大鼠丘脑前核内海马下托复合体谷氨酸能传入终末与皮质投射神经元的突触联系

目的 探讨大鼠丘脑前核-海马下托复合体神经元环路的突触结构及谷氨酸分布特征.方法 应用HRP束路追踪结合包埋后胶体金免疫电镜技术.结果 在丘脑前核内,可见HRP顺行标记的海马下托复合体传入轴突终末,终末多为卵圆形,内含圆形透亮突触小泡和数个线粒体.其做为突触前成分与HRP标记的树突或非HRP标记的树突形成非对称性突触.在谷氨酸胶体金免疫反应切片上,胶体金颗粒标记胞体、树突、轴突终末等.HRP标记的轴突终末和一些非HRP标记的与突触后成分形成非对称性突触的轴突终末(Gray Ⅰ型)内,胶体金颗粒密度明显大于背景(胞体、树突、Gray Ⅱ型轴突终末等)的胶体金颗粒密度.其平均胶体金颗粒密度为突触后树突的3倍多,为对称性轴突终末(Gray Ⅱ型)的6倍多.在两张邻近的连续切片,γ-氨基丁酸(GABA)胶体金免疫反应切片上,GABA胶体金颗粒浓重标记Gray Ⅱ型轴突终末,背景标记极少;而非对称性轴突终末(Gray Ⅰ型)胶体金颗粒标记极弱.谷氨酸胶体金免疫反应切片上,Gray Ⅱ型轴突终末胶体金颗粒标记极弱.GABA阳性轴突终末与HRP标记的树突形成对称性突触,在同一树突上可见GABA能轴突终末形成的对称性突触和其他轴突终末形成的非对称性突触.结论 丘脑前核内来自海马下托复合体投射神经元的轴突终末是谷氨酸能的;来自海马下托复合体皮质投射神经元轴突终末,在丘脑前核与投射至海马下托皮质的神经元树突形成非对称性轴-树突触.     

猫三叉神经尾侧脊束核—丘脑—皮质通路在丘脑水平的突触联系

本文采用HRP逆行追踪与顺行溃变结合法对猫三叉神经尾侧脊束核-丘脑-皮质通路在丘脑腹后内侧核内的突触联系型式进行了研究。在电镜下发现,丘脑腹后内侧核內有五种突触联系形式:(1)溃变轴突终末与HRP标记树突形成轴-树突触;(2)溃变轴突终末与HRP标记的胞体形成轴-体突触,上述两类突触型式为该通路在丘脑水平的直接突触联系方式,此外尚有(3)溃变轴突终末与非HRP标记的树突形成的轴-树突触;(4)HRP标记树突与非溃变轴突终末形成轴一树突触;(5)HRP标记树突与非HRP标记的含有突触小泡的突触前树突形成的树-树突触。本文首次报道了三叉丘系纤维与丘脑皮质投射神经元间的直接突触联系方式为轴-树和轴-体突触。同时也发现了以树突为中心的突触复合体,它是该通路在丘脑水平的一个显著特点。     

猫丘脑腹后外侧核内皮质—丘脑纤维终末与丘脑—皮质投射神经元之间的突触连接

用ＣＢ－ＨＲＰ逆行追踪与顺行溃变相结合的方法，对描丘脑腹后外侧核内的来自大脑皮质体感Ⅰ区的皮质—丘脑纤维终末与丘脑—皮质投射神经元之间的突触连接进行了电镜观察。向猫大脑皮质体感Ⅰ区内注射ＣＢ－ＨＲＰ５ｈ后，电解损毁原注射部位，术后动物存活４ｄ。电镜下发现丘脑瓜后外侧核内存在５种突触连接方式；（１）溃变的轴突终未与ＨＲＰ标记神经元胞体形成轴－体突触；（２）溃变的轴突终末与ＨＲＰ标记的树突形成轴—树突触；（３）溃变的轴突终末和其它突触前成分共同与中央树突形成汇聚型的突触复合体；（４）溃变的轴突终末与未标记树突形成的轴—树突触；（５）正常的轴突终末与ＨＲＰ标记神经元形成对称型的轴—体突触。     

