Mexiletine in the symptomatic treatment of diabetic peripheral neuropathy

OBJECTIVE

To evaluate the efficacy and safety of mexiletine in the symptomatic treatment of diabetic peripheral neuropathy (DPN).

METHODS

In this prospective, double-blind study, 29 patients were randomized to receive mexiletine 600 mg/d or matching placebo for 3 weeks. A four-item symptom score (FIS), which rated pain, dysesthesias, paresthesias, and nightly exacerbations of symptoms, and a 100-mm visual analog scale (VAS), which rated pain intensity, were completed by patients before and after treatment. At the end of treatment independent patient and investigator global assessments were made. Patients reported adverse effects after 1 and 3 weeks of treatment.

RESULTS

Treatment groups were similar at baseline. The difference between the median changes in FIS scores (mexiletine = 5.5, placebo = 2) was not statistically significant. Overall symptom response was similar in both treatment groups as demonstrated by both global assessments (p = 0.19). The mean change in VAS score from baseline to posttreatment was determined for both groups and the difference between these mean scores was 16.5 mm (95% CI, -7.1 to 40.2 mm) (p = 0.16). Inadequate statistical power (1-beta = 0.40) may have resulted from small sample size, small magnitude of effect, or variability in the measured effect. Adverse effects were more common in the mexiletine group, though not statistically significant. One patient receiving mexiletine was hospitalized for palpitations.

CONCLUSIONS

Because of conflicting reports of mexiletine's efficacy in the treatment of symptomatic DPN, this drug should be reserved for patients unresponsive or intolerant to standard therapy, without evidence of heart disease, and with sensations of burning heat, formication, or stabbing pain.

Androgen inhibition of vitellogenin gene expression in tilapia (Oreochromis niloticus)

Treatment of mature female tilapia (Oreochromis niloticus) with high levels of androgen (17 alpha-methyltestosterone, 17 alpha MT) results in a pronounced decline in plasma vitellogenin levels as determined by gel electrophoresis. Total RNA extracted from livers of treated fish and vehicle-injected controls was analyzed by Northern and slot blot hybridization using an oligonucleotide complementary to a sequence in the 3' end of tilapia vitellogenin mRNA. The probe revealed an mRNA of 6.5 kb in liver from the control mature female fish which was decreased by 85% by androgen treatment. As expected, estradiol (E2) treatment induced the 6.5-kb mRNA in mature male tilapia. The antiestrogen, tamoxifen, strongly decreased vitellogenin mRNA levels in mature females. Radioimmunoassay of serum from control and 17 alpha MT-treated female tilapia showed a marked reduction in serum E2 levels, from 11.4 +/- 2.6 ng/ml in controls to 2.2 +/- 0.13 ng/ml in treated fish. Tamoxifen, however, resulted in increased serum E2 levels, probably by blocking E2 negative feedback. The serum E2-lowering effect of 17 alpha MT suggests an inhibitory site of action on gonadotropin production at the hypothalamic-pituitary axis, possibly through an androgen receptor or through an estrogen receptor after local aromatization of 17 alpha MT.

Single-channel and whole-cell analysis of ethanol inhibition of NMDA-activated currents in cultured mouse cortical and hippocampal neurons

The effects of 0.1 to 500 mM ethanol on NMDA-activated currents were studied in primary cultures of mouse cortical and hippocampal neurons. In whole-cell recordings the IC50S for inhibition of NMDA-activated currents by ethanol were 129 mM +/- 20 mM in hippocampal neurons and 126 +/- 18 mM in cortical neurons. In single-channel recordings from excised outside-out patches of cortical neurons, ethanol inhibited total charge per minute with an IC50 of 174 +/- 23 mM, which was not significantly different from the IC50S for inhibition of whole-cell current. The reduction in mean open channel lifetime by ethanol was fit by the logistic equation with an apparent IC50 of 340 +/- 28 mM. Analysis of single-channel data indicated that ethanol inhibition of NMDA currents did not involve substantial changes in fast closed state kinetics, changes in open channel conductance, or block of the open channel. At the whole-cell IC50 of ethanol, mean open channel lifetime would decrease by 28% and frequency of opening would decline by 31% to account for the reduction in current. Single-channel data were consistent with ethanol being an allosteric modulator of gating which reduces agonist efficacy.

