Olfactory bulbectomy prevents the gonadal regression associated with short photoperiod in male golden hamsters

Retinofugal projections in the mouse

The laboratory mouse is increasingly a subject for visual system investigation, but there has been no comprehensive evaluation of this species' visual projections. Here, projections were visualized and mapped following intraocular injection of cholera toxin B subunit. Tissue was processed using standard procedures applied to 30 μm free-floating sections with diaminobenzidine as the chromogen. The mouse retina projects to ~46 brain regions, including 14 not previously described in this species. These include two amygdaloid nuclei, the horizontal limb of the diagonal band, the paraventricular hypothalamic nucleus, several visual thalamic nuclei, the paranigral nucleus, several pretectal nuclei, and the dorsal cortex of the inferior colliculus. Dense retinal patches were also observed in a narrow portion of the ipsilateral intermediate layer of the superior colliculus. The superior fasciculus of the accessory optic tract, which innervates the medial terminal nucleus, was also determined to be a terminal zone throughout its length. The results are compared with previous descriptions of projections from mouse intrinsically photoreceptive retinal ganglion cells, and with data from the hamster, Nile grass rat, and laboratory rat. The retinal projection patterns are similar in all four species, although there are many differences with respect to the details. The specific visual functions of most retinorecipient areas are unknown, but there is substantial convergence of retinal projections onto regions concerned with olfaction and audition.

Photoperiod mediated changes in olfactory bulb neurogenesis and olfactory behavior in male white-footed mice (Peromyscus leucopus)

Brain plasticity, in relation to new adult mammalian neurons generated in the subgranular zone of the hippocampus, has been well described. However, the functional outcome of new adult olfactory neurons born in the subventricular zone of the lateral ventricles is not clearly defined, as manipulating neurogenesis through various methods has given inconsistent and conflicting results in lab mice. Several small rodent species, including Peromyscus leucopus, display seasonal (photoperiodic) brain plasticity in brain volume, hippocampal function, and hippocampus-dependent behaviors; plasticity in the olfactory system of photoperiodic rodents remains largely uninvestigated. We exposed adult male P. leucopus to long day lengths (LD) and short day lengths (SD) for 10 to 15 weeks and then examined olfactory bulb cell proliferation and survival using the thymidine analog BrdU, olfactory bulb granule cell morphology using Golgi-Cox staining, and behavioral investigation of same-sex conspecific urine. SD mice did not differ from LD counterparts in granular cell morphology of the dendrites or in dendritic spine density. Although there were no differences due to photoperiod in habituation to water odor, SD mice rapidly habituated to male urine, whereas LD mice did not. In addition, short day induced changes in olfactory behavior were associated with increased neurogenesis in the caudal plexiform and granule cell layers of the olfactory bulb, an area known to preferentially respond to water-soluble odorants. Taken together, these data demonstrate that photoperiod, without altering olfactory bulb neuronal morphology, alters olfactory bulb neurogenesis and olfactory behavior in Peromyscus leucopus.

Influence of the olfactory bulbs on blood leukocytes and behavioral responses to infection in Siberian hamsters

Surgical removal of the olfactory bulb alters several aspects of immunological activity. This study investigated the role of the olfactory bulbs in the control of behavioral responses to simulated infection, and the environmental modulation of sickness behaviors by changes in day length. Adult male Siberian hamsters (Phodopus sungorus) were subjected to bilateral olfactory bulbectomy (OBx) or a sham surgical procedure, and were then exposed to long(15 h light/day; LD) or short (9 h light/day; SD) photoperiods for 8–12 weeks, after which circulating leukocytes and behavioral responses (anorexia, anhedonia, cachexia) to simulated gram-negative bacterial infections (i.p. lipopolysaccharide [LPS] treatment;0.625 mg/kg) were quantified. OBx treatment altered the effects of photoperiod on immune function in a trait-specific manner. LPS-induced anorexia was exacerbated in SD-OBx hamsters; LPS-induced anhedonia was exacerbated in LD-OBx hamsters; and photoperiodic differences in circulating leukocytes and LPS-induced cachexia were eliminated by OBx. Plasma cortisol concentrations did not differ between LD and SD hamsters, irrespective of olfactory bulb integrity. The data indicate that photoperiod affects immune function via OB-dependent and -independent mechanisms, and that changes in cortisol production are not required for photoperiodic changes in sickness behaviors to manifest.

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

In reproductively photoperiodic Syrian hamsters, removal of the olfactory bulbs (OBx) leads to a marked and sustained increase in gonadotrophin secretion which prevents normal testicular regression in short photoperiods. In contrast, among reproductively nonphotoperiodic 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 (9h 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 follicle-stimulating 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.

