Figure 1. Reactivity with brain tissue and neuron cultures of the CSF of patients with GABA_AR or GABA_BR antibodies.

The CSF of patient 2 showed extensive and diffuse immunostaining of the neuropil of cortical and subcortical regions (A; see the appendix for higher magnifications of selected brain regions). This pattern of brain and cerebellar staining is similar to that produced by the CSF of a patient with GABA_BR antibodies (C). However, patient 2 was negative for GABA_BR antibodies in a specific cell-based assay (data not shown). These findings suggested the presence of antibodies against a novel neuronal cell-surface antigen, which was confirmed in cultures of live rat hippocampal neurons (B). The CSF of the patient with GABA_BR antibodies also reacted with the neuronal cell surface, as expected (D). E and F show a similar study using CSF of a control patient without neuronal cell-surface antibodies. In B, D, and F the nucleus of the neurons was counterstained with DAPI. In A, C, and E the tissue was counterstained with haematoxylin.