Kazuhisa Hongou

Serine racemase is predominantly localized in neurons in mouse brain

D‐Serine is the endogenous ligand for the glycine binding site of the N‐methyl‐D‐aspartate (NMDA)‐type glutamate receptor (GluR) channel and is involved in the regulation of synaptic plasticity, neural network formation, and neurodegenerative disorders. D‐Serine is synthesized from L‐serine by serine racemase (SR), which was first reported to be localized in astrocytes. However, recently, SR mRNA and its protein have been detected in neurons. In this study, we examined the SR distribution in the brain during postnatal development and in cultured cells by using novel SR knockout mice as negative controls. We found that SR is predominantly localized in pyramidal neurons in the cerebral cortex and hippocampal CA1 region. Double immunofluorescence staining revealed that SR signals colocalized with those of the neuron‐specific nuclear protein, but not with the astrocytic markers glial fibrillary acid protein and 3‐phosphoglycerate dehydrogenase. In the striatum, we observed SR expression in γ‐aminobutyric acid (GABA)ergic medium‐spiny neurons. Furthermore, in the adult cerebellum, we detected weak but significant SR signals in GABAergic Purkinje cells. From these findings, we conclude that SR is expressed predominantly in many types of neuron in the brain and plays a key role in the regulation of brain functions under physiological and pathological conditions via the production of the neuromodulator D‐serine. J. Comp. Neurol. 510:641–654, 2008.

Rotavirus encephalitis mimicking afebrile benign convulsions in infants

A 2-year-old-boy had rotavirus gastroenteritis and demonstrated afebrile partial seizures with secondary generalization. The presence of rotavirus genome and anti-rotavirus IgG was detected in the cerebrospinal fluid. The genotype of VP4 was P8 and that of VP7 was G4. The imaging analysis by computed tomography and single photon emission computed tomography implied encephalitis. The seizures were well controlled by standard antiepileptic therapy, and the child experienced normal development with neither physical nor neurologic sequelae, which appeared to mimic benign infantile partial epilepsy.

Auditory event-related potentials in benign childhood epilepsy with centrotemporal spike: the effects of carbamazepine

To clarify the relationship between cognitive function and CBZ therapy, auditory event-related potentials (P300) were examined in 23 patients with Benign Childhood Epilepsy with Centrotemporal Spike (BCECT) compared with 54 normal controls. The results were 1) the mean P300 latency in BCECT (368 +/- 29 msec) was significantly prolonged compared with that in normal controls (349 +/- 30 msec), but most individual patients showed normal values. 2) The prolongation of P300 latency was greatest during the course of therapy. 3) On repeated examination of P300, P300 latency was found to gradually become shorter with age in spite of continuous CBZ therapy. At initiation of CBZ therapy, the P300 latency became shorter; on the other hand, P300 latency became shorter with the discontinuation of CBZ. 4) The age-corrected P300 latency showed a significant positive correlation with the serum concentration of CBZ. Our results suggest that CBZ therapy has both an undesirable effect (chronic impairment) and a desirable effect (improvement of underlying dysfunction caused by epileptogenesis) on cognitive function.

Changes of P300 latency with age in childhood epilepsy

Auditory event-related potentials (P300 latency; odd-ball paradigm) were examined in 129 patients with childhood epilepsies and 53 controls. The P300 latency in the patients with epilepsies (373 +/- 39.4 ms) was significantly longer than in controls (356 +/- 38.4), and the prolongation was greatest in the patients with symptomatic partial epilepsies (390 +/- 40.5), mild in those with idiopathic generalized epilepsies (370 +/- 24.3), and minimum in those with idiopathic partial epilepsies (363 +/- 28.9). Abnormal P300 latency occurred at all ages during childhood in patients with symptomatic partial epilepsies, and at older ages in patients with idiopathic generalized epilepsies. The shortening of latency with age was relatively small in patients with epilepsies compared with controls. These results suggest that the prolongation of P300 latency (i.e., existence of cognitive disturbance) displays characteristic changes with age in each epileptic syndrome.

Effects of antiepileptic drugs on EEG background activity in children with epilepsy: initial phase of therapy.

The effects of antiepileptic drugs (AED) on EEG background activity were evaluated in 37 newly treated children with epilepsy, compared with 46 age-matched healthy controls. Before AED therapy, the children with epilepsy, both partial (treated with carbamazepine, CBZ group) and generalized seizures (treated with valproic acid, VPA group), already exhibited significant slowing of EEG with increased delta and decreased alpha power. Following 3 to 6 months of AED therapy, this EEG slowing was enhanced in the CBZ group and reduced in the VPA group. Following 1 year of AED therapy, an increase in frequency was recognized in the CBZ group. These results suggest that 1) most children with epilepsy already exhibit slowing of the EEG at the onset of seizures, which may reflect CNS developmental deficit, 2) the short-term effects on EEG are different between CBZ and VPA, and 3) EEG development with age continues under continuous AED administration. The EEG background activity in children with epilepsy is affected by many factors, which include the underlying CNS dysfunction of the epilepsy itself and also AED therapy (type of AEDs, duration of therapy, etc).

