Sequential immunophenotypic analysis of mast cells in a case of systemic mast cell disease evolving to a mast cell leukemia

The immunophenotypic characteristics of both bone marrow (BM) and peripheral blood (PB) mast cells (MC), from a patient suffering from an aggressive systemic mast cell disease (SMCD), were sequentially analyzed by flow cytometry using direct immunofluorescence. Analysis was carried out at diagnosis, during clinical response induced by interferon alfa-2h/prednisone therapy, and later at relapse. Our results show that together with the CD117 and IgE characteristic markers, at diagnosis BM MC showed strong expression of CD11c, CD13, CD29, CD33, CD44, CD45, CD63, and CD71, and they were also positive for CD2, CD22, CD25, and CD54 although at a lower level. PB MC displayed similar immunophenotypic characteristics although they had a lower expression of CD11c, CD25, CD33, CD63, CD69, and CD71 with a higher reactivity for CD117. Unlike BM MC, PB MC were weakly positive for CD41a and CD61. Sequential studies showed decreased numbers of both BM and PB MC during clinical response associated with a higher expression of the CD29 and CD54 adhesion molecules. In turn, clinical relapse was related to increased numbers of PB and BM MC together with lower CD2, CD11c, CD45, and and CD54 expression and a higher reactivity for the CD117 and CD25 antigens. CD2 had become negative at the last follow-up study. In addition, an increased proportion of S-phase MC was observed at relapse. These findings suggest that the assessment of the quantitative expression of cell-adhesion molecules and growth-factor receptors together with cell cycle studies of mast cells could be of value for monitoring therapy and predicting clinical outcome in aggressive SMCD.

Efficacy of pegylated-liposomal doxorubicin in the treatment of AIDS-related Kaposi's sarcoma after failure of standard chemotherapy

PURPOSE

To determine the efficacy and safety of pegylated-liposomal doxorubicin in patients with AIDS and Kaposi's sarcoma (AIDS-KS) who experienced failure of standard chemotherapy.

METHODS

Fifty-three patients with advanced AIDS-KS who experienced disease progression or intolerable toxicities while receiving standard doxorubicin/bleomycin/vincristine (ABV) or bleomycin/vincristine (BV) chemotherapy were identified from a cohort of patients who were then treated with pegylated-liposomal doxorubicin. Patients received 20 mg/m2 pegylated-liposomal doxorubicin (Doxil; Sequus Pharmaceuticals, Inc, Menlo Park, CA) every 3 weeks.

RESULTS

Nineteen patients (36%) had a partial response (PR) and one patient had a clinical complete response (CCR). The median duration of response and time (from study entry) to treatment failure were 128 and 134 days, respectively. Of 28 patients who experienced disease progression while receiving combination regimens that contained standard doxorubicin, the PR rate was 32%, which suggests that the pegylated-liposomal encapsulation increases the therapeutic effect of doxorubicin. Patients obtained clinical benefits such as flattening of lesions (48%), improved lesion color (56%), relief of pain (45%), and loss of edema (83%). Forty-nine percent of patients had more than one clinical benefit. The most common adverse effect was leukopenia, which occurred in 40% of patients. Only 15% of patients had nausea and/or vomiting, none of which was severe; 9% experienced alopecia, also generally mild.

CONCLUSION

Pegylated-liposomal doxorubicin offers a new alternative for treatment of patients who have experienced failure of standard chemotherapy for AIDS-KS.

Simultaneous assay of nitrite, nitrate and chloride in meat products by flow injection

A flow injection (FI) analytical method for the simultaneous assay of nitrite, nitrate and chloride in meat products is reported. The method is based on the potentiometric determination of chloride using a tubular ISE and on the spectrophotometric determination of nitrite. The FI system consisted in splitting the flow after potentiometric detection using a tubular detector and the subsequent confluence of the flow before reaching the spectrophotometric detector. This allowed the reduction of nitrate to nitrite in part of the sample plug on an on-line copper cadmium reductor column. Since each channel had a different residence time, two peaks were obtained for nitrite and nitrite plus nitrate. Spectrophotometric determination was made after a diazotization-coupling reaction. The results obtained were in good agreement with reference procedures and showed adequate precision (RSDs less than 6% for chloride and nitrite and 2% for nitrate). A high sampling rate was obtained (120 determinations per hour corresponding to 40 samples per hour).

