Age-related ultrastructural and monoamine oxidase changes in the rat optic nerve.

The aim of this paper is to study the morphology and the distribution of the monoamine oxidase enzymatic system in the optic nerve of 4 month-old Wistar (young) and 28 month-old Wistar (old) rats. The optic nerve was harvested from 20 young and old rats. The segment of optic nerve was divided longitudinally into two pieces, each 0.1 mm in length. The first piece was used for transmission electron microscopy. The second piece was stained with histochemical reaction for monoamine oxidase. The agerelated changes in the optic nerve of rats include micro-anatomical details, ultrastructure and monoamine oxidase histochemical staining. A strong decrease of the thin nerve fibers and a swelling of the thick ones can be observed in optic nerve fibers of old rats. Increased monoamine oxidase histochemical staining of the optic nerve of aged rats is well demonstrated. The increase of meningeal shealth and the decrease of thin nerve fibers of the optic nerve in old rats are well documented. Morphological, ultrastructural and histochemical changes observed in optic nerve fibers of the old rats show a close relation with aging.

Ontogenic development of nerve fibers in human fetal livers: an immunohistochemical study using neural cell adhesion molecule (NCAM) and neuron-specific enolase (NSE).

The aim of the study was to investigate nerve fibers (NF) in human fetal livers. An immunohistochemical study was performed. NF were classified into portal tract innervation (PoI) and parenchymal innervation (PaI). The hilum area showed many Pol NF at 7 GW, and NF increased with gestational week (GW). Direct innervations to biliary epithelium were recognized. In large portal tracts, a few NCAM-positive mesenchymal cells were seen at 8 GW and many mesenchymal cells were noted around 12 GW. Apparent NF emerged around 15 GW, and NF increased with GW. Many NF plexuses were seen in 30-40 GW. In small portal tracts, no NF were seen in 7-10 GW. A few NCAM-positive mesenchymal cells emerged in 11 GW, and they increased thereafter. Apparent NF were seen around 20 GW and NF increased with GW. At term (40 GW), PoI NF were still immature. Ductal plate (DP) was positive for NCAM, NSE, chromogranin and synaptophysin, and direct innervations to DP were seen. The direct innervations to developing bile ducts and peribiliary glands were also seen. PaI NF were first seen at 21 GW and was consistent until 40 GW in which a few NF were seen in PaI. These observations suggest that PoI NF arise from committed portal mesenchyme. PaI NF are very immature at 40 GW. There are direct innervations to bile ducts, peribiliary glands, portal veins, hepatic arteries, and DP.

Cholinergic innervation of human mesenteric lymphatic vessels.

BACKGROUND: The cholinergic neurotransmission within the human mesenteric lymphatic vessels has been poorly studied. Therefore, our aim is to analyse the cholinergic nerve fibres of lymphatic vessels using the traditional enzymatic techniques of staining, plus the biochemical modifications of acetylcholinesterase (AChE) activity. MATERIALS AND METHODS: Specimens obtained from human mesenteric lymphatic vessels were subjected to the following experimental procedures: 1) drawing, cutting and staining of tissues; 2) staining of total nerve fibres; 3) enzymatic staining of cholinergic nerve fibres; 4) homogenisation of tissues; 5) biochemical amount of proteins; 6) biochemical amount of AChE activity; 6) quantitative analysis of images; 7) statistical analysis of data. RESULTS: The mesenteric lymphatic vessels show many AChE positive nerve fibres around their wall with an almost plexiform distribution. The incubation time was performed at 1 h (partial activity) and 6 h (total activity). Moreover, biochemical dosage of the same enzymatic activity confirms the results obtained with morphological methods. CONCLUSIONS: The homogenates of the studied tissues contain strong AChE activity. In our study, the lymphatic vessels appeared to contain few cholinergic nerve fibres. Therefore, it is expected that perivascular nerve stimulation stimulates cholinergic nerves innervating the mesenteric arteries to release the neurotransmitter AChE, which activates muscarinic or nicotinic receptors to modulate adrenergic neurotransmission. These results strongly suggest, that perivascular cholinergic nerves have little or no effect on the adrenergic nerve function in mesenteric arteries. The cholinergic nerves innervating mesenteric arteries do not mediate direct vascular responses.

Monoamine oxidase enzymes and oxidative stress in the rat optic nerve: age-related changes.

