Early and Dose-Dependent Decrease of Retrograde Axonal Transport in Acrylamide-Intoxicated Rats

The effect of retrograde axonal transport of doses of acrylamide ranging from 50 to 500 mg/kg was studied in sensory nerve of rats. Accumulation of trichloroacetic acid-phosphotungstic acid-insoluble label was measured in a collection segment distal to a double ligature placed on the sciatic nerve at intervals 9-15 h and 9-24 h following injection into the dorsal root ganglion of the fifth lumbar root of [35S]methionine and [3H]fucose. After a dose of 100 mg/kg of acrylamide no neurological signs of neuropathy had yet appeared, but retrograde buildup of protein label was significantly reduced for the long interval (2.20 +/- 0.49 arbitrary units (AU) (mean +/- SD) versus 2.81 +/- 0.57 AU in controls, 2p = 0.034). No abnormality of the short interval appeared before a dose of 500 mg/kg was reached. The retrograde transport abnormality was dose-related (r = -0.85, n = 28, and 2p = 1.2 x 10(-8)), as was the degree of neuropathy evaluated by "blind" neurological scoring (r = 0.88, n = 14, and 2p = 2.8 x 10(-5)). After a dose of 500 mg/kg, when the rats were severely disabled with almost total incoordination of the hindlegs, the retrograde accumulation of the long interval was profoundly depressed (1.08 +/- 0.28 AU versus 2.81 +/- 0.57 AU in controls, 2p = 1.2 x 10(-7)). Similar changes were seen in accumulation of glycoprotein label. After the rats had recovered for 4-10 weeks neurological signs of neuropathy had disappeared and the transport abnormality had improved. To test the specificity of acrylamide on the retrograde transport defect N-hydroxymethylacrylamide and methylene-bisacrylamide, which do not induce neuropathy, were studied. None of these related compounds influenced the transport. These observations imply that in acrylamide intoxication a defect in the amount of material carried by retrograde axonal transport rather than in "turnaround" time or in transport velocity is present, that the transport abnormality precedes the development of neuropathy, and that it is related to the degree of the neurological disability. We suggest that the retention of protein in the distal axons in the functional counterpart of the well-known accumulation of vesicular organelles in the preterminals.     

Host immune response against homologous challenge infection of Ancylostoma caninum larvae after application of effective anthelmintics

The development of immunity against Ancylostoma caninum larval reinfection has been investigated in mice after the primary infection has been treated with an effective anthelmintics. Experimentally A, caninum larvae infected mice treated with levamisole (5 x 40 mg/kg), thiabendazole (5 x 200 mg/kg), oxfendazole (5 x 100 mg/kg), or albendazole (5 x 100 mg/kg) when challenged with A. caninum larvae showed 47.77 to 55.81% larval reduction from the challenge dose indicating thereby the development of partial immunity.     

Induction of specific-locus and dominant lethal mutations in male mice in the low dose range by methyl methanesulfonate (MMS)

Methyl methanesulfonate (MMS) induces specific-locus and dominant lethal mutations in spermatozoa and spermatids of mice. A dose of 15 mg/kg b.w. of MMS induces 9% dominant lethal mutations in the most sensitive germ-cell stages, corresponding to the mating intervals 5-8 and 9-12 days post treatment. A dose of 150 mg/kg b.w. of MMS in the same mating intervals induces 100% dominant lethal mutations. The sensitivity pattern for the induction of dominant lethal and specific-locus mutations is the same. In the mating interval 5-8 days a dose of 20 mg/kg b.w. of MMS induced 3.8 x 10(-5) mutations per locus per gamete. The yield of specific-locus and dominant lethal mutations in the low dose range increases proportionally with the dose. A dose given in 2, 4 or 5 fractions yields the same frequency of mutations as a single injection of the total dose. The additivity of small doses proves that the pre-mutational lesions are not or only partially repaired in these stages and that MMS is not or only partially detoxified. In addition, the frequency of dominant lethal and specific-locus mutations depends on the germ-cell stage.     

