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Presentation of Case First admission. A sixty-one-year-old man was admitted to the hospital because of weakness of the arm and leg. For many years he had had hypertension; with guanethidine and hyd...

CAUDAL dysplasia, also known as sacrococcygeal agenesis or the caudal regression syndrome, is a congenital malformation characterized by varying degrees of developmental failure involving the lower lumbar, sacral, and coccygeal vertebrae, and the corresponding segments of the spinal cord. Patients so afflicted have neurological abnormalities that range in severity from mild impairment of bladder control to total motor and sensory paralysis below the level of the defect. This combination of anomalies was first clearly described by Hohl 1 in 1852, and since then more than 150 cases have been reported. 2 These reports have served to bring out clearly the distinctive anatomical changes and the clinical features of the disorder, but the neuropathological aspects have never been fully delineated. In the case to be presented here, we have had the opportunity of carrying out a more extensive neuropathological study than has been reported up

The general health status with particular reference to cardiovascular disease and serum lipids has been evaluated in a sample of Pygmies of the Ituri Forest. Malaria, filariasis, treponemal infection, and other diseases were found to be common. The Pygmy blood pressures were not greatly different from the blood pressures observed in studies of Americans. Functional heart murmurs were common. Instances of aortic valve incompetence, essential hypertension, and coarction of the aorta were found. Abnormal electrocardiograms were encountered at about the same frequency as has been reported in population studies in the United States but the repolarization abnormalities observed were more frequent and resembled those previously reported from South Africa. No electrocardiogram definitely diagnostic of myocardial infarction was found, but without anatomical studies the presence of coronary artery disease cannot be excluded. Very low serum cholesterol values were found and this finding is discussed in relationship to the Pygmies' diet, physical activity and coexistant disease.

Summary A biological warm stage has been constructed which controls and measures the temperature of a special electrically-coated and transparent glass plate by means of a two-thermistor-beaded probe and auxiliary apparatus. The stage can also be used to control the temperature of media while under the microscope. Because of its sensitivity and versatility, the warm stage has unlimited possibilities for application in the field of biology.

Missense mutations in two related genes, termed presenilin 1 (PS1) and presenilin 2 (PS2), cause dementia in a subset of early-onset familial Alzheimer's disease (FAD) pedigrees. In a variety of experimental in vitro and in vivo settings, FAD-linked presenilin variants influence the processing of the amyloid precursor protein (APP), leading to elevated levels of the highly fibrillogenic Aβ1–42 peptides that are preferentially deposited in the brains of Alzheimer Disease (AD) patients. In this report, we demonstrate that transgenic animals that coexpress an FAD-linked human PS1 variant (A246E) and a chimeric mouse/human APP harboring mutations linked to Swedish FAD kindreds (APP swe) develop numerous amyloid deposits much earlier than age-matched mice expressing APP swe and wild-type Hu PS1 or APP swe alone. These results provide evidence for the view that one pathogenic mechanism by which FAD-linked mutant PS1 causes AD is to accelerate the rate of β-amyloid deposition in brain.

The neurotoxin tetanospasmin causes tetanus when it reaches the central nervous system. In this autoradiographic study, 125-I-labeled tetanospasmin was injected into the leg muscles of rodents, and the nerves supplying these muscles were crushed. The labeled toxin accumulated within axons on the distal side of the crush. This study provides direct evidence for retrograde axonal transport of a macromolecular toxin that acts at synapses in the central nervous system.

