Early patterns of neuronal degeneration in the retina of the goldfish after optic nerve sectioning

The early patterns of retinal degeneration were studied in the goldfish after optic nerve sectioning by l.m. and e.m. Beginning on the 2nd postsurgical day there was an initial degeneration of neurons in the ganglion cell and inner nuclear layers of the central retina. Massive ganglion cell degeneration in the whole retina (60%) as well as degeneration of neurons in inner and outer nuclear layer of the peripheral retina was evident around the 7th postsurgical day. The early degenerating cells appeared to be cones and cone bipolars.     

Expression and distribution of phocein and members of the striatin family in neurones of rat peripheral ganglia

Phocein and members of the striatin family (striatin, SG2NA and zinedin) are intracellular proteins, mainly expressed in neurones of the mammalian central nervous system where they are thought to be involved in vesicular traffic and Ca(2+) signalling. Here, we have investigated whether these proteins are also present in the peripheral nervous system, by analysing their expression and distribution within sensory neurones of the vagal (nodose and jugular) ganglia, the petrosal ganglion, the dorsal root ganglion, and also in the sympathetic neurones of the superior cervical ganglion. RT-PCR experiments showed that mRNAs of phocein, striatin, SG2NA and zinedin are present in all studied peripheral ganglia. Immunocytochemical detections demonstrate that phocein, striatin and SG2NA are expressed in neurones of vagal, petrosal and dorsal root ganglia. Immunoblotting experiments confirm these data and in addition demonstrate that: (1) the proteins phocein, striatin and SG2NA are also present in the superior cervical ganglion and (2) zinedin is detected in all studied ganglia. The distribution appears to differ: immunoreactivity for striatin and SG2NA is found only in soma of sensory neurons, whereas immunoreactivity for phocein is observed in both soma and processes. Our study thus demonstrates that phocein and the members of the striatin family are expressed not only in central nervous system but also in the peripheral nervous system and, in particular, in afferent sensory neurones.     

Regeneration of neuron processes of the spinal ganglion after its experimental section in rats

Sensory fibers regeneration after dorsal root ganglion (DRG) section was studied in the rat. After middle cross-section of DRG-13 (left side) there were neurons in the proximal part with damage to peripheral processes and in the distal part with damage to central processes. Axonal ionophoresis of cobalt salts was used for the study of sensory fibers regeneration through the scar in DRG during 3, 7, 15, 30, 120 and 180 days after the damage. Peculiarity regeneration of the sensory fibers was shown in spite of damage localization near ganglion cells body, the regeneration of peripheral and central processes of ganglion cells started already on the 3rd day, and sprouting sensory fibers through the scar of DRG--on the 7th day.     

Metamorphosis of the central nervous system of Drosophila

The study of the metamorphosis of the central nervous system of Drosophila focused on the ventral CNS. Many larval neurons are conserved through metamorphosis but they show pronounced remodeling of both central and peripheral processes. In general, transmitter expression appears to be conserved through metamorphosis but there are some examples of possible changes. Large numbers of new, adult-specific neurons are added to this basic complement of persisting larval cells. These cells are produced during larval life by embryonic neuroblasts that had persisted into the larval stage. These new neurons arrest their development soon after their birth but then mature into functional neurons during metamorphosis. Programmed cell death is also important for sculpting the adult CNS. One round of cell death occurs shortly after pupariation and a second one after the emergence of the adult fly.     

