Effects of toluene exposure on signal transduction: toluene reduced the signaling via stimulation of human muscarinic acetylcholine receptor m2 subtypes in CHO cells

Alteration of brain neurotransmitters in female rat offspring induced by prenatal administration of 16 and 64 mg/kg of 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153)

PCB153 (2,2',4,4',5,5'-hexachlorobiphenyl), a non-coplanar PCB and the congener most widely distributed in the environment, was orally administered to pregnant Sprague-Dawley (Crj: CD (SD) IGS) rats from gestation day 10 through 16 at doses of 0 (control), 16 and 64 mg/kg body weight. Female pups were sacrificed at 1, 3, 6, and 9 wk, and at 1 yr of age to evaluate the differences in brain neurotransmitters and their metabolites between PCB153-exposed and control groups. Brain levels of norepinephrine (NE), 3-methoxy-4-hydroxyphenylglycol (MHPG), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5HT), 5-hydroxyindoleacetic acid (5HIAA), acetylcholine (ACh), and choline (Ch) in discrete brain regions or in whole brain were measured. At 1 to 3 wk after birth, brain levels of DA, DOPAC, HVA, 5HT and 5HIAA in PCB-exposed groups were higher than those of the control group. At 9 wk after birth, DA turnover was reduced in half of the four brain areas examined (forebrain and hindbrain), and 5HIAA levels were increased in all brain areas in the PCB-treated group compared to those of the control group. At 1 yr after birth, the levels of DA, DOPAC, and HVA in the hippocampus, hypothalamus, and medulla oblongata were lower in the PCB-exposed groups than in the control group. Prenatal exposure to PCB153 stimulated the turnover of 5HT neurons in the brain of female offspring at early stages (1 to 9 wk) of development. On the other hand, the turnover of DA neurons in the PCB-exposed groups was reduced in late stages (9 wk to 1 yr) of development compared with that of the control group. The brain neurotransmitters of dams treated with PCB were assayed at 3 wk after delivery (15 wk old), and decreases in DA, DOPAC, and HVA were observed. PCB153 reduced the activity of DA neurons in the brain of dams. These results are discussed in relation to health effects observed in humans exposed to PCBs.

The abused inhalant toluene increases dopamine release in the nucleus accumbens by directly stimulating ventral tegmental area neurons

Recreational abuse of toluene-containing volatile inhalants by adolescents is a significant public health problem. The mechanisms underlying the abuse potential of such substances remain unclear, but could involve increased activity in mesoaccumbal dopamine (DA) afferents innervating the nucleus accumbens (ACB). Here, using in vitro electrophysiology, we show that application of behaviorally relevant concentrations of toluene directly stimulates DA neurons in the ventral tegmental area (VTA), but not surrounding midbrain regions. Toluene stimulation of VTA neurons persists when synaptic transmission is reduced. Moreover, unlike non-DA neurons, the magnitude of VTA DA neuron firing does not decline during longer exposures designed to emulate 'huffing'. Using dual-probe in vivo microdialysis, we show that perfusion of toluene directly into the VTA increases DA concentrations in the VTA (somatodendritic release) and its terminal projection site, the ACB. These results provide the first demonstration that even brief exposure to toluene increases action potential drive onto mesoaccumbal VTA DA neurons, thereby enhancing DA release in the ACB. The finding that toluene stimulates mesoaccumbal neurotransmission by activating VTA DA neurons directly (independently of transynaptic inputs) provide insights into the neural substrates that may contribute to the initiation and pathophysiology of toluene abuse.