Alzheimer's disease is a progressive degenerative disease of the nervous system characterized neuropathologically by the presence of senile plaques and neurofibrillary tangles in amygdala, hippocampus and neocortex. Dysfunction and death of basal forebrain cholinergic neurones projecting to forebrain targets are associated with marked decreases in cholinergic markers, including the activity of choline acetyltransferase (ChAT). Although cortical levels of somatostatin and somatostatin receptors are reduced in Alzheimer's, no consistent changes have been reported in other neuropeptide systems. We have now examined in control and Alzheimer's brain tissues pre- and postsynaptic markers of corticotropin-releasing factor (CRF), a hypothalamic peptide regulating pituitary-adrenocortical secretion which also seems to act as a neurotransmitter in the central nervous system (CNS). We have found that in Alzheimer's, the concentrations of CRF-like immunoreactivity (CRF-IR) are reduced and that there are reciprocal increases in CRF receptor binding in affected cortical areas. These changes are significantly correlated with decrements in ChAT activity. Our results strongly support a neurotransmitter role for CRF in brain and demonstrate, for the first time, a modulation of CNS CRF receptors associated with altered CRF content. These observations further suggest a possible role for CRF in the pathophysiology of the dementia. Future therapies directed at increasing CRF levels in brain may prove useful for treatment.

Although several studies of Alzheimer's disease suggest that the frequency of neuritic plaques in the cerebral cortex is correlated with the severity of dementia and with reduction in presynaptic cholinergic markers in the cortex, the relationship between cholinergic cortical innervation and the pathogenesis of plaques is unknown. The hypothesis was tested that the neurites in the plaque consist, in part, of presynaptic cholinergic axons, many of which arise from neurons in the basal forebrain. This hypothesis was tested by analyzing the character and distribution of plaques in monkeys, aged 4 to 31 years, with staining for acetylcholin-esterase and also with Congo red and silver stains. Immature and mature plaques were rich in acetylcholinesterase. As the plaques matured, the amount of amyloid increased, and the number of neurites and the activity of acetylcholinesterase decreased. End-stage amyloid-rich plaques lacked acetylcholinesterase. These observations indicate that changes in cortical cholinergic innervation are an important feature in the pathogenesis and evolution of the neuritic plaque.

Exposure to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) reproduces certain clinical, pathological, and neurochemical features of Parkinson's disease. MPTP is metabolized by monoamine oxidase Type B to 1-methyl-4-phenylpyridine (MPP+), which is selectively accumulated by high-affinity uptake mechanisms into dopaminergic neurons. Lyden et al. described low-affinity binding of MPTP to synthetic and retinal melanin. We showed that MPP+ binds to neuromelanin with high affinity, suggesting that in MPTP neurotoxicity, MPP+ enters nigral neurons by the dopamine uptake system and binds to neuromelanin, which serves as a depot, continuously releasing MPP+ until it destroys the cells. This model predicts that agents which compete with MPP+ binding to neuromelanin should partially protect the dopamine neurons from MPTP-induced toxicity. The most potent identified competitor for MPP+ binding to melanin is the antimalarial drug chloroquine, which has a high affinity for melanins. In the present study, chloroquine, administered to monkeys in conventional anti-malarial doses before MPTP, protects them from MPTP-induced parkinsonian motor abnormalities, dopamine depletion in the striatum, and neuropathological changes in the substantia nigra.

Alzheimer's disease, Parkinson's disease, and progressive supranuclear palsy are all characterized by loss of neurons in the basal forebrain cholinergic system and by associated reductions in cortical presynaptic cholinergic markers, such as choline acetyltransferase. In this report, we identify that a major cortical receptor alteration in these disorders is a reduction in nicotinic receptors measured using both tritiated acetylcholine and levorotatory tritiated nicotine binding.

A patient had adversive seizures accompanied by unilateral pupillary dilatation. Neuropathologic examination showed a contusion involving the middle frontal gyrus contralateral to the pupil that dilated during the seizure. The clinical features and the location of this lesion (presumably the epileptogenic focus) correlate well with experimental studies in which pupillary changes have been observed during stimulation of the cerebral cortex. Unilateral mydriasis associated with contraversion of the eyes during seizures may have value in localizing epileptogenic foci.

Dementias occurring in Alzheimer9s disease, Parkinson9s disease, and progressive supranuclear palsy are associated with dysfunction and death of neurons in a variety of cell populations, including cholinergic, monoaminergic, and peptidergic systems. In the present investigation of these three disorders, we demonstrated decreased levels of corticotropin releasing factor (CRF)-like immunoreactivity in the frontal, temporal, and occipital poles of the neocortex. Moreover, reductions in peptidergic immunoreactivity correlated with reductions in the activity of choline acetyltransferase, the enzyme that catalyzes the formation of acetylcholine. The reduction in cortical CRF levels may be due to abnormalities of intrinsic cortical neurons or to dysfunction in neurons that contain CRF and innervate cortex.

