Relative replication fitness of a high-level 3'-azido-3'-deoxythymidine-resistant variant of human immunodeficiency virus type 1 possessing an amino acid deletion at codon 67 and a novel substitution (Thr-->Gly) at codon 69.

The combination of an amino acid deletion at codon 67 (delta 67) and Thr-to-Gly change at codon 69 (T69G) in the reverse transcriptase (RT) of human immunodeficiency virus type 1 (HIV-1) is associated with high-level resistance to multiple RT inhibitors. To determine the relative contributions of the delta 67 and T69G mutations on viral fitness, we performed a series of studies of HIV replication using recombinant variants. A high-level 3'-azido-3'-deoxythymidine (AZT)-resistant variant containing delta 67 plus T69G/K70R/L74I/K103N/T215F/K219Q in RT replicated as efficiently as wild-type virus (Wt). In contrast, the construct without delta 67 exhibited impaired replication (23% of growth of Wt). A competitive fitness study failed to reveal any differences in replication rates between the delta 67+T69G/K70R/L74I/K103N/T215F/+ ++K219Q mutant and Wt. Evaluation of proviral DNA sequences over a 3-year period in a patient harboring the multiresistant HIV revealed that the T69G mutation emerged in the context of a D67N/K70R/T215F/K219Q mutant backbone prior to appearance of the delta 67 deletion. To assess the impact of this stepwise accumulation of mutations on viral replication, a series of recombinant variants was constructed and analyzed for replication competence. The T69G mutation was found to confer 2',3'-dideoxyinosine resistance at the expense of fitness. Subsequently, the development of the delta 67 deletion led to a virus with improved replication and high-level AZT resistance.

Deficits in operant behaviour in monkeys treated with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).

Six adult Macaca fascicularis monkeys were trained to perform an instrumentally conditioned, visually-guided forearm reaching task for fruit juice reinforcement. Once animals were overtrained on this task, they were given intravenous injections of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (0.15 to 0.33 mg/kg). Animals were tested daily for performance in the previously learned behavioural task and were assessed daily for abnormalities in motor functioning. Monkeys developed deficits in operant task performance characterized by termination of responses after an initial series of responses and long pauses between responses. Once an animal stopped responding to the task, responses could often be reinitiated if the experimenter guided the monkey through the task. This type of performance deficit was seen both before and without the appearance of distinct parkinsonian motor signs. Animals which developed motor signs had extensive ventral mesencephalic cell loss while an animal with performance deficits but without motor signs had cell loss restricted to the ventral substantia nigra pars compacta. The results demonstrate that operant performance deficits can be observed in MPTP-treated monkeys independent of the appearance of motor deficits.