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The classic anthropological hypothesis known as the “obstetrical dilemma” is a well-known explanation for human altriciality, a condition that has significant implications for human social and behavioral evolution. The hypothesis holds that antagonistic selection for a large neonatal brain and a narrow, bipedal-adapted birth canal poses a problem for childbirth; the hominin “solution” is to truncate gestation, resulting in an altricial neonate. This explanation for human altriciality based on pelvic constraints persists despite data linking human life history to that of other species. Here, we present evidence that challenges the importance of pelvic morphology and mechanics in the evolution of human gestation and altriciality. Instead, our analyses suggest that limits to maternal metabolism are the primary constraints on human gestation length and fetal growth. Although pelvic remodeling and encephalization during hominin evolution contributed to the present parturitional difficulty, there is little evidence that pelvic constraints have altered the timing of birth.

The lack of supply and access to human tissue has prompted the development of xenotransplantation as a potential clinical modality for neural cell transplantation. The goal of the present study was to achieve a better understanding of the immune factors involved in neural xenograft rejection in primates. Initially, we quantified complement mediated cell lysis of porcine fetal neurons by primate serum and demonstrated that anti-C5 antibody treatment inhibited cell death. We then developed an immunosuppression protocol that included in vivo anti-C5 monoclonal antibody treatment, triple drug therapy (cyclosporine, methylprednisolone, azathioprine) and donor tissue derived from CD59 or H-transferase transgenic pigs and applied it to pig-to-primate neural cell transplant models. Pre-formed aGal, induced aGal and primate anti-mouse antibody (PAMA) titers were monitored to assess the immune response. Four primates were transplanted. The three CD59 neural cell recipients showed an induced anti-aGal response, whereas the H-transferase neural cell recipient exhibited consistently low anti-aGal titers. Two of these recipients contained surviving grafts as detected by immunohistochemistry using selected neural markers. Graft survival correlated with high dose cyclosporine treatment, complete complement blockade and the absence of an induced PAMA response to the murine anti-C5 monoclonal antibodies.

Neural and stem cell transplantation is emerging as a potential treatment for neurodegenerative diseases. Transplantation of specific committed neuroblasts (fetal neurons) to the adult brain provides such scientific exploration of these new potential therapies. Huntington's disease (HD) is a fatal, incurable autosomal dominant (CAG repeat expansion of huntingtin protein) neurodegenerative disorder with primary neuronal pathology within the caudate–putamen (striatum). In a clinical trial of human fetal striatal tissue transplantation, one patient died 18 months after transplantation from cardiovascular disease, and postmortem histological analysis demonstrated surviving transplanted cells with typical morphology of the developing striatum. Selective markers of both striatal projection and interneurons such as dopamine and c-AMP-related phosphoprotein, calretinin, acetylcholinesterase, choline acetyltransferase, tyrosine hydroxylase, calbindin, enkephalin, and substance P showed positive transplant regions clearly innervated by host tyrosine hydroxylase fibers. There was no histological evidence of immune rejection including microglia and macrophages. Notably, neuronal protein aggregates of mutated huntingtin, which is typical HD neuropathology, were not found within the transplanted fetal tissue. Thus, although there is a genetically predetermined process causing neuronal death within the HD striatum, implanted fetal neural cells lacking the mutant HD gene may be able to replace damaged host neurons and reconstitute damaged neuronal connections. This study demonstrates that grafts derived from human fetal striatal tissue can survive, develop, and are unaffected by the disease process, at least for 18 months, after transplantation into a patient with HD.

We used brain imaging to study long-term neurodegenerative and bioadaptive neurochemical changes in a primate model of Parkinson disease. We gradually induced a selective loss of nigros- triatal dopamine neurons, similar to that of Parkinson disease, by creating oxidative stress through infusion of the mitochondrial complex 1 inhibitor MPTP for 14 ± 5 months. Repeated evaluations over 3 years by positron emission tomography (PET) demonstrated progressive and persistent loss of neuronal dopamine pre-synaptic re-uptake sites; repeated magnetic resonance spectroscopy (MRS) studies indicated a 23-fold increase in lactate and macromolecules in the striatum region of the brain for up to 10 months after the last administration of MPTP. By 2 years after the MPTP infusions, these MRS striatal lactate and macromolecule values had returned to normal levels. In contrast, there were persistent increases in striatal choline and decreases in N- acetylaspartate. Thus, these combined PET/MRS studies demonstrate patterns of neurochemical changes that are both dynamic and persistent long after selective dopaminergic degeneration.

Alzheimer's disease (AD) is the most common neurodegenerative disorder that causes cognitive deficits in the elderly. Its neuropathology is characterized by amyloid deposition and specific cholinergic degeneration. To address the link between amyloid formation and cholinergic loss, we examined histologically the amyloid precursor protein (APP) changes following selective immunolesion of the basal forebrain cholinergic system with 192 IgG-saporin in rats at 6 months post-lesion. In such rats with cognitive deficits observed in Morris water maze tests, we found increased levels of APP by optical density measurements in regions of cholinergic denervation. APP elevation and performance in the water maze task correlate with reduction of acetyl-cholinesterase (AChE) activity in the frontal cortex and CA3 subfield of hippocampus. The data indicate that loss of cholinergic innervation can affect APP expression.

