Sadayoshi Shigeta

Enhancement of the immune response in vitro by arsenic

We examined the effect of arsenic (As) on the immune response of mice to sheep erythrocytes, assaying the spleen for plaque-forming cells (PFC). The effect of As on the PFC response to sheep erythrocytes was dose-dependent. At high doses of As the PFC response was erythrocytes was dose-dependent. At high doses of As the PFC response was suppressed, whereas it enhanced the response at low doses. The suppression was due to the cytotoxic action of As against lymphocytes generally. On the other hand, enhancement was seen on the addition of As at the start of the culture or as a result of pretreatment of normal spleen cells with As. Even low doses of As were cytotoxic, to both B and T cells. They differed, however, in their susceptibility to As. When normal spleen cells were added to the culture of As-treated spleen cells, the enhancement of the PFC response was reversed. Suppressor-inducer B cells, in the normal spleen cells, could not induce suppressor T cells from As-treated spleen cells. And As did not affect suppressor T cells. These findings indicate that As deletes the precursors of suppressor T cells from normal spleen cells, and thus enhances the immune response.

Changes in the amounts of neurotransmitters released from the striatum and spontaneous motor activity in rats exposed to high doses of toluene.

We studied the neurotoxicological effects of high-dose toluene exposure by measuring neurotransmitter release from the striatum and spontaneous motor activity in freemoving Tokai High Avoider (THA) male rats. The rats were exposed to 1,000, 2,000, and 4,000ppm toluene for 4 hours. During the 4-hour exposure period and each one hour pre- and post-exposure periods, acetylcholine (ACh), 3, 4-dihydroxyphenylacetic acid (DOPAC), homovanilic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) in the microdialysate from kthe striatum of each rat were measured continuously using microdialysis. Simultaneously, spontaneous motor activity of each rat was monitored using an Aimex device. The amounts of neurotransmitters released and spontaneous motor activity showed similar changes for every concentration of toluene exposure during those periods. Although minimal changes in neurotransmitters and motor activity were observed in the 1,000 ppm group, increases in neurotransmitter release and motor activity were observed in the 2,000 ppm group during the entire exposure period and also in the 4,000 ppm group during the early period of exposure. On the other hand, decreases in neurotransmitter release and motor activity were observed in the 4,000 ppm group during the late period of exposure. These findings indicate that the striatum influences motor activity via changes in the amounts of neurotransmitters released during the period of high-dose toluene exposure.