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PubMed1979

Competitive interaction between foreign nerves innervating frog skeletal muscle.

1. Competition between two foreign nerves innervating frog skeletal muscle has been studied by using pairs of somatic motor nerves (s.m.n.s) or one s.m.n. and the preganglionic splanchnic nerve (s.p.n.) implanted into a denervated sartorius muscle that has been transplanted to the lymph sac of the back. 2. A single s.m.n. implanted into the muscle succeeded in innervating essentially every fibre within 2--3 months; tetanic stimulation of the nerve elicited 9--100% of the maximal direct tetanus tension. Most of the e.p.p.s were suprathreshold, since a single indirect stimulus evoked a twitch 60--100% as large as that to a direct stimulus. 3. If two s.m.n.s were implanted simultaneously, tetanic stimulation of either elicited 80--100% of the maximal tension to direct stimulation. If one nerve was implanted 2--3 months before the other, the second, although usually less effective than the first, normally innervated 50--100% of the fibres, with approximately the same time course of innervation as a single s.m.n. 4. Mutual synaptic repression was seen on examination of twitch tensions. With either simultaneous or staggered innervation, stimulation of each s.m.n. resulted in a twitch of 30--50% of the total direct twitch tension, with little overlap between the fields driven by the two nerves. Intracellular recordings showed that the distribution of subthreshold and spike-producing e.p.p.s reflected the existence of separate twitch fields. Even if one s.m.n. was implanted several months before the other and had time to establish suprathreshold junctions on most muscle fibres, an s.m.n. implanted later was able to reduce sharply the effectiveness of many junctions from the earlier nerve while itself innervating most muscle fibres. 5. The subthreshold e.p.p.s had low quantal content, typically ten or fewer quanta/e.p.p. The min e.p.p. frequency was very low, while min e.p.p. amplitude appeared to be normal. 6. In the vast majority of muscle fibres, junctions from the two nerves were not within recording distance of each other. Hence, we infer that the competitive interaction was mediated somehow via the muscle fibre. 7. The preganglionic splanchnic nerve, which also successfully reinnervated frog skeletal muscle, competed with a foreign s.m.n. in ways which differ qualitatively from the competition by a second s.m.n. In the presence of a s.m.n., synapses of the s.p.n. were almost universally subthreshold. However, if the s.p.n. was implanted 2--3 months before the s.m.n., the s.m.n. was prevented for several months from innervating fibres driven by the s.p.n. This delay in s.m.n. reinnervation was greater than if the first nerve implanted was also an s.m.n. 8. After 6--8 months of dual innervation by s.m.n. and s.p.n., the s.m.n. became almost totally dominant. However, if the s.m.n. was then sectioned, the s.p.n. became as effective, within approximately 1 week, as it would have been in the absence of the s.m.n.

Animals↗
PubMed1979

On the purpose of selective innervation of guinea-pig superior cervical ganglion cells.

Preganglionic axons arising from different levels of the mammalian spinal cord make preferential connexions with different classes of superior cervical ganglion cells (Langley, 1892, 1900; Njå & Purves, 1977a). For example, preganglionic axons from the first thoracic segment (T1) make relatively strong connexions with ganglion cells activating end-organs of the eye; conversely, axons arising from T4 selectively innervate ganglion cells projecting to the ear. In the present work we have asked whether this selectivity reflects the function of the pre- and post-synaptic cells, and aspect of their respective positions, or some other criterion. 1. End-organs with different functions at the same locus (the eye) respond to stimulation of the same ventral roots; end-organs of a single modality (hairs or blood vessels) at different positions, however, tend to be activated by different spinal segments. Thus the segmental innervation of ganglion cells is correlated with the position rather than the function of post-ganglionic targets. 2. The role of target position in ganglion cell innervation was examined directly by recording from neurones sending axons to different destinations. Superior cervical ganglion cells running dorso-medially in a spinal nerve receive, on average, innervation from more caudal segments than cells projecting ventro-laterally. 3. These selective connexions do not depend on intraganglionic cell position: neurones located at different points along the major axes of the superior cervical ganglion receive, on average, the same segmental innervation. In accord with this observation, retrogradely labelled neurones innervating a particular target such as the eye or ear are widely and randomly distributed within a large portion of the ganglion. Thus the importance of post-ganglionic target position in ganglion cell innervation is not simply a reflexion of ganglionic topography. 4. We conclude that one purpose of the selective connexions in the superior cervical ganglion is to bring together preganglionic axons arising from different levels of the spinal cord and ganglion cells whose axons innervate particular regions of the superior cervical territory.