Ventromedial hypothalamic mediation of photoperiodic gonadal responses in male Syrian hamsters

Short day lengths induce testicular regression in seasonally breeding Syrian hamsters. To test whether the ventromedial hypothalamus is necessary to maintain reproductive quiescence once testicular regression has been achieved, photoregressed male hamsters were subjected to lesions of the ventromedial hypothalamus (VMHx), pinealectomy (Pinx), or sham operation (Sham). VMHx hamsters underwent accelerated gonadal recrudescence compared to Pinx and Sham hamsters. Recovery of prolactin concentrations (PRL) to values characteristic of long-day hamsters was hastened in the VMHx animals compared to Sham hamsters. Concentrations of follicle stimulating hormone (FSH) increased prematurely in both the VMHx and Pinx animals, beginning a few weeks after surgery. By the time the gonads had undergone recrudescence and the hamsters were refractory to melatonin, PRL and FSH concentrations had returned to baseline long-day values in all groups; there was no evidence of hypersecretion of either hormone in any of the animals with lesions. Melatonin concentrations of VMHx hamsters did not differ from those of sham-operated animals, but because only a single determination was made, it remains possible that VMH damage altered the duration of nightly melatonin secretion. An intact VMH appears to be essential for the continued maintenance of reproductive suppression induced by exposure to short day lengths; these and earlier findings suggest that the VMH-dorsomedial hypothalamic complex mediates regression of the reproductive apparatus during decreasing day lengths of late summer and early autumn and also is necessary to sustain regression during the winter months.

Neural pathway from the olfactory bulbs regulating tonic gonadotropin secretion

Removal of the olfactory bulbs of male golden hamsters results in a marked increase in tonic gonadotropin, prolactin and testosterone secretion which counteracts inhibitory effects of manipulations such as maintenance on short photoperiod, food restriction or treatment with gonadal steroids. The bulbectomy-induced increase in hormone secretion is interpreted to reflect a tonic inhibitory influence of the olfactory bulbs. This inhibition is not dependent upon chemosensory stimulation and may be mediated by olfactory bulb fibers projecting through the lateral olfactory tract to or through the olfactory tubercle. This review will relate these studies conducted on hamsters to results in other species, such as the rat, where the olfactory bulbs enhance serum gonadotropin levels.

Social cues attenuate photoresponsiveness of the male reproductive system in Siberian hamsters (Phodopus sungorus)

Transfer of adult Siberian hamsters (Phodopus sungorus) from long (16 h light and 8 h dark, 16L:8D) to short (8L:16D) daily photoperiods induces an involution of the gonads and a cessation of reproductive behavior 8 to 10 weeks later. However, when male and female long-day hamsters were paired on transfer to short photoperiods, the males' gonads did not undergo the typical short-day response. Similarly, when male long-day hamsters were paired with refractory females (i.e., females housed in short photoperiods for at least 28 weeks so that they became unresponsive to short photoperiods), the response of the males' reproductive system to short photoperiods also was attenuated. Thus, social cues can override or delay the effects of photoperiod on the testes of this species. These results suggest that the inhibitory effects of long durations of melatonin secretion (in response to short photoperiods) on the male hypothalamic-pituitary-gonadal axis may be attenuated by social cues such as contact with the opposite sex.

Removal of the olfactory bulbs delays photic reentrainment of circadian activity rhythms and modifies the reproductive axis in male Octodon degus

The diurnal rodent, Octodon degus, exhibits robust sex differences in several circadian measures, including circadian period (tau) and reentrainment rates to photic and nonphotic (social) zeitgebers. The neural substrates underlying such physiological differences remain unknown. In female degus, olfactory bulbectomies (BX) inhibit socially-facilitated reentrainment, but do not alter photic reentrainment, entrained measures, or tau in constant darkness (DD). This experiment investigated the effects of BX in male degus on (i) photic reentrainment rates of circadian rhythms following a 6-h phase advance of the light-dark (LD) cycle; (ii) photic entrainment; (iii) tau of free-running activity rhythms in DD; and (iv) body weight, paired testis weight, and the reproductive hormones, testosterone, androstenedione and follicle stimulating hormone (FSH). BX significantly delayed photic reentrainment rates. They did not, however, modify tau, the phase of activity onset or offset, amplitude or duration (alpha) of the activity rhythm, mean daily locomotor activity levels, or body weight. FSH, testosterone and androstenedione were unaffected by BX, whereas paired testis weights were significantly greater in BX degus compared with shams. Thus, the olfactory bulbs influence photic reentrainment of circadian rhythms and modestly affect the reproductive axis in male degus. Our results suggest that the olfactory bulbs may be a neural source of observed sex differences in photic reentrainment in degus, and highlight interspecies variation in the olfactory bulbs' effects on entrained and free-running circadian rhythms and on reproduction.