In this study, age-related changes in the monoamine oxidases (MAO) were studied in the optic nerve (ON) of both young and aged male rats. The aim of the study was to assess the role of MAO in age-related changes in the rat ON and explain the mechanisms of neuroprotection mediated by MAO-B-specific inhibitors. Fifteen three month old and fifteen 26 month old Sprague-Dawley rats were used. The animals were killed by terminal anaesthesia. Staining of MAO, quantitative analysis of images, biochemical assays and statistical analysis of data were carried out. Samples of the ON were washed in water, fixed in Bowen fluid, dehydrated and embedded in Entellan. Histological sections were stained for MAO-enzymatic activities. The specificity of the reaction was evaluated by incubating control sections in a medium either without substrate or without dye. The quantitative analysis of images was carried out at the same magnification and the same lighting using a Zeiss photomicroscope. The histochemical findings were compared with the biochemical results. After enzymatic staining, MAO could be demonstrated in the ON fibres of both young and aged animals; however, MAO were increased in the nerve fibres of the elderly rats. These morphological findings were confirmed biochemically. The possibility that age-related changes in MAO levels may be attributed to impaired energy production mechanisms and/or represent the consequence of reduced energy needs is discussed.

Preponderance of inhibitory versus excitatory intramuscular nerve fibres in human chagasic megacolon.

INTRODUCTION: Megacolon, chronic dilation of a colonic segment, is a frequent sign of Chagas disease. It is accompanied by an extensive neuron loss which, as shown recently, results in a partial, selective survival of nitrergic myenteric neurons. Here, we focused on the balance of intramuscular excitatory (choline acetyltransferase [ChAT]-immunoreactive) and inhibitory (neuronal nitric oxide synthase [NOS]- as well as vasoactive intestinal peptide [VIP]-immunoreactive) nerve fibres. MATERIALS AND METHODS: From surgically removed megacolonic segments of seven patients, three sets of cryosections (from non-dilated oral, megacolonic and non-dilated anal parts) were immunhistochemically triple-stained for ChAT, NOS and VIP. Separate area measurements of nerve profiles within the circular and longitudinal muscle layers, respectively, were compared with those of seven non-chagasic control patients. Additionally, wholemounts from the same regions were stained for NOS, VIP and neurofilaments (NF). RESULTS: The intramuscular nerve fibre density was significantly reduced in all three chagasic segments. The proportions of inhibitory (NOS only, VIP only, or NOS/VIP-coimmunoreactive) intramuscular nerves were 68 %/58 % (circular/longitudinal muscle, respectively) in the controls and increased to 75 %/69 % (oral parts), 84 %/76 % (megacolonic) and 87 %/94 % (anal) in chagasic specimens. In the myenteric plexus, NF-positive neurons co-staining for NOS and VIP also increased proportionally. The almost complete lack of dendritic structures in ganglia of chagasic specimens hampered morphological identification. DISCUSSION AND CONCLUSION: We suggest that preponderance of inhibitory, intramuscular nerve fibres may be one factor explaining the chronic dilation. Since the nerve fibre imbalance is most pronounced in the anal, non-dilated segment, other components of the motor apparatus (musculature, interstitial cells, submucosal neurons) have to be considered.

[Localization of cystathionine beta-synthase in digestive tract of the masu salmon Onchorhynchus masou (Teleostei)].

By immunohistochemical method the hydrogen sulfide (H2S)-producing system was studied in digestive tract in fry and adult individuals of the masu salmon Onchorhynchus masou. The total and age-related peculiarities have been revealed in morphology, distribution, and the amount of enteral cystathionine beta-synthase (CBS)-immunopositive neurons. They have been established to be present in fry only in esophagus a stomach, while in adult fish--along the entire length of the digestive tract, the number of marked cells in esophagus, stomach, and distal intestine exceeding that in the proximal and middle intestines. In fry and in adult fish the neurons and nerve fibers are located in branches of vagus, in intermuscular and submucosal nerve plexuses, in serosal and muscle layers. There are detected uni-, bi-, and much seldom the multipolar neurons surrounded by numerous poorly and undifferentiated nerve cells. Besides, the CBS-immunopositive netve fibers were present in the subepithelial area of the duct of swim bladder.

Immunoreactivity for high-affinity choline transporter colocalises with VAChT in human enteric nervous system.

