Amygdaloid inputs define a caudal component of the ventral striatum in primates

The ventral striatum mediates goal-directed behavior through limbic afferents. One well-established afferent to the ventral striatum is the amygdaloid complex, which projects throughout the shell and core of the nucleus accumbens, the rostral ventromedial caudate nucleus, and rostral ventromedial putamen. However, striatal regions caudal to the anterior commissure also receive inputs from the amygdala. These caudal areas contain histochemical and cytoarchitectural features that resemble the shell and core, based on our recent studies. Specifically, there is a calcium binding protein (CaBP)-poor region in the lateral amygdalostriatal area that resembles the "shell." To examine the idea that the caudal ventral striatum is part of the "classic" ventral striatum, we placed small injections of retrograde tracers throughout the caudal ventral striatum/amygdalostriatal area and charted the distribution of specific amygdaloid inputs. Amygdaloid inputs to the CaBP-poor zone in the lateral amygdalostriatal area arise from the basal nucleus, the magnocellular subdivision of the accessory basal nucleus, the periamygdaloid cortex, and the medial subdivision of the central nucleus, resembling that of the shell of the ventral striatum found in our previous studies. There are also amygdaloid inputs to CaBP-positive areas outside the shell, which originate mainly in the basal nucleus. Taken together, the "limbic-related" striatum forms a continuum from the rostral ventral striatum through the caudal ventral striatum/lateral amygdalostriatal area based on histochemical and cellular similarities, as well as inputs from the amygdala.     

Treatment with a γ-ketoaldehyde scavenger prevents working memory deficits in hApoE4 mice

Postmortem studies show pathological changes in the striatum in Alzheimer's disease (AD). Here, we examine the surface of the striatum in AD and assess whether changes of the surface are associated with impaired cognitive functioning. The shape of the striatum (n. accumbens, caudate nucleus, and putamen) was compared between 35 AD patients and 35 individuals without cognitive impairment. The striatum was automatically segmented from 3D T1 magnetic resonance images and automatic shape modeling tools (Growing Adaptive Meshes) were applied for morphometrical analysis. Repeated permutation tests were used to identify locations of consistent shape deformities of the striatal surface in AD. Linear regression models, corrected for age, gender, educational level, head size, and total brain parenchymal volume were used to assess the relation between cognitive performance and local surface deformities. In AD patients, differences of shape were observed on the medial head of the caudate nucleus and on the ventral lateral putamen, but not on the accumbens. The head of the caudate nucleus and ventral lateral putamen are characterized by extensive connections with the orbitofrontal and medial temporal cortices. Severity of cognitive impairment was associated with the degree of deformity of the surfaces of the accumbens, rostral medial caudate nucleus, and ventral lateral putamen. These findings provide evidence for the hypothesis that in AD primarily associative and limbic cerebral networks are affected.     

The centre me´dian and parafascicular thalamic nuclei project respectively to the sensorimotor and associative-limbic striatal territories in the squirrel monkey

The striatal projections of the centre me´dian (CM) and parafascicular (Pf) thalamic nuclei were examined in the squirrel monkey (Saimiri sciureus) by using the lectin wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) as an anterograde tracer. CM was found to project massively to the putamen, where terminal fields appeared principally in the form of oblique bands, and more diffusely to the dorsolateral border of the caudate nucleus. Striatal inputs from Pf were found more rostrally, especially in the ventromedial portion of the putamen, the entire ventromedial half of the caudate nucleus, and the ventral striatum including the nucleus accumbens and the olfactory tubercle. Pf terminal fields in the rostral striatum often displayed a patchy organization. Both CM and Pf projections were found to terminate in the matrix compartment of the striatum as defined by acetylcholinesterase staining. These results suggest that CM is more specifically involved in sensorimotor and Pf in associative and limbic aspects of basal ganglia function in primates.     

