Trimethyltin (TMT) Reduces Testosterone Production in Adult Leydig Cells in Rats.

Trimethyltin (TMT) is widely used as a plastic heat stabilizer and can cause severe toxicity. Here, the effects of TMT on testosterone production by adult Leydig cells and the related mechanisms of action were investigated. Eighteen adult male Sprague Dawley rats (56 days old) were randomly divided into 3 groups and given intraperitoneal injection of TMT for 21 consecutive days at the doses of 0 (vehicle control), 5, or 10 mg/kg/d. After treatment, trunk blood was collected for hormonal analysis. In addition, related gene and protein expression in testes was detected. At 10 mg/kg, TMT significantly reduced serum testosterone levels but increased serum luteinizing and follicle-stimulating hormone levels. The messenger RNA and protein levels of luteinizing hormone/chorionic gonadotropin receptor, steroidogenic acute regulatory protein, cytochrome P450 17-hydroxylase/17,20-lyase, follicle-stimulating hormone receptor, and SRY box 9 were significantly lower in the TMT-treated testes than in controls. Immunohistochemical study showed that TMT decreased adult Leydig cell number. In conclusion, these findings indicate that TMT reduced adult Leydig cell testosterone production in vivo by directly downregulating the expression of steroidogenic enzymes and decreasing adult Leydig cell number in the testis.

Valproic acid-mediated inhibition of trimethyltin-induced deficits in memory and learning in the rat does not directly depend on its anti-oxidant properties.

BACKGROUND: Trimethyltin (TMT) acts as a potent neurotoxic compound especially for the hippocampus. The effects of valproic acid (VPA) on TMT-induced learning and memory deficits were investigated. METHODS: The rats were divided into: (1) control, (2) TMT, (3) TMT-VPA 1, (4) TMT-VPA 5, (5) TMT-VPA 10. TMT was injected as a single dose (12 mg/kg, ip) in groups 2-5. The animals of groups 3-5 were treated by 1, 5, and 10 mg/kg of VPA for 2 weeks. Learning and memory deficits were assessed by Morris water maze (MWM) and passive avoidance (PA) tests. The markers of oxidative stress mainly malondialdehyde (MDA) level and total thiol content were measured in the brain regions. RESULTS: In MWM test, escape latency and traveled path in the TMT group were higher than control (p < 0.05 and p < 0.01). Treatment by 1, 5, and 10 mg/kg of VPA reduced escape latency and traveled path (p < 0.01-p < 0.001). In PA test, the time latency to enter the dark compartment in TMT group was lower than control group (p < 0.01). Treatment by 5 and 10 mg/kg of VPA increased the time latency (p < 0.05-p < 0.001). MDA concentration in hippocampal tissues of TMT group was higher while, total thiol content was lower than control ones (p < 0.05). Pretreatment with 10 mg/kg of VPA decreased the MDA level while, increased total thiol content (p < 0.01). CONCLUSIONS: The results of present study showed that VPA attenuates TMT-induced memory deficits. Protective effects against brain tissues oxidative damage might have a role in the beneficial effects of VPA.

Progressive increase of lysosomal enzyme activities in hippocampus associated with reduction of population spike in a rat model of neurodegeneration.

OBJECTIVES: Extensive effort has been made to identify early markers of neurodegeneration as late stages have no chance of treatment. Recently, many experimental models have been used to study hallmarks of neuronal injury. One of them is the model of trimethyltin (TMT)-induced damage associated with cognitive decline, thus called a model of Alzheimer-like disease. OBJECTIVE AND METHODS: Our aim was to study neuronal transmission in hippocampal slices of male Wistar rats affected with a single dose of TMT (7.5 mg/kg, i.p.) during the first three weeks of its action. The monitored time periods after TMT administration were days 1-3; 8-10 and 15-17. At the same time periods, right hippocampi were collected for determination of changes in specific activities of two lysosomal enzymes. Electrophysiological measurements were based on stimulation of Schäffer collaterals and registration of evoked responses in the stratum pyramidale and the stratum radiatum at the CA3-CA1 synapse. Specific activities of N-acetyl-ß-D-glucosaminidase (NAGA) and cathepsin D (Cat D) were determined spectrophotometrically. RESULTS: During three weeks after i.p. TMT administration to rats, we found a time-dependent reduction of postsynaptic neuronal firing, expressed by diminished population spike (PoS) amplitude recorded in the stratum pyramidale accompanied with marked increase in specific activity of NAGA to respective 111%, 163% and 252% in the 1st, 2nd and 3rd week compared to unaffected rats. In the stratum radiatum, reduction of the slope of excitatory postsynaptic potential was not time-dependent but almost constantly reduced from the 1st to 3rd week after TMT administration (55-60%) compared to control rats. Specific activity of lysosomal enzyme Cat D was significantly increased in the 3rd week after TMT administration. CONCLUSION: This work demonstrates a time-dependent reduction of somatic response in the hippocampus of TMT affected rats during the first three weeks. This reduction of neuronal firing was later accompanied with increase of specific activity of NAGA and Cat D, supporting evidence that lysosomal dysfunction may be one of the primary contributors to TMT-induced neurodegeneration.