Action Potentials↗
PubMed1980

On the predominantly single innervation of submandibular ganglion cells in the rat.

1. Simultaneous intracellular recordings were made from pairs of submandibular ganglion cells to examine why each of these neurons is generally innervated by a single preganglionic axon. 2. Impalements made within isolated clusters of two to fifty cells showed that a preganglionic axon typically innervates several neurons within a group. 3. The neurones innervated by a particular axon tended to be intermingled with other neurons; some neurons were innervated by an axon that was not shared by any of their immediate neighbours. 4. These results indicate a mechanism that causes a preganglionic axon to innervate exclusively many of the neurones it contacts, presumably by successful competition with nearby axons that initially innervate the same cells and continue to provide innervation to neighbouring neurones. 5. Re-innervation of adult ganglion cells shows that this mechanism persists or can be reactivated in maturity.

Action Potentials↗
PubMed1981

Restoration of focal multiple innervation in rat muscles by transmission block during a critical stage of development.

1. The soleus, extensor digitorum longus and peroneus tertius muscles of the hind leg were paralysed by botulinum toxin injection in neonatal rats varying in age from 8 to 31 days. The soleus muscle was similarly paralysed in adult rats.2. Muscles were excised after different periods of block, neuromuscular transmission was assessed in vitro, and the nerve terminal size and amount of terminal sprouting and multiple innervation determined histologically using silver (Ag) and zinc iodide-osmium (ZIO) tetroxide stains.3. Recovery from the block induced by botulinum toxin was more rapid in immature multiply-innervated muscles than in muscles of older rats in which all multiple innervation had been eliminated.4. Terminals in muscles blocked during the first month after birth grew rapidly in size and developed a characteristic granulose morphology in the first few days following the block. This change did not occur in fully adult rat solei.5. Sprouts growing from the terminals were infrequent in muscles paralysed before day 16. Terminal sprouts were more frequent in muscles paralysed between 16 and 31 days of age, but were very infrequent in adult solei.6. In confirmation of Thompson, Kuffler & Jansen (1979) paralysis begun at 10 days was followed initially by a continued fall in multiple innervation detected electrophysiologically. After 2 days the percentage of muscle fibres with more than one input rose. The extra inputs did not come from terminal sprouts. They innervated the single synaptic site on each muscle fibre as they do during normal synaptogenesis.7. The amount of multiple innervation regained 5-10 days after the start of paralysis became progressively less the later paralysis started and was approximately equal to the level existing at the time the block was begun. Thus paralysis starting on or after day 16 (when all excess inputs have normally withdrawn) caused no return of multiple innervation.8. The return of multiple inputs and the swelling of the nerve terminals are presumably responses of the motoneurone to growth stimuli from inactive muscle. It is not clear whether the return of multiple innervation in the 10-15 day old rats is due to reactivation of inputs still in close contact with the end-plate before withdrawal or to regrowth of partly retracted nerve branches.9. A parallel is drawn between the limited period when inactivity can reinstate multiple innervation, and the critical period in the developing visual cortex.

Aging↗
PubMed1985

The selective innervation of guinea-pig superior cervical ganglion cells by sprouts from intact preganglionic axons.

If the guinea-pig superior cervical ganglion is partially denervated in a way which spares some preganglionic axons arising from each of the spinal cord segments which normally innervate this ganglion (C8-T7), sprouting of the intact preganglionic axons occurs without a loss of selective end-organ responses to stimulation of individual ventral roots (Maehlen & Njå, 1981). In the present work we examine the selective innervation of individual ganglion cells by ventral roots after sprouting and compare it to that in normal ganglia. After sprouting the pattern of ganglion cell innervation by the intact preganglionic axons shows some of the features typical of normal ganglia. Thus each ganglion cell is strongly innervated by one or two neighbouring spinal cord segments, with the adjacent segments contributing a synaptic influence which diminishes with distance from the dominant one. Acutely after the partial denervation there is a tendency for the rostral segments to innervate ganglion cells more strongly than do caudal segments, compared to the situation in normal ganglia. The same is true following sprouting. The pattern of ganglion cell innervation observed after sprouting can be explained if the affinities of ganglion cells for innervation from particular spinal levels are assumed to be unchanged and the shift in the relative availability of different preganglionic axons, caused by the partial denervation, is taken into account. This view was substantiated by statistical analysis based on a model of selective synapse formation in the guinea-pig superior cervical ganglion. We conclude that the ability of individual ganglion cells to distinguish preganglionic axons arising from different spinal levels is maintained during sprouting. Moreover, the way in which selective recognition and the availability of different preganglionic axons combine to produce particular patterns of innervation appears to be similar in normal development and after partial denervation in maturity.

