Abstracts

Rationale: It is thought that postnatal developmental processes greatly affect mammalian brain function, ranging from development of circuitry for normal sensory processing to pathological conditions such as schizophrenia and depression in humans. Within the rodent brain, these developmental processes are particularly relevant during the first several weeks of life, and include the development of inhibitory neurons. One subset of inhibitory neurons that may play a role in these processes is somatostatin-expressing, dendritic targeting cells. A subset of these cells is labeled with GFP in a line of mice known as the GIN line (Oliva et al. 2000). Here, we studied how the electrophysiological properties of these cells developed in the somatosensory cortex of GIN mice between postnatal (P) ages P11 to P19, a time period that encompasses the onset of whisking in mice. Methods: Fluorescent cells were targeted for whole-cell current clamp recordings and a range of positive and negative current steps was presented to each cell. Results: We demonstrated that as the neocortical circuitry matured during this time, multiple GIN cell properties were altered. There was a decrease in rheobase current, and an increase in the degree of Ih-induced current sag as well as the gain of the input-output function for GIN cells. Surprisingly, the input resistance of these cells did not change throughout this time period, suggesting other mechanisms are responsible for the increase in rheobase current and gain. In contrast, excitatory cells showed an increase in rheobase current and a decrease in sag and gain during the same time period. Input resistance decreased in these cells, paralleling the decrease in rheobase current and gain. Conclusions: Collectively, these changes suggest that for the same level of input, GIN cells may increase their influence in the neocortical circuit throughout the developmental time period investigated.