Despite decades of research that has revolutionized the neurosciences, efforts to explain the major features of human brain evolution are still mostly based on superficial gross neuroanatomical features (e.g. size, sulcal patterns) and on theories of selection for high-level functions that lack precise neurobiological predictions (e.g. general intelligence, innate grammar). Beyond its large size we still lack an account of what makes a human brain different. However, advances in comparative neuroanatomy, developmental biology, and genetics have radically changed our understanding of brain development. These data challenge classic ideas about brain size, intelligence, and the addition of new functions, such as language, and they provide tools with which we can test hypotheses about how human brains diverge from other primate brains.

The movement disorder in Parkinson's disease results from the selective degeneration of a small group of dopaminergic neurons in the substantia nigra pars compacta region of the brain. A number of exploratory studies using human fetal tissue allografts have suggested that transplantation of dopaminergic neurons may become an effective treatment for patients with Parkinson's disease and the difficulty in obtaining human fetal tissue has generated interest in finding corresponding non-human donor cells. Here we report a post-mortem histological analysis of fetal pig neural cells that were placed unilaterally into the caudate-putamen brain region of a patient suffering from Parkinson's disease. Long-term (over seven months) graft survival was found and the presence of pig dopaminergic neurons and other pig neural and glial cells is documented. Pig neurons extended axons from the graft sites into the host brain. Furthermore, other graft derived cells were observed several millimeters from the implantation sites. Markers for human microglia and T-cells showed only low reactivity in direct proximity to the grafts. This is the first documentation of neural xenograft survival in the human brain and of appropriate growth of non-human dopaminergic neurons for a potential therapeutic response in Parkinson's disease.

The presence and specificity of axon guidance cues in the mature brain were examined by transplanting several types of xenogeneic neural cells from fetal pig brains into adult rat brains with selective neuronal loss. Committed neuronal phenotypes from cortical, mesencephalic and striatal fetal regions were implanted in homotopic or ectopic central nervous system locations. Using specific neurofilament and neural markers, axonal target selection by transplanted fetal neurons was determined throughout the central nervous system. Different types of donor neurons grew axons specifically to appropriate adjacent and distant host brain regions from ectopic or homotopic brain implantation sites and independent of the pattern of prior selective neuronal loss. Since the fetal donor neurons could orient axonal growth towards their normal synaptic termination zones, it shows that the adult brain also elaborates highly specific signals for axon guidance. These results obtained by xenotransplantation also demonstrate that the adult brain exhibits a latent potential for long-distance axon guidance that is evolutionarily conserved. These and related studies indicate that the necessary processes for connection of specific neurocircuitry also exist in the adult central nervous system, if axonal growth inhibition is overcome.

Neurotransplantation of human fetal dopamine (DA) neurons is currently being investigated as a therapeutic modality for Parkinson's disease (PD). However, the practical limitations of human fetal transplantation indicate a need for alternative methodologies. Using the 6-hydroxydopamine rat model of PD, we transplanted dopaminergic neurons derived from Embryonic Day 27 porcine fetuses into the denervated striatum of cyclosporine-A (CyA)-treated or non-CyA-treated rats. Functional recovery was assessed by amphetamine-induced rotation, and graft survival and morphology were analyzed using neuronal and glial immunostaining as well as in situ hybridization with a porcine repeat element DNA probe. A significant, sustained reduction in amphetamine-induced rotational asymmetry was present in the CyA-treated rats whereas the non-CyA-treated rats showed a transient behavioral recovery. The degree of rotational recovery was highly correlated to the number of surviving transplanted porcine dopaminergic neurons. TH+ neuronal survival and graft volume were significantly greater in the CyA-treated group as compared to the non-CyA group. By donor-specific neuronal and glial immunostaining as well as donor-specific DNA labeling, we demonstrate that porcine fetal neuroblasts are able to survive in the adult brain of immunosuppressed rats, mediate functional recovery, and extensively reinnervate the host striatum. These findings suggest that porcine DA neurons may be a suitable alternative to the use of human fetal tissue in neurotransplantation for PD.