Animals↗
PubMed1988

Somatotopy in the segmental innervation of the cat diaphragm.

A somatotopic organization in the segmental innervation of the cat diaphragm (DIA) was determined using evoked electromyographic responses and glycogen depletion of stimulated type II muscle fibers. With the use of the glycogen depletion method, the specific location and proportion of muscle fibers innervated by the fifth (C5) or sixth (C6) cervical ventral roots were determined for different regions of the DIA. The sternal and ventral portions of the costal and crural DIA regions were innervated primarily by C5. The dorsal portions of both the costal and crural regions were innervated primarily by C6. Thus the somatotopic organization in the segmental innervation of the DIA was not correlated with the anatomic division of the sternal, costal, and crural regions. Instead, the somatotopic projections of cervical ventral roots were organized in the ventrodorsal axis of each DIA region. This topographical pattern resulted in an extensive overlap of the DIA territories innervated by C5 and C6. Within a region, the fibers innervated by a specific ventral root were not randomly distributed but often followed fascicle divisions. This frequently resulted in a wide range in the proportion of fibers innervated by a ventral root even within a specific region.

Animals↗
PubMed1990

Motoneuron and muscle-unit properties after long-term direct innervation of soleus muscle by medial gastrocnemius nerve in cat.

1. This study addresses the following questions. 1) In a previous experiment, when the combined lateral gastrocnemius-soleus nerve was cross-innervated by the medial gastrocnemius (MG) nerve, was the predominance of slow muscle units in soleus muscle a result of selective routing of slow motor axons into soleus? 2) Is MG-nerve-induced conversion of soleus muscle fibers from slow to fast more complete at very long (18 mo vs. 9-11 mo) postoperative times? 3) Do MG motoneurons that cross-innervate soleus muscle recover their normal membrane electrical properties at very long postoperative times? 2. The proximal portion of approximately one-third of the MG nerve was coapted directly with the distally isolated soleus nerve. The MG muscle remained innervated by the unoperated portion of the MG nerve. At 6, 10, or 18 mos postoperative, motoneuron and/or muscle-unit properties were determined for MG motoneurons innervating MG, soleus, or neither muscle, and for axotomized soleus motoneurons. 3. In the partially denervated MG muscle, the proportions of motor units of each type were normal. This suggests that the population of MG motor axons that had been directed to the soleus nerve also contained a representative distribution of MG motoneuron types. 4. Most motor units (74%) in cross-innervated soleus (Xsoleus) were type S (based on muscle-unit contractile properties), in spite of the soleus nerve's having been cross-connected by approximately 75% fast MG motoneurons. Thus, even at very long postoperative times, slow soleus muscle units resisted conversion by fast MG motoneurons. 5. Thirty-two percent of MG motoneurons that had been cross-connected to soleus nerve elicited no measurable muscle contraction, compared with approximately 10% in previous reinnervation experiments in which the MG nerve was coapted with the MG or lateral gastrocnemius-soleus nerve. Thus MG motoneurons may be disadvantaged in their ability to innervate soleus muscle fibers. 6. It appears that at long postoperative times, those fast MG motoneurons tha had innervated large soleus muscle units had failed to convert those muscle fibers to fast types and had failed also to recover their normal motoneuron electrical properties. Conversion and recovery did occur for fast MG motoneurons that innervated small soleus muscle units and for slow MG motoneurons.

Animals↗
PubMed1997

Three-dimensional analysis of vestibular efferent neurons innervating semicircular canals of the gerbil.

