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PubMed1980

Developmental history of nervus terminalis in embryos of insectivorous bats.

Insectivorous bat embryos (Tadarida and Myotis) ranging from 6- to 16-mm C-R length were examined for the presence of the nervus terminalis. These embryos have no vomeronasal nerve with which the nervus terminalis could be confused. The nerve and associated ganglion cells first appear in the 7-mm embryo. As the embryo ages, a gradual increase in nerve size and ganglion cell numbers occurs. In the 13-mm embryo, nerve size and ganglion cell numbers are reduced, and in older embryos both nerve and cells are absent, as in the adult. The ganglion cells arise as clusters from the nasal septal epithelium. The largest number of cell clusters occurs in the 10.5-mm embryo. Their number then decreases and none are present in embryos of 13-mm and longer. These cells migrate centrally along the course of the nerve which accompanies the olfactory nerve from the nasal cavity roof to a level just caudal to the olfactory bulb, where the nervus terminalis turns dorsalward along the medial telencephalic wall surface. Except in the youngest and oldest embryos the nervus terminalis, where present, divides into two or three branches to pierce the hemispheric wall, one usually entering the region of the nucleus olfactorious anterior, and the other(s), the region of the medial septal nucleus. In some cases, several ganglion cells are present along the intrahemispheric course of the nerve fibers. All ganglion cells resemble those in various sensory ganglia, and so, are probably also sensory neurons.

Animals↗
PubMed1980

Distribution of iron in the gastrointestinal tract of the common vampire bat: evidence for macrophage-linked iron clearance.

Iron in the tissues of the digestive tract of the common vampire bat (Desmodus rotundus) has been studied using histochemical, electron microscopic, and autoradiographic methods. This animal is an obligate sanguivore and has a daily intake of dietary iron 800 times that of man. The amount and distribution of tissue iron is not affected by either a single blood meal or starvation but does reflect the degree of siderosis of each animal's liver and spleen. By 7 days after the injection of a trace amount of 55Fe into the peritoneal cavity, labelled siderotic macrophages are present both on the serosa and within the walls of the stomach and intestine. In the lower intestine, such cells can be derived from the germinal centers of Peyer's patches. Siderotic macrophages are often situated in the lamina propria under areas of siderotic epithelium. Label is also present in the apical cytoplasm of mucosal epithelial cells, a region of abundant siderosomes. The ultrastructure of these organelles is extremely variable. Accumulations of membranous whorls and stacks, "stippled bodies," ferritin molecules, and larger "ferruginous" complexes are bounded by one or a number of membranes. Iron is excreted when these epithelial cells are desquamated into the gut lumen. Similar Prussian blue-positive granules are present in the feces. Unlike other glandular cells, the parietal cells of the fundic caecum are siderotic. Their cytoplasm contains abundant siderosomes and ferritin with accumulations of amembranous ferritin bodies in the intracellular canalicular spaces. Prussian blue-positive granules are present in the lumens of fundic glands.

Animals↗
PubMed1984

Seasonal variations in pituitary thyrotropes of the hibernating bat Myotis lucifugus lucifugus: an immunohistochemical study.

Pituitary thyrotropes were identified throughout the year in the hibernating bat Myotis lucifugus lucifugus by means of light microscopic immunohistochemistry. These cells occupied a small proportion of the volume of the pars distalis (mean = 1.36% in males; mean = 1.52% in females) and exhibited a limited distribution pattern that was characteristic of all animals examined. Cells that were immunoreactive with an antiserum directed against the beta subunit of thyroid-stimulating hormone were most numerous in the median rostral and ventral regions; they were scarce or absent in the dorsal portion of the gland and in the extreme lateral wings. No significant seasonal variations were observed in this cell population in females. In males, however, immunoreactive thyrotropes occupied a significantly larger proportion of the pars distalis in June (following arousal from hibernation than at other times of year. No evidence of involution was observed in these anterior pituitary cells in either males or females during hibernation.