Increase in cochlear microphonic potential after toluene administration

Human and animal studies have shown that toluene can cause hearing loss. In the rat, the outer hair cells are first disrupted by the ototoxicant. Because of their particular sensitivity to toluene, the cochlear microphonic potential (CMP) was used for monitoring the cochlea activity of anesthetized rats exposed to both noise (band noise centered at 4 kHz) and toluene. In the present experiment, the conditions were specifically designed to study the toluene effects on CMP and not those of its metabolites. To this end, 100-microL injections of a vehicle containing different concentrations of solvent were made into the carotid artery connected to the tested cochlea. Interestingly, an injection of 116.2-mM toluene dramatically increased in the CMP amplitude (approximately 4 dB) in response to an 85-dB SPL noise. Moreover, the rise in CMP magnitude was intensity dependent at this concentration suggesting that toluene could inhibit the auditory efferent system involved in the inner-ear or/and middle-ear acoustic reflexes. Because acetylcholine is the neurotransmitter mediated by the auditory efferent bundles, injections of antagonists of cholinergic receptors (AchRs) such as atropine, 4-diphenylacetoxy-N-methylpiperidine-methiodide (mAchR antagonist) and dihydro-beta-erythroidine (nAchR antagonist) were also tested in this investigation. They all provoked rises in CMP having amplitudes as large as those obtained with toluene. The results showed for the first time in an in vivo study that toluene mimics the effects of AchR antagonists. It is likely that toluene might modify the response of protective acoustic reflexes.

Effects of perinatal exposure to bisphenol A on brain neurotransmitters in female rat offspring

Pregnant Sprague-Dawley (CD IGS) rats were orally administered doses of bisphenol A (BPA) at 4, 40, and 400 mg/kg, from gestation days 6 to postnatal day 20. Neurotransmitters such as dopamine (DA) and serotonin (5HT) were extracted from the brains of dams and female offspring, and measured using liquid chromatography. BPA at 400 mg/kg was toxic and dosed rats died. At 3 wk after birth, brain levels of 3,4-dihydroxyphenylacetic acid (DOPAC, a DA metabolite), homovanillic acid (HVA, a DA metabolite), 5HT, 5-hydroxyindoleacetic acid (5HIAA, a 5HT metabolite) in female offspring were increased and the HVA/DA ratio was high in some brain areas of BPA-treated groups as compared with controls. At the age of 6 wk, levels of choline (Ch) in BPA-treated groups at 4 and 40 mg/kg were higher than control in all of eight brain areas. No changes were observed in acetylcholine (ACh) contents. In 9-wk-old offspring, changes in monoamines and metabolites were scattered and not great. At 3 wk after delivery, levels of 5HIAA in some brain areas of dams treated with BPA were higher than in control dams. Dose dependent increases in HVA and the HVA/DA ratio of the occipital cortex, and in the HVA/DA ratio of the frontal cortex were observed. The turnover of DA and 5HT was accelerated in 3-wk-old offspring and dams. BPA possesses very weak estrogenic activity. Changes in cerebral neurotransmitters observed in offspring and dams in this study may have been related to the estrogenic activity of BPA. However, further investigation is needed to examine the contribution of hormonal activity to such neurotransmitter changes.

Toluene-induced locomotor activity is blocked by 6-hydroxydopamine lesions of the nucleus accumbens and the mGluR2/3 agonist LY379268

The abuse of volatile inhalants remains a prominent, yet poorly understood, form of substance abuse among youth. Nevertheless, the identification of a mechanism underlying the reinforcing properties of inhalants has been hampered by the lack of a clearly identifiable neural substrate upon which these chemicals act. One ingredient that is common to many abused inhalants is toluene, an organic solvent that is self-administered by nonhuman primates and rodents. Most drugs of abuse have been found to elicit forward locomotion in rats, an effect owing to the activation of mesoaccumbal dopamine (DA) pathways. Thus, the present study was undertaken using two different approaches to determine whether toluene-induced locomotor hyperactivity is also ultimately dependent upon DA neurotransmission in the mesolimbic nucleus accumbens (NAC). Here we report on the effects of 6-hydroxydopamine (6-OHDA) lesions of the NAC or pretreatment with the metabotropic mGlu2/3 receptor agonist LY379268 on toluene-induced locomotor activity. Both procedures, which are known to alter neurotransmission within the NAC, significantly attenuated toluene's locomotor stimulatory effects. These results provide strong support for a central mechanism of action of inhalants, which in the past has been more typically attributed to general nonspecific mechanisms throughout the brain. Moreover, as with other drugs of abuse, the NAC may be the final common pathway subserving toluene's abuse liability.