Influence of dietary nucleotides on liver structural recovery and hepatocyte binuclearity in cirrhosis induced by thioacetamide

Intake of thioacetamide in drinking water causes liver cirrhosis in rats, which exhibit many changes similar to human disease. Nucleotides play an important part in major cellular functions, and recent studies suggest that dietary nucleotides may be considered 'semi-essential' nutrients in situations when an inadequate dietary supply may affect the growth of tissues with a rapid turnover rate. The aim of this study was to assess the effect of dietary nucleotides on lesions in thioacetamide-cirrhotic rats, and to calculate the proportion of mono and binucleated hepatocytes in different experimental groups. Rats were given cirrhosis by oral intake of thioacetamide in the drinking water (300 mg/l) for four months. One group was treated with a standard nucleotide free diet, and another group was treated with the same diet supplemented with 250 mg of nucleotides per 100 g of diet for one and two weeks. A striking reduction (mean (SEM)) in the proportion of binucleated cells was seen in thioacetamide-cirrhotic rats (4.8 (1.3) v 21.4 (1.0)), showing a change in the mitotic mechanism in focal lesions. Cirrhotic rats that consumed a semipurified diet supplemented with nucleotides during two weeks showed considerable histological regeneration of the injured liver. These animals had significantly higher proportion of binucleated cells than did animals at the beginning of the recovery period (8.2 (1.2) v 4.8 (1.3)). In the second week of recovery, both types of diet (F = 5.54, p < 0.05) and the previous administration of thioacetamide (F = 142.82, p < 0.001) had significant effects on the percentage of binucleated hepatocytes.

Influence of administration of long-chain polyunsaturated fatty acids on process of histological recovery in liver cirrhosis produced by oral intake of thioacetamide

Patients with liver cirrhosis frequently show some degree of protein-energy malnutrition and obviously require nutritional support. In this study, the treatment of rats consisted of the ad libitum oral intake of a 300 mg/liter thioacetamide solution, used as drinking water for four months. Thioacetamide treatment produced a severe alteration in the plasma fatty acid profile with significant decreases of these, which mimicked changes described in human cirrhosis. This hepatotoxic agent causes nodular cirrhosis, with loss of the normal architecture of the liver and disruption of the vascular pattern. The goal of the study was to evaluate the influence of n-3 and n-6 series long-chain polyunsaturated fatty acid dietary supplementation in experimental animals and to assess the effects of those dietary components on structural recovery in the liver. Significant increases of saturated and monounsaturated fatty acids as well as n-6 polyunsaturated fatty acids were seen only in the animals given the n-6 polyunsaturated fatty acid supplemented diet. However, only rats given the standard diet exhibited some degree of histological regeneration.

20-Hydroxyeicosatetraenoic acid is formed in response to EGF and is a mitogen in rat proximal tubule

Hydroxyeicosatetraenoic acid (20-HETE) is a major cytochrome P-450-arachidonic acid metabolite in the rat kidney, and its synthesis along the nephron is specifically localized to the proximal tubule, where receptor density for epidermal growth factor (EGF) is the highest. EGF stimulated endogenous 20-HETE formation in a concentration and time-dependent manner, i.e., from 1.6 to 2.6 +/- 0.3 and 3.0 +/- 0.6 pmol 20-HETE.mg-1.min-1 at 10(-8) and 10(-7) M EGF, respectively. The effect of 20-HETE on proximal tubular cell proliferation was examined using primary cultures of rat proximal tubular cells and proximal tubular-derived cell lines, LLC-PK1 and opossum kidney OK. In both cell lines, 20-HETE increased thymidine incorporation into DNA with maximal effect at 10(-9) M. Addition of 20-HETE to serum-deprived LLC-PK1 or OK cells for 48 h caused a concentration-dependent increase in cell number with maximal effect at 10(-9) M. This effect was specific, as structurally similar eicosanoids such as 20-COOH-arachidonic acid, 19(R)-HETE, and 19(S)-HETE did not increase cell number. In 4-day primary cultures of proximal tubular cells, EGF (10(-9) M) and 20-HETE (10(-9) M) increased bromodeoxyuridine (BrdU) incorporation by 40 and 28%, respectively. Addition of both resulted in a twofold increase in BrdU incorporation. Although 20-HETE synthesis in cultured cells is greatly diminished with time, significant picomolar concentrations can be obtained in 4-day cultures. Addition of 17-octadecynoic acid (17-ODYA), an inhibitor of 20-HETE synthesis, significantly inhibited EGF-stimulated BrdU incorporation. The demonstrations that EGF stimulates proximal tubular 20-HETE production and that the latter is a potent mitogen to these cells suggests that 20-HETE may act as a mediator of the EGF effect on cellular growth in the proximal tubule.