Lesions of the ventral striatum mimic the effect of olfactory bulbectomy to prevent short photoperiod-induced testicular regression in golden hamsters

Bilateral olfactory bulbectomy (BX) or bilateral transection of the rostral lateral olfactory tract (LOT) at the level of the anterior olfactory nucleus markedly increases gonadotropin secretion and prevents the testicular regression associated with maintenance on short photoperiod in golden hamsters. In an effort to further elucidate the neural tracts involved in this influence on gonadotropin secretion, lesions were placed in several potential pathways. Hamsters underwent sham surgery (SH), bilateral BX, or electrolytic or radiofrequency lesions of the: medial nucleus of the amygdala (MeX) caudal LOT just rostral to the medial nucleus of the amygdala (LOTX); or ventral striatum (VSX). Lesions were either bilateral or unilateral with contralateral olfactory bulbectomy. All animals were then placed on short photoperiod (LD 10:14) for 10 weeks and testicular size and body weight were assessed at weekly intervals. Lesion placement was assessed in brain sections stained with cresyl violet and animals with misplaced lesions were excluded. The following represent the number of animals in each group undergoing testicular regression in response to short photoperiod: SH: 32/35; BX: 8/31 (P < 0.01 vs. SH); MeX: 5/5; caudal LOTX: 8/9 and VSX: 3/8 (P < 0.05 vs. SH). Serum LH, FSH and testosterone at the end of the study correlated with the testicular regression data. These results suggest that the tonic inhibitory effect of the olfactory bulbs on gonadotropin secretion is mediated by fibers that exit the LOT rostral to the amygdala and project medially, either passing through or synapsing in the ventral striatum.

Lesions in the bed nucleus of the stria terminalis, but not in the lateral septum, inhibit short-photoperiod-induced testicular regression in Syrian hamsters

The transfer of adult male hamsters from long days (LD) to short days (SD) (i.e. < 12 h of light per day) typically results in marked testicular regression and a decline in plasma testosterone concentrations. To help disclose key brain regions responsible for mediating this photoperiodic response male hamsters received either chemical (i.e. N-methyl-D-aspartate; NMDA) or radiofrequency current lesions in the bed nucleus of the stria terminalis (BNST), and were then exposed to SD for 15 or 12 weeks, respectively. Although body weights were similar between sham-lesioned controls and the NMDA-lesioned hamsters, the latter showed a significant attenuation of testicular regression; additionally, their plasma testosterone concentrations remained at typical LD levels. When radiofrequency current-lesioned hamsters were transferred from LD to SD they also failed to show significant signs of testicular regression, nor a decline in plasma testosterone concentrations, nor a complete arrest of spermatogenesis. In contrast, sham-lesioned controls or hamsters that were lesioned dorsally to the BNST at a site primarily involving the lateral septum all showed the expected degree of testicular regression, a decline in plasma testosterone concentrations, and complete arrest of spermatogenesis; body weights were similar in all of the experimental group. Taken together, these findings suggest that the BNST, a brain area traditionally not associated with reproductive function, may play an important role in mediating photoperiodic information to the neural circuits that control the reproductive axis.

The suprachiasmatic nucleus in the sheep: retinal projections and cytoarchitectural organization

The retinal innervation, cytoarchitectural, and immunohistochemical organization of the suprachiasmatic nucleus (SCN) was studied in the domestic sheep. The SCN is a large elongated nucleus extending rostrocaudally for roughly 3 mm in the hypothalamus. The morphology is unusual in that the rostral part of the nucleus extends out of the main mass of the hypothalamus onto the dorsal aspect of the optic chiasm. Following intraocular injection of wheat-germ agglutinin-horseradish peroxidase or tritiated amino acids, anterograde label is distributed throughout the SCN. Retinal innervation of the SCN is bilaterally symmetric or predominantly ipsilateral. Quantitative image analysis demonstrates that, although the amount of autoradiographic label is greatest in the ventral and central parts of the nucleus, density varies progressively between different regions. In addition to the SCN, retinal fibers are also seen in the medial preoptic area, the anterior and lateral hypothalamic area, the dorsomedial hypothalamus, the retrochiasmatic area, and the basal telencephalon. Whereas the SCN can be identified using several techniques, complete delineation of the nucleus requires combined tract tracing, cytoarchitectural, and histochemical criteria. Compared with the surrounding hypothalamic regions, the SCN contains smaller, more densely packed neurons, and is largely devoid of myelinated fibers. Cell soma sizes are smaller in the ventral SCN than in the dorsal or lateral parts, but an obvious regional transition is lacking. Using Nissl, myelin, acetylcholinesterase, and cytochrome oxidase staining, the SCN can be clearly distinguished in the rostral and medial regions, but is less differentiated toward the caudal pole. Immunohistochemical demonstration of several neuropeptides shows that the neurochemical organization of the sheep SCN is heterogeneous, but that it lacks a distinct compartmental organization. Populations of different neuropeptide-containing cells are found throughout the nucleus, although perikarya positive for vasoactive intestinal polypeptide and fibers labeled for methionine-enkephalin are predominant ventrally; neurophysin-immunoreactive cells are more prominent in the dorsal region and toward the caudal pole. The results suggest that the intrinsic organization of the sheep SCN is characterized by gradual regional transitions between different zones.