The controlled differentiation of mouse embryonic stem (ES) cells into near homogeneous populations of both neurons and skeletal muscle cells that can survive and function in vivo after transplantation is reported. We show that treatment of pluripotent ES cells with retinoic acid (RA) and dimethylsulfoxide (DMSO) induce differentiation of these cells into highly enriched populations of gamma-aminobutyric acid (GABA) expressing neurons and skeletal myoblasts, respectively. For neuronal differentiation, RA alone is sufficient to induce ES cells to differentiate into neuronal cells that show properties of postmitotic neurons both in vitro and in vivo. In vivo function of RA-induced neuronal cells was demonstrated by transplantation into the quinolinic acid lesioned striatum of rats (a rat model for Huntington's disease), where cells integrated and survived for up to 6 wk. The response of embryonic stem cells to DMSO to form muscle was less dramatic than that observed for RA. DMSO-induced ES cells formed mixed populations of muscle cells composed of cardiac, smooth, and skeletal muscle instead of homogeneous populations of a single muscle cell type. To determine whether the response of ES cells to DMSO induction could be further controlled, ES cells were stably transfected with a gene coding for the muscle-specific regulatory factor, MyoD. When induced with DMSO, ES cells constitutively expressing high levels of MyoD differentiated exclusively into skeletal myoblasts (no cardiac or smooth muscle cells) that fused to form myotubes capable of spontaneous contraction. Thus, the specific muscle cell type formed was controlled by the expression of MyoD. These results provided evidence that the specific cell type formed (whether it be muscle, neuronal, or other cell types) can be controlled in vitro. Further, these results demonstrated that ES cells can provide a source of multiple differentiated cell types that can be used for transplantation.

Clinical trials are under way using fetal cells to repair damaged neuronal circuitry. However, little is known about how transplanted immature neurons can grow anatomically correct connections in the adult central nervous system (CNS). We transplanted embryonic porcine neural cells in vivo into adult rat brains with neuronal and axonal loss typical of Parkinson's or Huntington's disease. Using complementary species-specific cellular markers, we found donor axons and CD44+ astroglial fibres in host white matter tracts up to 8 mm from CNS transplant sites, although only donor axons were capable of reaching correct gray matter target regions. This work demonstrates that adult host brain can orient growth of transplanted neurons and that there are differences in transplant donor glial and axonal growth patterns in cellular repair of the mature CNS.

Axonal growth from cortically placed fetal neural transplants to subcortical targets in adult hosts has been difficult to demonstrate and is assumed to be minimal; however, experiments using xenogeneic neural grafts of either human or porcine fetal tissues into the adult rat striatum, mesencephalon, and spinal cord have demonstrated the capability for long-distance axonal growth. This study reports similar results for porcine cortical xenografts placed in the adult rat cerebral cortex and compares these findings with results from cortical allografts. Adult rats that previously received unilateral cortical lesions by an oblique intracortical stereotaxic injection of quinolinic acid, were implanted with suspensions of either E14 rat or E38 xenogeneic porcine fetal cortical cells. Xenografted rats were immunosuppressed by cyclosporin A. The corpus callosum was intact in all cases and grafts were confined to the overlying cortex. After a 31-34 wk posttransplant survival period, acetylcholinesterase (AChE) staining and tyrosine hydroxylase (TH) immunocytochemistry revealed that both allo- and xenografts received host afferents. Retrograde tracer injections into the ipsilateral striatum and cerebral peduncle in allografted animals failed to show any axonal growth to either subcortical target. Using a porcine-specific axonal marker in xenografted animals, we found graft axons in white matter tracts (corpus callosum, internal capsule, cingulum bundle, and medial forebrain bundle) and within the caudate-putamen and both the ipsilateral and contralateral cerebral cortex. Graft axons were not found in the thalamus, midbrain, or spinal cord. In addition, using an antibody to porcine glial fibers, we observed more extensive graft glial fiber growth into the same host fiber tracts, as far caudally as the cerebral peduncle, but not into gray matter targets outside the cortex. These results demonstrate that porcine cortical xenograft axons and glia can extend from lesioned cerebral cortex to cortical and subcortical targets in the adult rat brain. These findings are relevant for prospects of repairing cortical damage and obtaining functional recovery.

To determine the role of major histocompatibility complex (MHC) class I in immunological rejection of neural xenotransplants, F(ab')2 fragments of a monoclonal antibody to porcine MHC class I were used to mask this complex on porcine fetal striatal cells transplanted into rat striata previously lesioned with quinolinic acid. Presence of MHC class I on the surface of porcine striatal cells was confirmed by fluorescence-activated cell sorting prior to F(ab')2 treatment. At three to four months post-transplantation, survival of F(ab')2-treated xenografts was assessed by means of donor-specific immunostaining and compared to that of untreated xenografts in non-immunosuppressed rats and in rats immunosuppressed with cyclosporine A. In this study, masking of donor MHC class I by F(ab')2 treatment resulted in enhanced xenografts survival compared to the non-immunosuppressed controls (graft survival rates, 52% and 7%, respectively; P < 0.005) at survival times up to four months. While xenograft survival in F(ab')2-treated animals was not significantly different from that in cyclosporine-treated rats (74% graft survival), mean graft volume in F(ab')2-treated animals was smaller than that in cyclosporine-treated animals (1.07 +/- 0.30 mm3 versus 3.14 +/- 0.51 mm3; P < 0.005). The cytoarchitectonic organization of the xenografts was similar in F(ab')2- and cyclosporine-treated animals, and grafts in both groups exhibited long distance target-directed axonal outgrowth. The pattern of immunoreactivity to porcine MHC class I in the xenografts corresponded to the regional distribution of donor glia. In xenografts undergoing rejection, infiltration with host inflammatory cells was restricted to necrotic graft remnants and spared the nearby host structures. We conclude that MHC class-I-restricted immune mechanisms play an important role in neural xenograft rejection and that masking of this complex on donor cells may provide a useful strategy for immunoprotection of neural xenografts.

