Autapses are synaptic contacts of a neuron’s axon onto its own dendrite and soma. In the neocortex, self-inhibiting autapses in GABAergic interneurons are abundant in number and play critical roles in regulating spike precision and network activity. Here we examine whether the principal glutamatergic pyramidal cells (PCs) also form functional autapses. In patch-clamp recording from both rodent and human PCs, we isolated autaptic responses and found that these occur predominantly in layer-5 PCs projecting to subcortical regions, with very few in those projecting to contralateral prefrontal cortex and layer 2/3 PCs. Moreover, PC autapses persist during development into adulthood. Surprisingly, they produce giant postsynaptic responses (∼5 fold greater than recurrent PC-PC synapses) that are exclusively mediated by AMPA receptors. Upon activation, autapses enhance burst firing, neuronal responsiveness and coincidence detection of synaptic inputs. These findings indicate that PC autapses are functional and represent an important circuit element in the neocortex.

Rasmussen encephalitis (RE) is a rare neurologic disorder of childhood characterized by unihemispheric inflammation, progressive neurologic deficits, and intractable focal epilepsy. The pathogenesis of RE is still enigmatic. Adenosine is a key endogenous signaling molecule with anticonvulsive and anti-inflammatory effects, and our previous work demonstrated that dysfunction of the adenosine kinase (ADK)–adenosine system and astrogliosis are the hallmarks of epilepsy. We hypothesized that the epileptogenic mechanisms underlying RE are related to changes in ADK expression and that those changes might be associated with the development of epilepsy in RE patients. Immunohistochemistry was used to examine the expression of ADK and glial fibrillary acidic protein in surgically resected human epileptic cortical specimens from RE patients (n = 12) and compared with control cortical tissues (n = 6). Adenosine kinase expression using Western blot and enzymatic activity for ADK were assessed in RE versus control samples. Focal astrogliosis and marked expression of ADK were observed in the lesions of RE. Significantly greater ADK expression in RE versus controls was demonstrated by Western blot, and greater enzymatic activity for ADK was demonstrated using an enzyme-coupled bioluminescent assay. These results suggest that upregulation of ADK is a common pathologic hallmark of RE and that ADK might be a target in the treatment of epilepsy associated with RE.

Rasmussen encephalitis (RE) is a rare neurological disorder characterized by unilateral inflammation of cerebral cortex and other structures, most notably the hippocampus, progressive cognitive deterioration, and pharmacoresistant focal epilepsy. The pathogenesis of RE with unilateral cortical atrophy and focal seizures is still enigmatic. Activation of adenosine A1 receptors (A1R) has been proven to prevent the spatial spread of seizures. We hypothesized that the epileptogenic mechanisms underlying RE are related to changes in neuronal A1R expression. Immunnohistochemistry was used to examine the expression of A1R and adenosine kinase (ADK) in cortical specimens from RE (n = 12), and compared with control cortical tissue. The quantification of A1R and ADK expression was evaluated by Western blot. A1R was predominantly localized in perinuclear of neurons and not in astrocytes or microglia. Upregulation of neuronal A1R was observed in the lesions of RE. Reactive astrocytes and subpopulation of remaining neurons demonstrated over-expression of the ADK within the lesions of RE. Significant increase of A1R and ADK expression in RE compared with controls was confirmed by Western blot. These results suggest that over-expression of ADK is a common pathologic hallmark of RE, and that upregulation of neuronal A1R in RE is crucial in preventing the spread of seizures.