Animals↗
PubMed1985

The bat pituitary cleft: phasic production and release of secretory granules by microvillous cells.

The ultrastructure of the two types of cells, ciliated and microvillous, lining the wall of the bat pituitary cleft was examined at different periods during the annual life cycle. Ciliated lining cells remained unchanged in structure throughout the yearly activity cycle. In contrast, microvillous lining cells exhibited striking cyclic morphological changes. Throughout the active phase of the life cycle and during most of the hibernating period, the structure of microvillous cells is unchanged. However, toward the end of hibernation, the cells produce and store large numbers of round to ovoid dense secretory granules. Just prior to arousal, the microvillous cells are packed with secretory granules. At arousal, the cells undergo marked degranulation; the granules appear to be discharged into the lumen of the cleft. Degranulation is followed by a period of proliferation of rough endoplasmic reticulum, the cavity of which is often filled with large paracrystalline inclusions. Within 1 month, microvillous cells return to a resting state and are devoid of secretory granules.

Animals↗
PubMed1985

Activation of osteoclasts and the repopulation of bone surfaces following hibernation in the bat, Myotis lucifugus.

In previous studies of the adult bat, Myotis lucifugus, bone loss that occurred during the hibernating period was attributed to osteocytic osteolysis, rather than osteoclastic activity. We have used histochemistry and light and electron microscopy to determine the functional state of the skeleton during the hibernating period. We find that during hibernation the marrow cavity of the long bones is filled with lipid deposits interspersed with vascular sinusoids containing mononuclear cells and red blood cells. The lipid deposits are found within fat cells and at extracellular sites. Hematopoietic cells are absent, osteoclasts are absent, and the bone surfaces are covered with quiescent bone-lining cells. Osteocytes retain their structural integrity and maintain canalicular systems with the bone lining cells and with other osteocytes. During the arousal period, osteoclasts reappear on the bone surface, followed in time by increased numbers of osteoblast-like cells. Perivascular cells undergo structural hypertrophy. Many mononuclear cells are now found in extravascular sites. The lipid content in the marrow is gradually reduced and replaced by hematopoietic cells. Each of these events occurs in a repeatable sequence that is related to the state of hibernation of Myotis lucifugus.

Animals↗
PubMed1987

Occurrence of cells containing paracrystalloid material in the intestinal lamina propria of the hibernating bat Myotis lucifugus.

A light and electron microscope study of the small intestine of the little brown bat, Myotis lucifugus, was carried out at several stages in the animal's annual life cycle. An unusual morphological observation was the presence of cells in the lamina propria of the small intestine which were packed with a conspicuous basophilic granular material that appeared crystalline. Moreover, such cells were present only during the hibernation period and were therefore called "hibernation crystalloid" (HC) cells. By light microscopy, the crystal-like material was not sudanophilic, did not stain for nucleic acids, and did not contain acid phosphatase; it did show reactivity when stained by the periodic acid-Schiff procedure. By electron microscopy, the crystal-like material was found to be present in smooth, membrane-enclosed vacuoles along with an amorphous, dense granular substance. The crystalline material occasionally formed rigid-appearing rods that reached lengths of 10 microns. The crystal-containing cells were contacted by axonal varicosities. It is suggested that these innervated HC cells represent a unique cell type with a gastrointestinal function, yet to be determined, that may be related to hibernation.

Animals↗
PubMed1988

Innervation and gap junction formation in the myometrium of pregnant little brown bats, Myotis lucifugus.