Organization of the ascending striatal afferents in monkeys

Horseradish peroxidase was injected in various parts of the caudate nucleus and the putamen of monkeys to ascertain the relative locations of striatal projecting cells in the mesencephalon. The nigrostriatal component, as expected, is the greatest but numerous cells of the mesencephalic raphe system also project to the striatum. The projections from the pars compacta are organized in a topographical manner in all principal planes. The rostral two thirds of the substantia nigra are related to the head of the caudate nucleus. Nigral neurons projecting to the putamen are more posteriorly located and display an anteroposterior topography. The medial two thirds of the pars compacta send efferents to the head of the caudate nucleus from ventromedial to laterodorsal regions, reflecting a mediolateral topographical relationship. An inverse relationship exists dorsoventrally between nigra and caudate so that ventral compacta cells project to dorsal caudate and the dorsally situated neurons project to ventral-ventro-medial caudate regions. The dorsal and lateral parts of the putamen are more intimately related to the lateral and posterior nigra; by contrast, the ventral and ventromedial putamen receives more afferents from medial and central regions of the substantia nigra. A large group of cells in the tegmentum dorsal and medial to the medial lemniscus shows continuity with the pars compacta, and has similar connections with the striatum. This cell group should be included with the pars compacta. Significant overlap exists between the projection fields in all planes, making the nigrostriatal topographical organization seem less than precise. This apparent lack of point-to-point reciprocity may be due to the considerable size difference between the striatum and the substantia nigra. The raphe nuclei project to the greater part of the striatum but more significantly to its ventral and medial regions. The paranigral cell group sends its efferents mainly to the ventral striatum.     

The centre médian and parafascicular thalamic nuclei project respectively to the sensorimotor and associative-limbic striatal territories in the squirrel monkey.

The striatal projections of the centre médian (CM) and parafascicular (Pf) thalamic nuclei were examined in the squirrel monkey (Saimiri sciureus) by using the lectin wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) as an anterograde tracer. CM was found to project massively to the putamen, where terminal fields appeared principally in the form of oblique bands, and more diffusely to the dorsolateral border of the caudate nucleus. Striatal inputs from Pf were found more rostrally, especially in the ventromedial portion of the putamen, the entire ventromedial half of the caudate nucleus, and the ventral striatum including the nucleus accumbens and the olfactory tubercle. Pf terminal fields in the rostral striatum often displayed a patchy organization. Both CM and Pf projections were found to terminate in the matrix compartment of the striatum as defined by acetylcholinesterase staining. These results suggest that CM is more specifically involved in sensorimotor and Pf in associative and limbic aspects of basal ganglia function in primates.     

Prefrontal cortical projections to longitudinal columns in the midbrain periaqueductal gray in Macaque monkeys

The origin and termination of prefrontal cortical projections to the periaqueductal gray (PAG) were defined with retrograde axonal tracers injected into the PAG and anterograde axonal tracers injected into the prefrontal cortex (PFC). The retrograde tracer experiments demonstrate projections to the PAG that arise primarily from the medial prefrontal areas 25, 32, and 10m, anterior cingulate, and dorsomedial areas 24b and 9, select orbital areas 14c, 13a, Iai, 12o, and caudal 12l, and ventrolateral area 6v. Only scattered cells were retrogradely labeled in other areas in the PFC. Caudal to the PFC, projections to the PAG also arise from the posterior cingulate cortex, the dorsal dysgranular, and granular parts of the temporal polar cortex, the ventral insula, and the dorsal bank of the superior temporal sulcus. Cells were also labeled in subcortical structures, including the central nucleus and ventrolateral part of the basal nucleus of the amygdala. The anterograde tracer experiments indicate that projections from distinct cortical areas terminate primarily in individual longitudinal PAG columns. The projections from medial prefrontal areas 10m, 25, and 32 end predominantly in the dorsolateral columns, bilaterally. Fibers from orbital areas 13a, Iai, 12o, and caudal 12l terminate primarily in the ventrolateral column, whereas fibers from dorsomedial areas 9 and 24b terminate mainly in the lateral column. The PFC areas that project to the PAG include most of the areas previously defined as the “medial prefrontal network.” The areas that comprise this network represent a visceromotor system, distinct from the sensory related “orbital network.” J. Comp. Neurol. 401:455–479, 1998. © 1998 Wiley-Liss, Inc.     