Anterograde labeling techniques were used to examine peripheral innervation patterns of vestibular efferent neurons in the crista ampullares of the gerbil. Vestibular efferent neurons were labeled by extracellular injections of biocytin or biotinylated dextran amine into the contralateral or ipsilateral dorsal subgroup of efferent cell bodies (group e) located dorsolateral to the facial nerve genu. Anterogradely labeled efferent terminal field varicosities consist mainly of boutons en passant with fewer of the terminal type. The bouton swellings are located predominately in apposition to the basolateral borders of the afferent calyces and type II hair cells, but several boutons were identified close to the hair cell apical border on both types. Three-dimensional reconstruction and morphological analysis of the terminal fields from these cells located in the sensory neuroepithelium of the anterior, horizontal, and posterior cristae were performed. We show that efferent neurons densely innervate each end organ in widespread terminal fields. Subepithelial bifurcations of parent axons were minimal, with extensive collateralization occurring after the axons penetrated the basement membrane of the neuroepithelium. Axonal branching ranged between the 6th and 27th orders and terminal field collecting area far exceeds that of the peripheral terminals of primary afferent neurons. The terminal fields of the efferent neurons display three morphologically heterogeneous types: central, peripheral, and planum. All cell types possess terminal fields displaying a high degree of anisotropy with orientations typically parallel to or within +/-45 degrees of the longitudinal axis if the crista. Terminal fields of the central and planum zones predominately project medially toward the transverse axis from the more laterally located penetration of the basement membrane by the parent axon. Peripheral zone terminal fields extend predominately toward the planum semilunatum. The innervation areas of efferent terminal fields display a trend from smallest to largest for the central, peripheral, and planum types, respectively. Neurons that innervate the central zone of the crista do not extend into the peripheral or planum regions. Conversely, those neurons with terminal fields in the peripheral or planum regions do not innervate the central zone of the sensory neuroepithelium. The central zone of the crista is innervated preferentially by efferent neurons with cell bodies located in the ipsilateral group e. The peripheral and planum zones of the crista are innervated preferentially by efferent neurons with cell bodies located in the contralateral group e. A model incorporating our anatomic observations is presented describing an ipsilateral closed-loop feedback between ipsilateral efferent neurons and the periphery and an open-loop feed-forward innervation from contralateral efferent neurons. A possible role for the vestibular efferent neurons in the modulation of semicircular canal afferent response dynamics is proposed.

Animals↗
PubMed1996

Innervation patterns of the lateral line stitches of the clawed frog, Xenopus laevis, and their reorganization during metamorphosis.

We quantitatively examined the afferent innervation pattern of the lateral line stitches of both larval and postmetamorphotic clawed frogs, Xenopus laevis, using a silver staining technique. We also studied the relevance of the number of neuromasts in a stitch to physiological properties, recording afferent activity with an electrode inserted directly into the neuromast. The innervation pattern changed during early metamorphosis, the fiber thickness increasing after the reorganization. We found three different innervation patterns: in type A stitches, the same two afferent fibers innervate all neuromasts; in type B stitches, one or two fibers innervate more than one stitch; in type C stitches, three to six fibers innervate a stitch. The distribution of the different types of stitches varied in different parts of the body. The frequency of type A stitches differed between larval trunk and larval head. For both larvae and juveniles, type B stitches were more frequent on ventral than dorsal areas, while type C stitches were more frequent on the head than on the trunk. Electrophysiological experiments indicated that the sensitivity of an afferent fiber increases with the number of neuromasts it innervates. This increase and the variation in innervation patterns shows that the single afferent fiber, not the stitch, is the functional unit of the lateral line periphery.

Afferent Pathways↗
PubMedDate not supplied

The age of striatum determines the pattern and extent of dopaminergic innervation: a nigrostriatal double graft study.