Extension and retraction of axonal projections by some developing neurons in the leech depends upon the existence of neighboring homologues. II. The AP and AE neurons

To assess the generality of our previous finding (Gao and Macagno, 1987) that segmental homologues play a role in the establishment of the pattern of axonal projections of the heart accessory HA neurons, we have extended our studies to two other identified leech neurons: the anterior pagoda (AP) neurons and the annulus erector (AE) motor neurons. Bilateral pairs of AP neurons are found in the first through the twentieth segmental ganglia (SG1 through SG20) of the leech ventral nerve cord. All AP neurons initially extend axonal projections to the contralateral periphery as well as longitudinal projections along the contralateral interganglionic connective nerves toward anterior and posterior neighboring ganglia. Although the peripheral projections are maintained by all AP neurons throughout the life of the animal, the longitudinal projections disappear in all but two segments: the AP neurons in SG1 maintain their anterior projections and extend them into the head ganglion, and those in SG20 maintain their posterior projections and extend them into SG21 and the tail ganglion. When single AP neurons are deleted anywhere along the nerve cord before processes begin to atrophy, however, the longitudinal projections are retained by their ipsilateral homologues in adjacent ganglia. The rescued processes appear to take over the projections of the deleted neurons. In cases where two or more AP neurons on the same side of the nerve cord are deleted from adjacent ganglia, a contralateral homologue sometimes extends projections to the periphery ipsilaterally or on both sides. We obtained similar results when we deleted single AE neurons from midbody ganglia. Thus, our experiments with three different identified neurons consistently show that the initial pattern of projections is the same in all ganglia, but that the existence of homologues in adjacent ganglia leads to the pruning of some of the initial projections. A consequence of this homologue-dependent process retraction is that neurons normally lacking neighboring homologues will have patterns of projections different from those neurons that do have such neighbors. Process loss by the HA, AP, and AE neurons may be the result either of competition for targets, inputs, or growth factors or of direct interactions among homologous cells.     

Distribution of tyrosine-hydroxylase-immunoreactive and dopamine-immunoreactive neurons in the central nervous system of the snail Helix pomatia

The distribution and characterization of dopamine-containing neurons are described in the different ganglia of the central nervous system of Helix on the basis of the distribution of tyrosine hydroxylase immunoreactive (TH-ir) and dopamine immunoreactive (DA-ir) neurons. Both TH-ir and DA-ir cell bodies of small diameter (10–25 m) can be observed in the buccal, cerebral and pedal ganglia, dominantly on their ventral surface, and concentrated in small groups close to the origin of the peripheral nerves. The viscero-parietal-pleural ganglion complex is free of immunoreactive cell bodies but contains a dense fiber system. The largest number of TH-ir and DA-ir neurons can be detected in the pedal, and cerebral ganglia. The average number of TH-ir and DA-ir neurons significantly differs but all the identifiable groups of TH-ir neurons also show DA-immunoreactivity. Therefore, we consider the TH-ir neurons in those groups as being DA-containing neurons. The amounts of DA in the different ganglia assayed by high performance liquid chromatography correspond to the distribution and number of TH-ir and DA-ir neurons in the different ganglia. The axon processes of the labeled small-diameter neurons send thin proximal branches toward the cell body layer but only rarely surround cell bodics, whereas distally they give off numerous branches in the neuropil and then leave the ganglion through the peripheral nerves. In the cerebral ganglia, the analysis of the TH-ir pathways indicates that the largest groups of labeled neurons send their processes through the peripheral nerves in a topographic order. These results furnish morphological evidence that DA-containing neurons of Helix pomatia have both central and peripheral roles in neuronal regulation.     

Regeneration of the parathyroid glands in experimental hyperthyroidism

By means of morphological, morphometric and radioautographic methods, regeneration of mechanically traumatized parathyroid glands has been studied in 22 euthyroid and 22 hyperthyroid rats on the 1st-20th days after the operation. The thyroid gland is stimulated by daily injection of thyrotropin (1 ME/100 g of body mass). Twelve non-operated animals (6 hyperthyroid and 6 euthyroid rats) serve as control. In the regenerating parathyroid glands of the hyperthyroid animals in comparison with the euthyroid ones, certain increase of proliferative activity is noted in parathyrocytes and in cells of the granular tissue on the 2d-6th days, a more pronounced hypertrophy of epitheliocytes on the 2d-20th days, hyperplasia of their nucleolar apparatus on the 2d-5th days. The experimental hyperthyroidism stimulates manifestation of restorative processes in the regenerating parathyroid glands during development of active inflammatory reaction in them; however, it does not influence the parameters of the organ's structure studied in the nonoperated animals.     

