Neural connections between the brain and the pineal gland of the golden hamster (Mesocricetus auratus)

Summary Neurons projecting from the brain to the pineal gland via the pineal stalk were investigated in the golden hamster with the use of the retrograde horseradish-peroxidase tracing method both in vivo and in vitro. Labelled perikarya were observed in the medial and lateral habenular nuclei as well as in the posterior commissure. Single cells located in the ependymal lining of the pineal- and suprapineal recesses were also retrogradely labelled. These results show that a distinct central innervation of the pineal gland exists in the golden hamster, in agreement with findings in other mammalian species investigated by means of a similar methodology. In addition, also direct signals from the cerebrospinal fluid to the parenchyma might be conducted via cells located within the ependymal layer of the pineal- and suprapineal recesses.This study was supported by grants from the Deutscher Akademischer Austauschdienst to M.M. (312/dk-4-is), the Deutsche Forschungsgemeinschaft to H.W.K. (Ko 758/2-2, 2-3), and the Carlsberg Foundation     

Synaptic ribbons during postnatal development of the pineal gland in the golden hamster (Mesocricetus auratus)

Summary Synaptic ribbons, functionally enigmatic structures of mammalian pinealocytes, were studied during the postnatal development of the pineal gland in the golden hamster (Mesocricetus auratus). On day 4 post partum, synaptic ribbons appear in cells that have already started to differentiate into pinealocytes. Between days 4 and 9, an increase in the number of synaptic ribbons occurs, concomitant with the continuing differentiation of the pineal tissue. Between days 9 and 16, when differentiation of this tissue is almost completed, the number of synaptic ribbons decreases and approaches that characteristic of the adult pineal gland. During development, the synaptic ribbons increase in length, and dense core vesicles are frequently found in the vicinity of these structures. It is assumed that a functional relationship exists between dense core vesicles and the synaptic ribbons, which are considered to be engaged in a certain form of secretory activity of the mammalian pineal gland.Supported by the Deutsche Forschungsgemeinschaft     

Diurnal variation in thermal and metabolic parameters of the golden hamster (Mesocricetus auratus)

The purpose of this study is to examine diurnal variation in several thermal and metabolic parameters of the golden hamster, Mesocricetus auratus. Metabolic rate, core temperature, and evaporative water loss were measured during night and day at several ambient temperatures. Wet minimal thermal conductance, dry minimal thermal conductance, basal metabolic rate, minimal net heat production and the lower critical temperature difference were estimated from these measurements. Wet and dry minimal thermal conductance, evaporative water loss, core temperature, basal metabolic rate, and lower critical temperature difference were greater during the active phase than during the resting phase. The diurnal variation in wet minimal thermal conductance was much smaller than that predicted from published allometric equations. The diurnal variation in wet minimal thermal conductance was 9% of the 24-h mean. The diurnal variation in dry minimal thermal conductance was 26% of the 24-h mean. The higher active-phase core temperature and basal metabolic rate may function to enhance peak metabolic performance during the active phase. The lower resting phase metabolism and core temperature may reduce energetic costs. The greater active-phase lower critical temperature difference may be a result of the greater active-phase basal metabolic rate. Diurnal variation in minimal thermal conductance may be caused by changes in peripheral circulation.Abbreviations BMR basal metabolic rate - T difference between core and ambient temperatures - T _1c lower critical temperature difference - EWL evaporative water loss - MTC minimal thermal conductance - MR metabolic rate - Q _ev evaporative heat loss - RQ respiratory quotient - T _a ambient temperature - T _c core temperature - T _1c lower critical temperature     

Development and retention of phenotypically specialized cells in pituitary allografts in the hamster (Mesocricetus auratus)