While dyskinetic movements have been reported in primates with unilateral excitotoxic lesions following stimulation by dopaminergic agonists, the presence and intensity of the dyskinetic syndromes have varied extensively with size and location of lesion. With the intent of producing a more reliable behavioral model of Huntington disease, anatomically-defined lesions of limited size were produced by magnetic resonance imaging-guided stereotaxic injection of quinolinic acid in specific regions within the caudate and putamen of rhesus monkeys. The location and extent of the lesions were verified by magnetic resonance imaging as well as quantitative positron emission tomography imaging with the dopamine D1 specific receptor ligand SCH 39166 as a marker for striatal output neurons. The quality, frequency and duration of dyskinetic movements were assessed and quantified before and after administration of 0.5 mg/kg apomorphine in multiple test sessions over several months. Selective unilateral lesions in the posterior putamen, but not in the anterior putamen or the head of the caudate, produced marked dystonia and dyskinesia after apomorphine administration. While combined unilateral lesions of the caudate and posterior putamen produced dyskinesia similar to selective posterior putaminal lesions, combined unilateral lesions of the anterior and posterior putamen did not elicit dyskenesia. On the basis of these results, one monkey received a bilateral selective lesion in the posterior putamen. This animal remained healthy and exhibited marked spontaneous Huntington-like chorea spontaneously in the first 48 h after lesioning and persistent apomorphine-induced dyskinesia thereafter. We conclude that bilateral selective excitotoxic lesions of the posterior putamen provide an improved model of the movement disorder of Huntington disease.

A method is described that promises to reduce some of the subjectivity of estimating the age and season of death from cementum increments in mammalian teeth recovered from archaeological sites. Computer image enhancement can increase clarity and computer image analysis can help to objectively distinguish increments, ascertain their number, and determine the nature of the outermost increment. The method is applied to modern mountain gazelle (Gazella gazella) teeth of known month of death from Israel and to prehistoric specimens from Hayonim Cave, Israel.

Fundamental ambiguities in the interpretation of brain/body allometric trends can only be resolved by analyzing relationships between ontogenetic brain/body growth processes in different groups. The ambiguous concept of adult encephalization confuses at least three distinct types of transformation of a common mammalian growth curve: scalar magnification, total curve didplacement, and changes in proportions of the pre- and postnatal phases of the curve. The conservative ratio between pre- and postnatal growth phases determines the apparent linearity of comparative brain/body allometry and can be explained by assuming that embyological neurogenetic processes ultimately determine both target brain and body size—the first directly and the second indirectly via neurohormonal regulation of somatic growth. Uneven taxonomic distribution of different ontogenetic growth patterns may explain many differences in the allometric trends at different taxonomic levels of analysis. The human brain grows exactly as if it was in a giant ape body; however, because of decoupled growth in different brain regions, it regulates body growth as though it were the size of a chimpanzee brain. Human encephalization exhibits an ontogenetic transformation not found in other mammalian groups.

The investigation of the neural basis and evolution of language abilities is best pursued as a search for language adaptations rather than as a search for the language faculty. The species uniqueness of language functions is contrasted with the conserved homologies linking human brain structures to anthropoid primate brain structures, and the failure to find species-specific neuroanatomical or genetic correlates of linguistically defined innate features of language (e.g., universal grammar). Comparisons to animal call systems demonstrate minimal anatomical overlap with language systems besides final output nuclei though molos control parallels, the anatomical substrates of gestural behavior, suggesting that language evolution did not proceed by progressive elaboration from nonhuman vocal communication. Although there are no unambiguus gross neuroanatomical dishomologies distinguishing human brains that would suggest a role in language processing, there are clear allometric deviations of quantitative traits, including both gross brain size and deviant scaling of internal structural relationships in human brains, that suggest plausible roles in language processing. Evidence of correlated changes in patterns of axonal connections also implicate the extensive allometric deviations of human brains with language adaptations. One of the most likely correlates of allometrically related connection change related to language evolution involves the existence of direct cortical projections to the nucleus ambiguous (the laryngeal control nucleus of the brainstem), which are likely absent in other mammals. This enables humans to have articulate control over the visceromotor lung and larynx control systems and to couple this with articulate control of the skeletal motor tongue, facial, and jaw muscles. Tracer studies and physiological recording studies of the macaque monkey ventral premotor and prefrontal cortex provide evidence of extensive homology of connectivity, suggesting that the circuits associated with these cortical areas were recruited for language processing during human evolution. Also, cells in adjacent macaque premotor cortex differentially fire with respect to self-initiated and other-initiated grasping behaviors. This suggests that the human homologue to this or nearby areas might be relevant to the mimicry necessary to acquire language. Genetic studies of human language adaptations have identified a gene, FOXP2, that is damaged in an inherited language deficit that affects automatizion of speech and syntactic processes. It turns out to be a highly conserved gene regulating forebrain basal ganglia development in embryogenesis. The human version of the gene contains two unique point mutations, neither of which is implicated in the language disorder. The functional differences produced by these changes are not known, but appear to have spread quickly in the early human population. The homologues to this gene in other species also play roles in vocal behavior. This genetic change is probably only one of a great many that contribute to the adaptation for language. These sources of comparative functional and anatomical information argue against saltationist scenarios that hypothesize a sudden recent appearance of language abilities, and instead suggest that many diverse adaptations converged to make language possible.