Corticostriatal connections of extrastriate visual areas in rhesus monkeys

The striatal connections of extrastriate visual areas were examined by the autoradiographic technique in rhesus monkeys. The medial as well as the dorsolateral extrastriate regions project preferentially to dorsal and lateral portions of the head and of the body of the caudate nucleus, as well as to the caudodorsal sector of the putamen. The rostral portion of the annectant gyrus has connections to the caudal sector of the body and to the genu, whereas projections from the caudal portion of the lower bank of the superior temporal sulcus are directed to dorsal and central sectors of the head and the body, to the genu and the tail, as well as to the caudal putamen. The ventrolateral extrastriate region is related mainly to the ventral sector of the body, to the genu and the tail, and to the caudal putamen. In contrast, the striatal projections of the ventromedial extrastriate cortex resemble those of the medial and dorsolateral regions. The caudal inferotemporal cortex is related strongly to the tail of the caudate nucleus and to the ventral putamen. The differential corticostriatal connectivity of the various extrastriate regions may contribute to the specific functional roles of these cortices. Thus, the connections from the dorsomedial, dorsolateral, and ventromedial areas to dorsal portions of the caudate nucleus and of the putamen may serve a visuospatial function. In contrast, the connections from the ventrolateral extrastriate and inferotemporal regions to the tail of the caudate nucleus and to the ventral putamen may have a role in visual object-related processes. © 1995 Wiley-Liss, Inc.     

Topographical organization and relationship with ventral striatal compartments of prefrontal corticostriatal projections in the rat.

The anterograde tracer Phaseolus vulgaris-leucoagglutinin was used to examine the topographical organization of the projections to the striatum arising from the various cytoarchitectonic subdivisions of the prefrontal cortex in the rat. The relationship of the prefrontal cortical fibres with the compartmental organization of the ventral striatum was assessed by combining PHA-L tracing and enkephalin-immunohistochemistry. The prefrontal cortex projects bilaterally with an ipsilateral predominance to the striatum, sparing only the lateral part of the caudate-putamen complex. Each of the cytoarchitectonic subfields of the prefrontal cortex has a longitudinally oriented striatal terminal field that overlaps slightly with those of adjacent prefrontal areas. The projections of the medial subdivision of the prefrontal cortex distribute to rostral and medial parts of the striatum, whereas the lateral prefrontal subdivision projects to more caudal and lateral striatal areas. The terminal fields of the orbital prefrontal areas involve midventral and ventromedial parts of the caudate-putamen complex. The projection of the ventral orbital area overlaps with that of the prelimbic area in the ventromedial part of the caudate-putamen. In the "shell" region of the nucleus accumbens, fibres arising from the prelimbic area concentrate in areas of high cell density that are weakly enkephalin-immunoreactive, whereas fibres from the infralimbic area avoid such areas. Rostrolaterally in the "core" region of the nucleus accumbens, fibres from deep layer V and layer VI of the dorsal part of the prelimbic area avoid the enkephalin-positive areas surrounding the anterior commissure and distribute in an inhomogeneous way over the intervening moderately enkephalin-immunoreactive compartment. The other prefrontal afferents show only a preference for, but are not restricted to, the latter compartment. In the border region between the nucleus accumbens and the ventromedial part of the caudate-putamen complex, patches of strong enkephalin immunoreactivity receive prefrontal cortical input from deep layer V and layer VI, whereas fibres from more superficial cortical layers project to the surrounding matrix. Individual cytoarchitectonic subfields of the prefrontal cortex thus have circumscribed terminal domains in the striatum. In combination with data on the organization of the midline and intralaminar thalamostriatal and thalamoprefrontal projections, the present results establish that the projections of the prefrontal cortical subfields converge in the striatum with those of their midline and intralaminar afferent nuclei. The present findings further demonstrate that the relationship of the prefrontal corticostriatal fibres with the neurochemical compartments of the ventral striatum can be influenced by both the areal and the laminar origin of the cortical afferents, depending on the particular ventral striatal region under consideration.     