Summary We used immunohistochemistry to identify cells present in pituitary allografts in the hamster. Hypophyses removed from neonatal hamsters or adenohypophyses removed from adult females were placed beneath renal capsules of hypophysectomized adult females. Serum PRL, LH, and GH concentrations were measured at two, five, and eight weeks after placement of allografts. Allografts were removed after eight weeks and stained for cells containing PRL, LH, FSH, GH, or ACTH. Allografts did not release LH or GH. Those of adult adenohypophyseal tissue released significantly more PRL. The morphology of allografts of neonatal hypophyseal tissue resembled that of the adult adenohypophysis in situ. Lactotrophs, corticotrophs, somatotrophs and LH-cells were observed; very few FSH-cells were present. Allografts of adult adenohypophyseal tissue contained pituitary cells, numerous cavities, often enclosing lymphoid cells, and fibrous tissue. Atypical lactotrophs were the numerically dominant cells in these allografts; all other cells were present. The LH-cells outnumbered FSH-cells. These observations suggest that: (a) development of normal adenohypophyseal morphology can occur in an ectopic position; (b) intracellular hormones are present in cells in an ectopic site; (c) development and retention of intracellular FSH is more dependent on occupation of the normal position of the adenohypophysis than is retention of intracellular LH; and (d) release of PRL occurs from atypical cells in allografts of adult adenohypophyseal tissue.     

Qualitative and quantitative comparison of the distribution of phosphorylated and non-phosphorylated neurofilament epitopes within central and peripheral axons of adult hamster (Mesocricetus auratus)

Summary The distribution of phosphorylated and nonphosphorylated neurofilament epitopes was determined immunocytochemically in adjacent 2 m-thick sections of sciatic nerve, ventral root and spinal cord. Staining was scored as either intense, moderate or absent and the proportion of labeled axons was calculated for each category. Nearly all sciatic nerve and ventral root axons were immunoreactive with both antibodies against phosphorylated and non-phosphorylated neurofilaments and there were no significant differences in the number of intensely- or moderately-labeled axons. Within the spinal cord however, while the majority of large caliber axons was stained with both antibodies, there was a significant number of small caliber axons which stained only with antibodies against phosphorylated neurofilaments. These results show that phosphorylated and nonphosphorylated neurofilaments are extensively codistributed in CNS and PNS axons, and that in the CNS, staining intensity for non-phosphorylated epitopes is less in the smaller axons.     

Circadian changes in synaptic ribbons and spherules in pinealocytes of the Syrian hamster (Mesocricetus auratus)

Summary In the present study, synaptic ribbons were studied morphologically and quantitatively in hamster pineal gland. The number of ribbons and spherules of hamster pinealocytes was counted over a 24-h period. The 24-h variations in the quantity of synaptic ribbons were found to parallel fluctuations in pineal melatonin concentrations. No significant circadian changes were observed for synaptic spherules, indicating different roles for these two structures.     

The bridge-partitioning complex of germ-cell intercellular bridges in the testis of the golden hamster

The bridge-partitioning complex present in pre-existing intercellular bridges of dividing spermatogonia in the juvenile golden hamster testis was studied by electron microscopy. There is a close temporal adjustment in the appearance of this structure to those stages of mitosis during which the cells are without a nuclear membrane, i.e., the bridge-partitioning complex is formed at the transition between prophase and prometaphase and gradually disappears during telophase. In addition, in a certain form of degenerative dividing germ cells, which completely lack a bridge-partitioning complex in pre-existing intercellular bridges, condensed chromatin not surrounded by a nuclear membrane occasionally projects through these open bridges and thus may well change over to a neighboring cell of the same clone. These results strongly indicate an essential barrier function of the bridge-partitioning complex. It temporarily prevents intraclonal exchange of nuclear material during those stages of mitosis where a nuclear membrane is lacking and, thus, maintains genetic integrity of male germ cells during synchronous divisions.     