猫丘脑中央外侧核内脊丘系终末与丘脑-皮质投射神经元之间的突触联系

本实验应用顺行溃变和HRP逆行追踪相结合的方法，首次在电镜水平对猫丘脑中央外侧核内脊丘系终末与丘脑-皮质投射神经元之间的突触联系进行了研究．在脊髓第4颈段刀切损毁一侧侧索和前索后，将HRP注射于同侧大脑前上薛氏回和中上薛氏回前端。在电镜下于损毁同侧中央外侧核内可见下列突触连结：（1）溃变的脊丘系轴突终末与标记树突形成的轴-树突触；（2）溃变的脊丘系轴突终末与非标记树突形成的轴-树突触，个别非标记树突含有突触小泡；（3）正常的轴突终末与HRP标记树突和胞体形成的轴-树突触和轮一体突触；（4）正常的两个轴突终末与HRP标记树突形成的轴-轴-树连续性突触；（5）非标记的含突触小泡的突触前树突与HRP标记树突形成的树-树突触。同时可见大量汇聚型突触复合体。本文首次报道在丘脑中央外侧核内，脊丘系终末与丘脑-皮质投射神经元之间存在着直接的突触联系。     

猫外侧颈核内脊颈纤维终末与颈丘脑投射神经元间的突触联系

本实验采用顺行溃变和ＨＲＰ逆行追踪结合的方法研究了猫脊颈丘脑通路在外侧颈核水平的突触联系。在脊髓颈段刀切损毁一侧背外侧索后将ＨＲＰ注射于对侧丘脑腹后外侧核。在电镜下于损毁同侧的外侧颈核内可见到下列突触联系：（１）溃变的轴突终末与ＨＲＰ标记的树突形成的轴—树突触；（２）溃变的轴突终末与标记的神经元胞体形成的轴—体突触；（３）溃变的轴突终末及正常的轴突终末与标记的中央树突形成的汇聚型突触复合体；（４）溃变的轴突终末与非标记的神经元树突和胞体形成的轴—树和轴—体突触；（５）正常轴突终末与标记的神经元树突和胞体形成的轴—树和轴—体突触。此外，在正常的神经元成分之间还可见到许多类型的突触。     

大鼠三叉神经本体感觉中枢通路二、三级核团内Parvalbumin样阳性神经元突触联系的电镜研究

本教研室以往的研究证实 Parvalbum in样免疫阳性细胞广泛分布于三叉神经本体感觉中枢四级通路的各级中继核团 ,其中有 30 %～ 5 0 %为投射神经元。本研究应用电镜免疫组织化学技术进一步对此通路第二、三级神经元所在地的 Parvalbumin样阳性神经元及其纤维和终末的突触联系进行了观察。结果显示 Parvalbum in样阳性结构主要形成以下几种突触联系 :( 1) Par-valbumin样阳性轴突与 Parvalbumin样阳性胞体或树突形成轴 -体或轴 -树突触 ,其中以非对称性突触为主 ,对称性突触较少 ;( 2 )Parvalbumin样阳性轴突分别与 Parvalbumin样阴性神经元的胞体或树突形成轴 -体或轴 -树突触 ,这些突触联系以对称性为主 ,非对称性大约占 30 %左右 ;( 3) Parvalbumin样阴性终末与 Parvalbumin样阳性树突形成以对称性为主的轴 -树突触 ,这种突触大约占所有突触联系的 5 0 %。以上结果表明 :面口部本体感觉信息由三叉神经中脑核神经元向丘脑腹后内侧核传递的过程中 ,Par-valbumin样阳性轴突终末可通过突触传导机制而兴奋或抑制二、三级核团内的投射或中间神经元而发挥其重要作用     

大鼠弓状核内神经紧张素能和P物质能阳性结构的免疫电镜双标记研究

用包埋前免疫电镜双标记技术研究大鼠下丘脑内的神经紧张素(NT)和P物质(SP)分布的超微结构。证实在弓状核内存在NT样和SP样免疫反应阳性的胞体、树突和轴突。NT样和SP样免疫反应阳性的树突和轴突均可接受免疫反应阴性结构的非对称性传入突触。SP样免疫反应阳性轴突终末除可与免疫反应阴性的树突和胞体形成对称性传出突触外, 还可与NT样免疫反应阳性胞体形成对称性轴-体突触。本研究首次直接证实大鼠弓状核内的NT能神经元接受SP能神经的支配。     

