Dendritic growth following labyrinthectomy in the squirrel monkey. Light and electron microscopic studies

Concentration-dependent differential induction of necrosis or apoptosis by HIV-1 lytic peptide 1

The mechanism by which human immunodeficiency virus type 1 induces depletion of CD4+ T-lymphocytes remains controversial, but may involve cytotoxic viral proteins. Synthetic peptides (lentivirus lytic peptide type 1) corresponding to the carboxyl terminus of the human immunodeficiency virus type 1 transmembrane glycoprotein induce cytopathology at concentrations of 100 nM and above. At these concentrations lentivirus lytic peptide type 1 disrupts mitochondrial integrity of CD4+ T-lymphoblastoid cells and induces other changes characteristic of necrosis. In contrast, at concentrations of 20 nM, lentivirus lytic peptide type 1 potently induces apoptosis. Thus, the mechanism by which human immunodeficiency virus type 1 mediates cell death, necrosis or apoptosis, may depend, in part, on the tissue concentration of transmembrane glycoprotein.

A morphological and morphometric study of the peripheral process of the human vestibular nerve following posterior cranial fossa neurectomy

Three vestibular nerve specimens removed at transmeatal neurectomy were studied in order to understand better retrograde degeneration and regeneration after vestibular neurectomy in the posterior cranial fossa. In two cases this procedure followed retrolabyrinthine retrosigmoid posterior fossa vestibular neurectomy. The subjects, three patients with Menière's disease, were compared with one another and two autopsy controls with no known otological problem. The specimens were obtained at the distal end of the internal auditory canal and transversely sectioned. Many collapsed Schwann cell basement membranes were observed. The ratio of small-diameter nerve fibres increased significantly after neurectomy. Onion bulb formation around myelinated nerve fibres with small diameters and Schwann cell proliferation around the soma of vestibular ganglion cells reflected remyelination. We conclude that peripheral processes of vestibular nerve fibres can undergo retrograde degeneration and subsequent regeneration after transection of the central process.

Both necrosis and apoptosis contribute to HIV-1-induced killing of CD4 cells

BACKGROUND

Data currently available on HIV-1-induced cytopathology is unclear regarding the mechanism of cell killing.

OBJECTIVE

To clarify the extent to which apoptosis or necrosis is involved in HIV-1-induced cell death in view of conflicting existing data.

METHODS

T lymphoblastoid cells or peripheral blood mononuclear cells were infected by various strains of HIV-1 and the numbers of apoptotic or necrotic cells were quantified at various times after infection using video-image analysis techniques; the results were compared with the amount of fragmented DNA using a quantitative method. Measurement of mitochondrial transmembrane potential (deltapsi(m)) and intracellular calcium concentrations [Ca2+]i was performed with fluorescent probes and fluorescence concentration analysis (FCA).

RESULTS

Although lymphoblastoid and monocytoid cells acutely infected by HIV-1 had increased levels of fragmented DNA, a marker of apoptotic cell death, few (<12%) had condensed chromatin and fragmented nuclei, the morphological features of apoptosis. The predominant alterations in acutely infected cells were distended endoplasmic reticulum and abnormal mitochondria; these ultrastructural changes are consistent with necrosis, although some infected cells simultaneously displayed features of both necrosis and apoptosis. Viability of cells persistently infected by HIV-1 was only minimally reduced from that of uninfected cells. This reduction was accounted for by an increased propensity of the persistently infected cells to die by apoptosis. Alterations in [Ca2+]i and deltapsi(m) occurred in both acutely and persistently infected cells.

CONCLUSION

Both necrosis and apoptosis contribute to HIV-1-induced killing of CD4 cells.

A dose-response analysis of the beneficial effects of the ACTH-(4-9) analogue, Org 2766, on behavioural recovery following unilateral labyrinthectomy in guinea-pig