The presence of opioidergic pinealocytes in the pineal gland of the European hamster (Cricetus cricetus): an immunocytochemical study

By use of antibodies raised against leu-enkephalin and met-enkephalin immunoreactive, opioidergic bi- and multipolar cells were demonstrated in the pineal gland of the European hamster. Ultrastructural analysis of these opioidergic cells revealed them to be pinealocytes. Processes emerged from the cell bodies and terminated in club-shaped swellings containing many small clear and some larger granular vesicles. Some of the terminals made synapse-like contacts with non-immunoreactive pinealocytes. The presence of the opioidergic pinealocytes strongly indicates that the pineal gland of the European hamster, in addition to its pinealopetal nervous regulation, is regulated by intrapineal peptidergic pinealocytes via a synaptic mechanism. A possible paracrine role of the opioidergic cells must also be considered.     

Male golden hamsters (<Emphasis Type="Italic">Mesocricetus auratus</Emphasis>) are more reactive than females to a visual predator cue

In most species of small mammals, males are exposed to higher levels of risk than females because they compete for mates, travel greater distances to find and procure mates, and/or defend a territory. This suggests that males and females might have different responses to risky situations, such as the presence of a predator. We tested responses to a visual predator cue (an owl silhouette) in male and female golden hamsters (Mesocricetus auratus). In a laboratory arena, there was no significant sex difference in the latency to enter the burrow or time spent in the burrow immediately after exposure to the owl silhouette. Males, however, were less likely to be active during the 3-min period following the animal’s exposure to the silhouette, indicating that male golden hamsters are more wary after exposure to an aerial predator cue than females. Most studies of responses to predators or predator cues have not considered sex differences, but our results show that males and females may have quite different responses to predator cues. Further work should be done to characterize and quantify sex differences in response to predators or predator cues.     

Body temperature and behaviour of golden hamsters (Mesocricetus auratus) and ground squirrels (Spermophilus tridecemlineatus) in a thermal gradient

Golden hamsters and thirteen-lined ground squirrels were maintained individually in a thermal gradient (14°C to 33°C) for several weeks under a 14L: 10D light-dark cycle. Animals of both species showed robust daily rhythms of body temperature and locomotor activity with acrophases consistent with the habits of the species (diurnal acrophases in the diurnal squirrels and nocturnal acrophases in the nocturnal hamsters). Hamsters showed a robust daily rhythm of temperature selection 180° out of phase with the rhythms of body temperature and locomotor activity. Squirrels did not show a daily rhythm of temperature selection. These results raise the hypothesis that a daily rhythm of temperature selection is exhibited by nocturnal but not by diurnal endotherms.     

Tissue specific expression and sequence analysis of a stress responsive gene<Emphasis Type="Italic"> Bre</Emphasis> in adult golden hamster (<Emphasis Type="Italic">Mesocricetus auratus</Emphasis>)

Bre (brain and reproductive organ-expressed) is a new and putative stress-modulating gene of yet unknown function. BRE has previously been shown to interact with type 1 tumor necrosis factor receptor (TNFR1) and modulate the action of TNF. Apart from the brain and reproductive organs, Bre and BRE are highly expressed in steroid producing tissues such as the adrenal gland. Here we report for the first time the cloning of the Bre gene from golden hamster, a model organism extremely valuable for reproduction and steroid research, and examination of its tissue specific expression. Sequence analysis demonstrated that the peptide sequence of BRE in hamster shares ~99% homology with those of human, monkey and mouse. The hamster Bre gene transcribed a ~1.8-kb mRNA which translated a 44-kDa protein. Bre was strongly expressed in neurons and luminal epithelia of urogenital, digestive and respiratory organs. Bre was also detected in lymphoid tissues and endocrine glands. Immunohistochemistry demonstrated a similar protein expression pattern. Exceptions to this included the adrenal gland, where a high level of Bre was accompanied by weak immunoreactivity; as well as the oocytes and islets of Langerhans, where BRE protein but not the mRNA was localized. These data indicated that Bre gene products were expressed in a wide variety of tissues other than the brain and reproductive organs, as was originally described. Based on our findings, we propose that Bre is a housekeeping gene in tissues that are constantly subjected to environmental hazards such as luminal epithelia. Our results further support the proposed role for BRE in endocrine and immune functions.     