Event-related potentials (P300) and EEG activity in childhood partial epilepsy

To clarify the relationship between the cognitive function and EEG activity, auditory event-related potentials (P300) were examined in 72 patients with partial epilepsy. Twenty-six patients (67 trials) had idiopathic partial epilepsies (IPE), and 46 (118 trials) symptomatic or cryptogenic partial epilepsies (SPE). For this study, patients undergoing carbamazepine monotherapy with a dose of less than 16 mg/kg/day were selected to rule out the effects of anti-epileptic drugs. The results were as follows: (1) The P300 latency tended to be prolonged in association with the EEG slowing in both epileptic groups. (2) There was no clear relationship between the frequency of paroxysmal discharges and the P300 latency. (3) The P300 latency was slightly prolonged in the patients with temporal foci compared with that in ones with extra-temporal foci. (4) There was no significant relationship between the generalization of focal paroxysmal discharges and the P300 latency. These results suggested that the influence of EEG abnormalities (particularly paroxysmal discharges) on the P300 latency is relatively little, and the cognitive dysfunction in partial epilepsies mainly originates from other factors such as the epileptogenic lesion itself.

Autoimmune neurological disorders associated with group-A beta-hemolytic streptococcal infection

Although central nervous system (CNS) disorders associated with group-A beta-hemolytic streptococcal (GABHS) infection occur only rarely, Sydenhams chorea is a well-recognized disease that can arise following infection. Children may develop a tic, obsessive compulsive disorder (OCD), and extrapyramidal movement subsequent to GABHS infection. These disorders have been termed pediatric autoimmune neuropsychiatric disorders associated with streptococci (PANDAS). Herein we report one case each of acute disseminated encephalomyelitis (ADEM), PANDAS and subacute encephalitis associated with GABHS infection. To evaluate the pathogenesis of the CNS disorders associated with GABHS infection, we measured levels of neurotransmitters, cytokines, anti-neuronal autoantibodies, and performed immunohistochemistry using patient sera to stain human brain sections. All three cases showed psychiatric behavioral disorders. Immunotherapy was effective, and homovanillic acid levels in the cerebrospinal fluid (CSF) were elevated at the acute stage in all three cases. In each case of ADEM and PANDAS, immunohistochemistry demonstrated neuronal impairment in the basal ganglia during the acute stage. Neuronal immunoreactivity was visualized in the cerebral cortex at the acute stage in the case of subacute encephalitis. There was no direct correlation between immunoreactivity of patient sera on the brain sections and positivity of anti-neuronal autoantibodies or CSF biomarkers. The results suggest that autoimmune responses may modulate neurotransmission, and the use of patient serum for immunohistochemistry is a sensitive screening method for the detection of anti-neuronal autoantibodies in CNS disorders associated with GABHS infection.

Decreased susceptibility to seizures induced by pentylenetetrazole in serine racemase knockout mice.

The N-methyl-D-aspartate (NMDA)-type glutamate receptor plays a key role in excitatory synaptic transmission. The overactivation of the NMDA receptor has been implicated in the development of epileptic seizures. D-Serine is a coagonist of the NMDA receptor and its biosynthesis is catalyzed by serine racemase (SR). Here, we examined the effect of d-serine deficiency on the seizures induced by a single injection of pentylenetetrazole (PTZ) using SR knockout (KO) mice. We found that, compared with wild-type (WT) mice, SR-KO mice showed the attenuation of seizure expression in terms of a significantly shortened duration of generalized seizures and resistance to generalized clonic-tonic seizures. Consistently, immunohistochemical analysis of c-Fos demonstrated that the numbers of cells expressing c-Fos induced by high-dose PTZ in the cerebral cortex, hippocampal CA1, hippocampal CA3, and the basolateral nucleus of the amygdala in WT mice were significantly higher than those in SR-KO mice. Moreover, PTZ induced an increase in extracellular glutamate level in the dentate gyrus of WT mice at two different time phases. However, such a PTZ-induced increase in glutamate level was completely inhibited in SR-KO mice. The present findings suggest that SR may be a target for the development of new therapeutic strategies for epileptic seizures.

Epileptic seizures and event-related potentials (P300) in childhood partial epilepsies

To clarify the relationship between cognitive function and clinical seizures, auditory event-related potentials (P300) were examined in 72 patients (185 trials) with partial epilepsy. Twenty-six patients (67 trials) had idiopathic partial epilepsies (IPE), and 46 (118 trials) symptomatic or cryptogenic partial epilepsies (SPE). In this study, to rule out the effects of epileptogenesis and other factors, we only examined patients with partial epilepsies undergoing carbamazepine (CBZ) monotherapy at doses of less than 16 mg/kg/day. The results were: 1) the mean age-corrected P300 latency in the patients with SPE (394 +/- 38 msec) was significantly prolonged compared with that in the patients with IPE (378 +/- 28). 2) The prolongation of the P300 latency had no relationship to the seizure frequency, seizure type or seizure duration. 3) In both epileptic groups, there was no significant correlation between the seizure-free period and the age-corrected P300 latency. Our results suggest that the effect of clinical seizures on the cognitive function may be relatively little, and that the cognitive dysfunction in partial epilepsies may mainly originate from epileptogenesis or other factors.

Changes in EEG Foci with Age in Childhood Partial Epilepsies

The age changes of epileptic foci on EEG were evaluated in 208 patients with childhood partial epilepsies, who were followed for more than 3 years. 1) The incidence of EEG foci in each region apparently differed with age. Frontal and central foci were frequent before school age and after adolescence. Temporal foci showed a peak around adolescence, and occipital foci a peak from 3 to 7 years, respectively. Parietal foci were rare at all ages. 2) The migration of EEG foci was recognized 171 times in 81 of the 208 patients (38.9%) during the clinical course. The migration was frequently seen at early school age and preadolescence, and the direction of migration was predominantly anterior to posterior at early school age, and posterior to anterior at preadolescence. These results suggest that EEG foci show characteristic changes with age during the clinical course, which may be related to maturation of the central nervous system.