Blocking conversion of GABAergic inhibition as a potential mechanism of propofol-mediated brain protection following resuscitation

Decoding the language of epigenetics during neural development is key for understanding development as well as developmental neurotoxicity

Neural development is a delicate process that can be disrupted by pollution that exerts detrimental impact on neural signaling. This commentary highlights recent discoveries in the arena of research at the interface of environmental toxicology and developmental neuroscience relating to toxicity mechanisms of bisphenol A (BPA), a ubiquitous chemical used in manufacturing of plastics and epoxy resins that is known to bind to and interfere with estrogen receptors, estrogen-receptor-related receptors and other receptors for gonadal steroids. It was recently observed that BPA disrupts the perinatal chloride shift, a key neurodevelopmental mechanism that brings down neuronal chloride from ~100 mM to ~20 mM within weeks. The chloride shift happens in all central nervous systems of vertebrates around parturition. High neuronal chloride supports neuron precursors' migrations, low neuronal chloride is the prerequisite for inhibitory action of neurotransmitters GABA and glycine, and thus an absolute requisite for normal functioning of the mature CNS. One critical contributor to the neuronal chloride shift is the concomitant upregulation of expression of the chloride-extruding transporter molecule, KCC2. We highlight recent findings including our discovery that BPA disrupts the chloride shift in a sex-specific manner by recruiting epigenetics mechanisms. These could be relevant for childhood neuropsychiatric disorders as well as for liability to develop chronic neuropsychiatric diseases later in life.

Propofol protects against impairment of learning-memory and imbalance of hippocampal Glu/GABA induced by electroconvulsive shock in depressed rats

PURPOSE

General anesthetics are believed to induce amnesia. However, propofol can ameliorate cognitive deficits induced by electroconvulsive therapy (ECT), a treatment for mental disorders. This study aimed at investigating the possible molecular mechanism as well as the effects of propofol on learning-memory impairment in depressed rats induced by ECS (electroconvulsive shock, the analog of ECT to animals).

METHODS

Rats were treated with ECS (or sham ECS) pretreated with intraperitoneal injection of propofol (100 mg/kg) (or normal saline, 0.01 l/kg) after being treated with chronic unpredictable mild stresses to reproduce an animal model of depression. Sucrose preference test, open field test, and Morris water maze were used to assess behavioral changes. Hippocampal glutamate (Glu) and γ-aminobutyric acid (GABA) levels were measured with liquid chromatography, and glutamic acid decarboxylase 65 (GAD65) was assayed immunohistochemically. Additionally, rats undergoing ECS that were pretreated with pentobarbital sodium (45 mg/kg) were included for behavioral tests and electroencephalogram recording for comparison with rats undergoing ECS that were pretreated with propofol or normal saline.

RESULTS

ECS rats pretreated with propofol or pentobarbital sodium exhibited similar decreased seizure durations as compared with ECS rats pretreated with normal saline. ECS pretreated with normal saline aggravated learning-memory deficits whereas ECS pretreated with propofol or pentobarbital sodium did not. Rats undergoing ECS pretreated with propofol showed better memory than those undergoing ECS after pretreatment with pentobarbital sodium. ECS pretreated with normal saline downregulated the ratio of Glu/GABA and upregulated GAD65 expression; all these molecular changes were nearly normalized to the level of control group by ECS pretreated with propofol. There were no significant differences of depressive behaviors between groups treated with ECS.

CONCLUSIONS

The data suggest that propofol alleviated ECS-induced learning-memory impairment without interfering with the antidepressant efficacy of ECS, possibly by inhibiting excessive expression of GAD65 and maintaining the balance between glutamatergic and GABAergic amino acids neurotransmitters in the hippocampus.