大鼠延髓孤束核吻侧段内脑啡肽免疫阳性轴突末梢与含阿片μ受体的γ-氨基丁酸能神经元之间的突触联系

目的:观察大鼠孤束核吻侧段(rNTS)内脑啡肽免疫反应阳性(ENK-ir)终末、γ-氨基丁酸免疫反应阳性(GA-BA-ir)神经元及阿片μ受体免疫反应阳性(MOR-ir)神经元三者之间的联系。方法:包埋前免疫组织化学方法显色结合免疫金颗粒双重标记后,电镜观察。结果:在电镜下可见ENK-ir产物主要定位于圆形清亮突触小泡及大颗粒囊泡表面,GABA-ir产物主要分布于胞体及树突内部,多见于粗面内质网及核糖体等结构,MOR-ir产物主要位于树突膜、线粒体膜、内质网膜等结构表面;ENK-ir轴突终末与GABA-ir神经元胞体及树突之间形成对称性和非对称性的突触联系,以对称性突触为主;ENK-ir轴突终末与MOR-ir神经元的胞体及树突形成以对称性突触为主的突触联系;GA-BA-ir与MOR-ir产物共存于神经元内,GABA/MOR-ir神经元与免疫反应阴性的终末形成对称性和非对称性突触,以对称性突触为主。结论:rNTS内的ENK-ir终末可能通过与MOR结合,调节GABA能神经元的活性,从而参与味觉信息的感受和调节。     

大鼠三叉神经本体觉中枢通路上第三级核团内PV样阳性终末与丘脑投射神经元的突触联系

目的 观察大鼠三叉神经本体觉中枢通路上第三级核团内Paralbumin样阳性轴突终末与丘脑投射神经元之间是否存在突触联系。方法 用HRP逆行追踪和包埋前免疫电镜相结合的双重标记法。将WGA-HRP注入丘脑腹后内侧核逆行标记投射神经元。结果 WGA-HRP注入丘脑腹后内侧核(VPM)后，WGA-HRP标记神经元主要分布在感觉主核背内侧部(Vpdm)、三叉上核尾外侧部(Vsup-CL)以及三叉神经运动核腹侧区(AVM)和上橄榄核背侧区(ADO)。电镜下可见PV样阳性神经元的轴突终末与WGA-HRP标记的胞体或者树突形成突触联系。另外PV阴性神经元的轴突终末也与WGA-HRP标记的胞体或树突形成突触联系，这些胞体或树突偶尔为PV阳性。结论 在三叉神经本体感觉信息从第三级神经元向丘脑腹后内侧核(VPM)传递的过程中，PV样阳性神经元可能通过突触传递机制而发挥作用。     

迷走神经背核尾侧内神经降压肽样免疫反应终末联系的电镜研究

用辣根过氧化物酶逆行标记法结合免疫细胞化学法（ＰＡＰ）法对大鼠迷走神经背核尾侧部内神经降压肽样免疫反应终末的核内联系进行了电镜下的研究。发现少量神经降压肽样免疫反应轴突终末与ＨＲＰ逆行标记的副交感节前神经元的树突构成非对称性突触；大多数神经降压肽样免疫反应轴突终末与末标记中间神经元的胞体和树突构成对称性或非对称性突触，以轴－树突触为主；未标记的轴突终末也可同ＨＲＰ逆行标记的副交感节前神经元的胞体和     