The effects of platelet-derived growth factor-BB and insulin-like growth factor-1 on epithelial dysplasia

Growth factors are multi-functional and multi-targeted proteins which play a significant role in wound healing. Platelet-derived growth factor B-chain homodimer (PDGF-BB) and insulin-like growth factor-1 (IGF-1) have demonstrated efficacy for periodontal regeneration in animal models. Although primarily associated with wound healing, PDGF-BB and IGF-1 also facilitate growth of a number of malignant neoplasms. Of particular concern to periodontists is epithelial dysplasia, a necessary precursor to squamous cell carcinoma, the most common oral malignancy. Certain risk factors for oral cancer, such as tobacco, age, and alcohol, are also associated with an increased incidence of periodontal disease. The effects of the combination of PDGF-BB and IGF-1 on epithelial dysplasia have not previously been reported. The purpose of this study was to examine the effects of the combination of PDGF-BB and IGF-1 on epithelial dysplasia induced in the buccal cheek pouch of the Syrian golden hamster. A total of 66 hamsters received 18 applications of 0.5% dimethylbenzanthracene (DMBA), a topical carcinogen, over a 6-week period for the induction of dysplasia. The hamsters were subsequently divided into a baseline and 3 experimental groups (growth factors, saline vehicle, untreated control). Following the final DMBA application (day 0), the baseline group (N = 6) was sacrificed, the growth factor group (N = 21) received a single injection in the cheek pouch containing 4 micrograms of PDGF-BB and 4 micrograms of IGF-1 in saline, the saline group (N = 19) received an injection in the cheek pouch containing the saline vehicle only, and the untreated control group (N = 20) received no injection. Animals in experimental groups were sacrificed on days 3, 6, and 10. The cheek pouches were harvested for histologic and histochemical evaluation. Dysplasia was histologically graded from 0 to 4. Statistical analysis of the histologic data revealed no significant differences either by sacrifice date or by group. Histochemical evaluation, via staining for gamma-glutamyl transpeptidase (GGT), a marker for dysplastic cell colonies, revealed that the density of GGT-positive cells in experimental groups differed significantly from baseline levels. No significant differences were detected between experimental groups. There was poor correlation between the density of GGT-positive cells and the histologic grading of dysplasia. It is concluded that exposure to PDGF-BB and IGF-1 had no demonstrable effect on epithelial dysplasia in this hamster model.

Role of hydrazine in the mechanism of isoniazid hepatotoxicity in rabbits

Isoniazid (INH) continues to be a highly effective drug in the chemoprophylaxis and treatment of tuberculosis; however, its use is associated with hepatotoxicity (predominantly hepatic necrosis) in 1-2% of individuals. The INH metabolites, acetylhydrazine and hydrazine, have each been implicated as the causative hepatotoxin in INH-induced hepatotoxicity. Using a model of INH-induced hepatotoxicity in rabbits, in which INH-induced hepatotoxicity manifests as hepatic necrosis, hepatic steatosis (hepatic fat accumulation) and hypertriglyceridaemia (elevated plasma triglycerides), we compared the severity of these measures of toxicity with plasma levels of INH, acetylhydrazine and hydrazine. Plasma INH and acetylhydrazine were not correlated with markers of INH-induced hepatic necrosis or fatty changes. Plasma hydrazine at 32 h was correlated significantly with plasma argininosuccinic acid lyase (ASAL, a sensitive marker of hepatic necrosis) activity as area under the curve (r2 = 0.54, P < 0.002) and log plasma ASAL activity at 48 h after the first dose of INH (r2 = 0.53, p < 0.005), but not with fatty changes. These results show in this model of INH-induced hepatotoxicity in rabbits that hydrazine, and not INH or acetylhydrazine, is most likely involved in the pathogenic mechanism of hepatic necrosis.

Patterns of kinship in groups of free-living sperm whales (Physeter macrocephalus) revealed by multiple molecular genetic analyses

Mature female sperm whales (Physeter macrocephalus) live in socially cohesive groups of 10-30, which include immature animals of both sexes, and within which there is communal care of the young. We examined kinship in such groups using analyses of microsatellite DNA, mitochondrial DNA sequence, and sex-linked markers on samples of sloughed skin collected noninvasively from animals in three groups off the coast of Ecuador. Social groups were defined through photographic identification of individuals. Each group contained about 26 members, mostly female (79%). Relatedness was greater within groups, as compared to between groups. Particular mitochondrial haplotypes were characteristic of groups, but all groups contained more than one haplotype. The data are generally consistent with each group being comprised of several matrillines from which males disperse at about the age of 6 years. There are indications of paternal relatedness among grouped individuals with different mitochondrial haplotypes, suggesting long-term associations between different matrilines.

