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Defective function of GABA-containing synaptic vesicles in mice lacking the AP-3B clathrin adaptor.

Nakatsu F, Okada M, Mori F, Kumazawa N, Iwasa H, Zhu G, Kasagi Y, Kamiya H, Harada A, Nishimura K, Takeuchi A, Miyazaki T, Watanabe M, Yuasa S, Manabe T, Wakabayashi K, Kaneko S, Saito T, Ohno H - J. Cell Biol. (2004)

Bottom Line: Although the physiological role of AP-3A has recently been elucidated, that of AP-3B remains unsolved.This facilitated the induction of long-term potentiation in the hippocampus and the abnormal propagation of neuronal excitability via the temporoammonic pathway.Thus, AP-3B plays a critical role in the normal formation and function of a subset of synaptic vesicles.

View Article: PubMed Central - PubMed

Affiliation: RIKEN Research Center for Allergy and Immunology, Kanagawa 230-0045, Japan.

ABSTRACT
AP-3 is a member of the adaptor protein (AP) complex family that regulates the vesicular transport of cargo proteins in the secretory and endocytic pathways. There are two isoforms of AP-3: the ubiquitously expressed AP-3A and the neuron-specific AP-3B. Although the physiological role of AP-3A has recently been elucidated, that of AP-3B remains unsolved. To address this question, we generated mice lacking mu3B, a subunit of AP-3B. mu3B-/- mice suffered from spontaneous epileptic seizures. Morphological abnormalities were observed at synapses in these mice. Biochemical studies demonstrated the impairment of gamma-aminobutyric acid (GABA) release because of, at least in part, the reduction of vesicular GABA transporter in mu3B-/- mice. This facilitated the induction of long-term potentiation in the hippocampus and the abnormal propagation of neuronal excitability via the temporoammonic pathway. Thus, AP-3B plays a critical role in the normal formation and function of a subset of synaptic vesicles. This work adds a new aspect to the pathogenesis of epilepsy.

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Abnormal propagation of neuronal excitability via TA pathway in μ3B−/−ΔNeo mice. (A) Schematic of neuronal circuits in EC–hippocampus pathway. Black arrows indicate the trisynaptic pathway that includes the perforant, mossy fiber and Schaffer collateral pathways. Red and blue arrows indicate excitatory and inhibitory projections in the TA pathway, respectively. (B) Change in fluorescence signal associated with propagation of neuronal excitabilities in EC–hippocampal formation of 4-wk-old (4w) and 8-wk-old (8w) wild-type (+/+) and μ3B−/−ΔNeo (−/−) mice after the electrical stimulation of EC layers II, III, and IV. Pseudo colors indicate >103-fold (change in fluorescence intensity/initial fluorescence intensity = ΔF/F) elevation in the amplitude of the fluorescence signal. (C) Mean values of optical signals in dentate gyrus and CA1 regions after the electrical stimulation of EC layers II, III, and IV in 4-wk-old wild-type (closed circle, n = 5), 4-wk-old μ3B−/−ΔNeo (open circle, n = 5), 8-wk-old wild-type (closed square, n = 5), and 8-wk-old μ3B−/−ΔNeo (open square, n = 4) mice. Ordinates indicate the change in fluorescence intensity/initial fluorescence intensity (ΔF/F), and abscissas indicate time after stimulation (msec).
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fig6: Abnormal propagation of neuronal excitability via TA pathway in μ3B−/−ΔNeo mice. (A) Schematic of neuronal circuits in EC–hippocampus pathway. Black arrows indicate the trisynaptic pathway that includes the perforant, mossy fiber and Schaffer collateral pathways. Red and blue arrows indicate excitatory and inhibitory projections in the TA pathway, respectively. (B) Change in fluorescence signal associated with propagation of neuronal excitabilities in EC–hippocampal formation of 4-wk-old (4w) and 8-wk-old (8w) wild-type (+/+) and μ3B−/−ΔNeo (−/−) mice after the electrical stimulation of EC layers II, III, and IV. Pseudo colors indicate >103-fold (change in fluorescence intensity/initial fluorescence intensity = ΔF/F) elevation in the amplitude of the fluorescence signal. (C) Mean values of optical signals in dentate gyrus and CA1 regions after the electrical stimulation of EC layers II, III, and IV in 4-wk-old wild-type (closed circle, n = 5), 4-wk-old μ3B−/−ΔNeo (open circle, n = 5), 8-wk-old wild-type (closed square, n = 5), and 8-wk-old μ3B−/−ΔNeo (open square, n = 4) mice. Ordinates indicate the change in fluorescence intensity/initial fluorescence intensity (ΔF/F), and abscissas indicate time after stimulation (msec).