Intercellular bridges between germ cells in the immature golden hamster testis: evidence for clonal and non-clonal mode of proliferation

Summary Intercellular bridges of prespermatogonia and of the first A-spermatogonia in the maturing testes of newborn to 17-day-old golden hamsters have been studied by electron microscopy. Incomplete cytokinesis of dividing M- and T₂-prespermatogonia and A-spermatogonia produces these bridges, which undergo different developmental fates. Bridges of the first A-spermatogonia are stable beyond subsequent mitoses of these cells; this gradually leads to the formation of bridge-connected groups of synchronously developing germ cells. Thus, the clonal mode of male germ cell proliferation is already established in this period of testis maturation. During mitoses, pre-existing bridges reversibly develop structural modifications, i.e. considerable elongation and formation of a bridge-partitioning complex. In contrast, intercellular bridges of prespermatogonia are mostly severed and become lost during subsequent mitoses of the cells involved; this results in separation of the germ cells and represents a mainly non-clonal mode of M- and T₂-prespermatogonial proliferation. Here, too, pre-existing bridges elongate and develop the bridge-partitioning complex during subsequent mitoses of the joined cells, but this is superposed and interrupted by the simultaneous process of disconnection of the bridges.Parts of this study were presented at the 85th meeting of the Anatomische Gesellschaft in Munich, April 1990     

Differential permeability of pineal capillaries to lanthanum ion in the rat (Rattus norvegicus), gerbil (Meriones unguiculatus) and golden hamster (Mesocricetus auratus)

Summary Capillaries in the pineal gland of the rat (Rattus norvegicus), gerbil (Meriones unguiculatus) and golden hamster (Mesocricetus auratus) were investigated by means of electron-microscopical tracer studies using lanthanum. The tracer was administered together with the fixative solution by perfusion via the left cardiac ventricle. In the rat, endothelial junctions of fenestrated capillaries are permeable to lanthanum. In the gerbil the tracer does not leave the capillaries, which are of the non-fenestrated type throughout the organ. In the golden hamster the two portions of the pineal system have different types of capillaries. While in the superficial pineal fenestrated capillaries permeable to lanthanum predominate, the deep pineal possesses capillaries that are, without exception, devoid of fenestrations and impermeable to the tracer. It is suggested that differences in the structure of the capillaries are related to differences in the extent of a specialized contact of the pineal gland to the third ventricle.The authors dedicate this paper to Professor H. Rollhäuser, Münster, on the occasion of his 65th birthday     

Tyrosine hydroxylase and neuropeptide-Y immunoreactivity in pineal glands developing in situ and in pineal grafts