Organization of the thalamostriatal projections in the rat, with special emphasis on the ventral striatum

The organization of the thalamic projections to the ventral striatum in the rat was studied by placing injections of the retrograde tracer cholera toxin subunit B in the ventral striatum and small deposits of the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) in individual midline and intralaminar thalamic nuclei. In order to provide a complete map of the midline and intralaminar thalamostriatal projections, PHA-L injections were also made in those parts of the intralaminar nuclei that project to the dorsal striatum. The relationship of thalamic afferent fibres with the compartmental organization of the ventral striatum was assessed by combining PHA-L tracing and enkephalin immunohistochemistry. The various midline and intralaminar thalamic nuclei project to longitudinally oriented striatal sectors. The paraventricular thalamic nucleus sends most of its fibres to medial parts of the nucleus accumbens and the olfactory tubercle, whereas smaller contingents of fibres terminate in the lateral part of the nucleus accumbens and the most ventral, medial, and caudal parts of the caudate-putamen complex. The projections of the parataenial nucleus are directed towards central and ventral parts of the nucleus accumbens and intermediate mediolateral parts of the olfactory tubercle. The intermediodorsal nucleus projects to lateral parts of the nucleus accumbens and the olfactory tubercle and to ventral parts of the caudate-putamen. The projection of the rhomboid nucleus is restricted to the rostrolateral extreme of the striatum. A diffuse projection to the ventral striatum arises from neurons ventral and caudal to the nucleus reuniens rather than from cells inside the nucleus. Fibres from the central medial nucleus terminate centrally and dorsolaterally in the rostral part of the nucleus accumbens and medially in the caudate-putamen. Successively more lateral positions in the caudate-putamen are occupied by fibres from the paracentral and central lateral nuclei, respectively. The lateral part of the parafascicular nucleus projects to the most lateral part of the caudate-putamen, whereas projections from the medial part of this nucleus terminate in the medial part of the caudate-putamen and in the dorsolateral part of the nucleus accumbens. Furthermore, a rostral to caudal gradient in a midline or intralaminar nucleus corresponds to a dorsal to ventral and rostral to caudal gradient in the striatum. In the ventral striatum, thalamic afferent fibres in the "shell" region of the nucleus accumbens avoid areas of high cell density and weak enkephalin immunoreactivity.(ABSTRACT TRUNCATED AT 400 WORDS)     

The amygdalostriatal projections in the monkey. An anterograde tracing study

Amygdalostriatal projections have been studied in the monkey with the autoradiographic method for demonstrating axonal transport of tritiated amino acids. Amygdaloid fibers were found to project in a roughly topographical manner to widespread areas of the striatum and ventral striatum, including the nucleus accumbens, the striatal-like portions of the olfactory tubercle, ventral portions of the putamen and ventral and caudal parts of the caudate nucleus. The parvicellular part of the basal nucleus and the amygdalohippocampal area appear to be the major sources of fibers to the nucleus accumbens, whereas projections to the tail of the caudate nucleus seem to arise mainly from the magnocellular part of the basal nucleus. In many of these areas, the amygdalostriatal fibers are concentrated in patches.     

Frontal eye field efferents in the macaque monkey: I. Subcortical pathways and topography of striatal and thalamic terminal fields

Anterograde tracers (tritiated leucine, proline, fucose; WGA-HRP) were injected into sites within the frontal eye fields (FEF) of nine macaque monkeys. Low thresholds (less than or equal to 50 microA) for electrically evoking saccadic eye movements were used to locate injection sites in four monkeys. Cases were grouped according to the amplitude of saccades evoked or predicted at the injection site. Dorsomedial prearcuate injection sites where large saccades were elicited were classified as lFEF cases, whereas ventrolateral prearcuate sites where small saccades were evoked were designated sFEF cases. One control case was injected in the medial postarcuate area 6. We found five descending fiber bundles from FEF; fibers to the striatum, which enter the caudate nucleus at or just rostral to the genu of the internal capsule; fibers to the claustrum, which travel in the external capsule; and transthalamic, subthalamic, and pedunculopontine fibers. Our results indicate that transthalamic and subthalamic pathways supply all terminal sites in the thalamus, subthalamus, and tegmentum of the midbrain and pons, whereas pedunculopontine fibers appear to terminate in the pontine and reticularis tegmenti pontis nucleus exclusively. Frontal eye field terminal fields in the striatum were topographically organized: lFEF projections terminated dorsal and rostral to sFEF projections. Thus, lFEF terminal fields were located centrally in the head and body of the caudate nucleus and a small dorsomedial portion of the putamen, whereas sFEF terminal fields were located in ventrolateral parts of the caudate body and ventromedial parts of the putamen. In the claustrum, lFEF projections terminated dorsal and rostral to sFEF projections. Projections from FEF terminated in ventral and caudal parts of the subthalamic nucleus without a clear topography. By comparison, terminal fields from medial postarcuate area 6 were located more caudally and laterally in the striatum and claustrum than projections from FEF, and more centrally in the subthalamic nucleus. In the thalamus, FEF terminal patches in some thalamic nuclei were also topographically organized. Projections from lFEF terminated in dorsal area X, dorsolateral medial dorsal nucleus, pars parvicellularis (MDpc), and the caudal pole of MDpc, whereas projections from sFEF terminated in ventral area X, medial dorsal nucleus, pars multiformis, and caudal medial dorsal nucleus pars densocellularis.(ABSTRACT TRUNCATED AT 400 WORDS)     