Pregnant Myotis lucifugus were captured in mist nets set outside a large maternity colony and, in most cases, were examined 12-15 hours later. Anterior and posterior halves of uteri were pinned to dental wax and either incubated in glyoxylic acid to produce adrenergic nerve fluorescence, or fixed in buffered glutaraldehyde for electron microscopy. Blood was collected for radioimmunoassay of plasma progesterone. We found no evidence of decreased nerve fluorescence even in late pregnancy when plasma progesterone levels were 10-20 times preovulatory values. Ultrastructural examination also showed no evidence of damage to, or destruction of, nerves in the myometrium. However, we did find gap junctions between myometrial muscle cells during the periparturient period in both normal and aborting bats. Gap junctions began to form several days before term, increased in number until parturition, then decreased dramatically within a day or two thereafter. The percentage of muscle cell plasma membrane involved in gap junction formation was closely correlated with plasma progesterone levels, although whether this is causal or coincidental is not certain. These data do not agree with the conclusions drawn from observations in other mammals that a disappearance of adrenergic nerves from the myometrium is associated with the initiation of parturition, or that gap junction formation is associated with changes in nerve function. They do, however, lend further support to the hypothesis that there is neurogenic control of myometrial contractility in M. lucifugus uteri at term.

Animals↗
PubMed1988

Ultrastructural immunocytochemical studies of the localization and distribution of somatostatin, calcitonin, calcitonin gene-related peptide, and substance P in the bat thyroid follicle.

Electron microscope immunocytochemistry was used to determine the intracellular localization and distribution among follicular elements of four peptides: calcitonin, somatostatin, calcitonin gene-related peptide (CGRP), and substance P in the thyroid glands of bats captured in the prehibernation phase of their annual life cycle. Previous studies have shown that this period of the hibernation-activity cycle is characterized by the accumulation and storage of secretory granules in parafollicular cells. Sites of binding of primary antisera to each of the four peptides were identified by means of affinity-purified secondary antisera directly coupled to colloidal gold particles. Calcitonin and somatostatin immunoreactivities were found in all parafollicular cells examined and in every secretory granule within these cells. CGRP was also found in all parafollicular cells examined (n = 75) but only in about half of their secretory granules. In contrast to these peptides, substance P immunoreactivity was not found in any parafollicular cells, but was localized exclusively in nerve endings within the basement membrane of the follicle.

Animals↗
PubMed1992

Fine structural characteristics of the zone of contact between the lower infundibular stem and the pituitary pars distalis in the little brown bat, Myotis lucifugus.

The purpose of this study was to examine the morphological characteristics of the pituitary gland in the little brown bat that might influence mechanisms of hypothalamic releasing hormone transport. Paraffin sections were prepared from whole crania to examine in situ the orientations of the three parts of the adenohypophysis (pars distalis, pars intermedia, and pars tuberalis) relative to the components of the neurohypophysis (pars nervosa and infundibular stem) and the basal hypothalamus. Of particular interest was the observation that the axis of the infundibular stem is directed posteriorly from the median eminence and occupies a depression in the dorsal surface of the pars distalis as it approaches the pars nervosa. Previous studies have revealed that neuronal projections containing releasing hormones extend into the infundibular stem in this species. Therefore, we conducted a fine structural study to determine whether the zone of contact between the infundibular stem and the pars distalis could represent a site of specialized interaction between hypophysiotropic hormones and their target cells. The results show that the sparse connective tissue along this boundary contains abundant fenestrated capillaries that are exposed on one side to neurosecretory axons and on the other to cells of the pars distalis. Furthermore, secretory cells nearest these capillaries exhibit ultrastructural evidence of heightened secretory activity. We conclude that the fine structural characteristics of this zone are consistent with localized mechanisms of releasing hormone transport.

Animals↗
PubMed1993

Giant mitochondria in the seromucous secretory cells of the accessory submandibular gland of the long-haired fruit bat, Stenonycteris lanosus.