Mentions: To investigate the influence of the impairment in GABAergic synapses on hippocampal transmission in μ3B−/−ΔNeo mice, we analyzed the propagation of neuronal excitability from the entorhinal cortex (EC) to the hippocampus using optical recording. It is well established that superficial layers of the EC project to the dentate gyrus granule cells via the perforant pathway, and to CA1 pyramidal cells via the temporoammonic (TA) pathway (Heinemann et al., 2000). The TA pathway is composed of both direct excitatory and indirect inhibitory GABAergic interneuron-associated projections (Fig. 6 A; Heinemann et al., 2000; Remondes and Schuman, 2002). In 4-wk-old wild-type and μ3B−/−ΔNeo mice as well as in 8-wk-old wild-type mice, the neuronal excitability evoked by electrical stimulation of layers II, III, and IV in EC propagated to the dentate gyrus via the perforant pathway, but not to the CA1 pyramidal cells via the TA pathway (Fig. 6, B and C). In contrast, the neuronal excitability propagated from EC to CA1 pyramidal cells in addition to the dentate gyrus in 8-wk-old μ3B−/−ΔNeo mice (Fig. 6, B and C). Consistent with our previous observation (Okada et al., 2004), the propagation of neuronal excitability via both perforant and TA pathways was observed in the presence of bicuculline, a GABAA receptor antagonist, in all cases (unpublished data). These results suggest that the abnormal excitability observed in μ3B−/−ΔNeo mice is due to the impairment in GABAergic inhibition in the TA pathway.


Defective function of GABA-containing synaptic vesicles in mice lacking the AP-3B clathrin adaptor.

Nakatsu F, Okada M, Mori F, Kumazawa N, Iwasa H, Zhu G, Kasagi Y, Kamiya H, Harada A, Nishimura K, Takeuchi A, Miyazaki T, Watanabe M, Yuasa S, Manabe T, Wakabayashi K, Kaneko S, Saito T, Ohno H - J. Cell Biol. (2004)

Abnormal propagation of neuronal excitability via TA pathway in μ3B−/−ΔNeo mice. (A) Schematic of neuronal circuits in EC–hippocampus pathway. Black arrows indicate the trisynaptic pathway that includes the perforant, mossy fiber and Schaffer collateral pathways. Red and blue arrows indicate excitatory and inhibitory projections in the TA pathway, respectively. (B) Change in fluorescence signal associated with propagation of neuronal excitabilities in EC–hippocampal formation of 4-wk-old (4w) and 8-wk-old (8w) wild-type (+/+) and μ3B−/−ΔNeo (−/−) mice after the electrical stimulation of EC layers II, III, and IV. Pseudo colors indicate >103-fold (change in fluorescence intensity/initial fluorescence intensity = ΔF/F) elevation in the amplitude of the fluorescence signal. (C) Mean values of optical signals in dentate gyrus and CA1 regions after the electrical stimulation of EC layers II, III, and IV in 4-wk-old wild-type (closed circle, n = 5), 4-wk-old μ3B−/−ΔNeo (open circle, n = 5), 8-wk-old wild-type (closed square, n = 5), and 8-wk-old μ3B−/−ΔNeo (open square, n = 4) mice. Ordinates indicate the change in fluorescence intensity/initial fluorescence intensity (ΔF/F), and abscissas indicate time after stimulation (msec).
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Related In: Results  -  Collection

