A hierarchical neuronal network for planning behavior

Planning a goal-directed sequence of behavior is a higher function of the human brain that relies on the integrity of prefrontal cortical areas. In the Tower of London test, a puzzle in which beads sliding on pegs must be moved to match a designated goal configuration, patients with lesioned prefrontal cortex show deficits in planning a goal-directed sequence of moves. We propose a neuronal network model of sequence planning that passes this test and, when lesioned, fails in a way that mimics prefrontal patients’ behavior. Our model comprises a descending planning system with hierarchically organized plan, operation, and gesture levels, and an ascending evaluative system that analyzes the problem and computes internal reward signals that index the correct/erroneous status of the plan. Multiple parallel pathways connecting the evaluative and planning systems amend the plan and adapt it to the current problem. The model illustrates how specialized hierarchically organized neuronal assemblies may collectively emulate central executive or supervisory functions of the human brain.

Chloroplast DNA evidence of colonization, adaptive radiation, and hybridization in the evolution of the Macaronesian flora.

Most evolutionary studies of oceanic islands have focused on the Pacific Ocean. There are very few examples from the Atlantic archipelagos, especially Macaronesia, despite their unusual combination of features, including a close proximity to the continent, a broad range of geological ages, and a biota linked to a source area that existed in the Mediterranean basin before the late Tertiary. A chloroplast DNA (cpDNA) restriction site analysis of Argyranthemum (Asteraceae: Anthemideae), the largest endemic genus of plants of any volcanic archipelago in the Atlantic Ocean, was performed to examine patterns of plant evolution in Macaronesia. cpDNA data indicated that Argyranthemum is a monophyletic group that has speciated recently. The cpDNA tree showed a weak correlation with the current sectional classification and insular distribution. Two major cpDNA lineages were identified. One was restricted to northern archipelagos--e.g., Madeira, Desertas, and Selvagens--and the second comprised taxa endemic to the southern archipelago--e.g., the Canary Islands. The two major radiations identified in the Canaries are correlated with distinct ecological habitats; one is restricted to ecological zones under the influence of the northeastern trade winds and the other to regions that are not affected by these winds. The patterns of phylogenetic relationships in Argyranthemum indicate that interisland colonization between similar ecological zones is the main mechanism for establishing founder populations. This phenomenon, combined with rapid radiation into distinct ecological zones and interspecific hybridization, is the primary explanation for species diversification.

Muscle-specific expression of Drosophila hsp70 in response to aging and oxidative stress.

Induction of Drosophila hsp70 protein was detected during aging in flight muscle and leg muscle in the absence of heat shock, using an hsp70-specific monoclonal antibody, and in transgenic flies containing hsp70-beta-galactosidase fusion protein reporter constructs. While hsp70 and reporter proteins were induced during aging, hsp70 message levels were not, indicating that aging-specific induction is primarily posttranscriptional. In contrast, hsp22 and hsp23 were found to be induced during aging at the RNA level and with a broader tissue distribution. The same muscle-specific hsp70 reporter expression pattern was observed in young flies mutant for catalase (H2O2:H2O2 oxidoreductase, EC 1.11.1.6). In catalase (cat) hypomorphic lines where flies survived to older ages, the time course of hsp70 reporter expression during aging was accelerated, and the initial and ultimate levels of expression were increased. The hsp70 reporter was also induced in young flies mutant for copper/zinc superoxide dismutase (superoxide:superoxide oxidoreductase, EC 1.15.1.1). Taken together, the results suggest that aging-specific hsp70 expression may be a result of oxidative damage.