Giant mitochondria, measuring up to 6.4 microns in diameter, are present in the seromucous secretory cells of the accessory submandibular gland of the long-haired fruit bat, Stenonycteris lanosus. These mitochondria, as well as all of the smaller ones in the same cells, contain in their matrix compartment an abundance of 33 nm threads that probably consist of protein. Some mitochondria, regardless of size, contain 5 nm helical filaments within an expanded crista. Despite their altered morphology, the enlarged mitochondria in the accessory submandibular gland of S. lanosus must be able to function normally in energy metabolism, since the secretory cells in which they are found elaborate numerous secretory granules.

Animals↗
PubMed1993

Unique features of the cauda epididymidal epithelium of hibernating bats may promote sperm longevity.

Measurements of extremely high osmolalities in cauda epididymidal fluids of hibernating bat species led to an investigation of the junctional complex morphology of the epithelium of this sperm storage site. Freeze fracture replicas revealed the presence, at certain times of the year, of a tight junction architecture that resembled that traditionally thought to be exclusive to the blood-testis barrier, the strongest permeability barrier in the body. It is hypothesized that seasonal establishment of these specialized Sertoli cell-like tight junctions is necessary to the maintenance of the high osmotic state of the luminal environment, allowing for the prevention of dilution of its contents by paracellular routes and its protection from bursting under the osmotic pressure contained within.

Animals↗
PubMed2003

Ultrastructural aspects of the follicular cells of the pars tuberalis in bats related to the seasonal cycle.

The topography and structure of the follicular cells and the follicular cavity of the hypophyseal pars tuberalis (PT) were studied in adult hibernating bats (Pipistrellus pipistrellus and Rhinolophus ferrumequinum) of both sexes, during the annual seasonal cycle and the reproductive cycle. The follicular cells were found to be organized around a central cavity. They showed a polyhedral shape and apical microvilli protruding into central cavities. During hibernation, the follicular cells showed active cytoplasmic organelles, clusters of glycogen particles, and lipid droplets. In the supranuclear cytoplasm, 9+2 type cilia, some dense bodies, microvesicular vacuoles, and thin actin-like filaments (rather scarce during autumn) were detected. The contents of the follicular cavity showed well-defined ultrastructural seasonal characteristics, with a colloid-like aspect during awakening and a strongly granular aspect during autumn oestrus and mating. Positive staining for PAS and paraldehyde fuchsin, and a marked reaction to lectins PHA-L4, MAM, and RCA 60 suggested the presence of sialo-glycoproteins in the follicular cavities. Both follicular and endocrine PT-specific cells appeared to mark the boundary of follicular cavities. This finding suggests that the follicular cavity contents are comprised of both types of cells, rather than by cell fragmentation or degeneration products.

Animals↗
PubMed2003

Expression of the Kv1.1 ion channel subunit in the auditory brainstem of the big brown bat, Eptesicus fuscus.

Voltage-gated potassium channels play an important role in shaping membrane properties that underlie neurons' discharge patterns and the ways in which they transform their input. In the auditory system, low threshold potassium currents such as those created by Kv1.1 subunits contribute to precise phaselocking and to transient onset responses that provide time markers for temporal features of sounds. The purpose of the present study was to compare information about the distribution of neurons expressing the KV 1.1 in the brainstem auditory nuclei with the distribution of neurons with known functional properties in the auditory system of the big brown bat, Eptesicus fuscus. We used immunocytochemistry and light microscopy to look at the distribution of Kv1.1 subunits in the brainstem auditory nuclei. There was prominent expression in cell types known to contain high levels of Kv1.1 in other species and known to respond to auditory signals with high temporal precision. These included octopus cells and spherical bushy cells of the cochlear nucleus and principal neurons of the medial nucleus of the trapezoid body. In addition, we found high levels of Kv1.1 in neurons of the columnar subdivision of the ventral nucleus of the lateral lemniscus and in ventral periolivary cell groups. Neurons with high levels of Kv1.1 were differentially distributed in the intermediate nucleus of the lateral lemniscus and in the inferior colliculus, suggesting that these structures contain functionally distinct cell populations, some of which may be involved in high-precision temporal processing.