Summary Postnatal development of the innervation of the pineal gland in situ as well as the reinnervation of pineal grafts by tyrosine hydroxylase (TH)- and neuropeptide Y (NPY)-immunoreactive nerve fibers were examined using the avidin-biotin-peroxidase immunohistochemical technique. TH-immunoreactive nerve fibers appeared in the pineal gland on the second postnatal day (P2) in both hamsters and gerbils. NPY-immunoreactive nerve fibers first appeared in the pineal gland of gerbils on P2 and in the hamsters on P3. By the seventh postnatal day (P7), the pineal glands of both hamsters and gerbils were richly innervated by TH- and NPY-fibers that appeared as smooth fibers or fibers with sporadic varicosities. By the age of 4 weeks, the innervation of the pineal glands of hamsters and gerbils by TH-and NPY-fibers was fully developed. Abundant TH- and NPY-fibers formed a dense meshwork in the parenchyma of the superficial and deep pineals. The great majority of the fibers bore a large number of varicosities. More NPY-fibers were found in the pineal glands of gerbils than hamsters. NPY fibers were distributed evenly throughout the pineal glands of the gerbil, but they were more often located in the central region of the superficial pineal of the hamster. For the pineal grafts, superficial pineals from neonatal and 4-week-old hamsters were transplanted to different sites in the third cerebral ventricle (infundibular recess, posterior third ventricle) or beneath the renal capsule. The pineal grafts from 4-week-old donors appeared to undergo severe degeneration and eventually disappeared. The pineal grafts from neonatal hamsters, however, successfully survived and became well integrated into their new locations. Abundant TH-and NPY-fibers in the host brain were found surrounding the pineal grafts placed in the third cerebral ventricle, but were only rarely seen entering the parenchyma of the grafts. A few TH-fibers were demonstrated in the renal grafts 4 weeks after transplantation. These studies describe the postnatal development of the innervation of the pineal glands in situ by TH-and NPY-nerve fibers, and demonstrate a lack of reinnervation of cerebroventricular pineal grafts by TH and NPY fibers from adjacent host brain.Portions of the results of this paper were previously reported in abstract form at the 1990 Meeting of The American Association of Anatomists (Anat Rec 226:57A)     

Evidence for biological rhythm in spermatogenesis in the pubertal hamster (Mesocricetus auratus): a flow cytometric study

The number of cells in the S-phase fraction of the cell cycle reflects proliferative activity. Using flow cytometry histograms and the Phoenix M+ cell cycle program, the percent of cells in the S-phase fraction was measured in single cell suspensions prepared from testes of hamsters of different ages. A cyclical pattern with a period of 9 days, superimposed on another rhythm with a 38 day period was observed (p < 0.01) during hamster maturation and it disappeared after the second spermatogenic wave, where the S phase values reached a plateau. It was concluded that maturing animals passed through a stage in which testicular biological rhythm was involved. Therefore it was concluded that it takes approximately two spermatogenic waves before the proliferation rate in the testis reached a steady state.     

Post-natal development of the pineal organ in the hamsters Phodopus sungorus and Mesocricetus auratus

Summary In Phodopus sungorus, as in other mammals, the pineal organ forms an important link in the transduction of photoperiodic information to the endocrine system. The sympathetic innervation, via the superior cervical ganglion, controls the metabolism of serotonin and melatonin in the pineal, which in turn is involved in the control of the gonads. In the present study, the post-natal development of this system was investigated. Specimens 1, 5, 10, and 15 days post partum (p.p.) and adults were treated with monoamine-oxidase-inhibitor and perfused under ether anesthesia via the aorta with a buffer containing glyoxylic acid, formaldehyde and Mg⁺⁺. The brains were then dissected out and treated according to Falck-Hillarp for fluorescence microscopy and microspectrofluorometry. Day 1: The nervi conarii had reached the pineal capsule, but only in a few cases was the pineal organ invaded and then only by a few fibers. Day 5: A rich green-fluorescing net of fibers was present in the entire organ, stalk and lamina intercalaris. No 5-HT fluorescence was observable. Day 10: Similar to the stage at 5 days a rich green-fluorescing nerve fiber net was observed throughout the pineal and a yellow fluorescence in the pineal perikarya. Day 15: The general appearance resembles the adult. The nerve fibers are masked by the intense yellow fluorescence of the pineal perikarya. Fading of the latter, however, allows the catecholamine fluorescence to be seen. Golden hamsters at an age of 15 days p.p. show a similar appearance to Phodopus at an age of 15 days. Microspectrofluorometric determinations indicated the catecholamine to be noradrenaline, and confirmed a 5-HT/5-HTP origin of the yellow fluorescence appearing between day 5 and day 10. The amount of 5-HT/5-HTP was considerably less at day 10 than at day 15 or in adults. Sympathectomy by extirpation of the superior cervical ganglion abolished the catecholamine fluorescence completely in the pineal body, stalk and lamina intercalaris.Supported by grants from the Swedish Natural Science Research Council (to P. Meurling and Th. van Veen), and the Royal Physiographic Society of Lund     