Anthelmintic profile of methyl 5(6)-(4-methylpiperidin-1-yl) carbonylbenzimidazole-2-carbamate in experimental helminthiases

Biological evaluation of methyl 5(6)-(4-methylpiperidin-1-yl) carbonylbenzimidazole-2-carbamate against Ancylostoma ceylanicum, Nippostrongylus brasiliensis, Syphacia obvelata, Hymenolepis nana, H. diminuta and Cysticercus fasciolaris in experimental animals is reported. The compound (mg/kg) causes 100% elimination of A. ceylanicum (25 x 1), N. brasiliensis (100 x 1), S. obvelata (50 x 1), H. nana (250 x 3) and C. fasciolaris (50 x 10). It was also effective against the developing larvae (L3, L4 and L5) of A. ceylanicum at a single oral dose of 100 mg/kg. Another study indicated that the compound elicits 100% response within 32 hr of drug administration. The drug is well tolerated and LD50 is greater than 4500 mg/kg.     

Acrylamide impairs fast and slow axonal transport in rat optic system

Effects of single and repeated doses of acrylamide on fast and slow axonal transport of radio labeled proteins following the injection of L-[4,5-³H] leucine have been studied in the optic system of male Sprague-Dawley rats. A single dose of acrylamide (100 mg/kg) had no effect, but higher concentrations (200–300 mg/kg) altered the distribution of fast axonally transported materials in optic nerves and optic tracts. Repeated doses of acrylamide (30 mg/kg/day, 5 days per week for 4 weeks) produced degeneration of tibial nerves but spared optic nerves and optic tracts. Fast axonal transport rate in optic axons was reduced by 50% (reduced to 4 mm/h from 8 mm/h) in acrylamide treated animals. Acrylamide also slowed the velocity of slow axonal transport of labeled proteins in optic axons to 1.0 mm per day from 1.3 mm per day. Since acrylamide impaired the rate of both fast and slow axonal transport in the absence of overt morphological damage, it can be concluded that deficit in axonal transport is an important factor in the pathogenesis of axonal degeneration in acrylamide neuropathy.     

Effects of long term low dose acrylamide exposure on rat bone marrow polychromatic erythrocytes

Abstract

I investigated whether long term low dose exposure to acrylamide increased micronucleus frequency in rat bone marrow polychromatic erythrocytes (PCEs). Twenty-five male and 25 female Wistar rats were used. Animals of each sex were segregated into two treatment groups and one control group. Each treatment group consisted of ten animals and each control group consisted of five animals. Acrylamide, 2 or 5 mg/kg/day, was administered to the treatment groups in their drinking water for 90 days. Twenty-four hours after the last treatment, bone marrow samples were obtained and analyzed for the frequency of micronucleated polychromatic erythrocytes (MNPCEs). The cytotoxic effect of acrylamide on bone marrow also was tested by assessing the polychromatic erythrocyte/normochromatic erythrocyte (PCE/NCE) ratio. Both doses of acrylamide significantly increased the frequency of MNPCEs in both male and female rats. Acrylamide also decreased the PCE/NCE ratio in both sexes compared to the control group. My study showed that chronic low dose exposure to acrylamide increased the formation of micronuclei in PCEs of male and female rat bone marrow.     

Verapamil contributes to the clastogenic effects of acrylamide, cyclophosphamide, and dioxidine on somatic cells of BALB/C and C57BL/6 mice

The chromosome aberration assay of metaphase bone marrow cells was used to study the clastogenic effects of acrylamide, cyclophosphamide, dioxidine, and their combinations with Verapamil (a calcium antagonist) in male BALB/C and C57BL/6 mice. Verapamil gavage at single (5 mg/kg) and repeated doses (2.5 and 5 mg/kg five times at 24-h intervals) significantly enhanced the clastogenic activity of acrylamide (50 and 100 mg/kg intraperitoneally) in BALB/C mice; in C57BL/6 mice, this effect was only observed when they received Verapamil at doses of 2.5 mg/kg for 5 days. Verapamil administered repeatedly (2.5–10 mg, gavage) significantly increased the clastogenic activity of cyclophosphamide (10 mg/kg intraperitoneally) in C57BL/6 mice. In BALB/C mice, this effect of Verapamil was only observed at a dose of 10 mg/kg (gavage). When injected intraperitoneally at a single dose of 0.1–0.4 mg/kg, Verapamil significantly enhanced the clastogenic activity of cyclophosphamide in mice of both strains. This calcium antagonist produced identical effects when administered to BALB/C mice intraperitoneally (2.5 and 5 mg/kg) and by gavage (5 mg/kg) and to C57BL/6 mice intraperitoneally (5 and 10 mg/kg) and by gavage (2.5 mg/kg). Repeated administration of Verapamil (at all doses tested) promoted the clastogenic effect of dioxidine (100 mg/kg intraperitoneally) on C57BL/6 mice, having no such influence on BALB/C mice. These results demonstrate the co-clastogenic activity of Verapamil in mice and suggest that its specific manifestations depend on the dose, method, and route of drug administration and the genotype of test animals.     