Embryonic neurons transplanted to the adult CNS extend axons only for a developmentally defined period. There are certain intercellular factors that control the axonal extension, one of which may be the expression of the bcl-2 protein. In this study, rats with complete striatal dopamine fiber denervation received embryonic day 14 mouse ventral mesencephalon cells overexpressing human bcl-2 or control wild-type ventral mesencephalon cells. All rats were treated with cyclosporine to prevent rejection and the surviving grafts were analyzed for cell survival and outgrowth of dopaminergic fibers. The results demonstrate that bcl-2 overexpression does not enhance neuronal graft survival. However, the bcl-2 overexpressing neurons had a higher number of dopaminergic fibers that grew longer distances. These results show that overexpression of bcl-2 can result in longer distance axonal growth of transplanted fetal dopaminergic neurons and that genetic modification of embryonic donor cells may enhance their ability to reinnervate a neuronal target territory.

Our understanding of speech and language disorders may be aided by information about the constraints and predispositions contributed by neural developmental processes. As soon as we begin to look at human neuroanatomy and development from a comparative perspective, it is possible to recognize a number of ways that human brains diverge from the general pattern of other ape and monkey brains. These divergences may offer clues to language evolution. Large-scale quantitative changes in the relative proportions of brain regions (as opposed to just overall expansion) offer some of the most obvious clues. Additional information about how axons are guided in their extensions to distant developmental targets and how competitive trophic processes sculpt these connections also provides a way to understand how gross quantitative changes in cell numbers could affect circuit organization and ultimately behavior.

The anatomical specificity of axon growth from fetal pig septal xenografts was studied by transplanting septal cells from E30–35 pig fetuses into cholinergic deafferented (192-IgG-saporin-infused) rats or into aged rats (> 18 months). Cell suspensions (100,000 cells/μl) were injected bilaterally into the dorsal and ventral hippocampus of immunosuppresed rats (10 mg/kg/day cyclosporine A). To assess axonal growth and synapse formation, acetylcholinesterase histochemistry, an antibody to choline acetyltransferase (ChAT), and three pig-positive/rat-negative antibodies: bovine 70kD neurofilament (NF70), human low-affinity NGF receptor (hNGFr), and human synaptobrevin (hSB) were used. In rats with surviving grafts at 6 months, NF70 axonal labeling was more extensive than either ChAT or hNGFr labeling. All three markers demonstrated graft axons extending selectively through the hippocampal CA fields and the molecular layer of the dentate gyrus. Graft axons did not extend into adjacent entorhinal cortex or neocortex. The distribution of pig hSB-positive synapses correlated with AChE-positive fiber outgrowth in to the host. Electron microscopic analysis of hSB-immunostained hippocampal sections revealed pig presynaptic terminals in contact with normal rat postsynaptic structures in the CA fields and the dentate gyrus. These data demonstrate target-appropriate growth of pig cholinergic axons and the formation of cross-species synapses in the deafferented or aged rat hippocampus.

Publisher Summary This chapter provides an overview of neural xenotransplantation—transplantation of fetal neuroblasts derived from homologous neural structures of a different (mammalian) species into the adult brain. Although evidence is accumulating in favor of the therapeutic potential of allogeneic neural transplantation in Parkinson's (and Huntington's) disease, the limited availability of human fetal neural tissue may pose serious limitations on clinical application of this potential treatment modality. The most optimal clinical situation would be a treatment that would make the graft acceptable and nonrejectable, currently all the studies suggest that it is only with cyclosporine and combinations of systemic immune suppression by which sufficient immunosuppressive effects are achieved. Moreover, the xenografts are rejected upon withdrawal of the immunosuppression. The current need for systemic cyclosporine (CsA) immunosuppression for extended xenotransplant survival highlights the need for more research into alternative immunological strategies to prevent neural transplant rejection. The single greatest risk factor for the patients in neural cell xenotransplantation is a rejection of the implanted cells. The second major risk factor is side effects from immunosuppressive treatments, such as cyclosporine.