Senile plaques are composed of neurites (enlarged axons, nerve terminals, and, possibly, dendrites) associated with focal deposits of amyloid. Plaques are present in small numbers in the amygdala, hippocampus, and neocortex in elderly primates and are abundant in these regions in individuals with Alzheimer’s disease. Aged macaques provide a model for investigations of plaques. One of the earliest abnormalities identified in these older animals is multifocal enlargement of individual axons within the cortex. Later, enlarged neurites appear in clusters (neurite plaques); in mixed plaques, neurites are associated with amyloid. In the oldest animals, many plaques show relatively greater proportions of amyloid. These observations are interpreted to indicate that axonal pathology is an early event and that plaques evolve from the neurite type to the amyloid type. Using antibody probes, we have identified abnormal axons and neurites derived from cholinergic, monoaminergic, and peptidergic systems. These axons and neurites also show accumulations of cytoskeletal antigens, including neurofilament peptides. Similarly, in human tissues, these approaches have identified abnormalities of the cytoskeleton and demonstrated a variety of transmitter-specific antigens in plaques.

The mechanism of action of botulinum toxin was analyzed by the use of calcium ionophores and black widow spider venom. Addition of calcium ionophores to nerve-muscle preparations blocked by botulinum toxin did not increase the frequency of miniature end plate potentials. However, the spider venom elicited a barrage of miniature end plate potentials after blockade by botulinum. Electron micrographs of preparations treated with botulinum toxin and then the spider venom revealed clumping of synaptic vesicles at release sites in the otherwise depleted nerve terminals. These findings indicate that the action of botulinum toxin is not due to deficient storage of acetylcholine in vesicles or blockade of calcium entry into nerve terminals. They suggest that the toxin interferes with the acetylcholine release process itself, possibly by blocking exocytosis at the release sites.

The total population of muscarinic receptors and a subpopulation of muscarinic receptors with high affinity for agonists were measured with [3H]quinuclidinyl benzilate and [3H]acetylcholine, respectively, in homogenates of cerebral cortex from control and Alzheimer's disease brains. No significant differences between control and Alzheimer's diseased cortex were found in either the total population of receptors or the subpopulation with high affinity for agonists in either the frontal or temporal poles. Nicotinic cholinergic receptors labeled by [3H]acetylcholine were measured in homogenates and by autoradiography in the same brain areas. In contrast to muscarinic sites, binding to nicotinic sites was markedly decreased in Alzheimer's disease cortex. Autoradiography of [3H]acetylcholine binding to nicotinic sites indicated that in control cortex these sites are more concentrated in laminae IV-VI than in the superficial laminae, and that in Alzheimer's disease there is loss of these sites in all cortical laminae.

In this study, tetanus toxin was microinjected into the ventral horn of the spinal cord of rats, producing local tetanus. The toxin was localized by immunocytochemical methods. Reaction product was visualized within synaptic terminals, particularly those on the soma and dendrites of motor neurons. The distribution of staining terminals was similar to that of labeled synapses, visualized by autoradiography, after microinjection of either [125I]tetanus toxin or [3H]glycine, the latter a major inhibitor transmitter in the spinal cord.

Chronic communicating hydrocephalus was produced in adult dogs by injection of silastic into the subarachnoid space. Electron microscopy was used to verify the sequence of pathologic changes in the ventricular wall. The pathologic findings were correlated with cisternographic images and measurements of cerebrospinal fluid (CSF) pressure. Early in hydrocephalus, the CSF pressure was increased and cisternograms showed ventricular entry and clearing; the ependyma was stretched and fluid accumulated in subependymal regions. In animals with chronic hydrocephalus, the CSF pressure was normal and cisternograms disclosed radioactivity persisting in the ventricles. At this time the ependyma was severely damaged, the subependymal white matter showed enlargement of the extracellular space, and degenerative changes were present in axons and myelin sheaths.