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fig6: Abnormal propagation of neuronal excitability via TA pathway in μ3B−/−ΔNeo mice. (A) Schematic of neuronal circuits in EC–hippocampus pathway. Black arrows indicate the trisynaptic pathway that includes the perforant, mossy fiber and Schaffer collateral pathways. Red and blue arrows indicate excitatory and inhibitory projections in the TA pathway, respectively. (B) Change in fluorescence signal associated with propagation of neuronal excitabilities in EC–hippocampal formation of 4-wk-old (4w) and 8-wk-old (8w) wild-type (+/+) and μ3B−/−ΔNeo (−/−) mice after the electrical stimulation of EC layers II, III, and IV. Pseudo colors indicate >103-fold (change in fluorescence intensity/initial fluorescence intensity = ΔF/F) elevation in the amplitude of the fluorescence signal. (C) Mean values of optical signals in dentate gyrus and CA1 regions after the electrical stimulation of EC layers II, III, and IV in 4-wk-old wild-type (closed circle, n = 5), 4-wk-old μ3B−/−ΔNeo (open circle, n = 5), 8-wk-old wild-type (closed square, n = 5), and 8-wk-old μ3B−/−ΔNeo (open square, n = 4) mice. Ordinates indicate the change in fluorescence intensity/initial fluorescence intensity (ΔF/F), and abscissas indicate time after stimulation (msec).
Mentions: To investigate the influence of the impairment in GABAergic synapses on hippocampal transmission in μ3B−/−ΔNeo mice, we analyzed the propagation of neuronal excitability from the entorhinal cortex (EC) to the hippocampus using optical recording. It is well established that superficial layers of the EC project to the dentate gyrus granule cells via the perforant pathway, and to CA1 pyramidal cells via the temporoammonic (TA) pathway (Heinemann et al., 2000). The TA pathway is composed of both direct excitatory and indirect inhibitory GABAergic interneuron-associated projections (Fig. 6 A; Heinemann et al., 2000; Remondes and Schuman, 2002). In 4-wk-old wild-type and μ3B−/−ΔNeo mice as well as in 8-wk-old wild-type mice, the neuronal excitability evoked by electrical stimulation of layers II, III, and IV in EC propagated to the dentate gyrus via the perforant pathway, but not to the CA1 pyramidal cells via the TA pathway (Fig. 6, B and C). In contrast, the neuronal excitability propagated from EC to CA1 pyramidal cells in addition to the dentate gyrus in 8-wk-old μ3B−/−ΔNeo mice (Fig. 6, B and C). Consistent with our previous observation (Okada et al., 2004), the propagation of neuronal excitability via both perforant and TA pathways was observed in the presence of bicuculline, a GABAA receptor antagonist, in all cases (unpublished data). These results suggest that the abnormal excitability observed in μ3B−/−ΔNeo mice is due to the impairment in GABAergic inhibition in the TA pathway.

Bottom Line: Although the physiological role of AP-3A has recently been elucidated, that of AP-3B remains unsolved.This facilitated the induction of long-term potentiation in the hippocampus and the abnormal propagation of neuronal excitability via the temporoammonic pathway.Thus, AP-3B plays a critical role in the normal formation and function of a subset of synaptic vesicles.

View Article: PubMed Central - PubMed

Affiliation: RIKEN Research Center for Allergy and Immunology, Kanagawa 230-0045, Japan.

ABSTRACT
AP-3 is a member of the adaptor protein (AP) complex family that regulates the vesicular transport of cargo proteins in the secretory and endocytic pathways. There are two isoforms of AP-3: the ubiquitously expressed AP-3A and the neuron-specific AP-3B. Although the physiological role of AP-3A has recently been elucidated, that of AP-3B remains unsolved. To address this question, we generated mice lacking mu3B, a subunit of AP-3B. mu3B-/- mice suffered from spontaneous epileptic seizures. Morphological abnormalities were observed at synapses in these mice. Biochemical studies demonstrated the impairment of gamma-aminobutyric acid (GABA) release because of, at least in part, the reduction of vesicular GABA transporter in mu3B-/- mice. This facilitated the induction of long-term potentiation in the hippocampus and the abnormal propagation of neuronal excitability via the temporoammonic pathway. Thus, AP-3B plays a critical role in the normal formation and function of a subset of synaptic vesicles. This work adds a new aspect to the pathogenesis of epilepsy.

Show MeSH
Related in: MedlinePlus