Serotonin modulation of cell excitability and of [3H]GABA and [3H]D-aspartate efflux in primary cultures of rat cortical neurons

Syntaxin 1B contributes to regulation of the dopaminergic system through GABA transmission in the CNS

In neuronal plasma membrane, two syntaxin isoforms, HPC-1/syntaxin 1A (STX1A) and syntaxin 1B (STX1B), are predominantly expressed as soluble N-ethylmaleimide-sensitive fusion attachment protein receptors, also known as t-SNAREs. We previously reported that glutamatergic and GABAergic synaptic transmissions are impaired in Stx1b null mutant (Stx1b^-/- ) mice but are almost normal in Stx1a null mutant (Stx1a^-/- ) mice. These observations suggested that STX1A and STX1B have distinct functions in fast synaptic transmission in the central nervous system (CNS). Interestingly, recent studies indicated that Stx1a^-/- or Stx1a^+/- mice exhibit disruption in the monoaminergic system in the CNS, causing unusual behaviour that is similar to neuropsychological alterations observed in psychiatric patients. Here, we studied whether STX1B contributes to the regulation of monoaminergic system and if STX1B is related to neuropsychological properties in human neuropsychological disorders similar to STX1A. We found that monoamine release in vitro was normal in Stx1b^+/- mice unlike Stx1a^-/- or Stx1a^+/- mice, but the basal extracellular dopamine (DA) concentration in the ventral striatum was increased. DA secretion in the ventral striatum is regulated by GABAergic neurons, and Stx1b^+/- mice exhibited reduced GABA release both in vitro and in vivo, disrupting the DAergic system in the CNS of these mice. We also found that Stx1b^+/- mice exhibited reduced pre-pulse inhibition (PPI), which is believed to represent one of the prominent schizotypal behavioural profiles of human psychiatric patients. The reduction in PPI was rescued by DA receptor antagonists. These observations indicated that STX1B contributes to excess activity of the DAergic system through regulation of GABAergic transmission.

Serotonin and prefrontal cortex function: neurons, networks, and circuits

Higher-order executive tasks such as learning, working memory, and behavioral flexibility depend on the prefrontal cortex (PFC), the brain region most elaborated in primates. The prominent innervation by serotonin neurons and the dense expression of serotonergic receptors in the PFC suggest that serotonin is a major modulator of its function. The most abundant serotonin receptors in the PFC, 5-HT1A, 5-HT2A and 5-HT3A receptors, are selectively expressed in distinct populations of pyramidal neurons and inhibitory interneurons, and play a critical role in modulating cortical activity and neural oscillations (brain waves). Serotonergic signaling is altered in many psychiatric disorders such as schizophrenia and depression, where parallel changes in receptor expression and brain waves have been observed. Furthermore, many psychiatric drug treatments target serotonergic receptors in the PFC. Thus, understanding the role of serotonergic neurotransmission in PFC function is of major clinical importance. Here, we review recent findings concerning the powerful influences of serotonin on single neurons, neural networks, and cortical circuits in the PFC of the rat, where the effects of serotonin have been most thoroughly studied.

An in vitro paradigm for diabetic cerebral oedema and its therapy: a critical role for taurine and water channels

The pathophysiology of cerebral oedema (CE) in diabetic ketoacidosis (DKA) remains enigmatic. We investigated the role of the idiogenic osmol taurine and aquaporin channels in an in vitro model, the SH-SY5Y neuroblastoma cell line, by sequentially mimicking DKA-like hyperglycemia/hypertonicity and hypotonic fluid therapy. Exposure to DKA-like hyperosmolarity led to shrinkage, while hypotonic fluid exposure led to cell swelling and impaired viability. Low sodium compensated in part for elevated glucose, pointing to a critical role for overall osmolality. Taurine, was synthesized and retained intracellularly during DKA-like hypertonicity, and released during hypotonicity, in part mitigating neuronal swelling. Metabolic labeling showed that the rate of taurine release was inadequate to fully prevent neuronal swelling during hypotonic fluid therapy following DKA-like hypertonicity. Under these conditions, Aquaporin4 & 9 channels were respectively down and up-regulated. Our study provides further novel insights into molecular mechanisms contributing to CE in DKA and its therapy.

A study on the influence of ethanol over the primary cultured rat cortical neurons by using the scanning electron microscopy

As an inhibitor and toxic factor of central nervous system, ethanol inhibits the action of the neurons and causes various kinds of neuronal damage. However, the precise mechanisms that ethanol-induced neuronal damage in the central nervous system remain unclear. In spite of thousands of published studies, little information is available on the neurons' morphological alteration in the central nervous system. In this study, we investigated the morphological alterations of the primary cultured rat cortical neurons after they were treated by different concentrations of ethanol using the scanning electron microscopy. Our results showed that the moderate or high concentration of ethanol could lead to morphological changes of these cultured rat cortical neurons, and they were closely associated with the duration of time. Our study will provide a new base for further studies on the effects of ethanol in the central nervous system.