In immunocytochemical studies, a polyclonal antiserotonin antibody was used to visualize fibers within the cingulate cortex of young and aged rhesus monkeys. Intricate and distinct patterns of serotoninergic processes were seen in anterior and posterior segments of cingulate cortex (Brodmann areas 24 and 23). In these regions of cortex, many multivaricose serotonin-immunoreactive axonal swellings were identified, and some of these immunostained neurites were associated with deposits of amyloid. These observations suggest that serotoninergic processes are involved in the formation of senile plaques in neocortex of aged macaques.

Biochemical markers for serotoninegic and catecholaminergic neurons in frontal and temporal poles were examined post mortem in brains of patients with Alzheimer's disease, Parkinson's disease, and the two combined. Binding of [3H]citalopram to serotoninergic uptake sites and levels of serotonin were Decemberreased by 40 to 50% in brains of persons in each disease category. In contrast, significant reductions of catecholaminergic markers were not detected. In all three disease groups, the choline acetyltransferase activity was reduced by 50 to 60%. Binding sites for adenosine (A1), muscarinic cholinergic, phencyclidine, β-adrenergic, and calcium antagonist receptors were unchanged. We conclude that substantial damage to serotoninergic neurons occurs in persons with Parkinson's and Alzheimer's diseases.

The present study examines levels of neurotransmitter messenger RNA (mRNA) at various stages after crush of postganglionic nerves in the superior cervical ganglia. Using complementary DNA (cDNA) probes, we demonstrated a reduction in ganglionic mRNA levels for tyrosine hydroxylase (TH) after axotomy. Concomitantly, actin and tubulin mRNA levels in ganglia were increased. Thus, in neurons of sympathetic ganglia, axotomy appears to be associated with a selective reduction in levels of TH mRNA, and, in turn, alters levels of protein and enzyme activities.

beta, beta'-Iminodipropionitrile (IDPN) produces neurofilamentous giant axonal swellings in proximal internodes of large myelinated axons. Secondary demyelinative changes result from the production of these axonal enlargements. Electrophysiological studies have demonstrated profound alterations in the electrical properties of motor neurons (MN) within the spinal cord. On the basis of intracellular recordings, it has been suggested that electrical contacts may exist between swollen axons and neighboring MN. In addition, the possibility remained that synaptic contacts develop on demyelinated axonal swellings. In the present study, we report the lack of either synapses on demyelinated axonal swellings or direct electrical contacts between neighboring MN. Axonal swellings are surrounded by attenuated processes of glial cells (probably fibrillary astrocytes), a finding discussed in terms of its possible role in the production of ephaptic transmission. There was considerable variation in the degree of axonal enlargements and in the extent of secondary (passive and active) demyelination. It is suggested that these morphological changes may represent structural correlates of some electrophysiological alterations observed in IDPN neuropathy.

Corticotropin-releasing hormone-like immunoreactivity (CRH-IR) was measured in control and Huntington's disease brain tissues obtained postmortem. The concentration of CRH-IR was markedly decreased in the caudate/putamen in Huntington's disease; the concentration of somatostatin-like immunoreactivity measured in the same extracts was significantly increased in the caudate/putamen in Huntington's disease compared with the control group. In contrast to previously reported decreases in CRH-IR in the cerebral cortex in Alzheimer's disease, Parkinson's disease and progressive supranuclear palsy, no significant differences were observed in the concentrations of CRH-IR between controls and Huntington's disease in frontal, parietal, temporal, occipital and cingulate cortex and in globus pallidus.