Visual system of the fossorial mole-lemmings, Ellobius talpinus and Ellobius lutescens

Ocular regression in subterranean species has been shown to be associated with a number of alterations in the retina and in retinal pathways. In order to examine the consequences of eye reduction, the visual system was studied in two species of the murine genus, Ellobius, a specialized fossorial rodent. The axial length of the eye is only 2.2 mm in E. lutescens and 2.9 mm in E. talpinus. The mean soma size of ganglion cells in Nissl-stained flatmounts is approximately 10 microns in E. lutescens and 12 microns in E. talpinus. The soma size distribution in both species appears unimodal and falls within a range of 6-17 microns in diameter. The topographic distribution of ganglion cells shows a weak centroperipheral gradient, and an area centralis cannot be distinguished. The total number of neurons in the ganglion cell layer in Nissl-stained flat mounts is 12,000 in E. lutescens and 28,500 in E. talpinus and, following injection of retrograde tracers in the superior colliculus, is, respectively, 3,600 and 20,000. Based on the axial length and maximum ganglion cell density, the calculated retinal magnification factor (20-26 microns/degree) and spatial resolution (0.4-0.9 cycles/degree) of these minute eyes are extremely reduced. Retinofugal projections, demonstrated by autoradiography and horseradish peroxidase histochemistry, are similar to those in other rodents. The superior colliculus is well developed and receives a predominantly contralateral projection. Ganglion cells projecting to the contralateral colliculus are distributed over the entire retina, while cells that project ipsilaterally are restricted to the ventrotemporal region. The dorsal lateral geniculate nucleus has clearly defined binocular and monocular segments, including a partial segregation of regions receiving ipsilateral or contralateral retinal innervation. In addition, a localized region of label is observed medial to the geniculate nucleus. The retina also sends a bilateral projection to the suprachiasmatic nucleus; the intergeniculate leaflet; the pretectum; and the medial, lateral, and dorsal terminal nuclei of the accessory optic system. Sparse retinal projections were also seen in the bed nucleus of the stria terminalis, the anterior thalamus, and the inferior colliculus. A substantial retinal projection is observed in the basal telencephalon, including the cortical amygdaloid region, the diagonal band of Broca, the olfactory tubercle, and the piriform cortex. The results suggest that the morphological constraints of reduced eye size are reflected in the retina by a generally homogeneous organization but that central visual projections are not substantially modified as in some more specialized, strictly subterranean rodents.

Neuroanatomical pathways linking vision and olfaction in mammals

Retinal projections to several telencephalic structures have been demonstrated in a wide range of mammalian species following intraocular injections of tritiated amino acids and cholera toxin subunit-B conjugated to horseradish peroxidase. Since these regions are also innervated by olfactory fibers, we investigated the distribution of convergent projections using simultaneous injections of different anterograde tracers in the eye and olfactory bulbs. Convergent projections from the retina and from the olfactory bulbs were observed in the piriform cortex, olfactory tubercle, the cortical region of the medial amygdala, lateral hypothalamus, and the bed nucleus of the stria terminalis. A few retinal fibers also invade the nucleus of the lateral olfactory tract, the bed nucleus of the accessory olfactory bulb and the diagonal band of Broca. Injections of retrograde tracers in the medial amygdala, the bed nucleus or the lateral hypothalamus shows that the visuo-olfactory convergence mainly involves projections originating from the accessory olfactory bulb, and to a lesser extent from the ventromedial region of the main olfactory bulb. Fewer than 20 retinotelencephalic ganglion cells were identified in the retina, mainly located contralateral to the injection site. Ganglion cells were medium sized and possessed two long slender opposing dendrites. These retinal and olfactory projections could provide an anatomical substrate for the modulation of gonadotropin hormone levels and the olfactory influence on light mediated rhythms related to reproductive physiology.

Olfactory bulbectomy induces reproductive recrudescence in golden hamsters on short photoperiod

Olfactory bulbectomy results in a marked increase in gonadotropin secretion and prevents the reproductive regression associated with short photoperiod when the olfactory bulbectomy is done before exposure to the inhibitory photoperiod. The present study tested whether olfactory bulbectomy would offset the influence of short photoperiod if done after the reproductive system had regressed. Adult golden hamsters Mesocricetus auratus were divided into four groups: early sham (surgery at week-4); early olfactory bulbectomy (surgery at week-4); late sham (surgery at week 14) and late olfactory bulbectomy (surgery at week 14). At t = 0, all golden hamsters were placed in a short photoperiod (L:D 10:14). Early olfactory bulbectomy prevented testicular regression; the late olfactory bulbectomy group recrudesced much earlier than the sham groups. These results indicate that the tonic inhibitory influence of the olfactory bulbs is required for initiation of short photoperiod induced testicular regression and is also essential for the maintenance of the regressed state.