Gene expression profiling as a tool to investigate the molecular machinery activated during hippocampal neurodegeneration induced by trimethyltin (TMT) administration.

Trimethyltin (TMT) is an organotin compound exhibiting neurotoxicant effects selectively localized in the limbic system and especially marked in the hippocampus, in both experimental animal models and accidentally exposed humans. TMT administration causes selective neuronal death involving either the granular neurons of the dentate gyrus or the pyramidal cells of the Cornu Ammonis, with a different pattern of localization depending on the different species studied or the dosage schedule. TMT is broadly used to realize experimental models of hippocampal neurodegeneration associated with cognitive impairment and temporal lobe epilepsy, though the molecular mechanisms underlying the associated selective neuronal death are still not conclusively clarified. Experimental evidence indicates that TMT-induced neurodegeneration is a complex event involving different pathogenetic mechanisms, probably acting differently in animal and cell models, which include neuroinflammation, intracellular calcium overload, and oxidative stress. Microarray-based, genome-wide expression analysis has been used to investigate the molecular scenario occurring in the TMT-injured brain in different in vivo and in vitro models, producing an overwhelming amount of data. The aim of this review is to discuss and rationalize the state-of-the-art on TMT-associated genome wide expression profiles in order to identify comparable and reproducible data that may allow focusing on significantly involved pathways.

Activation of c-Jun N-terminal kinase cascades is involved in part of the neuronal degeneration induced by trimethyltin in cortical neurons of mice.

The organotin trimethyltin (TMT) is known to cause neuronal degeneration in the central nervous system. A systemic injection of TMT produced neuronal damage in the cerebral frontal cortex of mice. To elucidate the mechanism(s) underlying the toxicity of TMT toward neurons, we prepared primary cultures of neurons from the cerebral cortex of mouse embryos for use in this study. Microscopic observations revealed that a continuous exposure to TMT produced neuronal damage with nuclear condensation in an incubation time-dependent manner up to 48 h. The neuronal damage induced by TMT was not blocked by N-methyl-D-aspartate receptor channel-blocker MK-801. The exposure to TMT produced an elevation of the phosphorylation level of c-Jun N-terminal kinase (JNK)(p46), but not JNK(p54), prior to neuronal death. Under the same conditions, a significant elevation was seen in the phosphorylation level of stress-activated protein kinase 1, which activates JNKs. Furthermore, TMT enhanced the expression and phosphorylation of c-Jun during a continuous exposure. The JNK inhibitor SP600125 was effective in significantly but only partially attenuating the TMT-induced nuclear condensation and accumulation of lactate dehydrogenase in the culture medium. Taken together, our data suggest that the neuronal damage induced by TMT was independent of excitotoxicity but that at least some of it was dependent on the JNK cascades in primary cultures of cortical neurons.

Protective effect of rutin against spatial memory impairment induced by trimethyltin in rats.

Rutin is a flavonoid with various biological activities that are beneficial to human health. Trimethyltin is a toxic organotin compound, and rats injected with trimethyltin serve as a useful in vivo model for studying spatial memory impairment and neurodegeneration in the hippocampus. The protective effect of rutin against the trimethyltin-induced spatial memory impairment and hippocampal neuron damage in rats was examined. Peroral administration of a single dose of trimethyltin (8.5 mg/kg) induced spatial memory loss and the extensive loss of CA3 pyramidal neurons in hippocampi, as indicated by the results of a Morris water maze task and histologic examination, respectively. Prolonged supplementation of rutin significantly reversed the trimethyltin-induced spatial memory impairment and the damage to pyramidal neurons in the hippocampal CA3b region, indicating an antioxidative effect of rutin. These results suggest that rutin in the diet may provide a protective effect against spatial memory impairment accompanied by hippocampal pyramidal neuron loss.

