Amino acid release from the intermediate medial hyperstriatum ventrale (IMHV) of day-old chicks following a one-trial passive avoidance task

Indirect evidence has implicated glutamate and gamma-amino butyric acid in memory formation for one-trial passive avoidance learning. We have further examined this by following the time course of glutamate and gamma-amino butyric acid release from slices prepared from the intermediate medial hyperstriatum ventrale of day-old chicks (Ross 1 Chunky) trained to avoid a bead covered in the aversant methylanthranilate. At various times after training, slices of left and right intermediate medial hyperstriatum ventrale were incubated in medium containing 50 mM potassium chloride and amino acid release was determined. Thirty minutes after training there was a bilateral increase in calcium-dependent glutamate release in slices from methylanthranilate-trained chicks compared to those trained to peck water. This increase was sustained until 1 h in the left hyperstriatum when an increase in calcium-dependent gamma-amino butyric acid release was also apparent. Glutamate uptake was also enhanced in left hyperstriatum (30 and 60 min) and in the right at 30 min. In the right intermediate medial hyperstriatum ventrale of methylanthranilate birds glutamate release was increased from 3 to 6.5 h and gamma-amino butyric acid at 6.5 h: a time that corresponded to the mobilization of a late process required if long-term memory was to be formed. These results confirm that the amino acids glutamate and gamma-amino butyric acid are released from the intermediate hyperstriatum ventrale in a calcium-dependent, neurotransmitter-like manner. Furthermore, changes in the release of these two amino acids accompany memory formation for a one-trial learning task in the day-old chick.     

High rates of paraquat-induced suicide in southern Trinidad.

The suicide rate in Trinidad and Tobago is much greater than that of its English-speaking Caribbean neighbors. Many of these suicides are paraquat induced. This research reviewed the deaths due to suicide in the area with the greatest agricultural activity in Trinidad for 1996 and identified, for further demographic and etiological investigation, cases in which paraquat was ingested as the agent of suicide. Of 48 cases of suicide for the year, 39 (81.3%) were due to paraquat poisoning. The incidence of paraquat-induced suicide was 8.0 per 100,000. Among the males, 47.8% were in the age group 25-34 (p < 0.001), and among the females 50.0% were in the 15-24 age group (p < 0.05). Family-of-origin disputes were the most frequently cited precipitant, followed by marital problems. Individuals of East Indian origin accounted for 89% of the suicide victims (p < 0.001). When compared with suicide by other methods in the country, these findings confirm that paraquat poisoning is a significant means of suicide in Trinidad and that young East Indian individuals are particularly vulnerable.