Differentiation of the midbrain dopaminergic pathways during mouse development

Dopaminergic (DA) neurons in the substantia nigra (SN) and ventral tegmental area (VTA) of the midbrain project to the dorsolateral caudate/putamen and to the ventromedially located nucleus accumbens, respectively, establishing the mesostriatal and the mesolimbic pathways. Disruptions in this system have been implicated in Parkinson's disease, drug addiction, schizophrenia, and attention deficit hyperactivity disorder. However, progress in our understanding has been hindered by a lack of knowledge of how these pathways develop. In this study, different retrograde tracers, placed into the dorsolateral caudate/putamen and the nucleus accumbens, were used to analyze the development of the dopaminergic pathways. In embryonic day 15 mouse embryos, both SN and VTA neurons, as well as their fibers, were doubly labeled by striatal injections into the dorsolateral and ventromedial striatum. However, by birth, the SN DA neurons were labeled exclusively by DiA placed in the dorsolateral striatum, and the VTA DA neurons were labeled only by DiI injected into the ventromedial striatum. These data suggest that initial projections from midbrain DA neurons target nonspecifically to both the dorsolateral striatum and the nucleus accumbens. Later during development, the separate mesostriatal and mesolimbic pathways differentiate through the selective elimination of mistargeted collaterals.     

Amygdaloid projections to subcortical structures within the basal forebrain and brainstem in the rat and cat

The efferent fiber connections of the nuclei of the amygdaloid complex with subcortical structures in the basal telencephalon, hypothalamus, midbrain, and pons have been studied in the rat and cat, using the autoradiographic method for tracing axonal connections. The cortical and thalamic projections of these nuclei have been described in previous papers (Krettek and Price, ′77b,c). Although the subcortical connections of the amygdaloid nuclei are widespread within the basal forebrain and brain stem, the projections of each nucleus have been found to be well defined, and distinct from those of the other amygdaloid nuclei. The basolateral amygdaloid nucleus projects heavily to the lateral division of the bed nucleus of the stria terminalis (BNST), to the caudal part of the substantia innominata, and to the ventral part of the corpus striatum (nucleus accumbens and ventral putamen) and the olfactory tubercle; it projects more lightly to the lateral hypothalamus. The central nucleus also projects to the lateral division of the BNST and the lateral hypothalamus, but in addition it sends fibers to the lateral part of the substantia nigra and the marginal nucleus of the brachium conjunctivum. The basomedial nucleus has projections to the ventral striatum and olfactory tubercle which are similar to those of the basolateral nucleus, but it also projects to the core of the ventromedial hypothalamic nucleus and the premammillary nucleus, and to a central zone of the BNST which overlaps the medial and lateral divisions. The medial nucleus also projects to the core of the ventromedial nucleus and the premammillary nucleus, but sends fibers to the medial division of the BNST and does not project to the ventral striatum. The posterior cortical nucleus projects to the premammillary nucleus and to the medial division of the BNST, but a projection from this nucleus to the ventromedial nucleus has not been demonstrated. Projections to the “shell” of the ventromedial nucleus have been found only from the ventral part of the subiculum and from a structure at the junction of the amygdala and the hippocampal formation, which has been termed the amygdalo-hippocampal area (AHA). The AHA also sends fibers to the medial part of the BNST and the premammillary nucleus. Virtually no subcortical projections outside the amygdala itself have been demonstrated from the lateral nucleus, or from the olfactory cortical areas around the amygdala (the anterior cortical nucleus, the periamygdaloid cortex, and the posterior prepiriform cortex). However, portions of the endopiriform nucleus deep to the prepiriform cortex project to the ventral putamen, and to the lateral hypothalamus.     