Cholinergic nerves are identified by labelling molecules in the ACh synthesis, release and destruction pathway. Recently, antibodies against another molecule in this pathway have been developed. Choline reuptake at the synapse occurs via the high-affinity choline transporter (CHT1). CHT1 immunoreactivity is present in cholinergic nerve fibres containing vesicular acetylcholine transporter (VAChT) in the human and rat central nervous system and rat enteric nervous system. We have examined whether CHT1 immunoreactivity is present in nerve fibres in human intestine and whether it is colocalised with markers of cholinergic, tachykinergic or nitrergic circuitry. Human ileum and colon were fixed, sectioned and processed for fluorescence immunohistochemistry with antibodies against CHT1, class III beta-tubulin (TUJ1), synaptophysin, common choline acetyl-transferase (cChAT), VAChT, nitric oxide synthase (NOS), substance P (SP) and vasoactive intestinal peptide (VIP). CHT1 immunoreactivity was present in many nerve fibres in the circular and longitudinal muscle, myenteric and submucosal ganglia, submucosa and mucosa in human colon and ileum and colocalised with immunoreactivity for TUJ1 and synaptophysin confirming its presence in nerve fibres. In nerve fibres in myenteric ganglia and muscle, CHT1 immunoreactivity colocalised with immunoreactivity for VAChT and cChAT. Some colocalisation occurred with SP immunoreactivity, but little with immunoreactivity for VIP or NOS. In the mucosa, CHT1 immunoreactivity colocalised with that for VIP and SP in nerve fibres and was also present in vascular nerve fibres in the submucosa and on epithelial cells on the luminal border of crypts. The colocalisation of CHT1 immunoreactivity with VAChT immunoreactivity in cholinergic enteric nerves in the human bowel thus suggests that CHT1 represents another marker of cholinergic nerves.

Resection of the nerves bundle from the sphenopalatine ganglia tend to increase the infarction volume following middle cerebral artery occlusion.

Blocking or impairment of the sphenopalatine ganglia (SPG) is an effective therapy of cluster headache and other pain syndromes. Contrarily, unilateral SPG-stimulation reduces infarction size in the rat permanent suture model. Well, what are the effects of the SPG damage on the following brain ischemia? This study was aimed to investigate the effects of resection of the nerves bundle from the SPG of rat on the brain lesions following middle cerebral artery occlusion (MCAO), and evaluated the roles of the nitric oxygen synthase (NOS) immunoreactive perivascular nerves of cerebral arteries in MCAO. We found that 7 days after bilateral resections of the nerves bundle from the SPG, the NOS activity perivascular nerves in the middle cerebral arteries disappeared, and the infarction volume and the TUNEL positive cells increased significantly after 24 h MCAO, which implicated that the NOS contained nerves from the SPG maybe have an important role in the MCAO.

Microanatomical and immunohistochemical study of the human lateral antebrachial cutaneous nerve of forearm at the antecubital fossa and its clinical implications.

Changes in the intraneural anatomy with age can cause poor prognosis of nerve repair in patients after nerve injury. The occurrence of Complex Regional Pain Syndrome-Type II, secondary to peripheral nerve injury, is common. The purpose of this study is to asses changes in cross-sectional anatomy of the lateral antebrachial cutaneous nerve of forearm (LCNF) at the antecubital fossa in the fascicular, nonfascicular components (adipose and nonadipose tissue), and sympathetic fibers area with respect to age. For the purpose of the study, 32 human (37-88 years) fresh cadaveric LCNF were collected from left-antecubital fossae and processed for histological, morphometric analysis [total cross-sectional (Asc), fascicular (Af), and nonfascicular area (Anonf)], and immunohistochemical method (tyrosine hydroxylase) for sympathetic fibers. The LCNF's average total cross-sectional area was 3.024 mm(2), and fascicular area was 0.582 mm(2). The average number of fascicles per mm(2) was 3.09. The cross-sectional area in the nerve was mainly occupied by nonfascicular connective tissue (80.75%). There was increased adipose tissue deposition (48.48% of Asc) and decreased collagen fibers (32.24% of Asc) in interfascicular domains without any definite relationship with age. The average sympathetic fiber area was 0.026 mm(2) within the nerve fascicular area without any correlation with age. In LCNF, there was more adipose tissue and less collagen fibers deposition in the interfascicular domains of all age cases, and this may act as an obstacle for nerve fiber regeneration on using LCNF as an interpositional nerve graft.

[Nitric oxide in the mechanisms of afferent innervations of arteries of the brain].

Structural elements of afferent innervations of brain arteries in rats such as receptors and nervous fibers, neurons of ganglia jugularis unit and the nucleus of a single way were investigated with the help of histochemical and electron cytochemical methods. The presence of three types of receptors and afferent fibers has been established in vessels. Neurons with positive reaction to NADPH-diaphorase have been allocated in the ganglia jugularis unit and the nucleus of a single way (17.4 and 24.5% accordingly).