In animal models of Parkinson's disease, transplanted fetal mesencephalic dopaminergic neurons can innervate the dopamine-depleted host brain, but it is unclear why large portions of the host striatum are left uninnervated. During normal development, the dopaminergic innervation first occurs in the form of a dense patchy pattern in the striatum, followed by a widespread nerve fiber network. Using intraocular double grafts we have investigated dopaminergic growth patterns initiated when ventral mesencephalic grafts innervate striatal targets. The fetal lateral ganglionic eminence was implanted into the anterior eye chamber. After maturation in oculo, fetal ventral mesencephalon was implanted and placed in contact with the first graft. In other animals the two pieces of tissue were implanted simultaneously. Tyrosine hydroxylase (TH) immunohistochemistry revealed a pattern of dense TH-positive patches throughout the total volume of the striatal grafts in simultaneously transplanted cografts, while a widespread, less dense, pattern was found when mature striatal transplants were innervated by fetal dopaminergic grafts. To investigate which type or types of growth patterns that developed after grafting to striatum in situ of an adult host, fetal ventral mesencephalic tissue was implanted into the lateral ventricle adjacent to the dopamine-lesioned striatum. After maturation of the mesencephalic graft, the fetal lateral ganglionic eminence was implanted into the reinnervated part of the host striatum. TH immunohistochemistry revealed a few nerve fibers within the striatal graft and the growth pattern was of the widespread type. In conclusion, grafted dopaminergic neurons preferably innervate mature striatum with a widespread sparse nerve fiber network, while the innervation of the immature striatum occurs in the form of dense patches. Furthermore, when the patchy pattern is formed, the total volume of the striatal target is innervated while growth of the widespread type terminates prior to reaching distal striatal parts. Thus, the growth pattern seems essential to the final volume that is innervated. Once the widespread growth pattern is initiated, the presence of immature striatum does not change the dopaminergic growth pattern.

Age Factors↗
PubMed2003

Lack of Bdnf and TrkB signalling in the postnatal cochlea leads to a spatial reshaping of innervation along the tonotopic axis and hearing loss.

Members of the neurotrophin gene family and their high-affinity Trk receptors control innervation of the cochlea during embryonic development. Lack of neurotrophin signalling in the cochlea has been well documented for early postnatal animals, resulting in a loss of cochlear sensory neurones and a region-specific reduction of target innervation along the tonotopic axis. However, how reduced neurotrophin signalling affects the innervation of the mature cochlea is currently unknown. Here, we have analysed the consequences of a lack of the TrkB receptor and its ligand, the neurotrophin brain-derived neurotrophic factor (Bdnf), in the late postnatal or adult cochlea using mouse mutants. During early postnatal development, mutant animals show a lack of afferent innervation of outer hair cells in the apical part of the cochlea, whereas nerve fibres in the basal part are maintained. Strikingly, this phenotype is reversed during subsequent maturation of the cochlea, which results in a normal pattern of outer hair cell innervation in the apex and loss of nerve fibres at the base in adult mutants. Measurements of auditory brain stem responses of these mice revealed a significant hearing loss. The observed innervation patterns correlate with opposing gradients of Bdnf and Nt3 expression in cochlear neurones along the tonotopic axis. Thus, the reshaping of innervation may be controlled by autocrine signalling between neurotrophins and their receptors in cochlear neurones. Our results indicate a substantial potential for re-innervation processes in the mature cochlea, which may also be of relevance for treatment of hearing loss in humans.

Animals↗
PubMed2004

Target-derived BMP signaling limits sensory neuron number and the extent of peripheral innervation in vivo.

The role of target-derived BMP signaling in development of sensory ganglia and the sensory innervation of the skin was examined in transgenic animals that overexpress either the BMP inhibitor noggin or BMP4 under the control of a keratin 14 (K14) promoter. Overexpression of noggin resulted in a significant increase in the number of neurons in the trigeminal and dorsal root ganglia. Conversely, overexpression of BMP4 resulted in a significant decrease in the number of dorsal root ganglion neurons. There was no significant change in proliferation of trigeminal ganglion neurons in the noggin transgenic animals, and neuron numbers did not undergo the normal developmental decrease between E12.5 and the adult, suggesting that programmed cell death was decreased in these animals. The increase in neuron numbers in the K14-noggin animals was followed by an extraordinary increase in the density of innervation in the skin and a marked change in the pattern of innervation by different types of fibers. Conversely, the density of innervation of the skin was decreased in the BMP4 overexpressing animals. Further Merkel cells and their innervation were increased in the K14-noggin mice and decreased in the K14-BMP4 mice. The changes in neuron numbers and the density of innervation were not accompanied by a change in the levels of neurotrophins in the skin. These findings indicate that the normal developmental decrease in neuron numbers in sensory ganglia depends upon BMP signaling, and that BMPs may limit both the final neuron number in sensory ganglia as well as the extent of innervation of targets. Coupled with prior observations, this suggests that BMP signaling may regulate the acquisition of dependence of neurons on neurotrophins for survival, as well as their dependence on target-derived neurotrophins for determining the density of innervation of the target.