Olfactory bulb removal lengthens the period of circannual rhythms and disrupts hibernation in golden-mantled ground squirrels

Removal of the olfactory bulbs lengthened the period of circannual rhythms (CARs) of body mass and plasma testosterone (T) concentrations in male golden-mantled ground squirrels, but did not otherwise alter their expression. The period of the CAR was approximately 2 months longer in bulbectomized than in sham-operated animals. Peak values of body mass and T were unaffected by bulbectomy. All neurologically intact, but only 50% of bulbectomized, squirrels displayed normal hibernation patterns. We conclude that the olfactory bulbs are not the site of essential circannual oscillators. Circannual reproductive and hibernation cycles of ground squirrels are less subject to modulation by the olfactory bulbs than are the corresponding rhythms of several non-circannual hamster species.

Visual system of a naturally microphthalmic mammal: the blind mole rat, Spalax ehrenbergi

Retinal projections and visual thalamo-cortical connections were studied in the subterranean mole rat, belonging to the superspecies Spalax ehrenbergi, by anterograde and retrograde tracing techniques. Quantitative image analysis was used to estimate the relative density and distribution of retinal input to different primary visual nuclei. The visual system of Spalax presents a mosaic of both regressive and progressive morphological features. Following intraocular injections of horseradish peroxidase conjugates, the retina was found to project bilaterally to all visual structures described as receiving retinal afferents in non-fossorial rodents. Structures involved in form analysis and visually guided behaviors are reduced in size by more than 90%, receive a sparse retinal innervation, and are cytoarchitecturally poorly differentiated. The dorsal lateral geniculate nucleus, as defined by cyto- and myelo-architecture, cytochrome oxidase, and acetylcholinesterase distribution as well as by afferent and efferent connections, consists of a narrow sheet 3-5 neurons thick, in the dorsal thalamus. Connections with visual cortex are topographically organized but multiple cortical injections result in widespread and overlapping distributions of geniculate neurons, thus indicating that the cortical map of visual space is imprecise. The superficial layers of the superior colliculus are collapsed to a single layer, and the diffuse ipsilateral distribution of retinal afferents also suggests a lack of precise retinotopic relations. In the pretectum, both the olivary pretectal nucleus and the nucleus of the optic tract could be identified as receiving ipsilateral and contralateral retinal projections. The ventral lateral geniculate nucleus is also bilaterally innervated, but distinct subdivisions of this nucleus or the intergeniculate leaflet could not be distinguished. The retina sends a sparse projection to the dorsal and lateral terminal nuclei of the accessory optic system. The medial terminal nucleus is not present. In contrast to the above, structures of the "non-image forming" visual pathway involved in photoperiodic perception are well developed in Spalax. The suprachiasmatic nucleus receives a bilateral projection from the retina and the absolute size, cytoarchitecture, density, and distribution of retinal afferents in Spalax are comparable with those of other rodents. A relatively hypertrophied retinal projection is observed in the bed nucleus of the stria terminalis. Other regions which receive sparse visual input include the lateral and anterior hypothalamic areas, the retrochiasmatic region, the sub-paraventricular zone, the paraventricular hypothalamic nucleus, the anteroventral and anterodorsal nuclei, the lateral habenula, the mediodorsal nucleus, and the basal telencephalon.(ABSTRACT TRUNCATED AT 400 WORDS)

Retinal projection to the olfactory tubercle and basal telencephalon in primates

The retinal projection to the basal telencephalon was studied in eight species of primates from the suborders Strepsirhini and Haplorhini, including one anthropoid primate, the gibbon. Animals received an intraocular injection of tritiated amino acids and the distribution of retinal fibers and terminals was demonstrated by autoradiographic techniques in horizontal and coronal sections. In all species a discrete group of labeled retinal fibers is observed to branch off from the dorsolateral aspect of the optic tract at the level of the suprachiasmatic nucleus. These fibers, destined to the basal telencephalon, are topographically distinct from the retinal fibers which innervate the suprachiasmatic nucleus and medial hypothalamic regions. The fibers of the retinotelencephalic tract course dorsally above the supraoptic nucleus through the lateral hypothalamic area and then proceed further rostrally and laterally below the diagonal band of Broca towards the olfactory tubercle. Within the olfactory tubercle, terminal distribution of label is observed in the mediocaudal region along the granular cell layer II. In the macaque this cellular layer shows a characteristic thickening in the region of retinal terminals which is evident in both coronal and horizontal section. In some species this labeled region is seen within the superficial bulge of the tubercle on the ventral aspect of basal telencephalon. In all primates the retinal projection to olfactory tubercle is bilateral. In prosimians label is predominantly contralateral to the injected eye, in New World monkeys label is equally distributed on both sides of the brain and in Old World monkeys label is mainly found ipsilaterally. Retinal fibers were also seen in the periamygdaloid region but never extended as far as piriform cortex. These results, in addition to previous studies in other mammalian orders, confirm that the basal telencephalon, and in particular the olfactory tubercle, constitutes a region of visual and olfactory convergence. This sensory integration may be related to photic and chemosensory modulation of reproductive physiology and behavior.

