or not exposed to the odor of urine. For the ORCH-COBR rats exposed to male urine the proportion of animals responding to mounts did not differ from that of their nonbulbectomized counterparts. In comparing the effects of COBR vs anterior olfactory bulb removal (AOBR) lordosis behavior occurred more frequently in COBR than in AOBR-ORCH rats. The lordosis quotient (LQ) was not affected by exposure to the odor of male urine in the nonbulbectomized ORCH rats. In contrast, it appeared to be higher in both COBR and AOBR animals than in their nonbulbectomized counterparts. The olfactory bulbs were then concluded to inhibit the display of lordosis behavior in the male rat. It was also thought that the olfactory stimuli originating from male urine were capable of releasing the hypothalamic structures involved in the control of lordosis behavior of the male rat from an olfactory inhibitory influence.

Establishment of normal synaptic density in deafferented olfactory cortex

The piriform cortex has been examined in rats following neonatal deafferentation produced by olfactory bulb removal. The denervated molecular layer of the piriform cortex grows to nearly its full adult thickness and the removed olfactory bulb axons are replaced by intracortical axons. The synaptic density of the molecular layer following this rearrangement is the same as that in the normal cortex.

Sexual behaviour and its olfactory control in the desert woodrat ( Neotoma lepida lepida)

In studies 1 and 2 nine pairs of desert woodrats ( Neotoma lepida lepida) were observed for copulatory behaviour when the female was in a state of naturally occurring oestrus (study 1) and following ovariectomy and oestrogen and progesterone replacement (study 2). Males and females respond in a similar way under conditions of natural and hormone-induced oestrus. Males show a consummatory pattern involving multiple mounts and ejaculations, with ejaculations occurring after single intromissions. Females show the lordosis reflex accompanied by hop-and-dart and ear-wiggling responses. In addition, both sexes show appetitive precopulatory behaviours; the male emits an audible rasping vocalization as he trails and mounts the female, following a period of intense sniffing of the female's anogenital region. The female also frequently approaches and sniffs the male. In study 3, the role of female odours in the sexual behaviour of the male was examined in eight of the nine pairs used in studies 1 and 2. This was done by applying to the anogenital region of ovariectomized females a combination of urine and vaginal secretions taken from familiar and unfamiliar, and oestrogen-primed or non-oestrogen-primed females. The results show that odours from oestrogen-primed females are not sufficient to elicit male sexual behaviour, if the female is not sexually active. In study 4 the eight males were tested for their preferences for urine and vaginal secretion odours taken from females in different reproductive states and applied to cotton swabs. These males spent more time sniffing unfamiliar oestrous odours than unfamiliar non-oestrous odours and more time sniffing oestrous odours from a familiar female over those taken from an unfamiliar female. In study 5, 12 sexually active males were tested with oestrogen-primed females before and after either olfactory bulb removal or sham-surgery. Bulbectomized animals ceased copulating with females although females showed precopulatory approaches. Taken together, these studies suggest that normal sexual behaviour in the male woodrat requires that the female both possess the attractive odours (of oestrus) and that she engage in appetitive precopulatory behaviour.

Regional changes in [ 3H]diazepam binding in the brains of mice after removal of the olfactory bulbs

[ 3H]Diazepam binding was assayed 3 weeks after surgery in 13 brain regions derived from sham-operated and bilaterally olfactory bulbectomized mice. In bulbectomized mice, [ 3H]diazepam binding was elevated 30% in the frontal cortex and 24% in the thalamus but decreased 26% in the striatum and 28% in the midbrain. These changes represented alterations in the number of binding sites. No binding changes were observed in the olfactory tubercle, amygdala, piriform cortex, olfactory peduncle, hypothalamus, hippocampus, colliculi, cerebellum, or pons-medulla of bulbectomized animals. These results are compared with the effects of other types of brain lesions on the brain benzodiazepine receptor, and are possibly related to the altered sensitivity of bulbectomized mice to benzodiazepines and convulsants.

Photoperiodic control of reproduction in olfactory-bulbectomized rats.