Cytoskeletal proteins have a characteristic distribution within neurons when immunocytochemical techniques are used on conventional paraffin sections. For example, phosphorylated neurofilaments are located within axons but are not normally present in the majority of perikarya of the central nervous system. This pattern can be altered in disease, and neurofilaments that accumulate within perikarya can be phosphorylated inappropriately. To determine whether retained neurofilaments were phosphorylated inappropriately, we used immunocytochemical techniques to examine several diseases in animals in which neurofilaments accumulate within neuronal perikarya. Our investigations of diseases with disparate etiologies show that, whenever neurofilaments are retained within the neuronal perikarya, they are phosphorylated. These results suggest that phosphorylation of neurofilaments in an inappropriate location, i.e. perikarya, may be a nonspecific disease-related response of neurons that can be initiated by a variety of cellular injuries.

Canine Inherited Ataxia (CIA) is an autosomal recessive cerebellar disease of Gordon Setters associated with degeneration of Purkinje and granule cells. To define specific biochemical correlates of neuronal loss, synaptic neurochemical parameters were measured in three cerebellar regions (vermis, "pars intermedia," and hemisphere) at early and late stages of this disease. At one and a half years of age, affected dogs showed the most severe lesions in the "pars intermedia," with a 39% decrease in the number of Purkinje cells and a 29% decrease in granule cells. Neurochemical measurements demonstrated decreased [3H]muscimol binding and elevations in norepinephrine concentration (248% above control) and [3H]glutamate receptor binding (118% above control). At five years of age, reduction of Purkinje cells in the three cerebellar regions ranged from 65 to 91% while loss of granule cells was between 13 and 53%. [3H]Muscimol binding remained low throughout the cerebellum (38 to 59% of control) and norepinephrine concentration and [3H]glutamate binding were markedly reduced from the levels observed at one and a half years. Glutamate decarboxylase activity, [3H]QNB binding and GABA concentration were relatively unaffected. Our results indicate that neurochemical parameters associated with cerebellar neuronal systems demonstrate specific alterations in a chronic degenerative disorder. This study also indicates the importance of evaluating neurochemical measurements with regard to both spared and degenerating neuronal systems and emphasizes the role of compensatory neurochemical alterations in cerebellar degenerative disorders.

One of the most striking manifestations of Down's syndrome is profound mental retardation. Furthermore, after 35 years of age, many patients with Down's syndrome develop clinical and pathological features of Alzheimer's disease. Since brains of patients with Alzheimer's disease show significant loss of neurons in the nucleus basalis of Meynert (nbM), we sought to establish normal standards of nbM neurons in persons with Down's syndrome and to determine whether reductions in the number of neurons occur with increasing age. The number and size of neurons in the nbM were measured in selected sagittal sections from 5 patients with Down's syndrome and 5 age-matched controls. The patients (age range, 16 to 56 years) had 29% fewer nbM neurons than controls, and the oldest patient had the lowest cell count of all subjects. The size of nbM neurons did not differ significantly between the two groups. Our results show that the nbM contains fewer neurons in young persons with Down's syndrome than in normal controls and suggest that the number of these nerve cells may be further reduced in older persons with Down's syndrome.

The density, type, and distributions of cortical senile plaques were determined in 6 aged rhesus monkeys. Plaque densities were highest in prefrontal and temporal cortices and lowest in occipital cortex. Neurite plaques contained many argentophilic neurites and little amyloid, mixed plaques had both neurites and amyloid, and amyloid plaques showed significant amounts of amyloid and fewer numbers of neurites. As total plaque densiry increased, there was a linear increase in the density of amyloid plaques, suggesting that plaques evolve from neurite, to mixed, to amyloid types.

Alzheimer's disease results from the degeneration of neurons. Degenerating nerve cells express atypical proteins, and amyloid is deposited. We suggest that some of these events are strongly influenced by genetic factors and age. Animal models should be useful in investigating the pathogenic mechanisms that lead to the brain abnormalities seen in this disease.

An improved histochemical method for light microscopic demonstration of acetylcholinesterase (AChE) has been developed. Axonal, dendritic, and perikaryal staining are well delineated, both in areas of low AChE content, such as cerebral cortex, and in areas of high AChE content, such as neostriatum. Axonal staining, including arborizations, stands out against a clear background devoid of diffuse reaction product.