Effects of dorsal and ventral striatal lesions on delayed matching trained with retractable levers

Recent evidence has suggested that thalamic amnesia results from damage to the intralaminar nuclei, an important source of input to striatum. To test the hypothesis that intralaminar damage disrupts functions mediated by striatum, we studied the effects of striatal lesions on a delayed matching task known to be affected by intralaminar lesions. Rats were trained to perform the task and given one of five treatments: sham surgery or a lesion of medial or lateral caudate/putamen, nucleus accumbens, or ventral striatum. Rats with ventral striatal lesions were impaired compared to all other groups. Rats with medial caudate/putamen or nucleus accumbens lesions were impaired compared to controls. The effects of ventral striatal lesions were sufficient to account for impairments in the accuracy and latency of delayed matching responses observed in previous studies of intralaminar and medial frontal cortical lesions. The ventral striatal lesions involved portions of ventral pallidum and thus it seems likely that they affected functions mediated by the nucleus accumbens as well as striatal areas of the tubercle. Serial reversal learning trained in the same apparatus with the same reinforcer was unaffected by all of the lesions. These results are discussed in terms of the roles of midline thalamic nuclei and of thalamo-cortico-striatal circuits in delayed conditional discrimination tasks.     

Organization of the pallium in the fire-bellied toad Bombina orientalis. I: Morphology and axonal projection pattern of neurons revealed by intracellular biocytin labeling

The cytoarchitecture and axonal projection pattern of pallial areas was studied in the fire-bellied toad Bombina orientalis by intracellular injection of biocytin into a total of 326 neurons forming 204 clusters. Five pallial regions were identified, differing in morphology and projection pattern of neurons. The rostral pallium receiving the bulk of dorsal thalamic afferents has reciprocal connections with all other pallial areas and projects to the septum, nucleus accumbens, and anterior dorsal striatum. The medial pallium projects bilaterally to the medial pallium, septum, nucleus accumbens, mediocentral amygdala, and hypothalamus and ipsilaterally to the rostral, dorsal, and lateral pallium. The ventral part of the medial pallium is distinguished by efferents to the eminentia thalami and the absence of contralateral projections. The dorsal pallium has only ipsilateral projections running to the rostral, medial, and lateral pallium; septum; nucleus accumbens; and eminentia thalami. The lateral pallium has ipsilateral projections to the olfactory bulbs and to the rostral, medial, dorsal, and ventral pallium. The ventral pallium including the striatopallial transition area (SPTA) has ipsilateral projections to the olfactory bulbs, rostral and lateral pallium, dorsal striatopallidum, vomeronasal amygdala, and hypothalamus. The medial pallium can be tentatively homologized with the mammalian hippocampal formation, the dorsal pallium with allocortical areas, the lateral pallium rostrally with the piriform and caudally with the entorhinal cortex, the ventral pallium with the accessory olfactory amygdala. The rostral pallium, with its projections to the dorsal and ventral striatopallidum, resembles the mammalian frontal cortex.     

Efferent connections of the centromedian and parafascicular thalamic nuclei in the squirrel monkey: a PHA-L study of subcortical projections.