Trimethyltin-evoked apoptosis of murine hippocampal granule neurons is accompanied by the expression of interleukin-1beta and interleukin-1 receptor antagonist in cells of ameboid phenotype, the majority of which are NG2-positive.

Interleukin-1beta (IL-1beta) has been implicated in various neuropathologies, while IL-1 receptor antagonist (IL-1ra) has been shown to reduce neuronal injury. We investigated the pattern of expression of both cytokines in murine hippocampus after trimethyltin (TMT) intoxication. Using a ribonuclease protection assay, we demonstrated induction of transcription of IL-1beta and IL-1ra 3 days following TMT treatment which correlated with the peak of neuronal apoptosis. At this time, immunocytochemical staining revealed enhanced expression of both cytokines in NG2 proteoglycan expressing ameboid cells located at the site of neurotoxic insult, some of which bound also the microglial marker, lectin. There was some overlap between NG2 and lectin staining. Our results suggest that the two cytokines are involved in apoptotic processes in dentate granule cells and indicate that the pro-apoptotic effect of IL-1beta prevails over the presumed protective action of IL-1ra. The novel finding of expression of both cytokines in NG2(+) cells of ameboid phenotype indicates that these cells, through the regulatory roles of pro- and anti-inflammatory cytokines, may be involved in control of neuronal death or survival after injury.

Preventable exposure to trimethyl tin chloride: a case report.

Trimethyl tin chloride (TMTC) is a highly toxic organotin compound that affects four main target organs: the brain, liver, immune system and skin. Exposure can occur by inhalation, ingestion or direct skin absorption. Trimethyl tin is but one of many hazardous substances with potentially serious health consequences to which individuals working in research laboratories may be exposed. We report a preventable case of TMTC exposure. Better understanding of the Canadian Workplace Hazardous Materials Information System (WHMIS) legislation and its applicability to the research laboratory situation would prevent such unnecessary exposure to hazardous substances.

Mechanisms of the apoptotic and necrotic actions of trimethyltin in cerebellar granule cells.

In evaluating mechanisms of trimethyltin (TMT)-initiated neuronal damage, the present study focused on involvement of reactive oxygen species, protein kinase C (PKC), and glutamate receptors. Exposure of cerebellar granule cells to TMT (0.01-0.1 microM) produced primarily apoptosis, but higher concentrations were associated with cellular lactate dehydrogenase efflux and necrosis. TMT increased generation of cellular reactive oxygen species, which was inhibited by either L-NAME (inhibitor of nitric oxide synthase, NOS) or catalase, indicating that both NO and H(2)O(2) are formed on TMT exposure. Since chelerythrine (selective PKC inhibitor) also inhibited oxidative species generation, PKC appears to play a significant role in TMT-induced oxidative stress. The metabotropic glutamate receptor antagonist, MCPG, (but not MK-801) prevented oxidative species generation, indicating significant involvement of metabotropic receptors (but not NMDA receptors) in TMT-induced oxidative stress. NOS involvement in the action of TMT was confirmed through measurement of nitrite, which increased concentration dependently. Nitrite accumulation was blocked by L-NAME, chelerythrine, or MCPG, showing that NO is generated by TMT and that associated changes in NOS are regulated by a PKC-mediated mechanism. Oxidative damage by TMT was demonstrated by detection of elevated malondialdehyde levels. It was concluded that low concentrations of TMT (0.01-0.1 microM) cause apoptotic cell death in which oxidative signaling is an important event. Higher concentrations of TMT initiate necrotic death, which involves both an oxidative and a non-oxidative component. TMT-induced necrosis but not apoptosis in granule cells is mediated by glutamate receptors.

N-chlorotaurine, a novel endogenous antimicrobial agent: tolerability testing in a mouse model.