Clinical, biological, and immunophenotypical characteristics of B-cell chronic lymphocytic leukemia with trisomy 12 by fluorescence in situ hybridization

The clinical, biological, and immunophenotypical characteristics of B-cell chronic lymphocytic leukemia (B-CLL) patients with trisomy 12 detected by fluorescence in situ hybridization (FISH) using a chromosome 12 alpha-centromeric probe (D12Z3) were analyzed in the present study. From a total of 104 consecutive B-CLL patients, 21 (20%) displayed trisomy 12, the percentage of trisomic cells ranging from 13% to 76%. From the clinico-biological point of view, patients with trisomy 12 were associated with atypical CLL morphology (43% vs 10%, P = 0.04) and BM diffuse pattern (75% vs. 25%, P = 0.02) together with increased WBC counts (141 +/- 220 vs. 58 +/- 67 x 10(9)/L, P = 0.04). In contrast, no association was detected between the presence of trisomy 12 and other disease characteristics such as age, sex, clinical stage, hepatomegaly, lymphadenopathies, haemoglobin levels and platelet counts, and the cell cycle distribution of PB leukocytes in both groups of patients. Trisomy 12 patients had a significantly higher expression of the FMC7 antigen both in percentage (34 +/- 34% vs. 13 +/- 20%, P = 0.02) and absolute numbers (29 +/- 62 vs. 7 +/- 17 x 10(9)/L, P = 0.007). No major differences were found regarding the expression of mouse rosettes, CD19+, and CD19+/CD5+ lymphocytes. Upon analyzing the correlations between the disease characteristics of trisomy 12 cases, significant associations were found between the percentage of trisomic cells and both the WBC count (r = 0.52, P = 0.02) and the PB lymphocyte count (r = 0.60, P = 0.007).(ABSTRACT TRUNCATED AT 250 WORDS)

A double-blind, multicenter comparative study of two regimens of clindamycin hydrochloride in the treatment of patients with acute streptococcal tonsillitis/pharyngitis

In a double-blind, prospective, randomized, multicenter study, 164 patients with a clinical and bacteriologic diagnosis of acute streptococcal tonsillitis/pharyngitis were enrolled to compare the efficacy and safety of two regimens of clindamycin. A rapid identification test of Group A beta-hemolytic streptococci (GABHS) was used to initiate the therapy; however, a positive tonsillar/pharyngeal culture was required at pretreatment to determine if the patient was assessable. Another culture was repeated at least 2 days after the 10 days of drug therapy. From 164 patients enrolled (mean age, 27.7 years; range, 14 to 60 years), 141 were assessable for efficacy; 22 patients were excluded because they did not have a positive culture at pretreatment and 1 patient did not complete the study due to a side effect (rash). All patients were included in the safety analysis. Patients received either clindamycin hydrochloride capsules 150 mg four times per day (QID) or clindamycin hydrochloride capsules 300 mg two times per day (BID) and placebo capsules BID for 10 days. There were no significant differences between groups in terms of demographics, medical history, and evolution of symptoms. The clinical efficacy rate in the two groups at day 12 was as follows: QID group--cured, 64 (92.8%) of 69 patients; improved, 5 (7.2%) of 69 patients; BID group--cured, 67 (93.1%) of 72 patients; improved, 5 (6.9%) of 72 patients. There were no significant differences between the groups. Both regimens were well tolerated with only 1 patient in the QID group who did not complete the therapy due to a rash.(ABSTRACT TRUNCATED AT 250 WORDS)

HIV-1 p17 synthetic peptide vaccine HGP-30: induction of immune response in human subjects and preliminary evidence of protection against HIV challenge in SCID mice