Verapamil contributes to the clastogenic effects of acrylamide, cyclophosphamide, and dioxidine on somatic cells of BALB/C and C57BL/6 mice

The chromosome aberration assay of metaphase bone marrow cells was used to study the clastogenic effects of acrylamide, cyclophosphamide, dioxidine, and their combinations with Verapamil (a calcium antagonist) in male BALB/C and C57BL/6 mice. Verapamil gavage at single (5 mg/kg) and repeated doses (2.5 and 5 mg/kg five times at 24-h intervals) significantly enhanced the clastogenic activity of acrylamide (50 and 100 mg/kg intraperitoneally) in BALB/C mice; in C57BL/6 mice, this effect was only observed when they received Verapamil at doses of 2.5 mg/kg for 5 days. Verapamil administered repeatedly (2.5-10 mg, gavage) significantly increased the clastogenic activity of cyclophosphamide (10 mg/kg intraperitoneally) in C57BL/6 mice. In BALB/C mice, this effect of Verapamil was only observed at a dose of 10 mg/kg (gavage). When injected intraperitoneally at a single dose of 0.1-0.4 mg/kg, Verapamil significantly enhanced the clastogenic activity of cyclophosphamide in mice of both strains. This calcium antagonist produced identical effects when administered to BALB/C mice intraperitoneally (2.5 and 5 mg/kg) and by gavage (5 mg/kg) and to C57BL/6 mice intraperitoneally (5 and 10 mg/kg) and by gavage (2.5 mg/kg). Repeated administration of Verapamil (at all doses tested) promoted the clastogenic effect of dioxidine (100 mg/kg intraperitoneally) on C57BL/6 mice, having no such influence on BALB/C mice. These results demonstrate the co-clastogenic activity of Verapamil in mice and suggest that its specific manifestations depend on the dose, method, and route of drug administration and the genotype of test animals.     

Acrylamide alters neurofilament protein gene expression in rat brain

Acrylamide, a prototype neurotoxin, alters neurofilament protein (NF) gene expression in rat brain. Levels of mRNA coding for neurofilament protein subunits NF-L, NF-M, and NF-H have been determined by Northern blot analysis using³²P-labeled cDNA probes. Acrylamide given acutely (100 mg/kg, single intraperitoneal injection) causes a selective increase in NF-M mRNA (approximately 50%) compared to controls. The expression of NF-L or NF-H mRNA is not affected by acrylamide. In contrast, chronic treatment with acrylamide [0.03% (w/v) in drinking water for 4 weeks] induces a modest but significant increase (approximately 22%) in NF-L mRNA compared to controls. Levels of NF-M, and NF-H mRNA are not altered by acrylamide treatment. The expression of -actin mRNA, an ubiquitous protein, is not affected by either treatment regimen of acrylamide. The results of this study show that acrylamide increases the expression of mRNA for NF protein subunits in rat brain. The increase of specific mRNA for NF subunits depends on the dose, duration and route of acrylamide administration.     

Induction of rat liver cytochrome P450 isoenzymes CYP 1A and CYP 2B by different fungicides, nitrofurans, and quercetin.

The genotoxic activity of environmental xenobiotics is manifested either in their direct interaction with cellular genetic material or in provoking secondary events, among which reactive oxygen species (ROS) production is a common phenomenon. Both pathways can be mediated by the activity of the cytochrome P450 monooxygenase system. We studied induction of the CYP 1A or CYP 2B monooxygenases in rat liver by the fungicides: thiram, captan, captafol, dodine and the drugs: nitrofurazone, furazolidone and the plant flavonoid: quercetin. A cytochrome P450 induction assay (CYPIA test) was used. S9 prepared from livers of rats treated with the test compounds were used to activate ethidium bromide (EtBr) (CYP 1A isoenzyme) or cyclophosphamide (CPA) (CYP 2B isoenzyme) in the Ames test.It was found that among the tested compounds, the most potent inducer of CYP 1A was furazolidone (3 x 80 mg/kg). Less potent was thiram (1 x 100mg/kg), as well as quercetin (3 x 80 mg/kg), and captafol (1 x 30 mg/kg). On the other hand, thiram (1 x 100 mg/kg), captafol (1 x 30 mg/kg), and quercetin (3 x 80 mg/kg) were most potent in the CYP 2B isoenzyme induction, while furazolidone (3 x 80 mg/kg), and nitrofurazone (3 x 80 mg/kg) appeared to be less potent in this respect. Captan and dodine (3 x 80 mg/kg) did not affect the activity of any of the cytochrome P450 isoenzymes.     