Glutamatergic components of the retrosplenial granular cortex in the rat

The ultrastructural characteristics, distribution and synaptic relationships of identified, glutamate-enriched thalamocortical axon terminals and cell bodies in the retrosplenial granular cortex of adult rats is described and compared with GABA-containing terminals and cell bodies, using postembedding immunogold immunohistochemistry and transmission electron microscopy in animals with injections of cholera toxin- horseradish peroxidase (CT-HRP) into the anterior thalamic nuclei. Anterogradely labelled terminals, identified by semi-crystalline deposits of HRP reaction product, were approximately 1 microm in diameter, contained round, clear synaptic vesicles, and established asymmetric (Gray type I) synaptic contacts with dendritic spines and small dendrites, some containing HRP reaction product, identifying them as dendrites of corticothalamic projection neurons. The highest densities of immunogold particles following glutamate immunostaining were found over such axon terminals and over similar axon terminals devoid of HRP reaction product. In serial sections immunoreacted for GABA, these axon terminals were unlabelled, whereas other axon terminals, establishing symmetric (Gray type II) synapses were heavily labelled. Cell bodies of putative pyramidal neurons, containing retrograde HRP label, were numerous in layers V-VI; some were also present in layers I-III. Most were overlain by high densities of gold particles in glutamate but not in GABA immunoreacted sections. These findings provide evidence that the terminals of projection neurons make synaptic contact with dendrites and dendritic spines in the ipsilateral retrosplenial granular cortex and that their targets include the dendrites of presumptive glutamatergic corticothalamic projection neurons.     

Glutamatergic components of the retrosplenial granular cortex in the rat

The ultrastructural characteristics, distribution and synaptic relationships of identified, glutamate-enriched thalamocortical axon terminals and cell bodies in the retrosplenial granular cortex of adult rats is described and compared with GABA-containing terminals and cell bodies, using postembedding immunogold immunohistochemistry and transmission electron microscopy in animals with injections of cholera toxin- horseradish peroxidase (CT-HRP) into the anterior thalamic nuclei. Anterogradely labelled terminals, identified by semi-crystalline deposits of HRP reaction product, were approximately 1 m in diameter, contained round, clear synaptic vesicles, and established asymmetric (Gray type I) synaptic contacts with dendritic spines and small dendrites, some containing HRP reaction product, identifying them as dendrites of corticothalamic projection neurons. The highest densities of immunogold particles following glutamate immunostaining were found over such axon terminals and over similar axon terminals devoid of HRP reaction product. In serial sections immunoreacted for GABA, these axon terminals were unlabelled, whereas other axon terminals, establishing symmetric (Gray type II) synapses were heavily labelled. Cell bodies of putative pyramidal neurons, containing retrograde HRP label, were numerous in layers V–VI; some were also present in layers I–III. Most were overlain by high densities of gold particles in glutamate but not in GABA immunoreacted sections. These findings provide evidence that the terminals of projection neurons make synaptic contact with dendrites and dendritic spines in the ipsilateral retrosplenial granular cortex and that their targets include the dendrites of presumptive glutamatergic corticothalamic projection neurons.     

GABA(B) receptors at glutamatergic synapses in the rat striatum

Although multiple effects of GABA(B) receptor activation on synaptic transmission in the striatum have been described, the precise locations of the receptors mediating these effects have not been determined. To address this issue, we carried out pre-embedding immunogold electron microscopy in the rat using antibodies against the GABA(B) receptor subunits, GABA(B1) and GABA(B2). In addition, to investigate the relationship between GABA(B) receptors and glutamatergic striatal afferents, we used antibodies against the vesicular glutamate transporters, vesicular glutamate transporter 1 and vesicular glutamate transporter 2, as markers for glutamatergic terminals. Immunolabeling for GABA(B1) and GABA(B2) was widely and similarly distributed in the striatum, with immunogold particles localized at both presynaptic and postsynaptic sites. The most commonly labeled structures were dendritic shafts and spines, as well as terminals forming asymmetric and symmetric synapses. In postsynaptic structures, the majority of labeling associated with the plasma membrane was localized at extrasynaptic sites, although immunogold particles were also found at the postsynaptic specialization of some symmetric, putative GABAergic synapses. Labeling in axon terminals was located within, or at the edge of, the presynaptic active zone, as well as at extrasynaptic sites. Double labeling for GABA(B) receptor subunits and vesicular glutamate transporters revealed that labeling for both GABA(B1) and GABA(B2) was localized on glutamatergic axon terminals that expressed either vesicular glutamate transporter 1 or vesicular glutamate transporter 2. The patterns of innervation of striatal neurons by the vesicular glutamate transporter 1- and vesicular glutamate transporter 2-positive terminals suggest that they are selective markers of corticostriatal and thalamostriatal afferents, respectively. These results thus provide evidence that presynaptic GABA(B) heteroreceptors are in a position to modulate the two major excitatory inputs to striatal spiny projection neurons arising in the cortex and thalamus. In addition, presynaptic GABA(B) autoreceptors are present on the terminals of spiny projection neurons and/or striatal GABAergic interneurons. Furthermore, the data indicate that GABA may also affect the excitability of striatal neurons via postsynaptic GABA(B) receptors.     