Delayed Treatment With Low-intensity Extracorporeal Shock Wave Therapy in an Irreversible Rat Model of Stress Urinary Incontinence.

OBJECTIVE: To determine the outcomes and mechanisms of delayed low-intensity extracorporeal shock wave therapy (Li-ESWT) in a rat model of irreversible stress urinary incontinence (SUI). MATERIALS AND METHODS: Twenty-four female Sprague-Dawley rats were randomly assigned into 3 groups: sham control, vaginal balloon dilation + ß-aminopropionitrile (BAPN; SUI group), and vaginal balloon dilation + BAPN + treatment with Li-ESWT (SUI-Li-ESWT group). An irreversible SUI model was developed by inhibiting the urethral structural recovery with BAPN daily for 5 weeks. Thereafter, in the SUI-Li-ESWT group, Li-ESWT was administered twice per week for 2 weeks. After a 1-week washout, all 24 rats were evaluated with functional and histologic studies at 17 weeks of age. Endogenous progenitor cells were detected via the EdU-labeling method. RESULTS: Functional analysis with leak point pressure testing showed that the SUI-Li-ESWT group had significantly higher leak point pressures compared with untreated rats. Increased urethral and vaginal smooth and striated muscle content and increased thickness of the vaginal wall were noted in the SUI-Li-ESWT group. The SUI group had significantly decreased neuronal nitric oxide /tyrosine hydroxylase positive nerves ratio in the smooth muscle layers of the urethra, while the SUI-Li-ESWT group had neuronal nitric oxide/tyrosine hydroxylase+ nerves ratio similar to that of the control group. The continuality of urothelial cell lining was also improved in the SUI-Li-ESWT group. In addition, there were significantly increased EdU-positive cells in the SUI-Li-ESWT group. CONCLUSION: Li-ESWT appears to increase smooth muscle content in the urethra and the vagina, increase the thickness of urethral wall, improve striated muscle content and neuromuscular junctions, restore the integrity of the urothelium, and increase the number of EdU-retaining progenitor cells in the urethral wall.

The constitutive activation of extracellular signal-regulated kinase 1 and 2 in periodontal ligament nerve fibers.

BACKGROUND: The extracellular signal-regulated kinases 1 and 2 (ERK1/2) have been implicated in the inflammation-dependent sensitization of nociceptors. Because the periodontal ligament (PDL) contains numerous nociceptors and mechanoceptors, phosphorylation of ERK1/2 was investigated in nerve fibers of the PDL to elucidate the role of constitutive local activation of ERK1/2 in peripheral sensitization. METHODS: Decalcified free-floating sections of rat molars with PDL were incubated using total (t)-ERK1/2 and phosphorylated (p)-ERK1/2 antibodies. For identification of nerve fibers in the PDL, double staining was performed using protein gene product 9.5 (PGP 9.5) with p-ERK1/2. To test whether p-ERK1/2 activated in sensory and mechanoreceptive terminals, double incubations were performed using p-ERK1/2 with calcitonin gene-related peptide (CGRP) and with calretinin. Labeled nerve fibers were quantified by the point-counting method. RESULTS: In cervical, midroot, and apical zones of the PDL, t-ERK1/2- and p-ERK1/2-labeled nerve fibers were found in close association with blood vessels. The p-ERK1/2-labeled free nerve fibers were often detected in cervical and apical areas of the PDL. In nerve fibers of the PDL, p-ERK1/2 was colocalized with PGP 9.5, CGRP, and calretinin. CONCLUSIONS: The perivascular distribution of t-ERK1/2 and p-ERK1/2 in nerve fibers in the PDL is compatible with a role for the constitutive activation of ERK1/2 in the neural regulation of blood vessels in the PDL. The colocalizations of p-ERK1/2 with CGRP and calretinin indicate that ERK1/2 is constitutively activated in a subpopulation of sensory and mechanoreceptive nerve terminals in the PDL.

[Nitroxidergic nerve fibers of intracerabral blood vessels].

Methods of light and electron microscopic histochemistry were applied to study the structure and distribution of NADPH-diaphorase-positive neurons and processes in the parietal area of rat cerebral cortex. It was found that the most of the neurons displayed close connections with the intracerebral vessels. In the cerebral cortex, the smallest distance between the axonal plasma membrane and smooth muscle cells of the intracerebral arteries was found to be no less than 0.3-0.5 microm. Neuronal cell bodies were located in the functionally important areas of the vessels (in the areas of lateral trunk branching and in arteriolar sources), while their processes accompanied the vessels, tightly embracing them with their branches. Quite often, the neurons, the dendrites of which make contacts with the bodies or processes of over- or underlying neurons, sent their nerve fibers to the arteries, veins and capillaries. Thus, nitroxidergic neurons or their groups may control the blood flow in the different areas of vascular bed, performing the functions of the local nerve center.