Evaluation of some adamantane-based synthetic trioxanes against Plasmodium knowlesi in rhesus monkeys

In our search for synthetic substitutes for artemisinin and its derivatives we had earlier prepared a series of adamantane-based 1, 2, 4-trioxanes 5a-c which had shown promising activity against P. berghei in Swiss mice. We have further evaluated these and two new compounds (5d-e) against Plasmodium knowlesi W1, a virulent malaria parasite in rhesus monkeys, in the dose range of 40-80 mg/kg x 5 days by intramuscular route. Trioxanes 5b and 5c showed 100% protection and cure at 80 mg/kg x 5 days, while trioxane 5a showed 71% cure at this dose. Detailed studies again showed 50% curative effect of 5a at 40 mg/kg x 5 days treatment.     

Enhancement of lipid peroxidation in rat liver on acute exposure to styrene and acrylamide a consequence of glutathione depletion

Lipid peroxidation, glutathione level and activity of glutathione-S-transferase were studied in liver and brain of rats 4 and 3 h after a single i.p. administration of 0, 25, 75, 100 mg/kg acrylamide or 0, 50, 100, 200, 600 mg/kg styrene, respectively. In liver both acrylamide and styrene caused an increase in lipid peroxidation and decrease in glutathione contents and activity of glutathione-S-transferase in a dose dependent manner, while in brain only acrylamide produced a decrease in glutathione content. The decrease in glutathione content was not always associated with increase of lipid peroxidation. The enhancement of lipid peroxidation occurred only when glutathione contents were depleted to certain critical levels. No effect of acrylamide or styrene was seen on lipid peroxidation under in vitro conditions. The addition of glutathione in the incubation mixture significantly inhibited the rate of lipid peroxidation of liver homogenates of acrylamide and styrene treated animals.The results suggest that enhancement of lipid peroxidation in liver on exposure to acrylamide or styrene is a consequence of depletion of glutathione to certain critical levels. The inhibition of glutathione-S-transferase activity by acrylamide and styrene suggests that detoxication of these neurotoxic compounds could be suppressed following acute exposure.     

In vivo growth inhibitory effect of Withania somnifera (Ashwagandha) on a transplantable mouse tumor, Sarcoma 180.

Withania somnifera is a medicinal plant used in the treatment of a variety of ailments in the Ayurvedic system. Alcoholic extract of the root of the plant was injected(ip) at daily doses of 200 to 1000 mg/kg body wt for 15 days starting from 24 hr after intradermal inoculation of 5 x 10(5) cells of S-180 in BALB/c mice. Solid tumor growth was monitored for 100 days. Doses of 400 mg/kg and above produced complete regression of tumor after an initial growth, the percentage of complete response (CR) increasing with increasing drug dose. A 55% CR was obtained at 1000 mg/kg drug administration, but this dose also produced some mortality among the animals. A significant increase in the volume doubling time and growth delay was seen when the drug dose was increased from 500 to 750 mg/kg body wt, but further increase in drug dose to 1000 mg/kg did not produce any significant increase in these responses. Cumulative doses of 7.5 to 10 g at daily doses of 500 or 750 mg/kg seems to produce a good response in this tumor.     

A comparison of genotoxicity between three common heterocyclic amines and acrylamide

Heterocyclic amines (HCAs), a group of genotoxic compounds formed during the heating of proteinaceous food items, have been known since the late 1970s. However, the genotoxic effect of these compounds in the low dose region has not yet been thoroughly studied. Here we used a sensitive flow cytometer-based micronucleus assay in mice to determine the frequency of micronucleated erythrocytes (fMPCE) of the three common HCAs, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), in the low dose region. We especially looked for any deviation from linearity of the dose-response curves. Male Balb/C mice were intra peritoneally injected with different doses of either PhIP (0-36 mg/kg b.w.), MeIQx (0-90 mg/kg b.w.) or IQ (0-40 mg/kg b.w.). In the case of PhIP, we found a significant dose-response relationship, while MeIQx and IQ did not display an increased fMPCE level. This flow cytometer method allows for determination of the DNA content of micronuclei. All three HCAs tested here yielded a low DNA content of micronuclei, indicating that they do not possess aneugenic effects. A comparison between the HCAs and acrylamide (AA), another heat induced genotoxic compound, revealed that the slope of the dose-response curve is about 10 times steeper for PhIP than AA. In spite of this, AA probably constitutes a higher human risk than HCAs since the intake is about a 100- to 1000-fold higher than the intake of HCAs.     