In situ hybridization with labeled probes will have widespread applicability for investigations of neuropathological processes occurring in humans and animals. At this stage in the development of this approach, it is important to determine the kinds of questions that can be usefully examined with this technique, recognizing that in situ hybridization needs to be complemented by other methods, e.g., RNA blots, radioimmunoassays, and immunocytochemistry.

The subperineurial injection of beta,beta'-iminodipropionitrile (IDPN) into rat sciatic nerves resulted in focal disorganization of the axonal cytoskeleton characterized by segregation of neurofilaments and microtubules. Shortly after injection, microtubules clustered together to form a central channel, while neurofilaments became chaotically arrayed between the microtubule channel and axolemma. Electron microscopic autoradiography disclosed that rapidly transported organelles were preferentially associated with the microtubule-enriched central channels. These studies indicate that IDPN acts at the level of the axon to disrupt interactions between cytoskeletal elements and show that rapidly transported constituents are preferentially conveyed in association with microtubules. The model provides an opportunity to dissect the interactions of the cytoskeletal elements and other organelles.

Recent years have witnessed considerable change in the conceptualization of the pathophysiology of the cognitive impairments in dementing disorders, as a result of synaptic neurochemical analyses. Profound reductions in the forebrain cholinergic projections occur in Alzheimer's disease. In GM1 gangliosidosis, variable alterations in neurotransmitter related processes that are located in synaptic membranes have been described. Exploitation of animal models of human disorders resulting in dementia may further clarify the dynamic alterations in the biochemical processes required for effective neurotransmission in cortex.

In the present study, the number of neurons (greater than 20 microns in diameter) within the lateral part of the pedunculopontine nucleus pars compacta (PPNc) was determined at six rostrocaudal levels in 3 subjects with progressive supranuclear palsy (PSP), in 9 subjects with Alzheimer's disease, and in 6 age-matched control subjects. At each level examined, significantly fewer neurons were present in patients with PSP than in control subjects (49 to 69% reduction). Significant differences in numbers of neurons were not demonstrated between control subjects and patients with Alzheimer's disease. The extent of pathological changes, particularly neurofibrillary tangles, was examined within the PPNc of subjects in these three groups. The average number of neurofibrillary tangles in a 12-microns-thick midlevel section of the lateral PPNc was 68.7 in subjects with PSP, 18.3 in those with Alzheimer's disease, and 3.0 in aged control subjects. These abnormalities of PPNc neurons in PSP may play important roles in some of the clinical features characteristic of this disease.

[11C]Carfentanil is a potent opioid agonist currently in use as a specific PET (position emission tomography) scan radioligand for brain μ opioid receptors. In order to investigate the receptor interactions of carfentanil in detail [3H]carfentanil was used as a radioligand for labelling receptors in rat and human brain tissue homogenates. [3H]Carfentanil was found to bind saturably and with high affinity (KD = 0.08 ± 0.01 nM) to membranes prepared from human cortical (Bmax = 42 ± 3 fmol/mg) and thalamic (Bmax = 84 ± 3 fmol/mg) tissues and rat cortex (Bmax = 82 ± 4 fmol/mg) and deincephalon (Bmax = 105 ± 5 fmol/mg). Association (1.23 ± 0.19 × 1010Mol−1 × min−1 and dissociation rate (0.19 ± 0.03 min−1) constants were determined in human cortical tissues; results from studies in rat cortical, and rat diencephalon tissue homogenates produced similar kinetic rate constants. Competition studies with a variety of drugs indicated that [3H]carfentanil interacts primarily with μ opioid receptors in the four tissues studied; the affinities of a series of non-radioactive opioid ligands were essentially identical in the four tissues (correlation coefficients = 0.88−0.93). Naloxone, morphine, DAGO ([D-Ala2-MePhe4-Gly-ol5]enkephalin), DADL (D-Ala2-D- Leu5]enkaphalin) and EKC (ethylketazocine) potently displaced specific [3H]carfentanil binding with nM potency while the κ agonist U-69593, the σ agonists (+)-SKF 10047, (+)-3-PPP ((3-hydroxyphenyl)-N-propylpiperidine) and haloperidol and PCP (phencyclidine) were less potent displacing agents. The higher affinities of DAGO and morphine versus DADL for the [3H]carfentanil binding site indicates that δ opioid receptors are not being labelled. These data indicate that [3H]carfentanil is a high affinity, specific μ opioid receptor radioligand that may be of use in vitro for studying μ opioid receptors and supports the PET scanning data indicating the μ opioid receptor specificity of [11C]carfentanil. The molecular kinetic rate constants determined in vitro will be of assistance in using modelling procedures to interpret PET scanning information.