The effects of superior ovarian nerve sectioning on ovulation in the guinea pig

The effects on spontaneous ovulation associated with the unilateral or bilateral sectioning of the superior ovarian nerves (SON) were analyzed in guinea pigs at different time intervals of the estrous cycle. Day 1 of the estrous cycle was defined as the day when the animal presents complete loss of the vaginal membrane (open vagina). Subsequent phases of the cycle were determined by counting the days after Day 1. All animals were autopsied on the fifth day of the estrous cycle after surgery. Sectioning the right, left, or both SONs on day 5 (early luteal phase) resulted in a significant increase in the number of fresh corpora lutea. Ovulation increased significantly when the left SON (L-SON) was sectioned during late follicular phase (day 1) and medium luteal phase (day 8). When surgery was performed on days 1 or 8, neither sectioning the right SON (R-SON) nor sectioning the SON bilaterally had an apparent effect on ovulation rates. Similarly, ovulation rates were not affected when unilateral (right or left) or bilateral sectioning of the SON was performed during late luteal phase two (day 12). Unilateral or bilateral sectioning of the SON performed during the early luteal phase (day 5) was associated with a significant decrease in uterine weight. A comparable effect was observed when the L-SON was sectioned during late follicular phase (day 1), or medium luteal phase (day 8). No effects on uterine weight were observed when unilateral or bilateral sectioning of the SON was performed during late luteal phase. Our results suggest that in the guinea pig the SON modulates ovulation, and that the degree of modulation varies along the estrous cycle. The strongest influence of the SONs on ovulation occurs during early luteal phase, and decrease thereafter, being absent by late luteal phase. In addition, sectioning the left or the right SON caused different responses by the ovaries of adult guinea pigs. This paper discusses the mechanisms by which ovulation increased when the SON was surgically cut.     

Cryostat sections for coexistence studies and preembedding electron microscopic immunocytochemistry of central and peripheral nervous system tissue

Perfusion-fixed tissue blocks were incubated in high molar sucrose solutions, shock frozen in melting isopentane, and sectioned on a conventional cryostat. Semithin sections (2-4 microns) alternatingly stained for parvalbumin and glutamate decarboxylase enabled us to demonstrate the coexistence of both antigens in the same cell. Thick sections (40 microns) of central and peripheral nervous system tissue were immunostained and processed for correlated light and electron microscopic studies. At the electron microscopic level, the preservation of ultrastructural features such as membranes and synaptic contacts was comparable to that normally seen in vibratome sectioned material. Hence, this technique can successfully be used for preembedding coexistence studies and electron microscopic preembedding immunocytochemistry when vibratome sectioning is problematic.     

Role of chemical afferents in the maintenance of rhythmic respiratory movements

In seven anesthetized cats central chemosensitivity was eliminated (cold block) and peripheral chemoreceptors were either stimulated or eliminated (sectioned) to test whether nonchemical vagal afferents can maintain rhythmic ventilation and to determine the relative contribution of the carotid and aortic chemoreceptors to ventilatory drive without central chemosensitivity. Elimination of all chemical afferents invariably induced apnea, whereas ventilation was reduced from 533 to 159 ml X min-1 during cold block of central chemosensitivity and to 478 ml X min-1 after sectioning both sinus nerves. Cold block with only the aortic chemoreceptors and vagal afferents intact produced apnea in four of six cases tested. Stimulation of peripheral chemoreceptors during cold block remained effective and interrupted apnea in three of the four cats with only aortic chemoreceptors intact. We conclude that the nonchemical vagal respiratory afferents alone are unable to maintain rhythmic ventilation. Respiratory rhythm generation is, under the conditions of our experiments, critically dependent on sufficient afferent input from chemical afferents. Of these, central chemosensitivity plays the major role, followed by carotid body and, least importantly, by aortic afferents.     