Weaver granule neurons are rescued by calcium channel antagonists and antibodies against a neurite outgrowth domain of the B2 chain of laminin

The weaver mutation impairs migration of the cerebellar granular neurons and induces neuronal death during the first two weeks of postnatal life. To elucidate the molecular mechanisms for the impaired neuronal migration, we investigated the rescue mechanisms of the weaver (wv/wv) granule neurons in vitro. We found that Fab2 fragments of antibodies against a neurite outgrowth domain of the B2 chain of laminin enhanced neurite outgrowth and neuronal migration of the weaver granule neurons on a laminin substratum and in the established cable culture system. The rescue of the weaver granule neurons by antibodies against the B2 chain of laminin may result from the neutralizing effect of these antibodies against the elevated B2 chain levels of the weaver brain. The L-type calcium channel blocker, verapamil (1-5 microM), also rescued the weaver granule neurons. High concentrations of MK-801 (10-20 microM), a glutamate receptor antagonist and voltage-gated calcium channel blocker, rescued the weaver granule neurons similar to verapamil, but low concentrations of MK-801 (1 microM) had no rescue effect. Simultaneous patch-clamp studies indicated that the weaver granule neurons did not express functional N-methyl-D-aspartate receptors further indicating that the rescue of the weaver granule neurons by MK-801 resulted from its known inhibition of voltage-gated calcium channels. The present results indicate that antibodies against the B2 chain of laminin, verapamil, and high concentrations of MK-801 protect the weaver granule neurons from the otherwise destructive action of the weaver gene. Thus, both the laminin system and calcium channel function contribute to the migration deficiency of the weaver granule neurons.

Immunohistochemical analysis of an equine model of synovitis-induced arthritis

OBJECTIVES

To use lipopolysaccharide (LPS) to create synovitis in the midcarpal joint of ponies, and to assess the morphologic, histochemical, and immunohistochemical effects of synovitis on articular cartilage of the third carpal bone.

ANIMALS

2- to 3-year-old ponies, 6 control (group 1) and 6 treated (group 2).

PROCEDURE

Synovitis was induced in 1 midcarpal joint of group-2 ponies by intra-articular injections of LPS (0.02 micrograms/kg of body weight), morphine (0.1 mg/kg), and saline solution (group 2a) and a morphine and saline solution alone in the contralateral midcarpal joint (group 2b). Articular cartilage sections and attached synovial membrane from the third carpal bones were examined by immunohistochemical distribution of interleukin 1 beta, tumor necrosis factor (TNF)-alpha, TNF receptors (P55, P75) and 3-B-3(-) epitopes, and by localization of proteoglycans (metachromatic staining). Proteoglycan extracts were assessed by metachromatic staining or western blotting and immunohistochemical staining, using anti-3-B- antibodies.

RESULTS

Enhanced immunoreactivity for the cytokines and receptors was found in inflamed synovial membrane and noncalcified cartilage (group 2a more than 2b). Metachromasia of the noncalcified cartilage was greater in group-1 than in group-2a and group-2b specimens. In group 2a, chondrocyte hypertrophy and enhanced immunoreactivity for 3-B-3(-) epitope in areas of increased cytokine immunoreactivity suggested possible phenotypic change of the chondrocytes in response to synovitis. Immunohistochemical analysis by western blotting of proteoglycan extracts indicated strong 3-B-3(-) epitope immunolocalization in group-2a, weaker staining in group-2b, and barely detectable stain in group-1 specimens, which correlated with in situ immunolocalization.

CONCLUSIONS

Intra-articular administration of LPS may be used to induce a synovial environment conductive to increased immunoreactivity of interleukin 1 beta, TNF-alpha, and its receptors in equine synovial membrane and articular cartilage. These cytokines may be involved in the early phenotypic change of chondrocytes that is believed to occur in osteoarthritis and is characterized in this study by enhanced 3-B-3(-) epitope immunoreactivity and chondrocyte hypertrophy.

Back pain in aircrew--an initial survey

BACKGROUND

In the early 1990's staff at a Royal Naval Air Station formed the view that pilots and observers of the Navy Lynx helicopter fleet appeared to have a higher incidence of back pain, to be seeking medical assistance more frequently and to be spending more time medically "unfit to fly" when compared to their counterparts in other helicopters.

HYPOTHESIS

To quantify the incidence of low back pain in helicopter aircrew by use of a questionnaire.