30-day-old male rats were (1) sham-operated or subjected to (2) removal of the olfactory bulbs, (3) olfactory bulbectomy and blinding (4) olfactory bulbectomy and pinealectomy or (5) olfactory bulbectomy, blinding and pinealectomy. Animals were exposed from 30 to 110 days of age to long-day (14 h of light per day) or short-day (8 h of light per day) photoperiods. The reproductive system of neurologically-intact rats was not affected by exposure to short days. Nor did bulbectomy affect the reproductive system of rats exposed to long days. However, bulbectomized, short-day rats had significantly lower body weights, reduced testicular and seminal vesicle weights and lower plasma testosterone levels than did bulbectomized, long-day rats. The effects of short-day exposure on bulbectomized rats were prevented by pinealectomy. Short-day exposure and blinding exerted similar effects in bulbectomized rats. The testes of rats from all groups contained elongated spermatids; blinding and short-day treatment had no effect on spermatogenesis. Neither mating behavior nor the number of young sired was influenced by photoperiod in bulbectomized or intact rats. Removal of the olfactory bulbs unmasks photoperiodic responsiveness in rats; the antigonadal effects of short-day exposure are mediated by the pineal gland in bulbectomized rats as in species traditionally designated photoperiodic. The mechanisms by which bulbectomy renders rats responsive to short days are considered.

Influence of boar contact on attainment of puberty in gilts after removal of the olfactory bulbs.

At 6-7 weeks of age the olfactory bulbs were removed from gilts which were then exposed to vasectomized boars for 30 min/day, starting on Day 160. Mean +/- s.e.m. age at first oestrus was similar in these gilts (230 +/- 15 days) to that in intact gilts not exposed to a boar (234 +/- 8 days) but greater (P < 0.05) than for sham- and un-operated gilts exposed to a boar (204 +/- 3 and 208 +/- 9 days, respectively). There were no differences in growth rate or ovulation rate at first oestrus. It is concluded that the main stimulus involved in the boar effect is olfactory in nature.

Induction of female and male mating patterns in female rats by gonadal steroids: effects of neonatal or adult olfactory bulbectomy.

Hormonally mediated sexual response patterns were evaluated in female rats receiving olfactory bulb ablations neonatally (Day 2) or in adulthood. In a test of females' reactivity to a caged male in an open field, estrogen and progesterone treatments increased the number of squares entered and the number of cage contacts, but olfactory bulb removal had no effect on these measures. During mating tests, the feminine sexual behavior of females bulbectomized on Day 2 was similar to that of control-operated females, whereas females bulbectomized as adults displayed enhanced levels of lordosis, darting, and ear wiggling. Lordosis varied with estrogen dose, whereas darting was progesterone-dependent. In tests of masculine copulatory behavior, the proportion of bulbectomized females (Day 2 and adult) that mounted was significantly lower than that of control-operated females. The effects of olfactory bulb removal, which vary with the age at ablation and the behavioral system investigated, are not mediated by a single neuroendocrine system and cannot be interpreted in terms of a unitary "arousal' construct.

Time-course of declining electrical activity in guinea-pig olfactory cortex after olfactory bulb removal

An electrophysiological study has been made of the degeneration of the afferent axons of the lateral olfactory tract (L.O.T.) which give rise to excitatory synapses throughout the olfactory cortex. These fibres were severed by removing one or both olfactory bulbs. Evoked potentials were recorded from slices of olfactory cortex in vitro prepared at various times after bulbectomy. Up to 1.6 days later, all potentials were similar to those of the unoperated side. Between 1.6 and 1.8 days there was a complete loss of evoked potential from both L.O.T. axons and postsynaptic neurones, which occurred synchronously at all points along a 5–6 mm length of the tract.

Effects of olfactory bulb removal and flank shock on copulation in male rats

Sexually experienced male rats received bilateral olfactory bulbectomy (BOB, N=9), unilateral olfactory bulbectomy (UOB, N=7) or a sham operation (Sham, N=8). Copulation was severely disrupted in BOB males, whereas only minimal effects on copulation were observed in UOB males. Penile reflexes were not affected by either operation. Intermittent flank shock stimulated copulation in 5/6 BOB males. The BOB males that ejaculated had longer intromission latencies and longer postejaculatory intromission intervals than did Sham males receiving a similar schedule of shocks. Even so, all BOB males that ejaculated with flank shock also resumed copulation and ejaculated a second time without further shocks. Three BOB males that ejaculated with flank shock were tested the following week without shock, and none of these males copulated. These results strengthen previous conclusions that the olfactory bulbs are critical for the initiation and maintenance of sexual arousal in male rats.