A comparison of genotoxicity between three common heterocyclic amines and acrylamide

Heterocyclic amines (HCAs), a group of genotoxic compounds formed during the heating of proteinaceous food items, have been known since the late 1970s. However, the genotoxic effect of these compounds in the low dose region has not yet been thoroughly studied. Here we used a sensitive flow cytometer-based micronucleus assay in mice to determine the frequency of micronucleated erythrocytes (fMPCE) of the three common HCAs, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), in the low dose region. We especially looked for any deviation from linearity of the dose–response curves. Male Balb/C mice were intra peritoneally injected with different doses of either PhIP (0–36 mg/kg b.w.), MeIQx (0–90 mg/kg b.w.) or IQ (0–40 mg/kg b.w.). In the case of PhIP, we found a significant dose–response relationship, while MeIQx and IQ did not display an increased fMPCE level. This flow cytometer method allows for determination of the DNA content of micronuclei. All three HCAs tested here yielded a low DNA content of micronuclei, indicating that they do not possess aneugenic effects. A comparison between the HCAs and acrylamide (AA), another heat induced genotoxic compound, revealed that the slope of the dose–response curve is about 10 times steeper for PhIP than AA. In spite of this, AA probably constitutes a higher human risk than HCAs since the intake is about a 100- to 1000-fold higher than the intake of HCAs.     

Mutagenic activity of 2-amino-N6-hydroxyadenine in the mouse spot test.

The base analogue 2-amino-N6-hydroxyadenine (AHA) was mutagenic in the spot test in (T x HT)F1 mouse embryos. Females were injected with single doses of 20 or 40 mg AHA per kg body weight on the 9th day of pregnancy. To rank the mutagenic potency of different compounds, the frequencies of genetically relevant spots induced by 1 mg/kg body weight were calculated. The observed somatic mutation frequency for 1 mg/kg AHA was lower (1.95 x 10(-3)) spots of genetic relevance) than that of mitomycin C (16 x 10(-3)), ethylnitrosourea (6.8 x 10(-3)) and cyclophosphamide (6.4 x 10(-3)) and therefore AHA was not classified as a very potent mutagen in this test system. The doubling dose to induce genetically relevant spots was calculated to be 20 mg/kg b.w. Based on these data, AHA is suggested to be a candidate to induce recessive specific-locus mutations in germ cells of mice.     

Effect of recombinant human growth hormone on urinary 15N-nitrogen balance in girls with Turner syndrome as compared to children with growth hormone deficiency

15N-nitrogen balances before and on human growth hormone (hGH) were studied in 13 girls with Turner syndrome (TS) aged 4.4-16 (median 13.2) years (45,X0 or equivalent, no X0/XX mosaicism, no estrogen replacement). The results were compared with those reported from 9 patients with growth hormone deficiency (GHD). The TS patients received subcutaneous hGH doses of 2 x 3 (group A, n = 6), 3 x 2 (group B, n = 3), or 2 x 6 (group C, n = 4) IU/m2 on consecutive days. The mean 15N dose given to the patients of groups A and C was higher (13.6 mg/kg) than that given to those of group B (2.7 mg/kg). The lower hGH doses in the first two groups induced small positive mean 15N balance changes (+0.6 +/- 0.6 mg/kg 15N, group A; +0.03 mg/kg, group B). The higher hGH dose in group C caused a more marked mean balance change (+3.0 mg/kg 15N) comparable to that in GHD patients (+3.2 mg/kg). Individual variation of response, however, was larger in patients with TS than in those with GHD. With low and high hGH doses, there were responders and nonresponders. It is concluded from this pilot study in a small number of cases that 15N balance studies might be potentially useful to choose the appropriate hGH dose for long-term treatment in TS patients.     