The subcortical projections of the centromedian (CM) and the parafascicular (Pf) thalamic nuclei were examined in the squirrel monkey (Saimiri sciureus) by using the lectin Phaseolus vulgaris-leucoagglutinin (PHA-L) as an anterograde tracer. Both CM and Pf project massively to the striatum where they arborize in a complementary fashion. On the one hand, CM innervates most of the putamen caudal to the anterior commissure, a dorsolateral rim of the putamen rostral to the anterior commissure, discrete areas of the head of the caudate nucleus close to the internal capsule, and a lateral sector of the body of the caudate nucleus. On the other hand, Pf provides a heavy input to the head, body, and tail of the caudate nucleus, and to the rostral putamen, excluding the areas innervated by CM. In addition, Pf projects more discretely to the nucleus accumbens and the olfactory tubercle. Therefore, the projections from both CM and Pf cover the entire striatum, with those from CM arborizing into the "sensorimotor" striatal territory and the ones from Pf innervating the "associative-limbic" striatal territory. Furthermore, CM and Pf project to extrastriatal subcortical structures, such as the globus pallidus, the subthalamic nucleus, and the substantia nigra, where they also terminate in a complementary fashion. Topographically and cytologically, Pf is closely related to the subparafascicular nucleus (sPf). The Pf-sPf complex projects to the hypothalamus, the substantia innominata, the peripeduncular nucleus, and the amygdala. It also gives rise to descending efferents arborizing in various brainstem structures, including the inferior olivary complex. Additional studies with retrograde double-labeling methods show that distinct cell groups within CM project to the motor cortex and the striatum. Likewise, separate neuronal populations within the CM-Pf-sPf complex give rise to striatal and brainstem projections, the former arising from CM and Pf and the latter mainly from sPf. The complementary nature of CM and Pf projections to the striatum and other basal ganglia components suggests that this thalamic complex participates in a highly ordered manner in the parallel processing of the information that flows through the basal ganglia.     

Striatal connections of the parietal association cortices in rhesus monkeys

The corticostriatal connections of the parietal association cortices were examined by the autoradiographic technique in rhesus monkeys. The results show that the rostral portion of the superior parietal lobule projects predominantly to the dorsal portion of the putamen, whereas the caudal portion of the superior parietal lobule and the cortex of the upper bank of the intraparietal sulcus have connections with the caudate nucleus as well as with the dorsal portion of the putamen. The medial parietal convexity cortex projects strongly to the caudate nucleus, and has less extensive projections to the putamen. In contrast, the medial parietal cortex within the caudal portion of the cingulate sulcus projects predominantly to the dorsal portion of the putamen, and has only minor connections with the caudate nucleus. The rostral portion of the inferior parietal lobule projects mainly to the ventral sector of the putamen, and has only minor connections with the caudate nucleus. The middle portion of the inferior parietal lobule has sizable projections to both the putamen and the caudate nucleus. The caudal portion of the inferior parietal lobule as well as the lower bank of the intraparietal sulcus project predominantly to the caudate nucleus, and have relatively minor connections with the putamen. The cortex of the parietal opercular region also shows a specific pattern of corticostriatal projections. Whereas the rostral portion projects exclusively to the ventral sector of the putamen, the caudal portion has connections to the caudate nucleus as well. Thus, it seems that parietostriatal projections show a differential topographic distribution; within both the superior and the inferior parietal region, as one progresses from rostral to caudal, there is a corresponding shift in the predominance of projections from the putamen to the caudate nucleus. In addition, with regard to the projections to the putamen, the superior parietal lobule is related mainly to the dorsal portion, and the inferior parietal lobule to the ventral portion. The striatal projections of the cortex of the caudal portion of the cingulate gyrus (corresponding in part to the supplementary sensory area) and of the rostral parietal opercular region (corresponding in part to the second somatosensory area) are directed almost exclusively to the dorsal and ventral sectors of the putamen, respectively. This pattern resembles that of the primary somatosensory cortex. The results are discussed with regard to the overall architectonic organization of the posterior parietal region. Possible functional aspects of parietostriatal connectivity are considered in the light of physiological and behavioral studies. © 1993 Wiley-Liss, Inc.     