METHODS

A questionnaire was used to establish the prevalence and nature of back pain in Naval aircrew (161) compared to a control group of randomly selected non-flying military personnel (310).

RESULTS

Results show that aircrew (82%) experience significantly more back pain than controls (52%) (p < 0.01) though the nature of pain was similar in both groups. Significantly more aircrew (73%) than controls (49%) (p < 0.01) reported a previous history of back pain and report pain in shoulders (19%), midback (42%), lower back (72%) and across the buttocks (12%). Ergonomic factors were thought to be causative. Of aircrew surveyed, 11 (8%) had been issued with personal lumbar supports which resulted in major subjective improvements in flight-related symptoms.

CONCLUSIONS

Helicopter aircrew have a higher incidence of back pain. Crew station design was identified as a major contributor to the prevalence of back pain while personal supports reduced the levels of discomfort. While these findings are not new, no significant steps have been taken to redesign the crew station. It is recommended that personal supports are provided to all aircrew and that a more detailed study of crew station ergonomics is indicated following a more comprehensive study of prevalence of back pain in Royal Navy aircrew.

Demonstration of an in vitro direct vascular relaxant effect of diuretics in the presence of plasma

OBJECTIVE

To determine whether diuretics have direct vascular actions and to compare the in vitro effects of a loop diuretic with thiazide and thiazide-like diuretics.

DESIGN

A randomized, double-blind, vehicle-controlled design was used to avoid experimenter bias.

METHODS

Concentration-response curves to hydrochlorothiazide, chlorthalidone, indapamide, and furosemide were tested on the following male Wistar rat vascular smooth muscle preparations: rat aortic rings, rat pulmonary artery rings, and rat mesenteric portal vein.

RESULTS

All four diuretics demonstrated no vasorelaxant action in Krebs solution. They all exhibited vasorelaxant actions in aortic and pulmonary artery rings when plasma was mixed with Krebs solution in a 50:50 ratio. The magnitude of the relaxation was greater in the aortic ring preparation. This direct vascular action was found to be concentration dependent and endothelium independent. The order of potency of the vasorelaxant action of the diuretics was (from most to least) indapamide, hydrochlorothiazide, chlorthalidone, and furosemide on both aortic and pulmonary artery rings.

CONCLUSION

Diuretics possess direct vasorelaxant effects that are dependent upon the presence of plasma; this action may contribute to their antihypertensive properties.

Nucleotide sequence of transferrin cDNAs and tissue-specific of the transferrin gene in Atlantic cod (Gadus morhua)

Atlantic cod (Gadus morhua) transferrin cDNAs were isolated from a liver cDNA library using a cod transferrin-derived polymerase chain reaction product as a hybridization probe. The composite nucleotide sequence of two overlapping clones was 2223 bp in length excluding the poly(A) sequence and was equivalent to 87% of the 3' end of the Atlantic salmon transferrin cDNA sequence. Comparison of the deduced amino acid sequence of cod, salmon, Xenopus and several mammalian transferrins revealed that the two fish sequences are more similar with respect to their amino acid sequence and the position of additions/deletions than to other vertebrate transferrins. Conservation of the iron-binding domains and cysteine residues involved in disulphide bridges indicates that all transferrins share similar tertiary structure and support the hypothesis that extant vertebrate transferrin genes were derived from a gene duplication before the divergence of fish, frogs and mammals. Cod transferrin mRNA was detected in both brain and liver RNA and to a much lesser extent in RNA isolated from kidney and heart in contrast to salmon and several other vertebrates in which the transferrin gene is not expressed in brain.

Hypothyroxinemia and phenytoin toxicity: a vicious circle

Phenytoin is a widely used anticonvulsant which has a relatively narrow therapeutic range of serum concentrations, 40-80 mmol/l (10-20 mg/l). Phenytoin is known to show concentration-dependent kinetics within this therapeutic range. Because of this, small changes in dose and minor alterations in hepatic metabolism of phenytoin may cause a disproportionately large affect on serum concentrations. Hypothyroidism is associated with inhibition of hepatic oxidative metabolism of many drugs. However, there is a general consensus in the literature that serum phenytoin clearance is not influenced by thyroid functional status. This report describes a 63 year-old female who developed decreased serum free T4 (8 pmol/l) and phenytoin toxicity. We identified three other similar case reports. We propose that the following vicious circle may be involved in this interaction: induction by phenytoin of hepatic enzymes involved in the metabolism of T4 and T3, decreased serum free T4 levels causing decreased activity of hepatic NADPH cytochrome P-450 reductase, a resultant decrease in hepatic P-450 IIC9 catalyzed hydroxylation of phenytoin, increased serum phenytoin concentrations and further induction of T4 and T3 hepatic metabolism.