Unilateral but not bilateral olfactory bulbectomy inhibits body weight gain in hamsters

The relation of the olfactory bulbs and photoperiod to the regulation of body weight was studied in male golden hamsters. Animals underwent sham operation, bilateral olfactory bulbectomy, or unilateral bulbectomy. They were left on long photoperiod for 5 weeks and then were transferred to short photoperiod for 11 weeks. The unilaterally olfactory bulbectomized hamsters gained less weight on long or short photoperiod than the sham operated group, while the bilaterally bulbectomized hamsters gained at least as much weight as the sham group. Thus, we report the novel finding that unilateral but not bilateral olfactory bulbectomy reduces body weight gain in male golden hamsters.

Photoperiodic regulation of prolactin release in male hamsters with hypothalamic knife cuts

Horizontal knife cuts placed dorsal to the paraventricular nucleus (PVN) of the hypothalamus prevent testicular regression in hamsters kept in short days. We examined the effects of these cuts on the photoperiodic modulation of the postcastration rise in gonadotropins, as well as on the release of prolactin in castrated and gonadally intact animals. The cuts blocked the inhibitory effects of short daylengths on the postcastration rise in circulating levels of gonadotropins. However, the cuts did not prevent the reduction in prolactin levels induced by short daylengths in castrated and gonadally intact animals. We conclude that dorsal connections of the PVN are not required for transduction of photoperiodic information used to regulate prolactin release. The knife cuts may remove tonic inhibitory influences on the release of follicle-stimulating hormone and luteinizing hormone, and thus produce elevated gonadotropin levels that mask the effects of nonstimulatory photoperiods on testicular size.

Retinofugal projections to the hypothalamus, anterior thalamus and basal forebrain in hamsters

In Part a of the study, the retinal inputs to the hypothalamus, anterior thalamus and basal forebrain of Syrian hamsters were studied using intraocular injections of horseradish peroxidase conjugated to cholera toxin (CT-HRP). In the hypothalamus, the heaviest retinal input was to the suprachiasmatic nucleus (SCN), however, many labeled fibers coursed through the SCN to reach more caudal, periventricular and lateral sites including the anterior and lateral hypothalamus, the paraventricular nucleus (PVN), the subparaventricular zone, the ventromedial nucleus and the pars compacta of the dorsomedial nucleus. Some of these fibers continued dorsally into the zona incerta (ZI). Other fibers emerged from the lateral optic chiasm and traveled either rostro-medially to end in the preoptic area (POA) or further laterally to reach the supraoptic nucleus. A subset of fibers extended laterally from the chiasm to form a well-defined tract which provided input to the pyriform cortex. The extrageniculate retinal input to the thalamus was to the anterior thalamic area (AT) via the stria terminalis. In Part b, injections of rhodamine-labeled latex microspheres were made in three brain areas that contained labeled fibers after intraocular injections of CT-HRP. Injections in the AT, PVN/ZI area and POA consistently produced a small number of labeled retinal ganglion cells, whereas control injections did not. Taken together, these results indicate that many regions of the brain involved in the control of reproductive and regulatory functions receive photic informations via direct retinal inputs. These retinal inputs may play a role in the photoperiodic modulation of physiology and behavior.

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).

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.

Olfactory bulb control of circadian activity rhythm in mice

Ablation of mouse olfactory bulbs lengthened the circadian period of wheel-running activity by 43 min and delayed the onset of entrained activity by 108 min. A transient increase in activity during the light phase of the 12:12 h light-dark photoperiod also occurred following surgery. These disruptions suggest that olfactory systems can modulate mammalian circadian rhythms.