Impaired cerebellar long-term potentiation in type I adenylyl cyclase mutant mice.

Activation of adenylyl cyclase and the consequent production of cAMP is a process that has been shown to be central to invertebrate model systems of information storage. In the vertebrate brain, it has been suggested that a presynaptic cascade involving Ca influx, cAMP production, and subsequent activation of cAMP-dependent protein kinase is necessary for induction of long-term potentiation (LTP) at the cerebellar parallel fiber-Purkinje cell synapse. We have used mutant mice in which the major Ca-sensitive adenylyl cyclase isoform of cerebellar cortex (type I) is deleted to show that this results in an approximately 65% reduction in cerebellar Ca-sensitive cyclase activity and a nearly complete blockade of cerebellar LTP assessed using granule cell-Purkinje cell pairs in culture. This blockade is not accompanied by alterations in a number of basal electrophysiological parameters and may be bypassed by application of an exogenous cAMP analog, suggesting that it results specifically from deletion of the type I adenylyl cyclase.

Localisation and function of nerves in the aortic root.

Neural structures have been shown to be present in valve cusp tissue. We aimed to characterise the influence of neuronal stimulation on the component structures of the aortic root and cusps. Specimens of sinus, sinotubular junction (STJ), annulus and cusp tissue were dissected from porcine aortic roots and either stimulated with electrical field stimulation (EFS) in isolated tissue baths or fixed for immunohistochemical characterisation of neuronal structures. Sinus, STJ and annular tissue all gave tetrodotoxin-sensitive, frequency-dependent contractions in response to EFS. Contractions in annular tissue were only evident in tissue from the left- and non-coronary cusps, but not from the right-coronary cusp. Cusp tissue gave no contractile response to EFS, however in the presence of 1 mumol tetrodotoxin a strong contractile response was evident. This contractile response was unmasked when cusp tissue was stimulated in the presence of a nitric oxide synthase or guanylate cyclase inhibitors. Immunohistochemical analysis identified a network of neurofilament positive fibers in tissue from all aortic root structures that were associated with the presence of tyrosine hydroxylase and choline acetyl transferase. The nerve fibers in cusp tissue were in close proximity to the endothelial surface and demonstrated positive staining for neuronal nitric oxide synthase. Nerves in the aortic valve exert a nitric oxide-mediated neurogenic dilator tone in cusp tissue and are capable of producing contractile responses in different components of the aortic root. These responses could influence valve function in health and disease.

Chemical sympathectomy increases susceptibility to ocular herpes simplex virus type 1 infection.

The cornea is one of the most highly innervated tissues in the mammalian host. We hypothesized changes to cornea innervation through chemical sympathectomy would significantly alter the host response to the neurotropic viral pathogen, herpes simplex virus type 1 (HSV-1) following ocular infection. Mice treated with 6-hydroxydopamine hydrobromide displayed reduced tyrosine hydroxylase-positive fibers residing in the cornea. Sympathectomized mice were also found to show a transient rise in virus recovered in infected tissues and succumbed to infection in greater numbers. Whereas there were no differences in infiltrating leukocyte populations including HSV-1-specific cytotoxic T lymphocytes in the infected tissue, an increase in substance P and a decrease in IFN-gamma levels in the trigeminal ganglion but not brain stem of sympathectomized mice were noted. Sympathectomized mice treated with the neurokinin-1 receptor antagonist L703,606 had delayed mortality implicating the involvement of substance P in HSV-1-mediated death.

Traumatic neuroma of the lower lip with intraepithelial nerve fibers.

A 42-year-old man had noticed a small tender papule on his lower lip, and the papule clinically became unnoticeable after cryosurgery. He visited our clinic because the lesion recurred up to the original size after 9 months. On examination, a linear scar and a papule, 4 mm in diameter, were observed on the mucosal lower lip. The papule was resected and histopathologically showed proliferation of nerve fibers in irregular and tortuous fascicles, thus establishing the diagnosis of traumatic neuroma. Immunohistochemical staining by antineuron-specific enolase (NSE) antibody showed proliferation of axons in the upper lamina propria and even in the mucosal epithelium overlying the tumor. Traumatic neuroma of the lower lip is very rare, and a literature search showed only one reported case. Intraepithelial proliferation of axons may be one of the characteristics of mucosal traumatic neuroma.

