Functional activities of the colon of the desert gerbil (Gerbillus cheesmani)

The effects of starvation and undernourishment on the potential differences (pd in mV), basal short-circuit current (Isc in microA/cm(2)), resistance (R in omega) and glucose-dependent short-circuit current (Isc in microA/cm(2)) across stripped sheets of proximal, mid and distal colon of the gerbil (Gerbillus cheesmani) were investigated. The effects of replacing sodium chloride by lithium chloride, replacing chloride in Krebs buffer by gluconate and removing bicarbonate from bathing buffers were also investigated. Starvation (4 days, water ad lib) and undernourishment (50% control food intake for 21 days) had no significant changes on pd and R of the three regions of stripped colon. Starvation increased the basal Isc in the proximal and the mid-colon only while undernourishment increased the basal Isc of three regions of the colon. In addition, starvation and undernourishment increased the glucose-dependent Isc in the three regions. Replacing sodium chloride by lithium chloride caused a slight decrease in the basal Isc of proximal and mid colon taken from starved animals. In undernourished gerbils, although there was a slight decrease in basal Isc of proximal and mid colon the big decrease was observed in Isc of the distal colon. Replacing chloride by gluconate had no effect on the Isc of the different regions of colon taken from fed and starved animals but decreased the Isc of the three regions of undernourished animals. The absence of bicarbonate reduced the Isc of proximal and mid colon taken from starved gerbils and those of three regions taken from undernourished animals. The results of the present study suggest that the Isc of proximal and mid colon from starved gerbils could result from active sodium transport together with bicarbonate secretion while the Isc of the three regions taken from undernourished gerbils results from active sodium absorption together with both chloride and bicarbonate secretion.     

The Harderian gland of the Dhub lizard Uromastyx microlepis of the Kuwaiti desert: an ultrastructural approach

Harderian glands exist in the orbits of most terrestrial vertebrates. The basic function of the gland is the lubrication of the eye. The present study was carried out to shed some light on the ultrastructure of the still enigmatic Harderian gland of the lizard Uromastyx microlepis, a common species in Kuwait and other Gulf areas. The Harderian gland of Uromastyx microlepis is well developed, relatively large in size and lingual in shape. The epithelial cells of the anterior part of the gland are characterized by the presence of membrane bound granules of almost homogeneous consistency. These secretory granules are gathered in compartments and separated by membranes and stacks of granular endoplasmic reticulum (GER). Most of the lumina were empty. Moderate amounts of GER, free ribosomes and pleiomorphic mitochondria were observed in the perinuclear area of the epithelial cells. The medial and caudal parts of the gland were rich in special secretory granules, GER, free ribosomes and pleiomorphic mitochondria. The anterior part of the gland could represent the future lacrimal gland of mammals. A network of myoepithelial cells was recognized around the gland tubules. While no melanocytes or lymphocytes were observed in the scarce interstitial tissue, macrophages, that might have an immune function in the gland, were observed.     

Effects of 5-hydroxytryptamine on the short-circuit current across the small intestine of the gerbil (Gerbillus cheesmani) in different dietary states

The effects of serosally added 5-hydroxytryptamine (5-HT, 100 microM) on the short circuit-current (Isc) across jejunum and ileum taken from fed, starved and undernourished (Gerbillus cheesmani) were investigated. The effects of the neurotoxin, tetrodotoxin (TTX, 10 microM) on the basal Isc as well as on the maximum increase in Isc induced by 5-HT were also studied. There were regional variations in the basal Isc as well as in the way by which the small intestine responds to 5-HT. The basal Isc was greater in jejunum than in ileum and such differences were TTX-sensitive. The maximum increase in Isc, which results from addition of 5-HT, was higher in jejunum than in ileum under all three feeding conditions. TTX reduced the maximum increase in Isc induced by 5-HT across stripped and intact intestine of the two regions in the three nutritional states. The 5-HT-induced Isc in the jejunum of both starved and undernourished gerbils and in the ileum of starved animals was the function of both submucosal and myenteric plexus. In jejunum and ileum taken from starved and undernourished gerbils the 5-HT-induced Isc was both chloride- and bicarbonate-dependent. Thus the results indicated that both starvation and undernourishment increase that response and such increases were TTX-sensitive and both chloride- and bicarbonate-dependent.     