24 hour blood pressure control with once-daily versus twice-daily formulations of diltiazem

The antihypertensive effects of once-daily diltiazem CD over a 24 hour period were compared with twice-daily diltiazem SR in 95 patients with mild to moderate hypertension using ambulatory blood pressure monitoring. This trial was designed as a multicenter, double-blind, parallel-group study. Following a 2 to 4 week placebo run-in period, diltiazem was administered as once-daily CD or twice-daily SR, starting with 180 mg daily and increasing to a maximum of 360 mg daily, to achieve a seated diastolic blood pressure goal of < or = 90 mmHg as measured by cuff between 08:00 and 10:00 in the morning. Following drug titration, patients received a maintenance dose of diltiazem for an additional 6 week follow-up phase. Twenty-four hour ambulatory blood pressure monitoring recordings were obtained at the end of the placebo, titration, and maintenance phases. Both diltiazem CD and diltiazem SR significantly reduced both systolic and diastolic blood pressure over the 24 hour day and maintained a normal circadian pattern. As well, treatment with once-a-day diltiazem CD significantly decreased the slope of the early morning rise of diastolic and mean blood pressure. Thus, diltiazem CD is as effective as diltiazem SR in lowering diastolic blood pressure over a 24 hour period and has the advantage of a once-daily formulation.

Multiconformational analysis of solution NOE data for the Ac-(L)proline-(D)alanine-NHMe dipeptide in a nonprotic solvent

Solution NOE data for the dipeptide, Ac-(L)proline-(D)alanine-NHMe (1), have been obtained in the viscous solvent, 75:25 polychlorotrifluoroethylene:chloroform-d1. In this solvent at a 500 MHz 1H NMR spectrometer frequency, 1 exhibits large, negative NOE enhancements. The quantified 2D-NOESY time courses for 1 are analyzed with the multiconformational analysis technique, conformer population analysis (CPA). Thus, experimental NOE data for a molecule that is known to adopt at least three conformational motifs are used to explore the factors influencing the structural characterization of conformationally supple molecules by NOE. Both the quantitative and qualitative interpretations of solution NOE data for the simple molecule, 1, are demonstrated to critically depend on the extent to which one relies on empirical force-field energetics to determine which structures are energetically viable and on the methods by which trial structures are generated. Other influences include the relative weighting of contributions to the fitting-error function by large vs small NOE cross peaks and inclusion vs exclusion of null data, i.e., whether the absence of NOE cross peaks is included in the fitting procedure. Factors that do not appear to exert significant influence on the interpretation of these NOE data include (1) whether conformational interconversion is assumed to be slow or fast with respect to T1, (2) the inclusion of diagonal cross-peak data in the fitting procedure, and (3) what structures are assumed in the calibration of rotational correlation times from the observed data.

A model of isoniazid-induced hepatotoxicity in rabbits

Isoniazid (INH) continues to be an effective drug used for chemoprophylaxis and treatment of tuberculosis. Unfortunately, INH is associated with significant hepatotoxicity in up to 2% of individuals exposed, and if this adverse event is not recognized early it can be fatal. Research on INH-induced hepatotoxicity has been hampered by the lack of a suitable animal model that closely resembles the toxicity in humans. The mechanism of INH-induced hepatotoxicity is still unknown. The present study describes the development of a reliable model of INH-induced hepatotoxicity in rabbits. The protocol involves repeated injections of INH over a 2-day period, resulting in significant hepatic necrosis as indicated by elevations of plasma argininosuccinic acid lyase activity. Pretreatment with phenobarbital increased the occurrence of INH-induced hepatic necrosis from approximately 60% (9 out of 15 rabbits) with INH alone to more than 90% (13 out of 14 rabbits). Morphological indices were used to demonstrate the presence of INH-induced hepatotoxicity, and biochemical indices were used to demonstrate both the presence and severity of INH-induced hepatotoxicity in this model. This model may prove useful for further investigations into the mechanism of INH-induced hepatotoxicity.