An HIV-1 p17 subunit vaccine, HGP-30, was evaluated in 38 HIV-1 seronegative individuals in phase I clinical trials in U.K. and U.S.A. The vaccine preparation induced cytotoxic T-cell (CTL) (11/25) and lymphocyte proliferation responses to KLH (19/20) and HGP-30/p17 (24/29) as well as antibody responses to HGP-30 (29/38) and KLH (38/38). The CTL activity was observed in a higher number of vaccine recipients (9/18) in the lower dose groups (10 and 25 micrograms/kg) than the vaccine recipients (2/7) in the 50 and 100 micrograms/kg dose group. These observations suggest that the 10-25 micrograms/kg vaccine dose may preferentially induce TH1 cell responses. TH1 cell responses have been suggested as important in inducing protective cell mediated immunity. The CTL response has been shown to be CD8+. In a pilot study in SCID mice, HIV-1 virus challenge studies in mice reconstituted with cells from an HGP-30 immunized individual showed protection against virus challenge as compared to SCID mice reconstituted with cells from a non-immunized subject. These studies suggest that HGP-30 is capable of inducing protective cellular immunity.

Arachidonic acid metabolism modulates vasopressin-induced renal vasoconstriction

Previous studies have shown that cytochrome P450-Arachidonic Acid (P450-AA) metabolites modify the vascular tone of several vessels and that vasopressin (AVP) stimulates P450-AA metabolism. Thus, in the present study, we decided to investigate if the vasoconstrictor effect of AVP is related to activation of P450-AA metabolism. We used the isolated perfused kidney of a rat, to test this hypothesis. Bolus injection of AVP (5.5, 11, 22 and 45 ng) increased the perfusion pressure of the isolated kidney of a rat by 66 +/- 2, 87 +/- 4, 110 +/- 2 and 130 +/- 3 mmHg respectively. This AVP-induced vasoconstriction was significantly reduced by inhibition of AA metabolism with ETYA, or 7 ethoxyresorsorufin (7ER). Furthermore, in vivo induction of P450 system with dexamethasone, enhanced the AVP-induced vasoconstrictor effect. Conversely, depletion of P450 system with SnCl2 diminished the vasoconstrictor response to AVP. Measurement of P450-14cAA metabolites in the renal effluent, showed the presence of 3 radioactive peaks. The % of the recovered radioactivity was 0.12 +/- 0.05%, 0.11 +/- 0.03% and 1.13 +/- 0.5% and corresponded to Dihydroxyeicosatrienoic acids (DHTs), Hydroxyeicosatetraenoic acids (HETEs) and Epoxyeicosatrienoic acids (EETs) respectively, when kidneys were stimulated by AVP (300 ng) the % recovered were 0.34 +/- 0.01%, 0.38 +/- 0.01% and 3.11 +/- 0.7% for the DHTs, HETEs and EETs respectively. Treatment with dexamethasone or SnCl2 potentiated or inhibited the AVP-dependent release of the P450-AA metabolites. In conclusion, we suggest that AVP stimulates AA metabolism via P450 pathway in the kidney and that these AA metabolites participate in the vasoconstrictor effect of AVP in the renal circulation.

Effect of dietary nucleotides on small intestinal repair after diarrhoea. Histological and ultrastructural changes

The effects of specific nutrients on intestinal maturation and repair after injury are practically unknown. The purpose of this work was to study the effects of dietary nucleotides on the repair of the intestinal mucosa after chronic diarrhoea induced by a lactose enriched diet in the weanling rat. One group of weanling rats was fed with a standard semipurified diet (control group), and another group was fed with the same diet containing lactose as the only soluble carbohydrate (lactose group). After 14 days the lactose group was allowed to recover for four weeks with the control diet (lactose-control group) or with the control diet supplemented with AMP, GMP, IMP, CMP, and UMP 50 mg/100 g each (lactose-nucleotide group). The control group was divided into two subgroups, which were fed with the control diet and the nucleotide supplemented diet for the same period (control-control group and control-nucleotide group). The lactose diet induced diarrhoea after 24 hours of feeding. Two weeks later there were changes in intestinal structure with loss of enterocyte microvillar surface, significant lymphocyte infiltration, supranuclear cytoplasmic vesiculation, decreased number of goblet cells, and enlarged mitochondria with low density and few cristae. After recovery from diarrhoea, animals fed the nucleotide enriched diet showed an intestinal histology and ultrastructure closer to that of the normal control group. Mitochondrial ultrastructure was closer to normal in comparison with the lactose-control diet group. In this second group the number of goblet cells as well as the villous height/crypt depth ratio was reduced and the number of intraepithelial lymphocytes increased compared with the nucleotide supplemented group. These results suggest that dietary nucleotides may be important nutrients for intestinal repair.