Responses of bulbospinal and laryngeal respiratory neurons to hypercapnia and hypoxia

The purpose was to evaluate activities of medullary respiratory neurons during equivalent changes in phrenic discharge resulting from hypercapnia and hypoxia. Decerebrate, cerebellectomized, paralyzed, and ventilated cats were used. Vagi were sectioned at left midcervical and right intrathoracic levels caudal to the origin of right recurrent laryngeal nerve. Activities of phrenic nerve and single respiratory neurons were monitored. Neurons exhibiting antidromic action potentials following stimulations of the spinal cord and recurrent laryngeal nerve were designated, respectively, bulbospinal or laryngeal. The remaining neurons were not antidromically activated. Hypercapnia caused significant augmentations of discharge frequencies for all neuronal groups. Many of these neurons had no change or declines of activity in hypoxia. We conclude that central chemoreceptor afferent influences are ubiquitous, but excitatory influences from carotid chemoreceptors are more limited in distribution among medullary respiratory neurons. Hypoxia will increase activities of neurons that receive sufficient excitatory peripheral chemoreceptor afferents to overcome direct depression by brain stem hypoxia. The possibility that responses of respiratory muscles to hypoxia are programmed within the medulla is discussed.     

Effect of nitric oxide on hyperpolarization-activated current in substantia gelatinosa neurons of rats

Central sensitization is the hyperexcitability of spinal processing after peripheral nerve injury or inflammation. This phenomenon may be associated with nitric oxide (NO) signal pathway in synapse. Here, we have investigated the effect of NO on hyperpolarization-activated inward current (I(h)) in substantia gelatinosa (SG) neurons, using the whole-cell patch clamp technique. I(h) was increased by the application of sodium nitro prusside (SNP, a NO donor) or 8Br-cGMP. The stimulatory effects of NO were abolished by guanylyl cyclase inhibitor, ODQ, suggesting that the effect of NO was mediated by cGMP. However, this effect of NO was not prevented by the pretreatment with KT5823, PKG inhibitor. Taken together, the activation of I(h) in SG neurons could be mediated by NO-cGMP dependent pathway. These results reveal an involvement of NO in excitability of SG neuron via the activation of I(h) may be associated with central sensitization.     

Localization of heart-innervating sympathetic neurons

Localization, amount, form of the bodies and maximal diameter of horseradish peroxidase (HP)-labelled neurons in the right stellate ganglion (SG) in the cat spinal cord have been investigated. HP application has been performed on the central parts of the SG connective branch with vagus nerve, or with the caudal cardiac nerve. In the neurons HP has been revealed after Straus or Mesulam method. In the SG, regardless the HP application place, the labelled neurons arrange in the zone, adjoining the place, where the caudal cardiac nerve and the connective branch get to the vagus nerve. In the spinal cord, when HP is applied on the connective branch, the labelled neurons are revealed in the lateral horns of the TI-TVI segments. The amount of the labelled neurons decreases in the rostro-caudal direction. Their greatest amount is revealed in the TI-TIII segments. When HP is applied on the central part of the caudal cardiac nerve, a small amount of the labelled neurons has been found in TI-TIII segments of the spinal cord only in one experiment. Thus, in the connective branch of the SG with the vagus nerve much more amount of the preganglionar fibers run than in the caudal cardiac nerve.     

