THE ROLE OF BURSTS IN SENSORY DISCRIMINATION AND RETENTION OF FAVORED INPUTS IN THE CULTURED NEURAL NETWORKS

The capacity of neural tissue to discriminiate the sensory signals determines how we recognise the world diversity. Dissociated cortical culture (DCC) homed in a multielectrode array allows mimicking neural networks of the brain and using it for investigation of neural computation processes. This in vivo-like in vitro system allows tracking and assessing structural and functional refinement, as well as the ability for information acquisition, processing, and coding in neural networks. We had an increased interest to the burst phenomenon as it represents one of the strongest tools for information coding. We were interested in whether the neural circuitry of DCC was capable of sensory discrimination and memorization of the preferred electric stimuli and to determine the role of bursts in these processes.Matured DCC from the 30th to 50th day of in vitro cultivation were used for the study. In order to simulate a variety of sensory inputs, 300 mV of single, paired-pulse (20 ms interstimulus interval), 1, 5, 10, 20 and 100 Hz stimuli for 1 sec were repeated at random time interval (>10 secs) from effective pairs of electrodes; Activity was registered from all active channels.The data revealed that during the variety of electric stimulations neurons increased activity in response to one of the stimulus types while responding less effectively to others. Single, 5Hz, and notably PP stimuli were the favored paradigms. The training phase frequently showed a progressive increase in activity level, with short burst prevalence. However, repetition of the preferred stimuli enhanced the occurrence of both tonic and burst evoked responses with prolonged duration throughout the testing phase.Data shows that neural circuits of DCC have high selectivity to physical properties and spatial position of the sensory inputs and produces early and late responses that include burst elements that may serve as the robust mechanism for reinforcement of the coding information needed for sensory discrimination and learning.

Sex-specific behavioral traits in the Brd2 mouse model of juvenile myoclonic epilepsy

Idiopathic generalized epilepsy represents about 30-35% of all epilepsies in humans. The bromodomain BRD2 gene has been repeatedly associated with the subsyndrome of juvenile myoclonic epilepsy (JME). Our previous work determined that mice haploinsufficient in Brd2 (Brd2+/-) have increased susceptibility to provoked seizures, develop spontaneous seizures and have significantly decreased gamma-aminobutyric acid (GABA) markers in the direct basal ganglia pathway as well as in the neocortex and superior colliculus. Here, we tested male and female Brd2+/- and wild-type littermate mice in a battery of behavioral tests (open field, tube dominance test, elevated plus maze, Morris water maze and Barnes maze) to identify whether Brd2 haploinsufficiency is associated with the human behavioral patterns, the so-called JME personality. Brd2+/- females but not males consistently displayed decreased anxiety. Furthermore, we found a highly significant dominance trait (aggression) in the Brd2+/- mice compared with the wild type, more pronounced in females. Brd2+/- mice of either sex did not differ from wild-type mice in spatial learning and memory tests. Compared with wild-type littermates, we found decreased numbers of GABA neurons in the basolateral amygdala, which is consistent with the increase in aggressive behavior. Our results indicate that Brd2+/- haploinsufficient mice show no cognitive impairment but have behavioral traits similar to those found in patients with JME (recklessness, aggression). This suggests that either the BRD2 gene is directly responsible for influencing many traits of JME or it controls upstream regulators of individual phenotypes.

Prenatal corticosteroids modify glutamatergic and GABAergic synapse genomic fabric: insights from a novel animal model of infantile spasms

Prenatal exposure to corticosteroids has long-term postnatal somatic and neurodevelopmental consequences. Animal studies indicate that corticosteroid exposure-associated alterations in the nervous system include hypothalamic function. Infants with infantile spasms, a devastating epileptic syndrome of infancy with characteristic spastic seizures, chaotic irregular waves on interictal electroencephalogram (hypsarhythmia) and mental deterioration, have decreased concentrations of adrenocorticotrophic hormone (ACTH) and cortisol in cerebrospinal fluid, strongly suggesting hypothalamic dysfunction. We have exploited this feature to develop a model of human infantile spasms by using repeated prenatal exposure to betamethasone and a postnatal trigger of developmentally relevant spasms with NMDA. The spasms triggered in prenatally primed rats are more severe compared to prenatally saline-injected ones and respond to ACTH, a treatment of choice for infantile spasms in humans. Using autoradiography and immunohistochemistry, we have identified a link between the spasms in our model and the hypothalamus, especially the arcuate nucleus. Transcriptomic analysis of the arcuate nucleus after prenatal priming with betamethasone but before trigger of spasms indicates that prenatal betamethasone exposure down-regulates genes encoding several important proteins participating in glutamatergic and GABAergic transmission. Interestingly, there were significant sex-specific alterations after prenatal betamethasone in synapse-related gene expression but no such sex differences were found in prenatally saline-injected controls. A pairwise relevance analysis revealed that, although the synapse gene expression in controls was independent of sex, these genes form topologically distinct gene fabrics in males and females and these fabrics are altered by betamethasone in a sex-specific manner. These findings may explain the sex differences with respect to both normal behaviour and the occurrence and severity of infantile spasms. Changes in transcript expression and their coordination may contribute to a molecular substrate of permanent neurodevelopmental changes (including infantile spasms) found after prenatal exposure to corticosteroids.