The striatum of the opossum, Didelphis virginiana. Description and experimental studies

The relationships and cytoarchitecture of the putamen, the caudate, the claustrum, the globus pallidus and the entopeduncular nuclei have been described for the opossum. The neocortical projections to these nuclei have ben studied by employing the Nauta-Gygax technique ('54) and the Swank Davenport modification of the Marchi technique ('34) on animals in which neocortical lesions were previously placed. Degenerating fibers from every cortical lesion were observed to terminate in both the putamen and the caudate with the Nauta-Gygax technique, whereas such connections were traced only to putamen woth the Marchi method. Terminations were present within the claustrum, but equivocal in the globus pallidus. In general, fibers from the more rostral cortices terminate in the rostral parts of both striatal nuclei, whereas fibers from more caudal neocortical areas project to more caudal parts of these same nuclei. In addition, the more dorsal or dorsomedial neocortical areas distribute more fibers to the caudate than to the putamen, whereas the opposite is true for the ventral or ventrolateral neocortical areas. Neocortical fibers did not project to the ventral, medial part of the head of the caudate which was cytoarchitectually different from the rest of the nucleus. A few fascicles of frontal, orbital and parietal origin terminated in the contralateral putamen and caudate after having decussated in the anterior commissure.     

Topographical projections from the thalamus, subthalamic nucleus and pedunculopontine tegmental nucleus to the striatum in the Japanese monkey, Macaca fuscata.

Topographical projections from the thalamus, subthalamic nucleus (STN) and pedunculopontine tegmental nucleus (PPN) to the striatum were examined in the Japanese monkey (Macaca fuscata) by using the retrograde axonal transport technique of WGA-HRP (wheat germ agglutinin-conjugated horseradish peroxidase). After WGA-HRP injection in the head of the caudate nucleus (CN) or putamen (Put), labeled neuronal cell bodies in the thalamus were distributed mainly in the nucleus ventralis anterior (VA)-nucleus ventralis lateralis (VL) complex and the nucleus centrum medianum (CM)-nucleus parafascicularis (Pf) complex, and additionally in the paraventricular, parataenial, rhomboid, reuniens, centrodorsal, centrolateral, paracentral, and centromedial nuclei. The data indicated that the pars principalis of VA (VApc) projected mainly to CN and additionally to Put, and that the pars magnocellularis of VA (VAmc) or pars oralis of VL (VLo) projected selectively to CN or Put, respectively. It was also indicated that CM projected to the middle and caudal parts of Put, while Pf projected to CN and the rostral part of the Put. The data further indicated that the dorsomedial, ventromedial, or lateral part of CM projected respectively to the dorsolateral, ventromedial, or intermediate part of Put, and that the medial or lateral part of Pf projected respectively to the medial or lateral part of the head of CN. Direct projections from STN and PPN to the striatum were confirmed. The subthalamostriatal projections showed a mediolateral topography. The PPN was shown to project bilaterally to the striatum with an ipsilateral predominance.     

Neuroanatomical basis of behavior: history and recent contributions

Considering the most recent contributions, the limbic cortical areas, originally known as the greater limbic lobe, besides the cingulated and the parahippocampal gyri also includes the insula and the posterior orbital cortex. In contrast to the nonlimbic cortical areas that project to the basal ganglia (particularly over the dorsal aspects of the striatum, constituted by the caudate nucleus and by the putamen), the limbic cortical areas are characterized by projecting to the hypothalamus and also to the ventral striatum (particularly to the nucleus accumbens). Once all the striatum projects to the globus pallidus which projects to the thalamus and then to the cortex, generating cortical-subcortical reentrant circuits, while the dorsal striatum and pallidum related cortico-subcortical loops are involved with motor activities, the ventral cortical-striatal-pallidal system is particularly related with behavior functions. The extended amygdala (central medial amygdala, stria terminalis or dorsal component, ventral component, and bed nucleus of stria terminalis) receives inputs primarily from the limbic cortical areas, is particularly modulated by the prefrontal cortex, and receives also direct connections from the thalamus that enables the amygdala to generate nonspecific and quick responses through its projections to the hypothalamus and to the brainstem. The ventral striatal-pallidal and the extended amygdala are then two basal forebrain macro-anatomical systems, that together with the basal nucleus of Meynert and with the septal-diagonal band system, constitute the main structures that are particularly connected with the limbic cortical areas, and that altogether project to the hypothalamus and to the brainstem which give rise to the autonomic, endocrine and somatosensory components of the emotional experiences, and that regulate the basic activities of drinking, eating, and related to the sexual behavior.