OBJECTIVE: To investigate the tolerability of N-chlorotaurine, a new antimicrobial agent, by application to the middle ear in a mouse model. METHODS: Five BALB/c mice were each injected through the tympanic membrane with 5 microL of 0.1%, 1.0%, and 10% N-chlorotaurine and compared with animals in which 0.9% isotonic sodium chloride solution, 0.2% gentamicin sulfate, and 0.25% trimethyltin chloride were instilled. Auditory brainstem responses to clicks were evaluated repeatedly between 4 and 75 days after injection, and histologic investigations of the inner ear were performed subsequently. Three additional groups of mice were injected with isotonic sodium chloride solution, 1.0% N-chlorotaurine, and 0.25% trimethyltin, and brainstem responses to tone bursts of 8, 16, and 32 kHz were tested. In addition, the middle ear was examined histologically. RESULTS: Mice treated with isotonic sodium chloride solution, 0.1% N-chlorotaurine, and 0.2% gentamicin sulfate did not show changes in response threshold. Treatment with 1.0% and 10% N-chlorotaurine caused a reversible increase in auditory brainstem response threshold by 20 dB 4 days after application because of local irritation around the perforation of the tympanic membrane. In contrast, 0.25% trimethyltin showed a permanent elevation of auditory brainstem response threshold of 10 to 15 dB and a scattered loss of outer hair cells predominantly in the apical turn. No alterations of the inner ear were observed in the other treatment groups. The mucous membrane of the middle ear remained unaffected in all test groups. CONCLUSION: Application of N-chlorotaurine to the middle ear is well tolerated without adverse effects and may be a useful new endogenous antimicrobial agent for local treatment of otologic infections.

Toxicokinetics of trimethyltin in four inbred strains of mice.

Sixteen week old male AKR/J, Balb/cByJ, C57B1/6J and DBA/2J mice received single i.p. injections of trimethyltin (TMT). The toxic effects were weight loss, hyperexcitability, tremor, clonic-tonic convulsion, posterior paresis and death. The minimum toxic dose was 1.8 mg/kg, for the AKR strain and 2.3 mg/kg for the other strains. The highest non-lethal dose was 2.7 mg/kg for the AKR, DBA/2 and C57B1/6 strains and 3.0 mg/kg for the Balb/c strain. Blood levels of TMT peaked within 1 h and declined with half-lives of approximately 1.5 days. Blood levels of TMT were lower in the C57B1/6 mice due to greater tissue binding of TMT in C57B1/6 mice. Some of the toxic endpoints showed different rank orders among the strains, leading us to conclude that more than one biological process is responsible for the acute toxic effects of TMT in mice.

GM1 ganglioside potentiates trimethyltin-induced expression of interleukin-1 beta and the nerve growth factor in reactive astrocytes in the rat hippocampus: an immunocytochemical study.

This study demonstrates potentiation by GM1 ganglioside treatment of trimethyltin (TMT) induced reactivity of astrocytes, and the expression of astroglial interleukin-1 beta (IL-1 beta) and nerve growth factor (NGF) immunoreactivities in the rat hippocampus. GM1 treatment also results in an increase of the number of IL-1 beta and NGF immunoreactive astrocytes. Both the intensity of gliosis and stimulation of IL-1 beta and NGF expression in astrocytes mostly occurs in the regions of heaviest neurodegeneration in the hippocampus (CA4/CA3c and CA1). It is tempting to assume that enhancement of astroglial NGF expression by GM1 ganglioside may play a role in the protective action of GM1 against neurotoxic insult.

Interleukin-1 receptor antagonist inhibits transient increase of plasma corticosterone in the initial phase of trimethyltin-induced hippocampal necrosis.

The temporal increase of plasma corticosterone (CORT) levels at 3 or 4 days after a single oral administration of trimethyltin (TMT) was suppressed by intracerebroventricular administration of the interleukin-1 receptor antagonist (IL-1ra). On the other hand, glutamate receptor antagonist (MK801) did not affect the TMT-induced CORT level increase. These results indicate that this transient activation of the hypothalamo-pituitary-adrenocortical axis in TMT-treated rats may be in part attributable to the neuroendocrine effects of IL-1 produced by microglia.

Altered expression of polysialylated NCAM in mouse hippocampus following trimethyltin administration.