Recombinant human erythropoietin and health-related quality of life of AIDS patients with anemia

To evaluate the effect of recombinant human erythropoietin on anemia and health-related quality of life in patients with acquired immunodeficiency syndrome (AIDS), we initiated an observational study with an open-label multicenter treatment protocol that involved multiple academic and community physicians in the United States. Our subjects comprised 251 anemic (i.e., hematocrit < 30%) patients with a clinical diagnosis of AIDS using 1987 CDC criteria, age > or = 12 years, and serum erythropoietin level < or = 500 IU/L. The initial dosage of recombinant human erythropoietin was 4,000 units subcutaneously for 6 days each week. Based on the patient's response to therapy, the dosage was increased sequentially to 8,000 units subcutaneously for 6 days per week. Our measurements included changes in mean hematocrit and health-related quality of life. The interview included measures of energy/fatigue; physical, social, role and cognitive function; depression; health perceptions; and life satisfaction. Adverse experiences were also documented to assess safety. Changes in mean hematocrit level from a baseline of 27.9% to 33.6% at week 12 (p < .0001) and 34.5% at week 24 (p < .0001) were observed in patients treated with recombinant human erythropoietin. Adverse experiences, not clearly associated with AIDS, were reported by 10% of patients. Increases in energy (p < .05) were observed after 12 and 24 weeks of drug therapy, and increases in health perceptions were seen after 24 weeks (p < .05). No statistically significant increases or decreases were observed on measures of physical functioning, cognitive functioning, depression, social functioning, or home management activities over the 24-week follow-up. Anemia correctors (defined as hematocrit > or = 38%) showed greater improvement in energy, health perceptions, home management, and role function than noncorrectors. Study dropouts and those who died had significantly worse scores for health-related quality of life at baseline compared to study completers. Thus, the AIDS patients with anemia and serum erythropoietin levels < or = 500 IU/L treated with recombinant human erythropoietin showed increased mean hematocrit and improved health perceptions and energy levels. The drug therapy was associated with increased feelings of energy, but it was not associated with other changes in health status and well-being in the AIDS patients completing the study. These observations need to be confirmed in randomized clinical trials.

Didanosine compared with continuation of zidovudine in HIV-infected patients with signs of clinical deterioration while receiving zidovudine. A randomized, double-blind clinical trial. The Bristol-Myers Squibb AI454-010 Study Group

OBJECTIVE

To determine the benefits of switching to didanosine compared with continuing zidovudine among patients infected with human immunodeficiency virus (HIV) who have previously used zidovudine and have signs of clinical deterioration.

DESIGN

Randomized, double-blind, two-armed, parallel, comparative clinical trial with a blinded, compassionate crossover provision at 12 weeks.

SETTING

Outpatient clinics at 19 tertiary care medical centers.

PATIENTS

312 patients infected with HIV who had received zidovudine for 6 months or more, had CD4 cell counts of 300/mm3 or less, and had signs of clinical deterioration within 12 weeks before study entry.

INTERVENTION

Peroral didanosine tablets (600 mg/d adjusted for weight, "high dose") or zidovudine capsules (600 mg/d).

MEASUREMENTS

Primary study end points were death, a new acquired immunodeficiency syndrome (AIDS)--defining event, or the combination of two new or recurrent HIV-related diagnoses with a 50% decrease in CD4 cells.

RESULTS

Switching to didanosine was associated with fewer end points than continuing zidovudine (relative risk [RR] for zidovudine:didanosine = 1.5; 95% Cl, 1.1 to 2.0). This benefit was consistent across subgroups of patients with either AIDS-related complex or AIDS and was most apparent among those with a CD4 count at entry of 100/mm3 or more (RR = 2.2; Cl, 1.1 to 4.4).

CONCLUSIONS

This study shows a positive treatment effect for switching from zidovudine to didanosine among patients with either AIDS-related complex or AIDS and validates the common practice of using clinical signs or a decrease in the CD4 count as an indication for changing therapy.