In order to assess the potential of embryonic stem cells to undergo neuronal differentiation in vivo, totipotent stem cells from mouse blastocysts (D3 and E14TG2a; previously expanded in the presence of leukemia inhibitory factor) were transplanted, with or without retinoic acid pretreatment, into adult mouse brain, adult lesioned rat brain, and into the mouse kidney capsule. Intracerebral grafts survived in 61% of cyclosporine immunosuppressed rats and 100% of mouse hosts, exhibited variable size and morphology, and both intracerebral and kidney capsule grafts developed large numbers of cells exhibiting neuronal morphology and immunoreactivity for neurofilament, neuron-specific enolase, tyrosine hydroxylase (TH), 5-hydroxytryptamine (5-HT), and cells immunoreactive for glial fibrillary acidic protein. Though graft size and histology were variable, typical grafts of 5-10 mm3 contained 10-20,000 TH+ neurons, whereas dopamine-beta-hydroxylase+ cells were rare. Most grafts also included nonneuronal regions. In intracerebral grafts, large numbers of astrocytes immunoreactive for glial fibrillary acidic protein were present. Both TH+ and 5-HT+ axons from intracerebral grafts grew into regions of the dopamine-lesioned host striatum. TH+ axons grew preferentially into striatal gray matter, while 5-HT+ axons showed no white/gray matter preference. These findings demonstrate that transplantation to the brain or kidney capsule can induce a significant fraction of totipotent embryonic stem cells to become putative dopaminergic or serotonergic neurons and that when transplanted to the brain these neurons are capable of innervating the adult host striatum.

Basic research using cell transplantation indicates that structural developmental mechanisms seen in immature brains can also function in the adult brain. As the brain matures, cellular migration and axonal growth is impeded. However, fetal neural transplantation studies have shown that directional cues are available for fetal axons to find specific host neurons in the adult brain. By reaching specific and distant CNS target zones, donor tissue with extended axonal growth periods demonstrate both an abundance and specificity of CNS neurotropic signals. The presence of specific guidance cues, despite strong inhibition of regenerative long-distance axonal growth, suggests that these cues play other physiological roles in the adult CNS, and could be utilized therapeutically for reconnection of neuronal pathways.

In order to determine whether the lateral ganglionic eminence (LGE) of the fetal telencephalon is the primary source of striatal precursors in striatal transplants and tissue cultures, cells derived exclusively from the LGE of fetal rat brains were transplanted into the quinolinic-acid-lesioned striatum of adult rats. After 2-3 months they produced grafts that were almost entirely AChE-positive as well as DARPP-32-, TH-, and calbindin-immunoreactive. The grafts were integrated into the host striatum so that host corticofugal fiber tracts interdigitated with graft tissues similar to the way they penetrate the gray matter of the normal striatum. Fast Blue dye injected into the ipsilateral globus pallidus of LGE grafted produced retrogradely labeled neurons within the grafts, but Fluorogold dye injected into the ipsilateral substantia nigra did not. In a separate experiment using DARPP-32-immunohistochemstry as a striatal marker, fetal (E16) and neonatal (P2) rat brains showed DARPP-32 immunoreactivity in the LGE but not in the adjacent medial ganglionic eminence (MGE). In summary, both fetal LGE cells and LGE grafts express specific striatal markers, and LGE grafts integrate into the host striatum and innervate the major striatal efferent target within the host brain. These data suggest that the LGE is the origin of cells committed to striatal phenotypes in the developing brain.

Porcine fetal lateral ganglionic eminence cells were transplanted into the quinolinic-acid-lesioned corpus striatum of immunosuppressed adult rats. The resulting grafts were analyzed for graft development with respect to donor age, donor cell dosage, and survival time from 5 to 22 weeks postimplantation. Graft development is prolonged by a factor of 3-4 times in porcine xenografts as compared to rat allografts. As grafts matured, neuronal somata developed in clusters that expressed acetylcholinesterase (AChE), tyrosine hydroxylase, and dopamine- and cAMP-associated phosphoprotein. These clusters were interspersed with AChE-poor graft regions consisting of small densely packed cells that stained for glial fibrillary acidic protein and porcine cluster of differentiation factor 44 (a species-specific glial marker). Graft axons could be selectively stained for 70-kDa neurofilament and were preferentially associated with ACHE-poor, glial-rich regions in younger grafts (8 weeks), but AChE-rich neuronal regions in older grafts (22 weeks). Both graft axons and graft glial fibers projected for long distances into the host internal capsule, external capsule, corpus callosum, and anterior commissure. Donor axons also innervated host target structures including the globus pallidus and substantia nigra. This demonstrates a prolonged development of striatal cells that is appropriate to the donor species and which produces long-distance target-specific axonal growth within the adult host brain.