Proper structuring of neural connections in the hippocampus is mediated by cell adhesion molecules, membrane-linked proteins involved in cell recognition and stabilization of cytoarchitecture. Modulated expression of the neural cell adhesion molecule (NCAM) at the synapse permits plasticity required for both learning and memory. Polysialylation of NCAM, particularly the synapse-specific 180 kDa isoform (NCAM180), allows hippocampal neurons to alter their neuronal connections during learning acquisition and memory consolidation in mature brain. These activity-dependent changes in NCAM expression represent a sensitive target for neurotoxicity. Trimethyltin (TMT), a potent hippocampal neurotoxicant, alters total NCAM expression in whole mouse hippocampus and impairs learning in rodents. To investigate the expression of polysialylated NCAM following TMT administration, Swiss-Webster mice were injected (i.p.) with 2.0 or 3.0 mg TMT/kg and sacrificed 6 hrs to 7 days later. Immunocytochemical staining for polysialylated NCAM (PSA-NCAM) revealed marked reduction of staining of hippocampal dentate granule cells 6-72 hours after TMT treatment. Partial recovery of hippocampal polysialylated NCAM was observed after 7 days. Immunoblot data indicated that loss of PSA-NCAM expression paralleled reductions seen in NCAM180 and markers of cytoskeletal integrity. Assays for proteolytic activity in hippocampus revealed rapid, reversible protease activation which correlated temporally with the reduction of NCAM180 and PSA-NCAM. Proteolytic degradation following hippocampal injury may serve to disrupt NCAM-mediated adhesion. Protracted loss of polysialylated NCAM in dentate gyrus following injury may serve as a useful marker in toxicant-induced learning disorders.

Rat strain- and gender-related differences in neurobehavioral screening: acute trimethyltin neurotoxicity.

Trimethyltin (TMT) produces unique pathological and behavioral changes after a single dose. In this study, TMT was used to examine the ability of a neurobehavioral screening battery (functional observational battery and motor activity) to characterize these behavioral changes in rats. The behavioral profile of TMT was obtained using these tests in male Long-Evans (LE) and Fischer 344 (F344) rats, to assess the influence of rat strain, and in LE males and females to evaluate gender-related differences. All rats were tested before dosing and again at 1, 7, 21, and 42 d after a single dose of either 0, 4, 6, or 8 mg/kg TMT-hydroxide (intravenously). In general, the characteristic syndrome of tremor, increased reactivity, and hyperactivity was observed; however, the magnitude and time course of these effects were much greater in F344 rats. Significant strain- but not gender-related differences were obtained when comparing TMT effects on different domains of neurological function. Comparisons of predosing data between male LE and F344 rats, as well as between male and female LE rats, revealed significant differences in baseline values for about half of the measures of the test battery. These preexisting differences, however, could not account for the observed dissimilarities in treatment effects. Quantitative and qualitative differences were evident to a greater extent when comparing LEs and F344s than between males and females. Therefore, conclusions based on these types of neurobehavioral screening data would be influenced considerably more by the differences between rat strains.

Acute trimethyltin exposure produces nonspecific effects on learning in rats working under a multiple repeated acquisition and performance schedule.

Previous research has explored the adverse effects of trimethyltin (TMT) on learning and memory in laboratory animals. Virtually all studies of TMT effects on learning have not, however, included appropriate controls to establish a selective effect on learning. This experiment investigated the effects of TMT on the repeated acquisition (learning) and performance of response sequences. Adult male Long-Evans rats, maintained at 300 g b.wt., were trained with food reinforcement under a multiple repeated acquisition (RA) and performance (P) schedule. The RA component required rats to learn a different three-member response sequence during each session (Center Right Left, RLC, RCL, LCR, or LRC); the correct response sequence remained constant in the P component (CLR). RA and P components alternated twice during a session. Rats were given 0, 4, or 8 mg/kg TMT IV after 30 sessions of stable baseline performance, and an additional 40 sessions were conducted following TMT. Prior to TMT, all groups maintained comparable accuracy levels in both RA and P components. Following TMT, significant decreases in both accuracy and response rate were obtained in the 8 mg/kg group. Thereafter, response rate and accuracy both recovered to near baseline levels, although large individual differences were observed. No selective effects of TMT were obtained on RA when compared to P. These data suggest that TMT-induced impairments on learning may be due to a generalized performance decrement rather than a specific effect on learning.

Elevation of intracellular calcium levels in spiral ganglion cells by trimethyltin.