Animals↗
PubMed1990

NGF mRNA expression in developing cutaneous epithelium related to innervation density.

To determine if the initial level of NGF mRNA in developing cutaneous epithelium is correlated with its final innervation density, we measured the concentration of NGF mRNA in the epithelia of the maxillary, mandibular and ophthalmic territories of trigeminal ganglion in the embryonic mouse. At the onset of neuronal death in the ganglion there were marked differences in the concentration of NGF mRNA in these epithelia: the level was highest in the epithelium of the densely innervated maxillary territory, it was lower in the epithelium of the moderately innervated mandibular territory and was lowest in the epithelium of the sparsely innervated ophthalmic territory. These regional differences in the level of NGF mRNA during the early stages of target field innervation suggest that the level of NGF production in target field cells, rather than regional differences in the access of innervating neurons to NGF, governs the number of neurons that survive. Because the same percentage cell death occurs in each of the subsets of trigeminal neurons that innervate the maxillary, mandibular and ophthalmic territories, regional differences in NGF synthesis are not responsible for establishing differences in innervation density, rather they maintain differences that arise earlier in development.

Animals↗
PubMed1987

Selective innervation of types of fibres in developing rat muscle.

The technique of glycogen depletion has been used to identify the types of muscle fibres innervated by individual motor neurones in the neonatal rat. This analysis shows that neonatal motor units are highly biased in their fibre type composition, even at times when the fibres receive extensive polyneuronal innervation. This finding suggests that the innervation of muscle fibres is somehow sorted according to type during early development. This sorting does not appear to occur during the removal of the polyneuronal innervation because little, if any, increase in the bias of unit compositions occurs as the number of synapses present in the muscle is reduced 2- to 3-fold. To determine whether the sorted innervation might be explained by a selective synaptogenesis, a study was made of the type compositions of units formed by reinnervation of neonatal soleus muscle. Glycogen depletion of single units 2 weeks following crush of the soleus nerve at postnatal day 2 showed that most of them (10/12) had biased type compositions which could not be explained by a random reinnervation. The location of fibres in the reinnervated motor units suggests that the regenerating axons innervated a novel set of fibres. The differentiation of fibres into types was apparently not changed during their reinnervation. These results imply that regenerating motor neurones in the neonatal rat selectively reinnervate muscle fibre types. These and other studies further imply that the organization of fibres into motor units during normal development does not occur, as is widely believed, by a random innervation of naive fibres and their subsequent differentiation under the influence of innervation.

Animals↗
PubMed1996

Novel dual innervation of a larval proleg muscle by two similar motoneurons in the tobacco hornworm Manduca sexta.

In Manduca sexta, the accessory planta retractor muscle (APRM), which retracts the larval proleg, is innervated by two excitatory motoneurons, the accessory planta retractor motoneurons (APRs). These muscles and motoneurons have been the focus of a number of developmental and behavioral studies. The present study investigated properties of the pair of APRs that innervate each APRM and determined their pattern of innervation of APRM fibers. Members of APR pairs could not be distinguished by their anatomical or electrical properties (resting membrane potential, input resistance and spike threshold). Spontaneous synaptic inputs to members of APR pairs were highly correlated, whereas spontaneous synaptic inputs to APRs and functionally dissimilar motoneurons were not well correlated. Synaptic inputs from identified mechanosensory neurons and interneurons to the two APRs were qualitatively similar, but the magnitude of the response to sensory stimulation sometimes differed within a pair. Both APRs produced large, rapidly rising excitatory junction potentials in APRM fibers. Within the APRM, some fibers were singly innervated by one or the other APR while the remaining fibers were dually innervated by both APRs. In dually innervated fibers, the motor terminals of the two APRs were spatially segregated. This innervation pattern appears to be unique among insects and shares some properties with the innervation of vertebrate muscle.

Animals↗
PubMed2004

Innervation of the proximal urethra of ovariectomized and estrogen-treated female rats.

