Regional heterogeneity for the intracranial self-administration of ethanolwithin the ventral tegmental area of female Wistar rats

Rationale: Because current findings indicate that the selectively bred alco hol-preferring P line of rats self-administers 50-200 mg% ethanol (EtOH) di rectly into the ventral tegmental area (VTA), whereas the alcohol-nonprefer ring NP line does not, it is important to determine whether unselected, com mon stock rats would self-administer EtOH directly into the VTA. In additio n, because neuroanatomical and self-administration studies indicate that th e VTA may be functionally heterogeneous, the present study was designed to determine whether there were subregional differences within the VTA for the intracranial self-administration (ICSA) of EtOH. Objectives: The objective of this study was to employ the ICSA technique to determine whether adult female Wistar rats would self-administer EtOH directly into the VTA, and wh ether regional heterogeneity existed for EtOH self-infusion within the VTA. Methods: Following surgery to implant guide cannulae aimed at either the p osterior or anterior VTA, subjects were placed in standard experimental cha mbers equipped with an 'active lever' [fixed ratio (FR)1 schedule of reinfo rcement], which caused the delivery of the infusate, and an 'inactive lever ', which had no programmed consequence. Subjects were assigned to groups th at self-administered either artificial cerebrospinal fluid (aCSF) throughou t, or 100-400 mg% EtOH for the first four sessions (acquisition), aCSF in s essions 5 and 6 (extinction), and EtOH again during session 7 (reinstatemen t). Results: During the four acquisition sessions, rats with posterior VTA placements readily self-administered 200 mg% and 250 mg% EtOH and discrimin ated between the active and inactive levers. These subjects also demonstrat ed extinction, when aCSF was substituted for EtOH, and reinstatement when E tOH was reintroduced. Rats with posterior VTA placements self-infused 300 m g% and 400 mg% EtOH, and demonstrated lever discrimination only during the initial acquisition sessions. In contrast, rats with anterior VTA placement s did not self-administer EtOH. Conclusions: The findings suggest that EtOH is reinforcing within the posterior VTA of Wistar rats, and the VTA is a f unctionally heterogeneous structure with regard to EtOH reinforcement.