1. After removal of the peripheral vestibular receptors in one inner ear (unilateral labyrinthectomy, UL), oculo-motor and postural symptoms occur but disappear over time in a process of recovery known as vestibular compensation. 2. ACTH-(4-10), a fragment of the adrenocorticotrophic hormone (ACTH) molecule, which is devoid of corticotrophic activity, has been shown to enhance vestibular compensation. The present study investigated the effect of the ACTH-(4-9) analogue, Org 2766, on vestibular compensation in guinea-pig. Org 2766 is reported to be more potent behaviourally than ACTH-(4-10). 3. After UL, Org 2766 was delivered via an osmotic minipump implanted s.c. to 30 animals randomly assigned to one of five conditions: 1, 5, 10, 20 or 40 nmol kg-1 Org 2766, every 4 h for 52 h post-UL. Although infusion was continuous, in the present study the doses are expressed as nmol per 4 h in order to compare the results to a previous study in which animals received a discrete dose of ACTH-(4-10) at the end of each 4 h period. All animals were compared to saline controls (n = 6). 4. Three symptoms of UL, spontaneous ocular nystagmus, roll head tilt and yaw head tilt, were measured every 4 h for 52 h, beginning at 10 h post-UL. 5. Rates of infusion of 1, 5 and 10 nmol kg-1 accelerated spontaneous nystagmus compensation; 20 nmol kg-1 produced a significant decrease in the frequency of spontaneous nystagmus, as well as accelerating its compensation; 40 nmol kg-1 had no significant effect on spontaneous nystagmus compensation. 6. In comparison to the effects of Org 2766 on spontaneous nystagmus compensation, Org 2766 had little effect on the compensation of the postural symptoms, yaw head tilt and roll head tilt. Only 5 and 40 nmol kg-1 produced a significant change in postural compensation, and this was a reduction in the rate of roll head tilt compensation.7. At the optimal infusion rate of 20 nmol kg-1 every 4 h, Org 2766 produced a similar effect on spontaneous nystagmus compensation to that of ACTH-(4-10). However, Org 2766 was effective in accelerating spontaneous nystagmus compensation at much smaller doses per 4 h period than ACTH-(4-10). Org 2766 did not have the same effect on. postural compensation as it had on the compensation of spontaneous nystagmus.

Neuronal degeneration of primary cochlear and vestibular innervations after local injection of sisomicin in the guinea pig

This paper reports on a dynamic study of the morphological changes within the cochlear and vestibular ganglia of the guinea pig after local application of Sisomicin in the inner ear. The treatment leads to a rapid, complete and irreversible destruction of the sensory cells in the cochlear and vestibular neuroepithelia. A progressive degeneration of the type I and type II afferent neurons, presenting a decreasing gradient from the base towards the apex of the cochlea, is rapidly observed and becomes almost complete as early as 15 days after the peripheral injury. Five months after the treatment the spiral ganglion cells have almost completely disappeared. At this time the vestibular ganglion cell density appears normal but the neurons exhibit important signs of alteration. Such damage to the cochlear and vestibular afferent neurons may result from either retrograde neuronal degeneration and/or direct neurotoxic effect of the drug. Thus the combination of the two mechanisms could lead to neuronal losses in spiral and Scarpa's ganglia after the local aminoglycoside intoxication of the inner ear. The difference in the time course of degeneration for these two afferent ganglia could be due to their specific susceptibilities or to their different anatomical locations.

Bone repair in the otic capsule of the rabbit

The repair of 1 mm drill hole lesions in rabbit long bones and otic capsules was studied in undecalcified sections. Following surgery, bone formation was monitored during 12 weeks by intravital sequential time labeling with bone-seeking fluorochromes. In diaphyseal bone, initial repair by trabecular woven bone was accompanied by a transient remodeling response in primary repair bone and the surrounding compacta. In comparison, capsular defects showed a slightly deficient initial repair by woven bone which, once formed, persisted unchanged with no subsequent osteonal remodeling. In the surrounding capsule, the remodeling response was subtle and its duration much shorter. Moreover, the centrifugal distribution of bone remodeling units around inner ear spaces was preserved, suggesting that capsular repair is affected by the same morphogenetic field that controls perilabyrinthine growth, modeling and remodeling. The significance of these findings is briefly discussed in relation to otosclerosis and cochlear implant strategies.

Pretreatment with MK-801 reduces spontaneous nystagmus following unilateral labyrinthectomy

Unilateral labyrinthectomy results in a syndrome of ocular motor and postural symptoms which abate over time in a process of behavioural recovery known as vestibular compensation. We have previously suggested that an increased Ca2+ influx in ipsilateral vestibular nucleus (VN) neurons at the time of the unilateral labyrinthectomy may exacerbate the depression of VN resting activity caused by the loss of excitatory input from the VIIIth nerve. In order to further test this hypothesis, we administered (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801; 1.0 or 2.5 mg/kg i.p.), which blocks Ca2+ influx via NMDA receptor-mediated ion channels, to guinea pigs 0.5 h before unilateral labyrinthectomy and examined the effects on three symptoms of unilateral labyrinthectomy: spontaneous ocular nystagmus, yaw head tilt and roll head tilt. Pretreatment with MK-801 significantly altered the time course of the vestibular compensation of spontaneous nystagmus and yaw head tilt but had no significant effect on roll head tilt; in particular, 2.5 mg/kg MK-801 depressed spontaneous nystagmus frequency at 10 and 20 h post-labyrinthectomy relative to saline controls (P less than 0.05, post-hoc Scheffé F-test). The reduction in spontaneous nystagmus frequency was not simply a result of extended anesthesia, since other control animals, which received additional injections of the general anesthetic in order to achieve equivalent sleep times to the MK-801 group, did not show reduced spontaneous nystagmus frequency.(ABSTRACT TRUNCATED AT 250 WORDS)