Zn2+ potentiates steady-state ATP activated currents in rat nodose ganglion neurons by increasing the burst duration of a 35 pS channel

Zn2+ and ATP are normally present in serum at low levels and are released from some neurons during synaptic activity. In whole-cell recordings, 10 microM Zn2+ potentiated steady-state currents in rat nodose ganglion nerve cells by 18% in 0.5 microM ATP and 120% in 2 microM ATP. Fluctuation analysis of whole-cell suggested the mechanism was increased burst duration. In single-channel recordings, 10 microM Zn2+ did not increase the ATP-activated channel conductance but did increase the mean burst duration of the 35 pS primary open conductance state. These observations indicate that Zn2+ potentiates the steady-state response to extracellular ATP by increasing the burst duration of the channels.

Comparison of the efficacy and safety of once-daily versus twice-daily formulations of diltiazem in the treatment of systemic hypertension. The Canadian Multicenter Diltiazem-CD Hypertension Trial Group

The efficacy and safety of optimally titrated once-daily (CD) and twice-daily (SR) diltiazem were compared in 111 patients with mild to moderate systemic hypertension [seated diastolic blood pressure (DBP) > or = 95 mmHg and < or = 114 mmHg] in a multicenter, randomized, double-blind, placebo run-in, parallel-group trial. Following a 4 week washout and placebo-controlled run-in period, patients were randomized to receive diltiazem CD 180 mg and matching placebo (n = 54), or diltiazem SR 90 mg bid (n = 57). Total daily doses were titrated from 180 mg to 360 mg to achieve a goal of seated DBP < 90 mmHg during a 6 week titration period. The patients continued to receive their optimal dose for a 6 week follow-up period. Ninety-six (96) patients (diltiazem CD: 47, diltiazem SR: 49) completed the study protocol, with 60% of the diltiazem CD and 55% of the diltiazem SR patients achieving the goal of seated DBP of < 90 mmHg (p = 0.685). Although significant decreases occurred in seated and standing measurements of diastolic and systolic BP and heart rate with treatment in both groups, there were no significant differences between treatment groups. Both medications were well tolerated, with a similar frequency of adverse effects [diltiazem CD: 24/54 (37%) patients; diltiazem SR: 24/57 (42.1%) patients] with the most frequently reported adverse effects being headache and edema.

Pharmacologic management of congestive heart failure

This article is a review of the pharmacologic management of congestive heart failure (CHF) and a summary of the medical literature that guides current treatment strategies. Despite advances in the treatment of CHF, it remains a common diagnosis with a poor prognosis. Because CHF is a progressive syndrome with heterogeneous features of cardiac dysfunction, effective management requires combination therapies and evolving treatment strategies. The mechanism of action, goals of therapy, and demonstrated efficacy of each of the various agents used in the treatment of CHF are discussed.

Increased proteolytic activity of the granule neurons may contribute to neuronal death in the weaver mouse cerebellum

The weaver mouse mutation is a genetic defect of unknown origin that leads to impairment of cerebellar granule neuronal migration and to neuronal cell death. We investigated laminin expression and proteolytic enzyme activity in this migration-deficient mouse mutant in vivo and in vitro to search for a molecular basis for the weaver defect. The weaver cerebellum showed a general increase in immunoreactivity for laminin, for a neurite outgrowth domain of the B2 chain of laminin, and for tissue plasminogen activator compared to the normal animals. Zymographic assays and immunocytochemistry confirmed that tissue plasminogen activator was the proteolytic enzyme synthesized in excess in the weaver mouse cerebellum in vivo. When placed in culture, the weaver granule neurons survived poorly on a laminin substratum, and failed to extend long neurites, unlike the normal cerebellar granule neurons. The cultured weaver granule neurons were proteolytically overactive and secreted excessive amounts of tissue plasminogen activator, which was likely to interfere with their neurite outgrowth potential on a laminin substratum. Indeed, the weaver granule neurons but not the normal neurons degraded laminin from their culture substratum and deposited a neurite outgrowth domain of the B2 chain of laminin onto their surfaces. Electrophysiology showed that the weaver granule neurons had poor resting membrane potentials (-38 V), whereas the normal neurons had normal resting membrane potentials of (-61 V). The resting membrane potentials of the weaver granule neurons were restored to near normal (-59 V) by a protease inhibitor, aprotinin. Aprotinin also rescued the weaver granule neurons from death on a laminin substratum and promoted their neurite outgrowth to the level of the normal animals. These results indicate that increased proteolytic activity accompanied with increased synthesis of laminin, and its B2 chain, distinguish the weaver mutation from the normal animals. These molecular changes may contribute to the impairment of granule neuronal migration and to the neuronal death, characteristic of the weaver mutation.