大鼠臂旁核内接受孤束核内脏传入之神经元同时接受中央杏仁核的反馈调节──溃变、HRP法结合包埋后免疫电镜研究

为研究来自孤束核的内脏传导信息在臂旁核水平是否接受中央杏仁核的反馈调节及其递质性质，以及孤束核—臂旁核—中央杏仁核传导通路中，在臂旁核水平是否接受ＧＡＢＡ的调节，本文将ＨＲＰ注入中央杏仁核进行顺、逆行标记，同时将兴奋性氨基酸毒素海人酸注入孤束核进行损毁，观实其顺行溃变终末，取外侧臂旁核超薄切片后结合抗ＧＡＢＡ的免疫电镜染色，观察发现有下列几种标记；（１）顺行溃变终末，所有的都与臂旁核神经元形成非对称性突触；（２）ＨＲＰ标记终末有两类：第一类和臂旁核神经元形成对称性突触，占ＨＲＰ标记终末总数的８０％以上，第二类与臂旁核神经元形成非对称性突触，另外有大量的ＨＲＰ标记的胞体和树突；（３）胶体金标记的ＧＡＢＡ阳性终末，皆与突触后结构形成对称性突触；（４）ＧＡＢＡ／ＨＲＰ双标记终末，具有ＧＡＢＡ免疫阳性终末和第一类ＨＲＰ标记终末的共同特征。上述几种标记在臂旁核内有以下几种关系：（１）溃变终末和ＧＡＢＡ阳性终末与同一个ＨＲＰ标记或非标记的突形成轴－树突触；（２）溃变终末和第一类ＨＲＰ标记终末共同终止于同一非标记讨突；（３）溃变终末与ＨＲＰ标记树突或胞位形成非对称性突触；（４）ＧＡＢＡ／ＨＲＰ双标记终末与非标记树突或胞体?     

A GABA immunocytochemical study of rat motor thalamus: light and electron microscopic observations.

A light and electron microscopic study of GABA-immunoreactive neurons and profiles in the ventroanterior-ventrolateral and ventromedial nuclei of rat dorsal thalamus was conducted using antiserum raised against GABA. Less than 1% of the neurons in these motor-related nuclei exhibited GABA immunoreactivity, confirming previous reports that these nuclei are largely devoid of interneurons. Immunoreactive neurons in the ventral anterior-ventral lateral complex and ventromedial nucleus were bipolar or multipolar in shape, and tended to be smaller than non-immunoreactive neurons. GABA immunoreactivity in the neuropil consisted of labeled axon terminals and myelinated and unmyelinated axons, and was lower in the ventral anterior-ventral lateral complex and ventromedial nucleus than in neighboring thalamic nuclei. The density of neuropil immunolabeling was slightly higher in ventral anterior-ventral lateral complex than in ventromedial nucleus. GABA-immunoreactive axon terminals, collectively termed MP boutons for their medium size and pleomorphic vesicles (and corresponding to "F" profiles of some previous studies of thalamic ultrastructure), formed symmetric synapses and puncta adhaerentia contacts predominantly with large and medium-diameter (i.e. proximal) non-immunoreactive dendrites. Approximately 12 and 18% of boutons in the ventral anterior-ventral lateral complex and ventromedial nucleus, respectively, were GABA-immunopositive. Many of these immunoreactive profiles probably arose from GABAergic neurons in the thalamic reticular nucleus, substantia nigra pars reticulata and entopeduncular nucleus. Two types of non-immunoreactive axon terminals were distinguished based on differences in morphology and synaptic termination sites. Boutons with small ovoid profiles and round vesicles that formed prominent asymmetric synapses onto small-diameter dendrites were observed. Mitochondria were rarely observed within these boutons, which arose from thin unmyelinated axons. These boutons composed approximately 82 and 74% of boutons in the ventral anterior-ventral lateral complex and ventromedial nucleus, respectively, and were considered to arise predominantly from neurons in the cerebral cortex. In contrast, boutons with large terminals that contained round or plemorphic vesicles and formed multiple asymmetric synapses predominantly with large-diameter dendrites were also observed. Puncta adhaerentia contacts were also common. Mitochondria were numerous within large boutons with round vesicles, which arose from myelinated axons. Many of the large boutons were likely to have originated from neurons in the cerebellar nuclei. Approximately 6% of the boutons in the ventral anterior-ventral lateral complex and 8% in ventromedial nucleus were of the large type.(ABSTRACT TRUNCATED AT 400 WORDS)     