Specificity of VIIIth nerve regeneration in lower vertebrates

From the initial studies of Sperry (Am. J. Physiol, 144:735-741, 1945) to more recent investigations, the regenerative capacity of the VIIIth cranial nerve in nonmammalian vertebrates has been noted for its robust and accurate recovery of functional connections after transection. The VIIIth cranial nerve contains nerve fibers that link functionally distinct sensory epithelial to various areas within the central nervous system (CNS), yet after transection these multiple components of the nerve navigate back to their original central target areas, without innervating inappropriate nuclei. A number of factors may be required to establish and direct VIIIth nerve regeneration. Cellular interactions appear to be necessary for the initiation of outgrowth and the maintenance of neural connections. The release of chemotropic substances from target cells has been postulated as the most likely mechanism guiding the reinnervation of central targets. Furthermore, the growth characteristics of these neurons in tissue culture, without target cells present, indicates that intrinsically regulated growth features may also contribute to the process of VIIIth nerve regeneration.

Regeneration of the eighth cranial nerve in the bullforg, Rana catesbeiana

The present study was done in order to document the ability of the eighth cranial nerve of the bullfrog (Rana catesbeiana) to regenerate, the anatomic characteristics of the regenerated fibers, and the specificity of projections from individual endorgan branches of the nerve. The eighth cranial nerve was sharply transected between the ganglion cells and the brain stem in 40 healthy bullfrogs and allowed to regenerate. Anatomic studies were performed in these animals a minimum of 3 months postoperatively. Horseradish peroxidase was used to label the whole vestibular nerve or its individual endorgan branches. Labeled regenerated fibers could be identified crossing the site of the nerve section and projecting centrally to the vestibular nuclei in a pattern similar to that of normal frogs. Labeling of individual branches showed that regenerated fibers innervated the same specific areas found in normal frogs. Unlike normal animals, both thick and thin fibers projected to the medial nucleus.

Remodeling patterns in the bony otic capsule of the dog

Quantum-type bone remodeling was studied in undecalcified temporal bones and long bone specimens from adult mongrel dogs by means of combined microradiography, osteofluorochrome labeling, and osteoid staining. The overall turnover rate of capsular bone was estimated to be low compared to that of extracapsular compact bone. Evolving secondary osteons were distributed centrifugally relative to the perilymphatic space. Moreover, a zone of bone tissue enclosing perilymphatic spaces was found completely devoid of evolving secondary osteons. Throughout the otic capsule, segmentary perivascular foci of resorption and formation were present. These findings indicate that remodeling of capsular bone is subject to sustained local inhibition. The significance of this conclusion is considered with special reference to otosclerosis.

Survival of the vestibular nerve after labyrinthectomy in the cat

Temporal bone studies in cat, monkey, and man demonstrate that the cell bodies of the primary vestibular neurons located in Scarpa's ganglion persist after labyrinthectomy. However, it is not known whether the centrally directed axon process of deafferented vestibular neurons survive or degenerate after labyrinthectomy. If the central axon were to persist, then the primary vestibular neuron could influence vestibular compensation or produce symptoms of vestibular dysfunction. In the present study the temporal bones and brain stem of four cats were prepared for light microscopic examination with hematoxylin-eosin, silver, and trichrome connective tissue stains. Cell counts within Scarpa's ganglion were performed. After labyrinthectomy, many intact axons were demonstrated in the brain stem, a finding that correlated with survival of neurons in Scarpa's ganglion. This study provides anatomic evidence that primary vestibular neurons that survive labyrinthectomy may retain their central axon processes. The persistence of this neural pathway and data from behavioral studies in the cat suggest that vestibular neurons may affect vestibular compensation after labyrinthectomy. Deafferented vestibular neurons may play a role in human vestibular compensation and dysfunction.