ECoG effects of peripheral deafferentation of prepyriform and visual cortices in rats

Freely-behaving Wistar albino male rats were prepared for chronic recording of the electrocorticographic (ECoG) activity of neo- and paleocortical areas and of the electromyogram of dorsal neck muscles. The effects of the uni- or bilateral removal of the main olfactory bulbs and adjacent structures on the prepyriform cortex (PPC) ECoG, and the possible ECoG modifications in the area 17 after bilateral eye enucleation were studied. In spite of the fact that the PPC general cycling pattern along the sleep-wakefulness cycle (SWC) was not appreciably affected by the olfactory deafferentation, this experimental maneuver did cause very marked alterations in the PPC ECoG during all of the observed SWC phases. On the other hand, no appreciable ECoG modifications could be detected in area 17 after the visual deafferentation. A comparison of these results with pertinent literature for cats and monkeys allows the formulation of some working hypotheses that deserve experimental testing in the future.

Lack of effect on sexual behaviour or the development of testicular function after removal of olfactory bulbs in prepubertal boars.

Bilateral olfactory bulb ablation was carried out surgically on 8 prepubertal Large White boars when they were 10-12 weeks of age. Between 26 weeks and slaughter at 47-49 weeks of age, androgen was determined in peripheral blood plasma of bulbectomized and unoperated control animals. The pigs were exposed to oestrous female pigs to observe mating behaviour, and to alien boars to observe aggressive behaviour. Saliva produced during behaviour tests was extracted with diethyl ether and levels of the pheromonal 16-androstene steroids in the extracts were determined by a colorimetric assay. After slaughter the testes, accessory organs and submaxillary glands were weighed, and pices of tissue together with olfactory epithelium were processed for light microscopy; fructose and zinc were determined in the seminal vesicles. The results showed that, contrary to findings in some rodents, prepubertal bilateral bulbectomy in the male pig had no significant effect on mating or aggressive behaviour, or testicular function in so far as complete spermatogenesis was present and normal levels of androgen and pheromone were maintained together with the integrity of the accessory organs. However, in keeping with findings in other species, the height of the olfactory epithelium was generally reduced in the bulbectomized pigs.

Transneuronal effects of olfactory bulb removal on choline acetyltransferase and glutamic acid decarboxylase activities in the olfactory tubercle

Transneuronal effects of olfactory bulb removal on choline acetyltransferase and glutamic acid decarboxylase activities in the olfactory tubercle

Neurochemical plasticity: increased glutamic acid decarboxylase activity in the olfactory tubercle following olfactory bulb removal during postnatal development

Neurochemical plasticity: increased glutamic acid decarboxylase activity in the olfactory tubercle following olfactory bulb removal during postnatal development

Inhibition of sexual maturation by a urinary pheromone in male prairie deer mice

Male prairie deer mice ( Peromyscus maniculatus bairdii) were treated from weaning until 8 weeks of age with chemical stimuli from conspecifics or with control substances. Growth of the testes and seminal vesicles was retarded in males that were reared in contact with soiled bedding material transferred from cages of adult males. No additional inhibition resulted from the physical presence of an adult male either continuously or for 1 hr per day. Application of urine collected from adult males to the noses of young males retarded seminal vesicle growth. Removal of the olfactory bulbs of males at 3 weeks of age blocked the inhibitory influence of urine on sexual maturation. Exposure to urine from adult females did not alter the growth of the reproductive organs in young males. The ability of a male deer mouse to retard the sexual maturation of young male conspecifics (Bediz, G. M., and Whitsett, J. M., 1979, J. Comp. Physiol. Psychol. 93, 493–500) appears to be a consequence of chemical stimuli excreted in its urine.