Free radical scavenging and radioprotective activity of dehydrozingerone against whole body gamma irradiation in Swiss albino mice

Dehydrozingerone (DZ) was explored for in vitro-in vivo antioxidant potential and in vivo radioprotective activity against whole body gamma irradiation in Swiss albino mice. DZ scavenged the ABTS (2, 2'-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) and DPPH (1, 1-dipehnyl-2-picrylhydrazyl) free radicals at room temp. DZ reduced Fe (III) to Fe (II) at pH 7.4 and scavenged the NADH/phenazine methosulfate generated superoxide radical in cell free system. DZ also scavenged the nitric oxide radical generated by sodium nitroprusside. To evaluate the radioprotective activity, mice were exposed to whole body gamma irradiation 30 min after the drug treatment at a dose rate of 1.66 Gy/min. Pretreatment with DZ 75, 100 and 125 mg/kg, i.p. reduced the radiation induced mortality and increased the mean survival times (MSTs). An i.p. dose of DZ 100 mg/kg was found the most effective dose in preventing radiation sickness and increasing the MST. Pretreatment DZ100 mg/kg maintained the spleen index (spleen weight/body weight x 100) and stimulates the endogenous spleen colony forming units (CFU). Pretreatment with DZ100 mg/kg maintained the villus height close to normal, prevents mucosal erosion and basement membrane damage in irradiated mice jejunum. However, no significant reductions in dead, inflammatory and mitotic cells were observed in DZ pretreated mice, but there was an increased in crypt cells proliferation and regeneration. Pretreatment with DZ100 mg/kg significantly elevated the endogenous antioxidant enzymes (GSH, GST and SOD) in mice at 2, 4 and 8 h post sham irradiation. Radiation induced fall in endogenous antioxidant enzymes was significantly prevented by DZ pretreatment. Pretreatment with DZ 75 and 100 mg/kg reduced the radiation induced micronucleated polychromatic erythrocytes (MPCE) and normochromatic erythrocytes (MNCE) in mice bone marrow. DZ also maintained the polychromatic erythrocytes (PCE) and normochromatic erythrocytes (NCE) ratio (P/N ratio) in irradiated mice. Dose modifying factor (DMF) was calculated by using the graded radiation dose (8.0, 9.0, 9.5 and 10 Gy). DZ 100 mg/kg elevated radiation LD(50) from 9.1 to 10.0 Gy, indicating the DMF of 1.09.     

Neurotoxicity of acrylamide in rats. I. Subacute intoxication. Absence of effect on incorporation of plasma phosphates into the acid-soluble phosphates of the sciatic nerve and the gastrocnemius muscle, in anatomic continuity and after neural section]

The subcutaneous injection of acrylamide (30 mg kg-1 day-1) in adult male rats induces a severe impairment of the general state of health and a progressive polyneuropathy at the cumulative dose of 180 mg/kg. At the cumulative dose of 400 mg acrylamide does not interfere with the incorporation of plasma inorganic phosphate into the inorganic and organic acid-soluble phosphate fractions of either the gastrocnemius muscle or the sciatic nerve Schwann cells. Nor does it modify the characteristic metabolic response of these fractions to Wallerian degeneration and neurogenic muscle atrophy.     

Sex related differences in the response of mice, rats and cats to administration of picrotoxin

Picrotoxin, 2.5 mg/kg, which was subconvulsive in male rats was 92% convulsive in female rats. Four mg/kg of picrotoxin, a dose which did not produce death in the male rats, was 75% lethal in the female rats. Picrotoxin also produced a significantly greater increase in the frequency of the spinal motoneurons discharge in the female than in male rats (444% of control compared to 222% of control). A similar significant difference to the analogous treatment was obtained in the female and male cats (439% of control compared to 368% of control). To counteract the picrotoxin-induced increased frequency of the spinal motoneurons discharge a double dose of diazepam had to be given to females of both species. A sex related difference in the occurrence of convulsions, latency and death following picrotoxin administration was also present in mice. However, mice responded in an opposite direction to rats and cats. Three mg/kg of picrotoxin was 100% convulsive and 27% lethal in male mice, while only 40% convulsive and 0% lethal in female mice. In male mice treated with a 100% lethal dose of picrotoxin, diazepam, 3.0 mg/kg, did not diminish the occurrence of convulsions but reduced the incidence of death to 70%. In equally treated female mice the same dose of diazepam reduced the occurrence of convulsions from 100 to 70% and the incidence of death to 10%. The existence of sex related differences in the response of mice, rats and cats to administration of picrotoxin might have its origin in the dimorphisms of the GABA system in these animal species.