Regenerating axons have been intensively studied with regard to the mechanisms and determinants of elongation, and several lines of evidence suggest that the delivery of cytoskeletal proteins (tubulin and actin, in particular) are correlates of outgrowth and may be rate limiting (see Lasek and Hoffman, 1976; Wujck and Lasek. 1983). In addition lo changes in axonal length, regeneration involves marked changes in axonal caliber and in cytoskeletal composition. The rcgcneraling axon provides the best available system in which to test critically the hypotheses underlying several of our recent studies. These hypotheses are that neurofilament content is the major correlate of axonal caliber and that axonal neurofilament content is, in turn, determined, in large part, by neurofilament delivery via slow axonal transport. This review will first summarize the general problem of the determinants of axonal caliber and then focus on recent data from regenerating nerves. These data can be considered in terms of three regions of the regenerating axon—the proximal stump, the maturing sprouts, and the distal sprouts.

Immunohistochemical studies have suggested that corticotropin-releasing factor (CRF) was a transmitter of the olivocerebellar projection. We used in situ hybridization histochemistry with a 35S-labeled oligodeoxyribonucleotide probe for CRF mRNA to show that inferior olivary neurons of rats, baboons, and humans synthesize CRF.

This presentation will review some of the roles of axonal transport abnormalities in the pathogeneses of axonal degenerations. Slowly evolving degeneration of peripheral nervous system or central nervous system axons occurs in a variety of human neurological diseases. Examples include heritable processes such as Friedreich’s ataxia and Charcot-Marie-Tooth Disease, sporadic disorders such as amyotrophic lateral sclerosis (motor neuron disease), and diseases caused by neurotoxins. In these disorders, the pathogenetic mechanisms responsible for the axonal changes have been conjectural. Defects in the maintenance of the axon have been hypothesized to result from abnormalities of axonal transport systems. Early studies of axonal transport in experimental models of chronic axonal disease produced conflicting and generally disappointing results, with only limited correlation between axonal transport abnormalities and axonal pathology. Rapid recent advances in understanding these processes reflect the use of more focused strategies to detect partial or selective transport defects.

Aluminum chloride injected into the cisterna magna of 3-to 4-week-old rabbits is known to produce neurofibrillary changes in the perikarya and dendrites of neurons of the spinal cord and brainstem. This report calls attention to the early appearance and prominence of neurofibrillary swellings in proximal axons of affected neurons. One and 2 days after intoxication, large axonal swellings containing maloriented neurofilaments were present in the ventral horns. Over the next days and weeks, neurofilaments accumulated in the neuronal perikarya and dendrites. Two months after injection, abnormalities in the cell bodies were less apparent but occasional giant axonal swellings persisted in the ventral horn. This sequence of pathological changes, reflecting disorganization of the neuronal cytoskeleton, may result from an increase in synthesis of neurofilament polypeptides, and impairment in integration of these constituents into the neuronal cytoskeleton, or a defect in the intracellular transport of neurofilaments.