Seasonal changes in testicular contents and plasma concentrations of androgens in the desert gerbil (Gerbillus gerbillus)

Gerbils were caught in the Béni-Abbès area (Algeria). Testicular endocrine activity was highest in spring (testicular wt 298 +/- 10 mg; seminal vesicle wt 603 +/- 62 mg; testicular testosterone and androstenedione content 9.2 +/- 1.7 and 0.5 +/- 0.1 ng/testis; plasma testosterone 832 +/- 200 pg/ml). Values decreased in summer, were lowest in late summer and in autumn (84 +/- 17 mg; 40 +/- 14 mg; 0.20 +/- 0.06 and 0.02 +/- 0.01 ng/testis; 228 +/- 54 pg/ml, respectively) and increased again in winter (December-January). The onset of testicular endocrine activity was concomitant with the lowest temperatures and the shortest photoperiod; it increased when temperatures and daylength were increasing and began to decline when temperatures and photoperiod were still maximal. These seasonal changes in the endocrine activity of the testis of the gerbil differ from those of the sand rat inhabiting the same area.     

Stereochemistry of 2,3-alkanediols obtained from the Harderian gland of Mongolian gerbil (Meriones unguiculatus)

The stereochemistry of the alcohol moieties of 2,3-alkanediol diacyl esters obtained from the Harderian gland of the Mongolian gerbil was investigated. There were five major 2,3-alkanediols, C14-C22 (even carbon numbers), all having the erythro configuration as determined by GC-MS analysis of their isopropylidene derivatives in comparison with synthetic erythro- and threo-2,3-hexadecanediols. 13C-NMR spectroscopy of the synthetic materials showed distinct differences of chemical shift at the C-1, C-3, and C-4 carbons, from which the native 2,3-alkanediols were definitely determined to be in the erythro series. The absolute configurations of the C-2 and C-3 asymmetric centers were assigned as 2S and 3R, respectively, based on known 2S,3R-octanediol.     

Effects of tetrodotoxin and ion replacements on the short-circuit current induced by Escherichia coli heat stable enterotoxin across small intestine of the gerbil (Gerbillus cheesmani)

The effects of mucosally added Escherichia coli heat stable enterotoxin (STa 30 ng ml(-1)) on the basal short-circuit current (Isc in microA cm(-2)) across stripped and unstripped sheets of jejuna and ilea taken from fed, starved (4 days, water ad lib) and undernourished (50% control food intake for 21 days) gerbil (Gerbillus cheesmani) were investigated. The effect of neurotoxin tetrodotoxin (TTX 10 microM) and the effects of replacing chloride by gluconate or the effects of removing bicarbonate from bathing buffers on the maximum increase in Isc induced by STa were also investigated. The maximum increase in Isc which resulted from the addition of STa were significantly higher in jejuna and ilea taken from starved and undernourished gerbils when compared with the fed control both using stripped and unstripped sheets. In the two regions of the small intestine taken from fed and starved animals TTX reduced the maximum increase in Isc induced by STa across unstripped sheets only. Moreover in jejuna and ilea taken from undernourished gerbils TTX reduced significantly the maximum increase in Isc induced by STa across stripped and unstripped sheets. Replacing chloride by gluconate decreased the maximum increase in Isc induced by STa across jejuna and ilea taken from undernourished gerbils only. Removing bicarbonates from bathing buffer decreased the maximum increase in Isc across the jejuna and ilea taken from starved and undernourished gerbils.     