Photoperiodic changes in opiate binding and their functional implications in golden hamsters

Daylength modulates gonadotropin secretion, gonadal steroid hormone feedback, sexual behavior and body weight in male golden hamsters. Endogenous opiates regulate each of these phenomena, and the ability of opiate receptor blockade to elevate serum LH secretion is photoperiod-dependent. We used in vitro autoradiography to localize and quantify effects of daylength in golden hamsters. Hamsters were exposed to stimulatory (14 h light: 10 h dark) or inhibitory (10 h light: 14 h dark) photoperiods for 10 weeks before specific [3H]naloxone binding was assessed. Short days significantly decreased binding in medial amygdala and the intercalated amygdaloid nucleus. This effect was reversed by superior cervical ganglionectomy. No significant effects of daylength were observed in other amygdaloid, hypothalamic or preoptic areas. Lesions of the medial amygdala decreased copulatory behavior, short day-induced weight loss, and anogenital chemoinvestigation but did not affect gonadal regression or other forms of chemoinvestigation. These lesions facilitated testosterone's negative feedback on luteinizing hormone in long days but did not interfere with the potentiation of negative feedback by short days.

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

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.

Knife cuts lateral but not dorsal to the hypothalamic paraventricular nucleus abolish gonadal responses to photoperiod in female hamsters (Mesocricetus auratus)

Horizontal and parasagittal knife cuts in the hypothalamus of female hamsters (Mesocricetus auratus) were employed to investigate the neural pathways that mediate gonadal responses to photoperiod. Bilateral horizontal knife cuts placed dorsal to the paraventricular nucleus (PVN) did not prevent short-day-induced acyclicity and uterine regression. On the other hand, regardless of photoperiod, animals with bilateral parasagittal knife cuts placed lateral to the PVN continued to exhibit regular 4-day estrous cycles and stimulated uteri. Thus, parasagittal cuts prevented the effects of short days on reproductive physiology. This finding suggests that the lateral efferent projections from the PVN represent an important component of the neural pathway mediating reproductive photoperiodism in female hamsters.

Studies on the effects of the pineal hormone melatonin on an androgen-insensitive rat prostatic adenocarcinoma, the Dunning R 3327 HIF tumor

The effects of the pineal indole melatonin on a transplantable androgen-insensitive fast-growing rat prostatic adenocarcinoma, the Dunning R 3327 HIF tumor, were examined. Afternoon injections of melatonin given to intact male rats enhanced tumor growth, while leading to a reduction in the weights of gonads and dorsal and ventral prostates. In anosmic hosts, this treatment had no effect on tumor growth or reproductive organ size. In castrated anosmic hosts, melatonin injections led to reductions in the growth of tumors, when compared with those in castrated hosts. Continuously available melatonin, in beeswax pellets, had no effect on growth of these tumors. These results are discussed in relation to the anticancer effects of melatonin and the effects of tumors on endogenous melatonin rhythms.

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

A recent study has shown that olfactory bulbectomy (BX) will prevent reproductive regression associated with short photoperiod in male golden hamsters. The results of experiments reported in this paper show that bulbectomized hamsters on long or short photoperiod still show a large nocturnal elevation in pineal melatonin production and that BX inhibits the reproductive regression induced by exogenous melatonin in pinealectomized hamsters. The data therefore indicate that BX does not inhibit short photoperiod induced testicular regression by altering melatonin secretion.

Species differences in the distribution of substance P and tyrosine hydroxylase immunoreactivity in the olfactory bulb

These studies document species differences in the distribution of the peptide substance P and the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH) within a central nervous system region of a number of mammalian species including the mouse, rat, guinea pig, rabbit, cat, and two species of hamster (Chinese and Syrian). Substance P-containing neuronal perikarya were observed in the main olfactory bulb (MOB) of both species of the hamster, but not in the MOB of the other species examined. In the accessory olfactory bulb (AOB), however, neuronal staining was observed in all species except the mouse. The number of stained somata and their intensity varied such that label was most prominent in the rat followed in decreasing order by the rabbit, guinea pig, cat, and hamster. The mouse displayed no perikaryal staining. Stained somata in AOB were found in the internal granule cell layer with dendritic processes ramifying through the internal plexiform layer to arborize within the mitral cell layer. The distribution of substance P-stained neurons in the MOB also differed between the two hamster strains. In the Syrian hamster, neurons were primarily juxtaglomerular. In the Chinese hamster, labeled perikarya were found in both the juxtaglomerular region and within the superficial aspect of the external plexiform layer (EPL). The mean longest diameter of the majority of substance P-labeled neurons in both species was greater than 10 micron, suggesting that they were tufted cells. Those in the EPL of the Chinese hamster were the largest (17 micron). Species differences also were observed in the distribution of substance P-positive axons and terminals within the MOB. Label was distributed primarily in the internal granule cell layer of the Syrian hamster and the internal plexiform layer of the Chinese hamster. Tyrosine hydroxylase staining was similar among species with the exception of the Syrian hamster. In the latter species, an additional large population of neurons was found within the external plexiform layer. In all other species, TH-stained neurons were found scattered throughout the MOB and occasionally the AOB but were not numerous in the EPL. Although most TH neurons were larger than 10 microns, in all species a population of smaller TH cells was observed primarily in the glomerular layer, suggesting that most neurons labeled with TH are tufted cells but that some may be periglomerular cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Olfactory bulbectomy prevents short photoperiod-induced anestrus in female golden hamsters

