O'Donnell P, Lavín A, Enquist L W, Grace A A, Card J P
Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
J Neurosci. 1997 Mar 15;17(6):2143-67. doi: 10.1523/JNEUROSCI.17-06-02143.1997.
One of the primary outputs of the nucleus accumbens is directed to the mediodorsal thalamic nucleus (MD) via its projections to the ventral pallidum (VP), with the core and shell regions of the accumbens projecting to the lateral and medial aspects of the VP, respectively. In this study, the multisynaptic organization of nucleus accumbens projections was assessed using intracerebral injections of an attenuated strain of pseudorabies virus, a neurotropic alpha herpesvirus that replicates in synaptically linked neurons. Injection of pseudorabies virus into different regions of the MD or reticular thalamic nucleus (RTN) produced retrograde transynaptic infections that revealed multisynaptic interactions between these areas and the basal forebrain. Immunohistochemical localization of viral antigen at short postinoculation intervals confirmed that the medial MD (m-MD) receives direct projections from the medial VP, rostral RTN, and other regions previously shown to project to this region of the thalamus. At longer survival intervals, injections confined to the m-MD resulted in transynaptic infection of neurons in the accumbens shell but not in the core. Injections that also included the central segment of the MD produced retrograde infection of neurons in the lateral VP and the polymorph (pallidal) region of the olfactory tubercle (OT) and transynaptic infection of a small number of neurons in the rostral accumbens core. Injections in the lateral MD resulted in retrograde infection in the globus pallidus (GP) and in transynaptic infection in the caudate-putamen. Viral injections into the rostroventral pole of the RTN infected neurons in the medial and lateral VP and at longer postinoculation intervals, led to transynaptic infection of scattered neurons in the shell and core. Injection of virus into the intermediate RTN resulted in infection of medial VP neurons and second-order infection of neurons in the accumbens shell. Injections in the caudal RTN or the lateral MD resulted in direct retrograde labeling of cells within the GP and transynaptic infection of neurons in the caudate-putamen. These results indicate that the main output of VP neurons receiving inputs from the shell of the accumbens is heavily directed to the m-MD, whereas a small number of core neurons appear to influence the central MD via the lateral VP. Further segregation in the flow of information to the MD is apparent in the organization of VP and GP projections to subdivisions of the RTN that give rise to MD afferents. Collectively, these data provide a morphological basis for the control of the thalamocortical system by ventral striatal regions, in which parallel connections to the RTN may exert control over activity states of cortical regions.
伏隔核的主要输出之一是通过其向腹侧苍白球（VP）的投射，定向至丘脑背内侧核（MD），伏隔核的核心区和壳区分别投射至VP的外侧和内侧。在本研究中，使用脑内注射减毒伪狂犬病病毒来评估伏隔核投射的多突触组织，伪狂犬病病毒是一种嗜神经性α疱疹病毒，在突触连接的神经元中复制。将伪狂犬病病毒注射到MD或丘脑网状核（RTN）的不同区域会产生逆行跨突触感染，揭示了这些区域与基底前脑之间的多突触相互作用。接种后短时间间隔内病毒抗原的免疫组织化学定位证实，内侧MD（m-MD）接受来自内侧VP、嘴侧RTN以及先前显示投射至丘脑该区域的其他区域的直接投射。在更长的存活时间间隔时，局限于m-MD的注射导致伏隔核壳区神经元的跨突触感染，但核心区未出现感染。还包括MD中央段的注射导致外侧VP和嗅结节（OT）多形（苍白球）区神经元的逆行感染，以及嘴侧伏隔核核心区少量神经元的跨突触感染。外侧MD的注射导致苍白球（GP）的逆行感染和尾状核-壳核的跨突触感染。将病毒注射到RTN的嘴腹侧极会感染内侧和外侧VP的神经元，在接种后更长时间间隔时，导致壳区和核心区散在神经元的跨突触感染。将病毒注射到中间RTN会导致内侧VP神经元的感染以及伏隔核壳区神经元的二级感染。尾侧RTN或外侧MD的注射导致GP内细胞的直接逆行标记以及尾状核-壳核神经元的跨突触感染。这些结果表明，接受来自伏隔核壳区输入的VP神经元的主要输出大量定向至m-MD，而少量核心神经元似乎通过外侧VP影响中央MD。在向MD的信息流中的进一步分离在VP和GP向产生MD传入纤维的RTN亚区的投射组织中很明显。总体而言，这些数据为腹侧纹状体区域对丘脑皮质系统的控制提供了形态学基础，其中与RTN的平行连接可能对皮质区域的活动状态施加控制。