The origin of multiple sex chromosomes in the gerbil Gerbillus gerbillus (Rodentia: Gerbillinae)

The sex chromosomes of the partly sympatric species of gerbils Gerbillus pyramidum and G. gerbillus (Mammalia: Gerbillinae) were investigated by a variety of light- and electron-microscope methods, including DNA replication banding and synaptonemal complex (SC) techniques. The sex-chromosome mechanism of G. pyramidum is of the maleXY:femaleXX type, whereas that of G. gerbillus is of the less common maleXY1Y2:femaleXX system. The results include the demonstration that the X chromosomes of both species are compound. One segment is added to the X chromosome of G. pyramidum, leading to an increase in length from the standard 5% to approximately 7.3%, whereas two different extra segments increase the length of the X chromosome of G. gerbillus to approximately 11% of the length of the haploid genome. In both cases the extra material is autosomal and is also represented in the respective Y chromosomes. Classifying heterochromatin by the variation in staining quality was helpful in elucidating the possible origin of the different chromosome segments, including the pericentromeric regions. Observations on meiotic chromosome pairing and chiasma formation have confirmed the homologies established by band comparisons. The occurrence of chiasmata between the sex chromosomes supports the autosomal origin of the pairing segments. These and other findings have been interpreted in the framework of a multistep evolutionary model. This sequence starts from a hypothetical pair of sex chromosomes, the X element of which amounts to 5% of the haploid genome, and leads through three translocations involving two pairs of autosomes and one pericentric inversion to the most complex situation of this series, manifested in G. gerbillus. The adaptive value, if any, of autosome incorporation into the sex chromosomes repeatedly occurring here is unknown. It is, however, a remarkable fact that in one species, G. gerbillus, the complex sex-chromosome constitution is conserved over vast geographic distances, and in the other, G. pyramidum, the compound X and Y chromosomes withstand change in the face of extreme autosome restructuring.     

Metabolic adaptations of the gerbil, Gerbillus campestris, to a desert climate. Comparison with white mice

Metabolic rate of gerbils was lower than that of mice (35%). We tried to assess the part played by brown adipose tissue in this low level. Mitochondrial respiration (state 4), protein content and cytochrome-oxidase activity of interscapular BAT mitochondria were very low in gerbils compared to mice, whereas in liver and muscle these parameters were not significantly different. Like in fasting animals, the low level of basal energy expenditure of gerbils may be ascribed to low activity of BAT.     

Ultrastructural localization of acetylcholinesterase (AChE) activity in the chicken Harderian gland

Localization of acetylcholinesterase (AChE) was investigated in the chicken Harderian gland at the electron microscopic level. Nerve cells in the pterygopalatine ganglion showed AChE activity. They had a pale and large nucleus which was round or oval in shape. Reaction product of AChE was detected between the nuclear envelopes; in the cisterna of rough endoplasmic reticulum and the lumen of the Golgi lamellae, and on the plasma membrane of the nerve cell. In the interstitium of the gland, nerve fibers showing AChE activity were easily found. They were often seen in the perivascular space and between plasma cells. These nerve fibers had varicosities in contact with plasma cells and the endothelium or the smooth muscle fiber of the blood vessels. AChE-positive varicosities or terminals contained many small clear vesicles (about 50nm in diameter) and a few large dense-cored vesicles (about 100 nm in diameter). No contacts of nerve fibers with acinar cells or the ductal epithelium were observed in the present study. Our data indicate that cholinergic nerves play distinct roles in the regulation of the immune function of the chicken Harderian gland.     

Thermoregulation and metabolism in the smallest African gerbil, Gerbillus pusillus

The effect of temperature on thermoregulation, metabolism, evaporative water loss and thermal conductance was studied in Gerbillus pusillus . Its resting body temperature (TB) was 34·6°C, approximately 5°C higher than the mean ambient temperature (TA) encountered in its burrow. As TA increased above 34°C, its ability to lose heat to the environment decreased. It overcame this problem by tolerating increases in TB to a non-lethal maximum of 41°C, whilst also eliminating increasing quantities of obligate heat by pulmocutaneous evaporation and conduction.
Metabolic rate was 41% lower than that predicted from Kleiber's (1975) allometric equation. This confers a considerable saving in energy in an environment where food is often scarce, whilst simultaneously reducing heat production and the degree of gaseous exchange in the already oxygen-poor and carbon dioxide-rich environment encountered in the plugged burrows of its natural milieu.
Gerbillus pusillus , therefore, does not maintain strict homeothermy and utilizes a labile TB and reduced metabolic rate as an adaptive mechanism for survival in the arid zones of tropical Africa.     