Runx1 selectively regulates cell fate specification and axonal projections of dorsal root ganglion neurons

Runx1-deficient mice die around embryonic day 11.5 due to impaired hematopoiesis. This early death prevents the analysis of the role of Runx1 in the development of sensory ganglia. To overcome the early embryonic lethality, we adopted a new approach to utilize transgenic Runx1-deficient mice in which hematopoietic cells are selectively rescued by Runx1 expression under the control of GATA-1 promoter. In Runx1-deficient mice, the total number of dorsal root ganglion (DRG) neurons was increased, probably because of an increased proliferative activity of DRG progenitor cells and decreased apoptosis. In the mutant DRG, TrkA-positive neurons and peptidergic neurons were increased, while c-ret-positive neurons were decreased. Axonal projections were also altered, in that both central and peripheral projections of CGRP-positive axons were increased. In the dorsal horn of the spinal cord, projections of CGRP-positive axons expanded to the deeper layer, IIi, from the normal terminal area, I/IIo. Our results suggest that Runx1 is involved in the cell fate specification of cutaneous neurons, as well as their projections to central and peripheral targets.     

Ipsilateral vagotomy to unilaterally ovariectomized pre-pubertal rats modifies compensatory ovarian responses

The present study evaluates the participation of the vagus nerve in pre-pubertal rats with unilateral ovariectomy on puberty onset, and on progesterone, testosterone and estradiol serum levels, and the compensatory responses of the ovary. Unilateral vagotomy did not modify the onset of puberty in unilaterally ovariectomized rats. Ovulation rates of animals with the left vagus nerve sectioned and the left ovary in-situ was lower than in rats with only unilateral ovariectomy. Sectioning the left vagus to 32-day old rats with the left ovary in-situ resulted in lower compensatory ovarian hypertrophy than in rats with right unilateral ovariectomy. Twenty-eight or 32-day old animals with sectioning of the right vagus nerve and the right ovary in situ showed higher compensatory ovulation. Twenty-eight -day old rats with the right ovary in situ had higher progesterone and testosterone levels than animals of the same age with the left ovary in-situ. Compared to animals with the right ovary in situ, animals treated at 32-days of age, sectioning the ipsi-lateral vagus nerve resulted in higher progesterone levels. Higher progesterone levels were observed in 28- and 32 days old rats with the left ovary in situ and left vagus nerve sectioned. Thirty-two day old animals with the right ovary in situ and right vagus nerve sectioned had higher progesterone levels than rats of the same age with the left ovary in situ and left vagus nerve sectioned. Left vagotomy to 28-day old rats with the left ovary in situ resulted in higher testosterone levels, a reverse response to that observed in animals with sectioning of the right vagus and the right ovary in situ. Thirty-two day old rats with the left ovary in situ and left vagus nerve sectioned showed lower testosterone levels than animals without vagotomy and with the left ovary in situ.     

Promoting and directing axon outgrowth

Establishment of appropriate neuronal connections during development and regeneration requires the extension of processes that must then grow in the correct direction, find and recognize their targets, and make synapses with them. During development, embryonic neurons gradually establish central and peripheral connections in an evolving cellular environment in which neurotrophic factors are provided by supporting and target cells that promote neuronal survival, differentiation, and process outgrowth. Some cells also release neurotropic factors that direct the outgrowth of neuronal processes toward their targets. Following development the neurotrophic requirements of some adult neurons change so that, although they respond to neurotrophic factors, they no longer require exogenous neurotrophins to survive or to extend processes. Within the central nervous system (CNS), the ability of neurons to extend processes is eventually lost because of a change in their cellular environment from outgrowth permissive to inhibitory. Thus, neuronal connections that are lost in the adult CNS are rarely reestablished. In contrast, the environment of the adult peripheral nervous system fosters process outgrowth and synapse formation. This article discusses the neurotrophic requirements of embryonic and adult neurons, as well as the importance of neurotropic factors in directing the outgrowth of regenerating adult axons.     

