Unilateral Bulbectomy Research Articles

Habituation of stimulus-elicited investigation in gerbils after olfactory bulbectomy

Normal gerbils habituate rapidly when presented with a novel object in the stimulus-elicited investigation paradigm. In this paradigm, gentled gerbils are given a series of one minute trials with a novel object in a small arena. They are then given a series of similar trials in which the odor of strange male gerbils is under one of five holes in the floor of the same arena. Gerbils with bilateral olfactory bulbectomies habituated more slowly to the object than normal gerbils or those anosmized peripherally by unilateral bulbectomy combined with stitching of the contralateral naris. In contrast, the two anosmic groups habituated at the same rate as normal gerbils when tested for investigation of five holes and odor although neither group of anosmic gerbils selectively localized the odor. In comparison to normal gerbils with no specific odor present, habituation was delayed for both experimental groups. In addition, both anosmic groups habituated normally on an activity score. Therefore, it was concluded that habituation can be affected differentially by the surgical conditions dependent on the task being measured. These data support the hypotheses (a) that the olfactory bulbs have a role in behaviors that are not dependent on olfactory information and (b) that habituation is not a single process mediated uniformly for all behaviors.

Plasticity of connections of the olfactory sensory neuron: Regeneration into the forebrain following bulbectomy in the neonatal mouse

Neonatal mice underwent unilateral bulbectomy, which included the main and accessory olfactory bulbs. From 5 days of survival onward, there was a marked anterior displacement of the frontal cortex into the cavity previously occupied by the bulb. As a result of the bulbectomy and consequent damage to olfactory axons, the olfactory perikarya underwent retrograde degeneration. New neurons were then reconstituted from stem cells within the olfactory neuroepithelium. By 20 postoperative days the new olfactory axons had reached the level of the lamina cribrosa and by 30 days the fibers had penetrated into the telencephalon and had formed typical glomerular structures within the host tissue. Fibers were directed to either the paleo- or neocortex where they were observed in close proximity to large cortical neurons. The formation of glomeruli persisted over the course of the study (180 days) and showed an expansion within the cortical tissue up to 60 days of survival. The identification of these fibers and glomerular structures as olfactory was confirmed by immunohistochemical techniques using antisera to the specific olfactory protein. Ultrastructural observations clearly indicated the typical glomerular pattern of the structures and demonstrated synaptic contacts between the sensory terminals and dendritic processes, as yet unidentified, originating from the surrounding cerebral matrix. Our observations thus demonstrate that following bulbectomy and retrograde degeneration of olfactory neurons, the cells can regenerate in the absence of their normal target. Furthermore, the newly formed axons can penetrate a ‘foreign’ environment, the cerebral cortex, and form typical glomerular structures and corresponding sensory synapses. The findings suggest a heretofore unsuspected degree of plasticity in the olfactory system as well as in the cerebral cortex.

Evidence of a neurotransmitter role for aspartate and γ‐aminobutyric acid in the rat olfactory cortex

1. Using a cortical cup technique, the release of seven endogenous amino acids from the isolated rat olfactory cortex slice has been monitored.2. Electrical stimulation of the lateral olfactory tract at a frequency of 4 min(-1) was accompanied by a significant increase in the release of aspartate, GABA and taurine; the release of GABA and aspartate but not that of taurine was Ca(2+)-dependent.3. Chronic unilateral bulbectomy was accompanied by a specific, significant fall in the aspartate content of the olfactory cortex which reached a maximum 5 days after surgery and persisted for at least a further 5 days. Electrical stimulation of the lateral olfactory tract of such preparations did not release any of the amino acids under investigation.4. When slices from the unoperated side were exposed to solutions containing 25 mM-K+ or stimulated with electrodes placed directly on the cortex enclosed by the cup there was a Ca(2+)-dependent release of aspartate and GABA accompanied by a Ca(2+)-independent release of taurine. Following chronic bulbectomy, these procedures failed to evoke significant release of aspartate whereas the characteristics of GABA and taurine release were unaltered.5. It is concluded that aspartate may be the excitatory transmitter of some of the terminals of the lateral olfactory tract fibres and that GABA may be a transmitter at some inhibitory synapses of the rat olfactory cortex.

Effects of olfactory bulb ablation and androgen on marking and agonistic behavior in male Mongolian gerbils (Meriones unguiculatus).

Male Mongolian gerbils, selected for high marking frequency, were paired with male opponents, and marking and fighting behavior were recorded. Animals then underwent castration, bilateral bulbectomy, unilateral bulbectomy, the combined operations, or a sham operation; and their behavior was again observed. All operated animals showed drastic reduction in both marking and aggressive encounters. Injections of testosterone propionate (TP) produced complete restoration of marking in castrates, but not in bilaterally or unilaterally bulbectomized animals or combined operates. The exhibition of aggression after injections of TP, however, was enhanced to supernormal levels in bulbectomized or bulbectomized-castrated animals. The results suggest the following: that removal of the olfactory bulbs may eliminate a critical neural input necessary for the normal expression of marking and agonistic; that although marking and fighting are influences by olfactory input and gonadal steroids, their regulatory mechanisms may not be identical; and that removal of the bulbs may sensitize a neural mechanism controlling aggression, thus potentiating its elicitation following administration of exogenous androgen.

The influence of olfaction on sexual behavior in the male golden hamster (Mesocricetus auratus).

AbstractAblation of the olfactory bulbs terminates the sexually oriented behavior patterns shown by the male hamster towards the female. All aspects of overt copulatory behavior including mounting are immediately eliminated. Investigatory behavior is decreased significantly and orientation of attention to the hindquarters of the animal being investigated (sexual orientation) is lost over a one to two week interval. This disruption of sexually oriented behavior patterns occurs regardless of the degree of experience of the male in mating prior to the bulbectomy. Unilateral bulbectomy or sham bulbectomy does not disrupt, even temporarily, the mating pattern.Evidence that the lack of mating behavior following bulbectomy is indeed due to anosmia was provided by rendering animals temporarily anosmic by use of zinc sulfate in the nasal cavities. Full recovery of sexual activity occurred within four to six days following this treatment. A second treatment produced a similar result.Naive males, raised in isolation, can show a normal copulatory pattern on first exposure to a receptive female. Naive males do not distinguish between diestrus (non receptive) and estrus (receptive) vaginal secretions from the female.The release of sexual arousal requires olfactory input in the male hamster, conditioning to other cues does not occur. However, differentiation between receptive and non‐receptive females appears to be a positive learned response. The absolute dependence of the male hamster on olfactory cues for sexual arousal has an obvious adaptive value in a species where the female tends to be dominant in encounters and the male, if unable to escape, can be maimed or killed during the course of a fight.