Distribution of RET immunoreactivity in the rodent spinal cord and changes after nerve injury.

RET (for "rearranged during transfection") is a transmembrane tyrosine kinase signaling receptor for members of the glial cell line-derived neurotrophic factor (GDNF) family of ligands. We used RET immunohistochemistry (IHC), double-labeling immunofluorescence (IF), and in situ hybridization (ISH) in adult naïve and nerve-injured rats to study the distribution of RET in the spinal cord. In the dorsal horn, strong RET-immunoreactive (-ir) fibers were abundant in lamina II-inner (II(i)), although this labeling was preferentially observed after an antigen-unmasking procedure. After dorsal rhizotomy, RET-ir fibers in lamina II(i) completely disappeared from the dorsal horn, indicating that they were all primary afferents. After peripheral axotomy, RET-ir in primary afferents decreased in lamina II(i) and appeared to increase slightly in laminae III and IV. RET-ir was also observed in neurons and dendrites throughout the dorsal horn. Some RET-ir neurons in lamina I had the morphological appearance of nociceptive projection neurons, which was confirmed by the finding that 53% of RET-ir neurons in lamina I colocalized with neurokinin-1. GDNF-ir terminals were in close proximity to RET-ir neurons in the superficial dorsal horn. In the ventral horn, RET-ir was strongly expressed by motoneurons, with the strongest staining in small, presumably gamma-motoneurons. Increased RET expression following peripheral axotomy was most pronounced in alpha-motoneurons. The expression and regulation pattern of RET in the spinal cord are in line with its involvement in regenerative processes following nerve injury. The presence of RET in dorsal horn neurons, including nociceptive projection neurons, suggests that RET also has a role in signal transduction at the spinal level. This role may include mediating the effects of GDNF released from nociceptive afferent fibers.

Demonstration of choline acetyltransferase of a peripheral type in the rat heart.

Cholinergic innervation of the heart has been analyzed using cholinergic markers including acetylcholinesterase, choline acetyltransferase (ChAT), and vesicular acetylcholine transporter (VAChT). In the present study we demonstrate putative cholinergic nerves in the rat heart using an antibody to ChAT of a peripheral type (pChAT), which is the product of a splice variant of ChAT mRNA and preferentially localized to peripheral cholinergic nerves. Expression of mRNAs for pChAT and the conventional form of ChAT (cChAT) were verified in the rat atrium by RT-PCR. Localization of both protein products in the atrium was confirmed by Western blotting. Virtually all neurons and small intensely fluorescent cells in the intrinsic cardiac ganglia were stained immunohistochemically for pChAT. The density of pChAT-positive fibers was very high in the conducting system, high in both atria, the right atrium in particular, and low in the ventricular walls. pChAT and VAChT immunoreactivities were closely associated in some fibers and fiber bundles in the ventricular walls. These results indicate that intrinsic cardiac neurons homogeneously express both pChAT and cChAT. Furthermore, innervation of the ventricular walls by pChAT- and VAChT-positive fibers provides morphological evidence for a significant role of cholinergic mechanisms in ventricular functions.

Early development of the optic nerve in the turtle Mauremys leprosa.

We show the distribution of the neural and non-neural elements in the early development of the optic nerve in the freshwater turtle, Mauremys leprosa, using light and electron microscopy. The first optic axons invaded the ventral periphery of the optic stalk in close relationship to the radial neuroepithelial processes. Growth cones were thus exclusively located in the ventral margin. As development progressed, growth cones were present in ventral and dorsal regions, including the dorsal periphery, where they intermingled with mature axons. However, growth cones predominated in the ventral part and axonal profiles dorsally, reflecting a dorsal to ventral gradient of maturation. The size and morphology of growth cones depended on the developmental stage and the region of the optic nerve. At early stages, most growth cones were of irregular shape, showing abundant lamellipodia. At the following stages, they tended to be larger and more complex in the ventral third than in intermediate and dorsal portions, suggesting a differential behavior of the growth cones along the ventro-dorsal axis. The arrival of optic axons at the optic stalk involved the progressive transformation of neuroepithelial cells into glial cells. Simultaneously with the fiber invasion, an important number of cells died by apoptosis in the dorsal wall of the optic nerve. These findings are discussed in relation to the results described in the developing optic nerve of other vertebrates.