Immunoelectron microscopic study of γ-aminobutyric acid inputs to identified thalamocortical projection neurons in the anterior thalamus of the rat

 We have carried out a semi-quantitative ultrastructural study to determine the characteristics and distribution of γ-aminobutyric acid (GABA)-containing constituents of the anterodorsal (AD) and anteroventral (AV) thalamic nuclei in adult rats. We used a polyclonal antibody to GABA and a postembedding immunogold detection method in animals in which the cortical projection neurons of these nuclei had been labelled by retrograde transport of cholera toxin/horseradish peroxidase (HRP) injected into the retrosplenial granular cortex. Two types of GABA-immunopositive structures were identified, with gold particle densities 4–40 times higher than the highest densities over blood-vessel lumens and areas of empty resin: (1) an apparently homogeneous population of axon terminals with Gray type-2 (symmetric) synaptic contacts corresponding to F-axon terminals; and (2) small–medium sized myelinated axons scattered individually or in small groups within the neuropil which may be their parent axons. These axons and terminals may originate from the ipsilateral thalamic reticular nucleus; others may arise from the basal forebrain or brainstem. The GABA-immunopositive terminals comprised approximately 16% of all axon terminal profiles in AD and 12% in AV, a significant difference. However, because the immunoreactive axon terminals in AD were significantly larger than those in AV (1.09±0.47 μm² vs 0.90±0.43 μm²) and would therefore be encountered more frequently, it is not possible to conclude that the GABAergic innervation of AD is heavier than that of AV. The GABA-positive terminals established synaptic contacts with cell bodies and dendrites of all sizes (some of which were HRP-labelled) with the following frequency distribution (AD/AV, no significant difference): somata 5%/7%; large dendrites (≥1.5 μm) 14%/9%; medium dendrites (1.00–1.49 μm) 35%/45% and small dendrites (<1 μm) 46%/40%. Despite evidence from previous studies, we found no evidence in this study for the presence of GABAergic interneurons or for GABA-containing projection neurons in AD or AV. Received: 4 March 1998 / Accepted: 15 January 1999     

Parvalbumin and GABA in the developing somatosensory thalamus of the rat: an immunocytochemical ultrastructural correlation

The calcium binding protein parvalbumin (PV) is widely distributed in the mammalian nervous system and its relationship with GABAergic neurons differs within thalamic nuclei and animal species. In the rat somatosensory thalamus PV immunoreactive (ir) neurons were found only in the GABAergic reticular thalamic nucleus (RT), while a dense PVir neuropil is present in the ventrobasal complex (VB). In this study the distribution and relationship of PV and GABA were investigated in RT and VB during postnatal development at electron microscopic level. The pre-embedding immunoperoxidase detection of PV was combined with the post-embedding immunogold localization of GABA. In RT, at all developmental ages, neuronal cell bodies, dendrites and rare axonal terminals were both PVir and GABAir. In VB during the first postnatal week several small vesicle-containing profiles were double-labelled and some of them were identifiable as synaptic terminals. From postnatal day 7 (P7) to P9 the medial part of VB was more intensely PVir than the lateral one and some differences in the sequence of maturation of PVir terminals were noted between these two VB subdivisions. Single-labelled PVir profiles were first observed at P8, whereas single-labelled PVir terminals appeared at P12 and at P15 they became more frequent and larger, showing the typical morphology of ascending afferents described in adult VB. These results demonstrate the late expression of PV and acquisition of adult morphology in ascending terminals of rat VB during postnatal development in comparison with the innervation arising from the GABAergic RT.     