Harderian gland ultrastructure of the black sea bottlenose dolphin (Tursiops truncatus ponticus)

Examination of the Harderian gland structure of the Black Sea bottlenose dolphin, Tursiops truncatus ponticus, at macroscopic, microscopic, and electron microscopic levels shows significant sexual dimorphism. The epithelial cells of male and female glands are different cell types, capable of producing chemically different products. Secretory cells in both sexes contain secretion granules that produce a secretion consisting mainly of proteins and carbohydrates, but thought to be sex-specific in composition. The female glands also contain lipid secretion granules. It is suggested that in the bottlenose dolphin the Harderian gland functions to produce sexually distinct pheromones and may have other physiological activities, e.g., participating in local immunological or endocrine-related reactions. © 1994 Wiley-Liss, Inc.     

Peptidergic innervation of the rat Harderian gland

Summary The immunohistochemical localization of vasoactive intestinal polypeptide (VIP), Neurotensin (NT), cholestokinin (CCK), Neuropeptide Y (NPY), and calcitonin-gene-related peptide (CGRP) in rat Harderian glands was examined. Numerous VIP- and CCK-like immunoreactive nerves were found in close apposition to the acini. Sparse numbers of NT-, NPY-, and CGRP-like immunoreactive nerves were observed in close proximity to the acini and blood vessels. Some VIP-like immunoreactive nerves were shown to be co-localized with acetylcholinesterasepositive cholinergic nerves.     

Frequent Harderian gland adenocarcinomas in inbred white-footed mice (Peromyscus leucopus)

In 1997, three lines of inbred Peromyscus leucopus--GS109A, GS16A1, and GS16B--were acquired by the Peromyscus Genetic Stock Center. Since then, records have been kept on tumors detected by visible inspection of live animals. The inbred lines GS109A and GS16A1 presented tumors with frequencies substantially higher than that of the other inbred line or of random-bred P. leucopus stock. The average age of detection was 456 +/- 75 days (n = 24) for GS109A and 568 +/- 168 days (n = 12) for GS16A1 respectively. Surprisingly, the majority of the tumors (23 of 24 for GS109A and 8 of 12 for GS16A1) appeared to be Harderian gland lesions. During the same time period only a single tumor, a fibrosarcoma, was noted in the other inbred strain (GS16B), and one Harderian gland tumor was detected in the random bred stock. On the basis of the number of animals born to each group, tumor frequencies were approximately 22.7%, 8.3%, 0.67%, and 0.07%, for GS109A, GS16A1, GS16B, and randombred P. leucopus stock, respectively. The periocular tumors appeared to be highly malignant, with elevated mitotic indices, marked anaplasia, and metastases to regional lymph nodes and lungs. The tumors were readily transplantable to other animals of the same line. Among various other species, malignant Harderian gland tumors are relatively rare.     

Peptidergic innervation of the rat Harderian gland

The immunohistochemical localization of vasoactive intestinal polypeptide (VIP), Neurotensin (NT), cholecystokinin (CCK), Neuropeptide Y (NPY), and calcitonin-gene-related peptide (CGRP) in rat Harderian glands was examined. Numerous VIP- and CCK-like immunoreactive nerves were found in close apposition to the acini. Sparse numbers of NT-, NPY-, and CGRP-like immunoreactive nerves were observed in close proximity to the acini and blood vessels. Some VIP-like immunoreactive nerves were shown to be co-localized with acetylcholinesterase-positive cholinergic nerves.