Intermediate-term memory in Aplysia involves neurotrophin signaling, transcription, and DNA methylation.

Long-term but not short-term memory and synaptic plasticity in many brain areas require neurotrophin signaling, transcription, and epigenetic mechanisms including DNA methylation. However, it has been difficult to relate these cellular mechanisms directly to behavior because of the immense complexity of the mammalian brain. To address that problem, we and others have examined numerically simpler systems such as the hermaphroditic marine mollusk Aplysia californica. As a further simplification, we have used a semi-intact preparation of the Aplysia siphon withdrawal reflex in which it is possible to relate cellular plasticity directly to behavioral learning. We find that inhibitors of neurotrophin signaling, transcription, and DNA methylation block sensitization and classical conditioning beginning ∼1 h after the start of training, which is in the time range of an intermediate-term stage of plasticity that combines elements of short- and long-term plasticity and may form a bridge between them. Injection of decitabine (an inhibitor of DNA methylation that may have other actions in these experiments) into an LE sensory neuron blocks the neural correlates of conditioning in the same time range. In addition, we found that both DNA and RNA methylation in the abdominal ganglion are correlated with learning in the same preparations. These results begin to suggest the functions and integration of these different molecular mechanisms during behavioral learning.

Isolated nocardial brain abscess in an immunocompetent patient with lung adenocarcinoma: A case report.

Brain metastases are common in non-small cell lung cancer (NSCLC) and can often be the presenting symptom. However, it is important to consider other etiologies for brain masses even in patients with a malignancy with a propensity to metastasize. We discuss the case of a 60 year-old immunocompetent male who presented with neurologic deficits thought to be secondary to brain metastases in the setting of an incidentally discovered lung cancer. Instead, the mass proved to be a rare isolated Nocardial brain abscess.