Brain-type fatty acid-binding protein (B-FABP) belongs to a family of intracellular lipid-binding proteins. B-FABP exhibits a binding affinity to long-chain fatty acids (FAs) whose effects on brain functions including development, emotion, learning and memory have been proposed. B-FABP is localized in the ventricular germinal cells in embryonic brain and astrocytes in developing and mature brain of rodents. In the present study we generated the mouse harboring a null mutation in the B-FABP gene and studied its phenotype. B-FABP mutant mice exhibited the enhanced anxiety and increased fear memory as well as the decreased content of docosahexaenoic acid (DHA) in their brain during the neonatal period without detection of any histological changes in the brain. In the adult brain, B-FABP was localized more numerously to the astrocytes in the amygdala and septal area than to those in the hippocampal area. Analysis of FA content in the amygdala of adult brain revealed that arachidonic and palmitic acids increased significantly in the mutant mice compared with wild-type. Furthermore, the response of N-methyl-d-aspartate receptor-mediated current to DHA in isolated neurons from B-FABP mutant brain was significantly decreased compared with that of wild-type, while no significant differences were detected in behavioral responses related to the spatial learning/memory or in the hippocampal long-term potentiation. These data indicate that B-FABP is crucially involved in the fear memory and anxiety through its binding with FAs and/or its own direct effects on pertinent metabolism/signaling of FAs.

The ganglioside GM3 synthase (SAT-I), encoded by a single-copy gene, is a primary glycosyltransferase for the synthesis of complex gangliosides. In SAT-I null mice, hearing ability, assessed by brainstem auditory-evoked potentials (BAEP), was impaired at the onset of hearing and had been completely lost by 17 days after birth (P17), showing a deformity in hair cells in the organ of Corti. By 2 months of age, the organ of Corti had selectively and completely disappeared without effect on balance or motor function or in the histology of vestibule. Interestingly, spatiotemporal changes in localization of individual gangliosides, including GM3 and GT1b, were observed during the postnatal development and maturation of the normal inner ear. GM3 expressed in almost all regions of cochlea at P3, but at the onset of hearing it distinctly localized in stria vascularis, spiral ganglion, and the organ of Corti. In addition, SAT-I null mice maintain the function of stria vascularis, because normal potassium concentration and endocochlear potential of endolymph were observed even when they lost the BAEP completely. Thus, the defect of hearing ability of SAT-I null mice could be attributed to the functional disorganization of the organ of Corti, and the expression of gangliosides, especially GM3, during the early part of the functional maturation of the cochlea could be essential for the acquisition and maintenance of hearing function.auditory system ͉ cochlea ͉ deafness ͉ knockout mice ͉ sialyltransferase G angliosides [i.e., glycosphingolipids (GSLs)] containing sialic acid are abundant in central nervous tissues and are considered to have important roles in controlling development, proliferation, differentiation, and maintenance of neural tissues and cells (1). Gangliosides usually reside in the outer leaflet of the cell membrane and are concentrated in microdomains specialized for cell adhesion and cell signaling (2, 3). The first product in the biosynthetic pathway of the ganglio-series gangliosides is GM3, which serves as a common precursor for the a-series and b-series gangliosides (Fig. 1). The sialyltransferase responsible for GM3 synthesis is the GM3 synthase (EC 2.4.99.9), also known by the names SAT-I (used here), ST3GalV, and Siat 9. The gene encoding this enzyme has been identified by several research laboratories, including ours (4-6).In the study presented here, we generated mice deficient in GM3 synthase (SAT-I Ϫ/Ϫ mice) (7) and examined their general behavior, including their motor function, learning and memory, and sensory function. Interestingly, SAT-I Ϫ/Ϫ mice exhibited no startle reflex in response to various acoustic stimulations, yet they did demonstrate normal startle responses to air puffing, suggesting a hearing impairment. Electrophysiological and histological analyses of the auditory system of the SAT-I Ϫ/Ϫ mice further revealed that the organ of Corti in the inner ear is selectively degenerated in these animals. ResultsAbsence of Acoustic Startle Response in SAT-I Null Mice. GM3 synthase null (SAT...

Nystatin‐perforated patch recordings were made from mechanically dissociated basolateral amygdala neurons with preserved intact native presynaptic nerve terminals to study the mechanism of 5‐HT3 receptor‐mediated serotonergic modulation of GABAergic inhibition. The specific 5‐HT3 agonist mCPBG (1 μM) rapidly facilitated the frequency of GABAergic miniature inhibitory postsynaptic currents (mIPSCs) and this facilitation desensitized within 1 min. Tropisetron (30 nM), a specific 5‐HT3 antagonist, blocked the mCPBG effect. mCPBG augmented mIPSC amplitude. However, no direct postsynaptic serotonergic currents were evoked by mCPBG. Neither GABA‐evoked current amplitude nor the kinetics of individual GABAergic mIPSCs were affected by mCPBG. Therefore, the augmentation is unlikely to be due to postsynaptic effects evoked by mCPBG. At higher concentrations mCPBG produced shorter‐duration facilitation of miniature events. While mCPBG increased the mIPSC frequency in calcium‐containing solution with Cd2+, this increase was absent in Ca2+‐free external solution. It appears that the Ca2+ influx through voltage‐dependent calcium channels was not as crucial as that through 5‐HT3 receptors for synaptic GABA release. When two pulses of mCPBG (each 1 μM, 1 min) were given, the response to the second pulse elicited full recovery when the interval between pulses was at least 9 min. Protein kinase A (PKA) activation by 8‐Br‐cAMP (300 μM) shortened and PKA inhibition by Rp‐cAMP (100 μM) prolonged the recovery time. PKA activity did not affect the time course of fast desensitization. Our results suggest that a 5‐HT3‐specific agonist acts on presynaptic nerve terminals facilitating synaptic GABA release without postsynaptic effects. The facilitation requires calcium influx through presynaptic 5‐HT3 receptors. PKA modulates the recovery process from desensitization of presynaptic 5‐HT3 receptor‐mediated regulation of synaptic GABA release.

Spontaneous miniature outward currents (SMOCs) were observed in mechanically dissociated rat Meynert neurons using nystatin perforated patch recordings under voltage‐clamp conditions. SMOCs were blocked by apamin, a selective blocker of small conductance Ca2+‐activated K+ (SK) channels, but not by blockers for other types of Ca2+‐activated K+ channel. Ryanodine (10‐100 μm) reduced both the amplitude and frequency of SMOCs. Caffeine (1 mm) increased the SMOC frequency. Blockers of the sarco/endoplasmic reticulum Ca2+‐ATPase completely abolished SMOCs, indicating a requirement for functioning sarco/endoplasmic reticulum (SR/ER) Ca2+ stores. Both Cd2+‐containing and Ca2+‐free solutions partially inhibited SMOC frequency, a result which suggests that Ca2+ influx contributes to, but is not essential for, SMOC generation. Thus, SMOCs are SK currents linked to ryanodine‐ and caffeine‐sensitive SR/ER Ca2+ stores, and are only indirectly influenced by extracellular Ca2+ influx. The development of this new, minimally invasive mechanical dissociation method has revealed that SMOCs are common in native CNS neurons.

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