The neurotoxicant, trimethyltin (TMT) produces cochlear impairment at far lower dose levels and far more rapidly than it does central nervous system effects. The initial effects of TMT in the cochlea, in vivo, are consistent with disruption of the inner hair cell type-1 spiral ganglion cell synapse although it is uncertain whether the effect is on presynaptic and/or postsynaptic units. This synapse is believed to be an excitatory glutamatergic one, providing the possibility that TMT could induce an excitotoxic process resulting in elevations in intracellular calcium ([Ca2+]i). The objective of this study was to determine whether TMT had direct toxic effects on the postsynaptic spiral ganglion cells studied in primary culture and to identify the role of extracellular calcium in such an effect. The marker of interest was the effect of this agent on [Ca2+]i levels as determined using quantitation of the fluorescent calcium dye, Fura-2. TMT did induce a marked and sustained elevation in [Ca2+]i level in the spiral ganglion cells that appeared to have a rapid initial phase and a slower saturating phase. Studies performed using calcium-free medium showed that elevation of [Ca2+]i in spiral ganglion cells by TMT was attenuated but not entirely blocked. Further, the L-type calcium channel blocker, nifedipine, was able to inhibit the initial increase in [Ca2+]i, suggesting that at least this phase of the TMT effect was mediated by calcium channels, although nifedipine had no significant effect on the time to reach the maximal [Ca2+]i level. Parallel control experiments performed using application of exogenous glutamate and depolarizing K+ concentrations also produced elevation in [Ca2+]i levels. The data indicate that TMT elevates [Ca2+]i in isolated spiral ganglion cells both by increasing extracellular uptake via Ca2+ channels and also by releasing Ca2+ from intracellular stores. Thus TMT ototoxicity appears to include a direct postsynaptic toxic event.

Induction of trimethyltin neurotoxicity by dietary administration.

Groups of 12 male and 12 female rats were fed diets containing 0 or 8ppm trimethyltin chloride for up to 25 days. All the animals were observed prior to the study start and daily throughout the study for any changes in clinical condition. In addition, detailed clinical observations, including quantitative assessments of landing foot splay, sensory perception, muscle weakness and locomotor activity were monitored during the study. At the end of the study, the rats were killed and subjected to a full Post-mortem. Selected nervous system tissues were removed, processed and examined microscopically. Clinical signs typical of trimethyltin neurotoxicity (e.g. aggression, shaking and convulsions) were seen in rats receiving diets containing 8ppm trimethyltin chloride for as little as 22 days. Neuropathological lesions consisting of extensive neuronal cell necrosis in the limbic region of the brain, vacuolar degeneration of ventral horn cells of the spinal cord and a marginal increase in Wallerian-type degeneration were seen. The study demonstrates that trimethyltin neurotoxicity can be induced by dietary administration and that both male and female rats are equally sensitive.

The neuropathology of trimethyltin in the marmoset (Callithrix jacchus) hippocampal formation.

The effects of single and repeated doses of trimethyltin (TMT) treatment on the central nervous system (CNS) of the marmoset were investigated. For the acute-dose experiment adult animals were administered 3 mg/kg of TMT chloride (ip) and were then observed for changes in behavior. Within 24 hr postinjection all animals developed tremors, ataxia, and unresponsiveness. Half of the animals had severe clinical deterioration and died at 2 to 3 days following treatment. Surviving marmosets were sacrificed and the brain was subsequently perfusion-fixed for light microscopic examination. Neuronal degeneration was observed in many cells of the Ammon's horn and fascia dentata of the hippocampus. For the chronic-dose experiment, adult marmosets received (ip) weekly doses of 0.75 mg/kg of TMT chloride for 24 weeks. No evident clinical signs or behavioral changes were observed in any of the treated animals. Histological examination revealed neuropathological changes comparatively similar but less severe than those observed in the acute-treated animals. The differences in toxicity effects between acute and chronic TMT administration are compared and discussed.

Trimethyltin-induced c-fos expression: adolescent vs neonatal rat hippocampus.

In the adult animal, the immediate early genes such as c-fos and c-jun, and other activity-dependent genes such as ornithine decarboxylase (ODC) are induced within minutes to hours in response to perturbations to the cellular environment. We have examined the induction of these genes following acute exposure to trimethyltin (TMT) using Northern blot analysis. The induction of these genes within the hippocampus and the cerebellum was examined half an hour following acute exposure to TMT (4 mg/kg, sc). In the neonatal (PND 4) rat hippocampus, the basal expression of c-fos, c-jun, and ODC appeared to be unaltered following TMT exposure. However, in the adolescent (PND 35) rat, TMT exposure produced a dramatic induction of c-fos mRNA in the hippocampus within half an hour, while beta-actin expression remained constant. No TMT-induced changes in the expression of c-fos were seen in the cerebellum of adolescent animals. Furthermore, expression of c-jun mRNA was not altered in either the mature hippocampus or the cerebellum half an hour following TMT exposure. These results suggest that c-fos may be involved in the response of the brain to TMT in an age-dependent and region-specific manner.