The proximal urethra plays a central role in maintaining urinary continence, and sympathetic excitatory innervation to urethral smooth muscle is a major factor in promoting tonic contraction of this organ. Elevated estrogen levels are often associated with incontinence in humans. Because elevated estrogen levels result in degeneration of sympathetic nerves from the closely related uterine smooth muscle, we examined the effects of chronic estrogen administration on proximal urethral innervation. Ovariectomized virgin female rats received either vehicle or 17 beta-estradiol for 1 week, and smooth muscle size and parasympathetic, sensory and sympathetic nerve densities were assessed quantitatively throughout the first 3 mm of the proximal urethral smooth muscle. In vehicle-infused ovariectomized rats, parasympathetic nerves immunoreactive for vesicular acetylcholine transporter were most abundant, while calcitonin gene-related peptide-immunoreactive sensory nerves and tyrosine hydroxylase-immunoreactive sympathetic nerves were less numerous. The densities of parasympathetic and sensory nerves remained constant along the proximal urethra, while sympathetic nerves showed a significant increase along a proximal-distal gradient. Administration of 17beta-estradiol for 7 days via subcutaneous osmotic pump did not change smooth muscle area in sections, and neither densities nor total innervation of any nerve population was altered. These findings reveal a rich cholinergic innervation of the proximal urethra, and a pronounced gradient in sympathetic innervation. Unlike the embryologically similar uterine smooth muscle, estrogen does not influence muscle size or composition of innervation, indicating that estrogen's actions on innervation are highly target-specific. Thus, estrogen's effects on urinary continence apparently occur independently of any significant remodeling of smooth muscle or resident innervation.

Animals↗
PubMed2003

Local innervation patterns of the metathoracic flexor and extensor tibiae motor neurons in the cricket Gryllus bimaculatus.

To elucidate neural mechanisms underlying walking and jumping in insects, motor neurons supplying femoral muscles have been identified mainly in locusts and katydids, but not in crickets. In this study, the motor innervation patterns of the metathoracic flexor and extensor tibiae muscles in the cricket, Gryllus bimaculatus were investigated by differential back-fills and nerve recordings. Whereas the extensor tibiae muscle has an innervation pattern similar to that of other orthopterans, the flexor has an innervation unique to this species. The main body of the flexor muscle is divided into the proximal, middle and distal regions, which receive morphologically unique terminations from almost non-overlapping sets of motor neurons. The proximal region is innervated by about 12 moderate-sized excitatory motor neurons and two inhibitory neurons while the middle and distal regions are innervated by three and four large excitatory motor neurons, respectively. The most-distally located accessory flexor muscle, inserting on a common flexor apodeme with the main muscle, is innervated by at least four small excitatory (slow-type) and two common inhibitory motor neurons. The two excitatory and two inhibitory motor neurons that innervate the accessory flexor muscle also innervate the proximal bundles of the main flexor muscle. This suggests that the most proximal and distal parts of the flexor muscle participate synergistically in fine motor control while the rest participates in powerful drive of tibial flexion movement.

Animals↗
PubMed1993

Autonomic innervations in the middle ear and pharynx.

Autonomic innervations of the mucosa in the middle ear and pharynx were investigated by retrograde labelling of the autonomic ganglia with horseradish peroxidase (HRP). Of the sympathetic ganglia, the superior cervical ganglion (SCG), middle cervical ganglion (MCG) and stellate ganglion (StG) were examined, and of the parasympathetic ganglia, the pterygopalatine ganglion (PpG) and the otic ganglion (OtG) were examined. Sympathetic innervation of the middle ear mucosa was accomplished by fibers originating in the ipsilateral SCG, but not by those originating in the MSG or StG. Parasympathetic innervation was by fibers originating in the ipsilateral PpG, but not by those originating in the OtG. The epipharynx received sympathetic innervation from the ipsilateral SCG, but not from the MCG or StG. Its parasympathetic innervation was from the PpG bilaterally, but not from the OtG. Sympathetic innervation of the mesopharynx was supplied by the SCG, MCG and StG, but no parasympathetic supply came from the PpG or the OtG. Sympathetic innervation was bilateral, but predominantly from the ipsilateral side. The hypopharynx resembled the mesopharynx, but had more innervation from the MCG and StG.

Animals↗