Evidence that olfactory bulbectomy does not influence testicular regression in golden hamsters on short photoperiod by altering pineal melatonin production

Pieper, David R.; Reíter, Russel J.; Unthank, P. D.; Addy, J. F.

doi:10.1007/bf00695328

Cited by 13 publications

(8 citation statements)

References 22 publications

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“…One of the main findings of the work described in this paper is that the olfactory bulbs exert a strong inhibitory influence on long- in hamsters on long photoperiod, combined with previous data showing that BX blocks the action of exogenous melatonin injections (7)(8)(9) and that BX does not alter peak pineal melatonin concentrations (7), suggest that BX does not increase gonadotropin release by inhibiting the ability of melatonin to suppress gonadotropin secretion. Rather, BX apparently prevents the testicular regression associated with short photoperiod by increasing gonadotropin secretion independently of the photoperiod or pineal gland.…”

Section: Fkperiments I and Iisupporting

confidence: 61%

“…Testiculur index TI was determined by non-invasively measuring the length and width of the left testis through a moistened scrota1 sac in unanesthetized animals. The mm length x mm width divided by g body weight x 10 is an indication of testis size relative to body weight (7,29). increasing gonadotropin secretion is unrelated to blocking olfactory or pheromonal input from other hamsters.…”

Section: Housingmentioning

confidence: 99%

“…While the effects of BX are most prominent when the procedure is performed pre-pubertally ( 5 ) , some effects on tonic gonadotropin secretion have been reported in animals bulbectomized as adults (6). The effects of the olfactory bulbs on the response to photoperiod are not mediated by altering melatonin secretion or pineal gland function (7)(8)(9). BX may enhance gonadotropin secretion in part by inhibiting the negative feedback of testosterone (1 0).…”

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confidence: 99%

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

Pieper

Lobocki

Thompson

et al. 1990

J Neuroendocrinology

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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:lOD). Maintenance on 10L:14D 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 folliclestimulating 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.

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Section: Fkperiments I and Iisupporting

confidence: 61%

Section: Housingmentioning

confidence: 99%

mentioning

confidence: 99%

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

Pieper

Lobocki

Thompson

et al. 1990

J Neuroendocrinology

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“…Expansion of circadian alpha and the consequent increase in the duration of nocturnal melatonin secretion [10,40] are necessary for reproductive inhibition in short days [14]. In light of the strong temporal relation between the circadian pattern of locomotor activity and melatonin secretion [12] and the absence of evidence that OBx markedly affects entrainment to short days [5] or pineal melatonin production [29], we propose that pre-pineal events necessary for reproductive responses to short days are not affected by OBx in Siberian hamsters.…”

Section: Discussionmentioning

confidence: 99%

Reproductive responses to photoperiod persist in olfactory bulbectomized Siberian hamsters (Phodopus sungorus)

Prendergast

Pyter

Galang

et al. 2009

Behavioural Brain Research

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In reproductively photoperiodic Syrian hamsters, removal of the olfactory bulbs leads to a marked and sustained increase in gonadotrophin secretion which prevents normal testicular regression in short photoperiods. In contrast, among reproductively non-photoperiodic laboratory strains of rats and mice, bulbectomy unmasks reproductive responses to photoperiod. The role of the olfactory bulbs has been proposed to have opposite effects on responsiveness to photoperiod, depending on the photoperiodicity of the reproductive system; however, Syrian hamsters are the only reproductively photoperiodic rodent species for which the role of the olfactory bulb in reproductive endocrinology has been assessed. This experiment evaluated the role of the olfactory bulbs in the photoperiodic control of reproduction in Siberian hamsters (Phodopus sungorus), an established model species for the study of neural substrates mediating seasonality. Relative to control hamsters housed in long days (15 h light/day), exposure of adult male hamsters to short days (9 h light/day) for 8 weeks led to a temporal expansion of the pattern of nocturnal locomotor activity, testicular regression, decreases in testosterone (T) production, and undetectable levels of plasma folliclestimulating hormone (FSH). Bilateral olfactory bulbectomy failed to affect any of these responses to short days. The patterns of entrainment to long and short days suggests that pre-pineal mechanisms involved in photoperiodic timekeeping are functioning normally in OBx hamsters. The absence of increases in FSH following bulbectomy in long days is incompatible with the hypothesis that the olfactory bulbs provide tonic inhibition of the HPG axis in this species. In marked contrast to Syrian hamsters, the olfactory bulbs of Siberian hamsters play essentially no role in the modulation of tonic gonadotrophin production or gonadotrophin responses to photoperiod.

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“…In hamsters, BX results in an elevation of tonic gonadotropin and prolactin levels in serum when the animals are maintained on long or short photoperiod (11,27). This effect of the olfactory bulbs in the hamster is not related t % altering serum melatonin (28,29). Rather, the olfactory bulbs act in part by altering testosterone feedback on gonadotropin secretion, but also have effects on the post-castration increase in LH and FSH (30).…”

Section: --Exmentioning

confidence: 99%

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

Pieper

Lobocki

Thompson

et al. 1990

J Neuroendocrinology

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Unlike seasonally breeding species such as the Syrian hamster, Sprague-Dawley laboratory rats do not normally respond to short photoperiod (6L:18D) 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:lOD (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 14L:lOD. Six to 8 weeks later, all animals were castrated and placed on 6L:18D or returned to 14L:lOD. Eight weeks following castration, the rats were implanted with Silastic capsules containing 0, 10, 20 or 40 mm testosterone. The post-castration increase in serum luteinizing hormone and folliclestimulating hormone was lower in the BX khan 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).Golden hamsters undergo marked seasonal variations in reproductive competence (1-3). The inhibition of gonadotropin secretion associated with winter-like photoperiods is induced by pineal melatonin, which acts in large part b...

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Evidence that olfactory bulbectomy does not influence testicular regression in golden hamsters on short photoperiod by altering pineal melatonin production

Cited by 13 publications

References 22 publications

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

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

Reproductive responses to photoperiod persist in olfactory bulbectomized Siberian hamsters (Phodopus sungorus)

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

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