Abstracts

Rationale: Common symptoms experienced by epileptic patients with sleep disorders include decreased sleep efficiency, greater sleep fragmentation, and longer sleep latency. These symptoms are seen in members of the non-epileptic population with dysregulation of the hypocretin network. Hypocretin neurons are located in the lateral hypothalamus (LH) and stimulate arousal pathways. Extracellular adenosine is responsible for promoting sleep by inhibiting the spontaneous activity of the hypocretin neurons via the A1 receptor (A1R). The Kcna1-null mouse, a Kv1.1 potassium channel knockout (KO) mouse, is a well defined model for temporal lobe epilepsy (TLE). We have previously shown that KO mice display the same symptoms seen in hypocretin dysregulation. We hypothesize that KO mice would exhibit injury in the LH, an area of the brain with multisynaptic connections to limbic structures such as the seizure-genic hippocampus. We know that astrogliosis reduces adenosine's inhibitory tone in the hippocampus by increasing expression of adenosine kinase (ADK), an enzyme responsible for regulating adenosine levels. Therefore we hypothesize that injury present in the LH accounts for hypocretin dysregulation. Methods: The extent of injury in the LH was determined using immunohistochemical staining of WT and KO LH. Blood-brain barrier (BBB) permeability was measured using anti-mouse ImmunoglobulinG (IgG) to identify free antibodies. Glial fibrillary acidic protein (GFAP) was used as a marker to determine extent of astrogliosis. Expression of ADK was determined in LH with western blotting. Changes in A1R expression were also determined using western blot. Sensitivity of LH to the A1R agonist, cyclopentyladenosine (CPA), was determined using multi-unit recordings acquired with an extracellular multi-electrode array and sorted based on characteristics of hypocretin neurons. Results: KO mice show signs of injury in the lateral hypothalamus. BBB permeability in the KO LH was observed as punctate and diffuse IgG staining. Reactive astrocytes were observed in KO LH. Expression of ADK as determined by western blot did not differ (n = 6 per group). A1R protein expression was reduced in the KO LH (n=6 per group, p < .05). Spontaneous activity decreased following application of CPA in both WT and KO LH, however KO LH was relatively less sensitive (n = 15, p < .0001). Conclusions: We determined changes in the LH of a mouse model of TLE. As previously shown, KO mice also exhibit sleep disorder symptoms that are similar to those associated with a hypocretin dysregulation. We hypothesized that this dysregulation may be caused by injury in the LH affecting adenosine tone. Increase in IgG staining in KO LH suggests a compromised BBB. Injury was further evident by the presence of reactive astrocytes. Reduction in A1R expression and a decreased efficacy of an A1R-specific agonist suggests a reduction in adenosinergic regulation in KO LH. Together, these data suggest injury and reduced inhibitory adenosine tone in the LH of an epileptic mouse model may contribute to sleep disorder comorbidities.