Alterations in axonal caliber and neurofilament content have been associated with altered neurofilament transport in several models of neurofibrillary degeneration. Acrylamide intoxication provides a prototype of distal axonal degeneration, the most frequent pattern of axonal pathology in human and experimental neurotoxic injury. Neurofibrillary changes are a variable and often minor aspect of the early pathological changes observed in acrylamide intoxication, and previous studies of slow axonal transport have produced conflicting results. In this study, we have correlated slow axonal transport, specifically neurofilament transport, with structural changes in the sciatic nerve complex of rats exposed to acrylamide. To study direct toxic effects of acrylamide, young rats were given a single dose of acrylamide (75 mg/kg, i.p.). A second group received daily injections of acrylamide at a lower dose (30 mg/kg, i.p.) in order to study animals with established acrylamide neuropathy. The slow component of axonal transport was labeled by intraspinal injections of [35S] methionine. Transport of individual slow component polypeptides was compared to profiles obtained from age-matched controls. Similarly intoxicated rats were perfused for morphometric and morphological studies. Results demonstrate that two different abnormalities of the slow component of axonal transport arise at different stages during the development of experimental acrylamide neuropathy. Both patterns of altered transport have structural correlates which reflect the changes in neurofilament transport. Following a single high dose, there was a modest retardation of the leading edge of the slow component. At this time, neurofilaments accumulated in proximal axons with formation of axonal swellings. During chronic administration, when distal axonal degeneration was present, the proportion of neurofilaments in the slow component was markedly reduced, and there was prominent loss of caliber in proximal axons. We suggest that these early changes represent a direct toxic effect of acrylamide on slow transport, whereas the later changes reflect reordering of slow transport as a neuronal response to toxin-induced axonal injury. This latter effect is of sufficient magnitude to obscure the acrylamide-induced retardation of slow transport.

Neurofibrillary changes are pathological hallmarks of a variety of neurotoxic and degenerative disorders. Progress during the last five years in reconstructing the pathogenesis of neurofibrillary changes has resulted from correlations of ultrastructural findings with aberrations in the axonal transport of neurofilament proteins. The first neurotoxic agent studied in this fashion was β,β’-iminodipropionitrile (IDPN) (Griffin et al., 1978). Recently, comparable studies have become available on aluminum (Troncoso et al., 1983; Bizzi et al., 1984; Parhad et al., 1984), colchicine (Komiya and Kurokawa, 1980), 3,4-dimethyl-2,5-hexanedione (DMHD) (Griffin et al., 1984), acrylamide (Sidenius and Jakobsen, 1983; Gold et al., 1985), and 2,5- hexanedione (Gold, Griffin, Price, unpublished observation).

Administration of beta,beta'-iminodipropionitrile (IDPN) to rodents has previously been shown to produce neurofilament-filled axonal swellings in the proximal regions of motor and sensory nerve fibers. Because of the distinctive distribution of these swellings, IDPN has been classed as a proximal axonopathy and thereby distinguished from other disorders in which similar axonal swellings occur in the distal parts of the axon (distal axonopathies). This report describes the pathology in the peripheral nerves of cats which received intermittent injections of IDPN and calls attention to two previously undescribed pathological changes. First, in addition to the typical proximal swellings associated with IDPN, these animals developed numerous axonal swellings within the distal branches of the sciatic nerve. Distal swellings were present as early as 23 days after initiation of intoxication, indicating that they formed locally (rather than developing in the proximal axon and undergoing transport into the distal regions). The second finding was Wallerian-like degeneration within the affected nerve branches. These changes in the distal sciatic nerve and its branches closely resembled the pathology of the distal axonopathies produced by agents such as the neurotoxic hexacarbons and carbon disulfide. The pathological similarities suggest that IDPN may share with these agents pathogenetic mechanisms to an extent not previously suspected.

Recent evidence indicates that the nucleus basalis of Meynert, a distinct population of basal forebrain neurons, is a major source of cholinergic innervation of the cerebral cortex. Postmortem studies have previously demonstrated profound reduction in the presynaptic markers for cholinergic neurons in the cortex of patients with Alzheimer's disease and senile dementia of the Alzheimer's type. The results of this study show that neurons of the nucleus basalis of Meynert undergo a profound (greater than 75 percent) and selective degeneration in these patients and provide a pathological substrate of the cholinergic deficiency in their brains. Demonstration of selective degeneration of such neurons represents the first documentation of a loss of a transmitter-specific neuronal population in a major disorder of higher cortical function and, as such, points to a critical subcortical lesion in Alzheimer's patients.