Light Microscopic Identification and Photography of Golgi Impregnated Central Nervous System Neurons During Sectioning for Electron Microscopy

A method is described for a rapid and systematic light microscopic documentation of Golgi impregnated neurons while they are being sectioned for electron microscopy. A drawing under the light microscope of a Golgi impregnated neuron is made first; subsequently thin door of the tissue containing this neuron are cut in the same plane as for light microscopy. During thin sectioning the chuck containing the block is taken out of the ultramicrotome at regular intervals and placed in a special device under a light microscope. The neuron is photographed to record the stage of sectioning. Comparison of the micrographs indicates which put of the and its dendritic tree are contained in the thin sections. No semithin sections are used and therefore no material is lost for reconstruction.     

Light microscopic identification and photography of Golgi impregnated central nervous system neurons during sectioning for electron microscopy.

A method is described for a rapid and systematic light microscopic documentation of Golgi impregnated neurons while they are being sectioned for electron microscopy. A drawing under the light microscope of a Golgi impregnated neuron is made first; subsequently thin sections of the tissue containing this neuron are cut in the same plane as for light microscopy. During thin sectioning the chuck containing the block is taken out of the ultramicrotome at regular intervals and placed in a special device under a light microscope. The neuron is photographed to record the stage of sectioning. Comparison of the micrographs indicates which part of the neuron and its dendritic tree are contained in the thin sections. No semithin sections are used and therefore no material is lost for reconstruction.     

The Plasticity of the DRG Neurons Belonging to Different Subpopulations After Dorsal Rhizotomy

SUMMARY 1. The plasticity of sensory neurons following the injury to their axons is very important for prognosis of recovery of afferent fibers with different modality. It is evident that the response of dorsal root ganglion (DRG) neurons after peripheral axotomy is different depending on the deficiency in neurotrophic factors from peripheral region. The loss of cells appears earlier and is more severe in B-cells (small, dark cells with unmyelinated axons) than in A-cells (large, light cells with myelinated axons).2. We studied using immunohistochemical methods the response of DRG neurons to dorsal rhizotomy and combined injury of central and peripheral neuronal processes. A quantitative analysis of DRG neurons tagged by the selective markers isolectin B4 (IB4) and the heavy molecular component of the neurofilament triplet (NF200) antibody, selective for subpopulations of small and large/medium DRG neurons, respectively, was performed after dorsal rhizotomy, peripheral axotomy, and their combination.3. The number of NF200⁺-neurons is reduced substantially after both dorsal rhizotomy and peripheral axotomy, while the decrease of IB4⁺-neurons is observed only in combined injury, i.e., dorsal rhizotomy accompanied with sciatic nerve injury.4. Our results show that distinct subpopulations of DRG neurons respond differently to the injury of their central processes. The number of NF200⁺-neurons decreases to greater degree following dorsal rhizotomy in comparison to IB4⁺-neurons.     

THE ULTRASTRUCTURE AND DISPOSITION OF VESICULATED NERVE PROCESSES IN SMOOTH MUSCLE

The walls of the gastrointestinal tract and urinary bladder of rats were fixed in osmium tetroxide, embedded in methacrylate, and sectioned for electron microscopy. The examination of sections of smooth muscle tissue with the electron microscope reveals the presence of bundles of unmyelinated nerve fibers within the intercellular spaces. In addition, vesiculated nerve processes, bounded on their outer surfaces by delicate plasma membranes and typically containing varying quantities of synaptic vesicles and mitochondria, make intimate contact with the surface of smooth muscle cells. These nerve processes are similar in structure and disposition to nerve endings previously described in skeletal muscle, in the central nervous system, in peripheral ganglia, in receptors, and in glands. It is concluded that the relationships existing between vesiculated nerve processes and the surface of smooth muscle cells constitute neuromuscular junctions. Profiles of protrusions of smooth muscle cells are often seen protruding into the intercellular spaces. Here they occur singly or in groups, originating from one or more cells. Because of the plane of section the protrusions may sometimes appear as individual entities between the muscle cells. In such cases care must be exercised in their identification because they have characteristics similar to sectioned nerve processes which also occur in the intercellular spaces.