Fetal striatal grafts are found to have a modular organization revealed by acetylcholinesterase (AChE) histochemistry. The AChE-rich zones represent the only portions of these grafts that are anatomically and functionally integrated into the host brain. In this study, the medial and lateral ganglionic eminences (MGEs and LGEs) were selectively dissected from the basal telencephalon of embryonic-day-14 (E14) rat fetuses to compare their relative contributions to the AChE-rich fraction of intrastriatal grafts. Separate cell suspensions prepared from either eminence were stereotaxically implanted into excitotoxically lesioned neostriatum of adult rats. Eight weeks after transplantation, grafts of the MGE were compared with those of the LGE with respect to the proportion of AChE-rich zones, graft size, graft morphology, and afferent dopaminergic innervation as revealed by tyrosine hydroxylase (TH) immunostaining. The mean AChE-rich fraction in LGE grafts (87% +/- 4%) was markedly greater than the AChE-rich fraction in MGE grafts (25% +/- 10%). The LGE grafts were also morphologically better incorporated into the lesioned host striatum, partially reconstituting the striatal morphology. There was no statistically significant difference in graft size between the two groups. The AChE-rich LGE grafts were TH immunoreactive, whereas the AChE-poor MGE grafts were not. We conclude that grafts derived exclusively from the fetal LGE reconstitute the striatal morphology and consist almost entirely of AChE-rich zones.

The movements of the tongue in feeding and vocalization are enabled by a complex system of interdigitated muscle fibers in the tongue body. Because of this complexity, the detailed anatomical connections between individual intrinsic tongue muscles and corresponding motoneurons in the hypoglossal nucleus have not been described for any mammal. In this study we describe the distribution of retrogradely labeled neurons in the hypoglossal nucleus, following injections of wheat-germ agglutinin-horseradish peroxidase into different regions of the tongue of 21 cynomolgus monkeys. These experiments demonstrate a spatial organization of hypoglossal motoneurons that reflects the anatomical and functional organization of tongue body muscles: motoneurons innervating the transversus and verticalis muscles are located in medial hypoglossal nucleus regions, motoneurons innervating the genioglossus are located in intermediate hypoglossal nucleus regions, motoneurons innervating the hyoglossus and inferior longitudinalis are located in ventrolateral hypoglossal nucleus regions, and motoneurons innervating the styloglossus and superior longitudinalis are located in dorsolateral hypoglossal nucleus regions. Motoneurons innervating the suprahyoid muscle, the geniohyoid, are situated in a cell column separated ventrally from the main body of the hypoglossal nucleus. Motoneurons innervating the palatoglossus are located in the nucleus ambiguus and, possibly, in dorsolateral hypoglossal nucleus regions. Motoneurons of the medial divisions of the hypoglossal nucleus innervate tongue muscles that are oriented in planes transverse to the long axis of the tongue whereas motoneurons of the lateral divisions innervate tongue muscles that are oriented parallel to this axis. These results suggest that the segregation of motoneurons corresponds to the functional distinction between tongue protrusion and retrusion.

Injections of the retrograde/anterograde tracers Wheat Germ Agglutinin-Horseradish peroxidase (WGA-HRP) into the cortex along the banks of the inferior limb of the arcuate sulcus in the cortex of 4 macaque monkeys (Macaca fascicularis) were used to investigate its c corticocortical connections. All injections produced transported label within the sulcus principalis, the ventral lateral prefrontal cortex, the anterior cingulate sulcus and the dorsal insular cortex. The distribution of label within each of these areas differed slightly depending on the injection site. Injections along the caudal bank of the inferior arcuate sulcus label premotor, supplementary motor, and precentral motor areas but produce relatively sparse prefrontal labeling. Posteriorly label is transported to the inferior parietal cortex and the dorsal opercular bank of the Sylvian fissure. Injections along the rostral bank of the sulcus do not label motor areas but produce labeling in dorsal, lateral and orbital prefrontal areas, and in cortex along the ventral bank of the superior branch of the arcuate sulcus. Posteriorly label is transported to cortical areas in the superior temporal gyrus including the dorsal bank of the superior temporal sulcus. The more dorsal rostral bank injection produced both superior temporal and some sparse inferior parietal labeling and the more ventral rostral bank injection produced extensive superior temporal labeling but no parietal labeling. No labeling was ever seen in cortex ventral to the fundus of the superior temporal sulcus. Although other auditory recipient prefrontal areas have been reported, this is the first demonstration of a region chiefly devoted to auditory connections within the ventral frontal cortex. Its adjacency to areas associated with vocal muscle movement, and its connections to midline cortical areas associated with vocal functions in both primates and humans may provide important clues to the organization of Broca's language area.

There are significant structural and functional differences between primate calls and human speech. In addition, these two forms of vocal communication appear to largely depend on nonhomologous brain structures. However, an analysis of the underlying axonal circuitry of these brain systems suggests that there are significant interrelationships between them, both in functional and in evolutionary terms. Based on both primate neuroanatomical studies and humanin vivo mapping studies it is argued that the ventral prefrontal area is the critical link, both functionally and anatomically between these distinct vocal systems. A model of human brain evolution with respect to language is proposed in which limbic-midbrain vocalization circuits became progressively subordinated to the activity of prefrontal-midbrain and frontalmotor circuits for regulating facial gesture, skilled oral food manipulation, and conditional association learning. Quantitative and developmental data are used to suggest that this resulted from the relative enlargement of prefrontal areas and the consequences this has on the relative proportions of different corticomidbrain and diencephalic-midbrain projections. Although humans exhibit a significantly reduced call repertoire, it is argued that the display-vocalization circuits that play the central role in all other primate communication have neither been eliminated, supplanted nor suppressed by language systems. They have instead become integrated into the more distributed language circuits and play a ubiquitous though subordinate role in all normal language processes.