Action Potentials↗
PubMed2001

The inner ear macular sensory epithelia of the Daubenton's bat.

The inner ear macular sensory epithelia of the Daubenton's bat were examined quantitatively to estimate the area and total number of hair cells. Ultrastructural examination of the sensory epithelium reveals two main types of hair cells: the chalice-innervated hair cell and the bouton-innervated hair cell. The existence of an intermediate type, with a nerve ending covering the lateral side of the hair cell, indicates that the chalice-innervated hair cells are derived from bouton-innervated hair cells. Thus, at least a part of the bouton-innervated hair cells forms a transitional stage. A number of immature as well as apoptotic hair cells were observed. It is suggested that a continuous production of new hair cells takes place in mature individuals, probably based on transdifferentiation of supporting cells.

Acoustic Maculae↗
PubMed2007

Parallel thalamocortical pathways for echolocation and passive sound localization in a gleaning bat, Antrozous pallidus.

We present evidence for parallel auditory thalamocortical pathways that serve two different behaviors. The pallid bat listens for prey-generated noise (5-35 kHz) to localize prey, while reserving echolocation [downward frequency-modulated (FM) sweeps, 60-30 kHz] for obstacle avoidance. Its auditory cortex contains a tonotopic map representing frequencies from 6 to 70 kHz. The high-frequency (BF > 30 kHz) representation is dominated by FM sweep-selective neurons, whereas most neurons tuned to lower frequencies prefer noise. Retrograde tracer injections into these physiologically distinct cortical regions revealed that the high-frequency region receives input from the suprageniculate (SG) nucleus, but not the ventral division of the medial geniculate body (MGBv), in all experiments (n = 9). In contrast, the low-frequency region receives tonotopically organized input from the MGBv in all experiments (n = 16). Labeling in the SG was observed in only two of these experiments. Both cortical regions also receive sparse inputs from medial (MGBm) and parts of the dorsal division (MGBd) outside the SG. These results show that the low- and high-frequency regions of a single tonotopic map receive dominant inputs from different thalamic divisions. Within the low-frequency region, most neurons are binaurally inhibited, and an orderly map of interaural intensity difference (IID) sensitivity is present. We show that the input to the IID map arises from topographically organized projections from the MGBv. As observed in other species, a frequency-dependent organization is observed in the lateromedial direction in the MGBv. These data demonstrate that MGBv-to-auditory cortex connections are organized with respect to both frequency and binaural selectivity.

Action Potentials↗
PubMed1985

Functional organization of the cochlear nucleus of rufous horseshoe bats (Rhinolophus rouxi): frequencies and internal connections are arranged in slabs.

The functional organization of the cochlear nucleus (CN) was studied with physiological recording and anatomical tracing techniques. Recordings were made from single CN neurons to examine their temporal firing patterns to tone burst stimuli and their frequency tuning characteristics. Recording loci of individual neurons were carefully monitored in order to understand how the functional properties of a cell relate to its location within the CN. We found that tonal frequencies were systematically represented in each of the three CN divisions (anteroventral, AVCN; posteroventral, PVCN; dorsal, DCN). Eight temporal response patterns were observed in CN neurons when stimulated at units' best excitatory frequencies (BF). With a few exceptions, neurons in each CN division could generate all eight firing patterns with different distributions for the three division. A focal injection of horseradish peroxidase (HRP), at the end of the physiological study, to a group of neurons possessing a similar BF in one CN division resulted in anterograde labeling of nerve terminals in the other two divisions at precisely the areas where the same frequency band was processed in these divisions. Labeled terminals in each division were closely congregated in the form of a thin slab. The slab orientation was division specific whereas its location was frequency specific, which could be predicted on the basis of physiological data. HRP injections into the DCN also resulted in retrograde labeling of somata in the AVCN and PVCN. On the other hand, only DCN neurons were retrogradely labeled when HRP was injected into the AVCN or the PVCN. These data showed how the three CN divisions are internally connected. Furthermore, retrogradely labeled cells occupied the same slabs where we found anterogradely labeled nerve terminals. Additionally, in a group of bats, HRP was injected into various functionally (i.e., BF) identified regions of the central nucleus of the inferior coliculus (IC) to clarify the type and location of CN projecting neurons. Retrogradely labeled cells in individual CN divisions likewise were arranged in slabs whose locations in the CN nuclei depended on the BFs of neurons at the injection site in the IC. These results show that slabs represent units of functional organization (i.e., tonal frequency, local connection and central projection) in the CN.