Magnetic resonance imaging in full-term infants with repetitive focal seizures

We report two full-term infants who developed repetitive focal seizures within the first 48 hours of life. Neither infant had predisposing factors and there were no abnormalities on a computed tomography (CT) scan performed on day 2 of life. Magnetic resonance imaging (MRI) performed during the second week of life showed a focal hemorrhagic infarction in both patients. We conclude that either an MRI or a contrast-enhanced CT scan should be obtained within 1 week in patients in whom the initial imaging technique failed to reveal a focal lesion, at which time a cerebral infarction can be diagnosed with greater sensitivity.

B-cell chronic lymphocytic leukaemia: prognostic value of the immunophenotype and the clinico-haematological features

Sixty-two previously untreated patients with B-cell chronic lymphocytic leukaemia were analysed to study the prognostic value of both the immunologic phenotype and the clinicobiologic characteristics. Univariate studies showed that none of the immunological markers analysed, sheep-rosette, mouse-rosette, slg, and HLA/DR, CD20, FMC7, CD5, and CD9 antigens, had a significant influence on survival. On the other hand, several clinical and haematological characteristics were identified as being associated with survival: 1) clinical features--presence of lymphadenopathies (P less than .05) and hepatomegaly and/or splenomegaly (P less than .04); 2) haematologic parameters--presence of anaemia and/or thrombopenia (P less than .05), the absolute peripheral blood lymphocyte count (P less than .03), and the presence of hypogammaglobulinemia (P less than .08); 3) biochemical parameters--serum uric acid (P less than .03); and 4) bone marrow histopathological features--biopsy pattern (P less than .04) and the percentage of lymphocytes in bone marrow aspirate (P less than .03). Both the Rai staging and the International Workshop on CLL staging systems were effective in identifying groups of patients with significantly different prognoses (P less than .05). Multivariate regression analysis demonstrated that the combination of three clinicopathologic characteristics (bone marrow histopathologic pattern, absolute peripheral blood lymphocyte count, and the presence or not of hypogammaglobulinaemia) had the strongest predictive relationship with survival time. In summary, our findings show that the clinicobiological and anatomopathologic parameters have much more prognostic relevance than the immunological markers analysed in the present study.

A pilot study of diethyldithiocarbamate in patients with acquired immune deficiency syndrome (AIDS) and the AIDS-related complex

We investigated the use of diethyldithiocarbamate (DTC, or Imuthiolr, Merieux Institute) as a therapeutic agent in patients with Acquired Immune Deficiency Syndrome (AIDS) and AIDS-Related Complex (ARC). Patients were prospectively stratified and randomized to receive DTC 200 mg/m2 intravenously weekly for 16 weeks or no therapy, followed by crossover to the opposite arm for an equal period. Forty-four patients were entered and forty were evaluable. There was a statistically significant decrease in symptoms in the DTC treated patients compared to the controls (p = .002). There was a significant improvement in lymphadenopathy in the treated patients compared to the controls (p = .005). One patient showed disappearance of splenomegaly, one clearing of antifungal agent-resistant perianal moniliasis, and one clearing of hairy leukoplakia. No significant differences in progression were noted. No changes were seen in any of the immunological parameters measured. There was no significant toxicity. Because of the changes in symptoms and in lymphadenopathy, we suggest that further study of DTC, both alone and in combination with other agents, may be indicated.

Spatial and temporal correlation between early nerve fiber growth and neuroepithelial cell death in the chick embryo retina

The distribution of cell death in the ventral pycnotic zone of the chick embryo retina was studied in Hamburger-Hamilton's stages 16 to 25 (2 1/2 to 4 1/2 days of incubation). The number of fragments appearing in the retina increases notably from stage 20 at which stage they are limited almost exclusively to the optic disc region. At the same time optic fibers are seen in this area for the first time. In stage 24 cell death phenomena are numerous in the ventral retina, and become even more extensive in the following stage. Stage 25 meanwhile sees a drop in cell death in the dorsal retina. The overall picture presented by cell remains and young ganglion cells indicates that in stages 19-23 cell death occurs mainly in the zone between the ganglion cells of the posterior pole and the optic stalk. In the stage 25 retina most of the cell fragments of the ventral retina are found on either side of the fissure, while ganglion cells in the process of sending out axons toward the fissure appear laterally (nasally and temporally) to these zones of degeneration. Hence a spatial and temporal correlation is established between fiber growth and neuroepithelial cell degeneration, allowing us to construct a hypothesis with regard to the role that cell death might play in setting up an initial pattern of optic fiber growth.