Connections of the perirhinal cortex in the.rat brain were studied using anterograde (3H-proline/leucine) and retrograde (horseradish peroxidase) tracers. The perirhinal cortex receives major projections from medial precen-tral, anterior cingulate, prelimbic, ventral lateral orbital, ventral and posterior agranular insular, temporal, superior and granular parietal, lateral occipital, agranular retrosplenial, and ectorhinal cortices, and from the pre-subiculum, subiculum, and diagonal band of Broca. Rostral neocortical areas project predominantly to rostral perirhinal regions while more caudal neocortical and subicular areas project predominantly to caudal perirhinal regions. Terminal fields are further segregated within perirhinal cortex to either the dorsal or ventral banks of the rhinal sulcus. All afferents from frontal areas terminate predominantly in the deep layers of its ventral bank; afferents from temporal, parietal, and lateral occipital areas terminate predominantly in the deep and superficial layers along its dorsal bank; and afferents from ectorhinal cortex terminate in a column within its dorsal bank. Cortical cells which project to perirhinal areas are found predominantly in layer II and the superficial part of layer III. However, ventrolateral orbital, parietal, and lateral occipital cortex projections originate predominantly from layer V. Perirhinal areas also receive afferents from the nucleus reuniens of the thalamus, lateral nucleus of the amygdala, claustrum, supramammillary nuclei, and the dorsal raphe nuclei.

The unusually large size of the human brain with respect to the human body as compared to other mammals is a dominating fact in the study of human evolution. No account of the similarities and differences between human and other primate brains is complete without accounting for this quantitative fact. The intuitive correlation between this statistic, encephalization, and the seemingly astronomical gulf between human and non-human intellectual capabilities has led many to argue that this disproportionate size in itself reflects the fundamental adaptation in human brain evolution (Dubois, 1898; 1924; von Bonin, 1952; Jerison, 1973; Van Valen, 1974; Gould, 1975, Passingham, 1975a).

The distribution of motoneurons innervating the primary depressor and elevator muscles of the wing of the domestic pigeon (Columba livia) was studied by using the retrograde axonal tracer lectin-conjugated horseradish peroxidase (WGA-HRP). Injection of WGA-HRP into the pectoralis (pars thoracicus) labeled neurons in the ventromedial corner of the lateral motor column of the spinal cord. These neurons were arranged in a column extending from spinal segment X or XI to spinal segment XII or XIII. The pectoralis, the primary depressor muscle of the wing, consists of two parts which are anatomically and functionally distinct, the sternobrachialis (SB) and thoracobrachialis (TB). Injection into the SB labeled neurons in the rostral and middle regions of the pectoralis motoneuron column. In contrast, injection into the TB labeled neurons in the middle and caudal regions of the pectoralis motoneuron column. Injection into the primary elevator muscle of the wing, the supracoracoideus, labeled neurons in the lateral motor column in spinal segments X and XI. These motoneurons were located dorsolateral to motoneurons labeled following pectoralis injection. These data demonstrate musculotopic segregation of the motoneurons innervating the primary flight muscles in the pigeon and, further, illustrate that the SB and TB subregions of the pectoralis are innervated by discrete aggregations of motoneurons.

The concentration of norepinephrine (NE) in the neocortex of the mouse has been determined radioenzymatically from the thirteenth embryonic (E13) through the sixtieth postnatal (P60) days. Detectable levels of the transmitter are present on E14, coincident with the emergence of the cortical plate. NE concentrations increase rapidly thereafter to reach a level 57% of adult values by P4. Subsequently, through P8 there is a decline followed again by a more gradual rise to maximum, or adult, concentrations by P30.

The investigation of the neural basis for human language abilities has principally proceeded in neuropsychological and neurosurgical contexts with the study of brain damaged patients exhibiting aphasia, patients undergoing electrical stimulation mapping during neurosurgical procedures, and through the recent use of new in vivo imaging techniques of the working conscious brain. As powerful and illuminating as these approaches have been, there are still major gaps in our understanding of language systems of the brain and as yet no comprehensive model of language processing. One of the most serious gaps is the lack of circuit information regarding the neural connections of brain areas involved in linguistic processes. And despite the enormous progress in developing animal models for many other brain functions the uniqueness of linguistic abilities and uncertainties about their neural substrates have seemingly provided little hope of useful non-human models of language processes. However, more complete connectional data and informative non-human models are potentially available through a broader understanding of neuroanatomical homologies.