Animals↗
PubMed1985

Topographic organization of facial motoneurons to individual pinna muscles in rat (Rattus rattus) and bat (Rousettus aegyptiacus).

The location and number of motoneurons to individual pinna muscles were determined by retrograde transport of horseradish peroxidase in rat and flying fox. The degree of ear mobility differs considerably between these species in that rats perform simpler ear movements while flying foxes move their pinnae in a sophisticated way. Five pinna muscles were investigated in each species. Motoneurons lay within the medial subdivision of the facial motor nucleus extending over its entire rostrocaudal length. They were topographically organized; however, a somatotopic order could not be observed. With one exception homologous pinna muscles were represented in corresponding areas in both species, supporting the idea of a common representation of ear muscles in mammals. In rat, motoneuron pools overlapped considerably, whereas in flying fox overlap was minute. A total of 1,110 and 1,646 motoneurons were labeled in rat and flying fox, respectively. We conclude that the higher number of pinna motoneurons in the latter species in addition to the more clear-cut topography provide the structural substrates that underlie differences in the quality of ear movements as seen in bats vis-a-vis other mammals.

Animals↗
PubMed1988

Connections of the superior olivary complex in the rufous horseshoe bat Rhinolophus rouxi.

In the rufous horseshoe bat (Rhinolophus rouxi), the superior olivary complex contains four main divisions. In comparison with other species, the most lateral division is clearly homologous to the lateral superior olive (LSO); the most medial division is homologous to the medial nucleus of the trapezoid body (MNTB). Lying between these landmarks, in approximately the position of the medial superior olive (MSO) of other mammals, are two additional divisions that are cytoarchitecturally distinct from one another yet do not greatly resemble the MSO of nonecholocating mammals such as the cat. We refer to these nuclei as the dorsal medial superior olive (DMSO) and the ventral medial superior olive (VMSO). We examined the afferent and efferent connections of all of these cell groups with retrograde and anterograde transport of WGA-HRP from the superior olivary complex. In the same animals we recorded the binaural response properties of single units in the superior olivary complex. Virtually all units recorded in LSO were excitatory to the ipsilateral ear and inhibitory to the contralateral ear (EI); all of the units sampled in the MNTB and most of those sampled in the VMSO responded only to the contralateral ear (OE). In DMSO the binaural properties of units were varied: the number of units that were inhibitory to the ipsilateral ear and excitatory to the contralateral ear (IE) was about equal to the number of units excitatory to both ears (EE); a few units had OE responses; no units had EI responses. Connectional correlates for these binaural response properties are seen in the patterns of retrograde transport from WGA-HRP injections in the divisions of the superior olive. The LSO receives projections from the ipsilateral cochlear nucleus and MNTB; MNTB receives projections from the contralateral cochlear nucleus. The DMSO and VMSO both receive bilateral projections from the cochlear nuclei. The results of retrograde and anterograde transport suggest that VMSO, in addition, receives projections from the ipsilateral MNTB. The LSO, DMSO, and VMSO all project to the ventral two-thirds of the central nucleus of the inferior colliculus, and their targets are approximately coextensive. However, the LSO projects bilaterally to the inferior colliculus, whereas the medial cell groups project mainly ipsilaterally.

Acoustic Stimulation↗