Ultrastructure and synaptic relations of neural elements containing glutamic acid decarboxylase (GAD) in the perigeniculate nucleus of the cat

Summary The perigeniculate nucleus of the cat (PGN) was examined at light and electron microscopic levels after immunocytochemical labeling for the gamma-aminobutyric acid (GABA) synthesizing enzyme, glutamic acid decarboxylase (GAD). In light microscopic sections, virtually all perikarya were found to be labeled (GAD+), as well as proximal dendrites, fibres and punctiform elements. Cells in the thalamic reticular nucleus (TRN) dorsal to PGN were also labeled. Ultrastructural analysis of PGN showed immunoreactivity in all somata, in dendrites and in the following vesicle containing profiles: 1.) F1 terminals, which are characterized by large size, dark mitochondria, and pleomorphic vesicles. These terminals form symmetrical synaptic contacts with somata, somatic spines and with dendrites of GAD+ PGN cells. 2.) F2 terminals, which are smaller than F1 terminals, contain also pleomorphic vesicles and frequently make serial synapses of the symmetric type with other F2 terminals. Presumably, F1 terminals are formed by collaterals of PGN-cell axons and F2 terminals by vesicle containing dendrites of PGN cells. Terminals devoid of immunoreactivity included: 1.) RLD terminals characterized by large size, round vesicles, dark mitochondria, and by asymmetric synaptic contacts with somata, especially with somatic spines, and with dendrites of GAD+ perigeniculate neurons; 2.) RSD terminals, characterized by small size, round vesicles and dark mitochondria, which make asymmetric synapses with GAD+ dendrites of medium and small size; 3.) Multivesicular (MV) terminals with variably shaped vesicles including dense core vesicles synapsing on GAD+ dendrites. There are reasons to believe that RSD terminals belong to corticofugal axons and RLD terminals to collateral axons of LGN relay cells. The origin of MV terminals remains to be determined. The GABAergic nature of the PGN cells conforms with the presumed function of these cells as mediators of inhibition of LGN relay cells. The complex synaptic relations observed between GAD+ elements in the PGN would allow for reciprocal inhibition between perigeniculate cells.Supported in part by NIH grants EY02877 to V.M. Montero and HD 03352 to the Waisman Center     

Investigations of the cholinergic modulation of GABA release in rat thalamus slices

The thalamus receives a dense cholinergic projection from the pedunculopontine tegmentum. A number of physiological studies have demonstrated that this projection causes a dramatic change in thalamic activity during the transition from sleep to wakefulness. Previous anatomical investigations have found that muscarinic type 2 receptors are densely distributed on the dendritic terminals of GABAergic interneurons, as well as the somata and proximal dendrites of GABAergic cells in the thalamic reticular nucleus. Since these structures are the synaptic targets of cholinergic terminals in the thalamus, it appears likely that thalamic pedunculopontine tegmentum terminals can activate muscarinic type 2 receptors on GABAergic cells. To test whether activation of muscarinic type 2 receptors affects the release of GABA in the thalamus, we have begun pharmacological studies using slices prepared from the rat thalamus. We have found that the application of the nonspecific muscarinic agonist, methacholine, and the muscarinic type 2-selective agonist, oxotremorine.sesquifumarate, diminished both the baseline, and K(+) triggered release of [(3)H]GABA from thalamic slices. This effect was calcium dependent, and blocked by the nonselective muscarinic antagonist atropine, the muscarinic type 2-selective antagonist, methoctramine, but not the muscarinic type 1 antagonist, pirenzepine. Thus, it appears that one function of the pedunculopontine tegmentum projection is to decrease the release of GABA through activation of muscarinic type 2 receptors. This decrease in inhibition may play an important role in regulating thalamic activity during changes in states of arousal.