When female golden hamsters are maintained on a photoperiod of less than 12.5 h of light per day, they go into a pineal gland-induced anestrus in 6-10 weeks. This acyclicity is similar in certain respects to the testicular regression which occurs in male golden hamsters maintained on a short photoperiod. A recent study has indicated that pre-pubertal olfactory bulbectomy (BX) will prevent the testicular regression in adult male hamsters exposed to a short photoperiod. The present study tested the effect of pre-pubertal or adult BX on the anestrus associated with maintenance of adult female golden hamsters on short photoperiod. In Expt. 1, hamsters were pre-pubertally sham BX (SH) or BX (23-25 days of age) and then maintained on LD 14:10 or LD 6:18 for 15 weeks. In Expt. 2, hamsters were SH or BX as adults (63-65 days of age) and maintained on LD 6:18 for 13 weeks. The estrous cycles of all animals were monitored on a daily basis. In Expt. 1, all animals on LD 14:10 had regular estrous cycles for the duration of the study. Sixty percent of the SH group on LD 6:18 became anestrous, whereas 87.5% of the BX group on LD 6:18 continued having regular cycles. In Expt. 2, 80% of the SH group became anestrous while 90% of the BX group continued having regular estrous cycles. The possible mechanisms whereby BX affects the cyclicity of female hamsters is discussed. The fact that BX resulted in increased morning gonadotropin levels and ovarian weight in animals on LD 14:10, as well as in the hamsters on short photoperiod, suggests that there is a relationship between the olfactory bulb and the reproductive system that is independent of the photoperiod, in addition to more dramatic effects of olfaction on reproduction in animals on a short photoperiod.

Photoperiodic control of seasonal body weight cycles in hamsters

Syrian (Mesocricetus auratus) and Siberian (Phodopus sungorus sungorus) hamsters exhibit seasonal changes in body weight mainly by altering their carcass lipid stores. These seasonal changes are triggered largely by the photoperiod. Although both species exhibit gonadal regression when exposed to short photoperiods ("winterlike") daylength), they show opposite body weight changes. Syrian hamsters gain weight, but Siberian hamsters lose weight following short photoperiod exposure. Syrian hamsters prepare for overwintering by increasing energy stored as carcass lipid. In contrast, Siberian hamsters decrease their metabolic mass and therefore require lower energy intake for energy maintenance. In Syrian, and perhaps Siberian hamsters the short day-induced weight changes are exaggerated by high fat diets. Both species show photoperiod-induced changes in body weight without changing their food intake, suggesting a metabolic basis for these effects. In Syrian hamsters, the obesity is not secondary to gonadal regression, whereas in Siberian hamsters, the decrease in body weight is independent of the gonads for males but may be dependent upon the gonads in females. The pineal gland and its hormone, melatonin, are important transducers of photoperiodic signals in hamsters. This is certainly true for Siberian hamsters, in which pinealectomy blocks the short day-induced body weight loss. In contrast, pinealectomy has little effect on short day-induced weight gain in Syrian hamsters. Nevertheless, in both species, the body weight and gonadal changes induced by short day exposure are mimicked by systemic administration of melatonin in long day-housed animals. Thus, for these two hamster species, the same hormone, melatonin, produces opposite effects on body weight but does so by affecting the same carcass component. The target sites of action for the effects of melatonin on body weight change, energy metabolism, and reproductive status are not known. However, the suprachiasmatic and paraventricular nuclei of the hypothalamus are potentially important sites of action. The target site(s) and mechanism(s) of action for the pineal/melatonin-independent effect of photoperiod on body weight in Syrian hamsters are also unknown. This photoperiodic response is highly unusual among mammals in that it is not pineal-dependent. Studies of the mechanisms underlying these body weight changes in Syrian and Siberian hamsters may provide fundamental knowledge about how environmental influences affect obesity and they may also provide insight into the various strategies for overwintering shaped by natural selection.(ABSTRACT TRUNCATED AT 400 WORDS)

Horizontal knife cuts in the suprachiasmatic area prevent hamster gonadal responses to photoperiod

We used horizontal knife cuts near the suprachiasmatic nucleus (SCN) to investigate the route for day-length information transmission from the SCN to the paraventricular nucleus (PVN). Testicular regression was blocked in animals with knife cuts dorsal to the SCN that spanned its entire rostrocaudal extent, and in PVN-ablated animals. Misplaced cuts in the ventral preoptic area also prevented gonadal regression. These neural insults did not systematically affect the circadian control of activity rhythms. The pathway from the SCN to the pineal runs from the dorsal border of the SCN and travels through the periventricular area toward the PVN.