Nucleolus-like bodies in the pineal gland of the Djungarian hamster (Phodopus sungorus)

Summary Light- and electron-microscopic observations on the pineal gland of Phodopus sungorus revealed intracytoplasmic inclusions resembling nucleolus-like bodies similar to those found in other regions of the central nervous system. Bernhard's EDTA method was used to confirm that these inclusions were nucleolus-like bodies. These structures were rarely found in pinealocytes of sexually active longday animals, whereas large numbers of them were observed in pinealocytes of sexually quiescent short-day animals. Nucleolus-like bodies may therefore be involved in pineal secretion.     

Thermal dependence of serotonergic modulation of neural activity in the hamster

1. The modulatory effect of serotonin on CA1 pyramidal cells in the hamster (Mesocricetus auratus) hippocampus was examined over a range of temperatures. 2. Following repetitive Schaffer collateral/commissural stimulation, changes in the amplitude of population spikes (the synchronous firing of CA1 pyramidal cells) were recorded in the hamster, a hibernator. Amplitudes were measured after 10 microM serotonin was added to and then withdrawn from the perfusing medium with the temperature of the bath fixed at different temperatures. 3. Between 35 degrees C and 15 degrees C a depression in population spike amplitude of at least 10% was seen in 36 of 43 trials, with an average depression of 68%. No significant temperature dependence of the depressive effect was seen. 4. Following the removal of serotonin from the perfusate, the spike amplitude was enhanced over the same range of temperatures, averaging 33% higher than control values. The enhancement was most pronounced at 35 degrees C and 15 degrees C and smallest at 25 degrees C. 5. Thus, over the entire temperature range of 35 degrees C to 15 degrees C, serotonin exerted a dual modulatory effect on the spike amplitude, a depression followed by an enhancement. Serotonin's modulatory effects on pyramidal cell excitation persist over temperatures encountered as the hamster enters hibernation.     

Cerebrospinal fluid-contacting area in the pineal recess of the vole (Microtus agrestis), Guinea Pig (Cavia cobaya), and rhesus monkey (Macaca mulatta)

Summary The ventricular lining in the pineal recess of the vole (Microtus agrestis), guinea pig (Cavia cobaya) and Rhesus monkey (Macaca mulatta) was investigated light and electron microscopically. Deep in the pineal recess of all three species the ependymal lining exhibits interruptions. A varying proportion of pinealocytes penetrates through this ependymal area, so that the surface of the protruding cells is directly exposed to the cerebrospinal fluid (CSF). At their base, these cells are anchored in the hypependymal tissue by means of processes. It is conjectured that these pinealocytes are engaged in secreting pineal substances into the CSF, as various physiological findings appear to indicate.     

Infectivity, growth, development and pathology of Echinostoma caproni (Trematoda) in the golden hamster

Laboratory hamsters (Mesocricetus auratus) were experimentally infected with 75 ± 15 metacercarial cysts of Echinostoma caproni. Worms were recovered from days 7 to 89 post-infection with eight to 90 (average 37) parasites in the small intestine. Worm wet weights averaged 0.85 mg at 10 days, 1.8 mg at 17 days, 3.4 mg at 45 days, and 7.7 mg at 89 days; average dry weights for the identical days were, 0.15, 0.30, 0.70 and 2.2 mg, respectively. The average body area of worms fixed in hot (80°C) alcohol-formalin-acetic acid was 0.21 mm² on day 3, 4.9 mm² on day 10, and 17.7 mm² on day 42. Clinical signs in some hamsters included progressive unthriftiness and watery diarrhea. Gross examination revealed enlarged lymphatic nodules along the length of the small intestine. The histopathological responses of hamsters to the parasite showed erosion of the intestinal villi with lymphocytic infiltration being the primary response; hemorrhagic areas were also observed in the villi.