David M. Jacobowitz

Bio: David M. Jacobowitz is an academic researcher from National Institutes of Health. The author has contributed to research in topics: Calretinin & Hypothalamus. The author has an hindex of 84, co-authored 389 publications receiving 26673 citations. Previous affiliations of David M. Jacobowitz include Uniformed Services University of the Health Sciences & Hebrew University of Jerusalem.

A primate model of parkinsonism: selective destruction of dopaminergic neurons in the pars compacta of the substantia nigra by N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.

Abstract: A syndrome similar to idiopathic parkinsonism developed after intravenous self-administration of an illicit drug preparation in which N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (NMPTP) might have been responsible for the toxicity. In the present study we show that intravenous administration of NMPTP to the rhesus monkey produces a disorder like parkinsonism (akinesia, rigidity, postural tremor, flexed posture, eyelid closure, drooling) that is reversed by the administration of L-dopa. NMPTP treatment decreases the release of dopamine and dopamine accumulates in swollen, distorted axons in the nigrostriatal pathway just above the substantia nigra, followed by severe nerve cell loss in the pars compacta of the substantia nigra and a marked reduction in the dopamine content of the striatum. The pathological and biochemical changes produced by NMPTP are similar to the well-established changes in patients with parkinsonism. Thus, the NMPTP-treated monkey provides a model that can be used to examine mechanisms and explore therapies of parkinsonism.

Topographic atlas of catecholamine and acetylcholinesterase-containing neurons in the rat brain. I. Forebrain (telencephalon, diencephalon).

Abstract: A complete stereotaxic neuroanatomical atlas of the rat hindbrain was prepared using transverse serial sections stained with Luxol fast blue and cresyl violet. Catecholamine-containing cell bodies and fiber terminals were identified by the histofluorescence method. The acetylcholinesterase distribution was histochemically localized. A detailed stereotaxic atlas of the catecholaminergic and acetylcholinesterase-containing structures is presented.

Pharmacological Actions of 6-Hydroxydopamine

Abstract: From the previous discussions, it is apparent that 6-OHDA produces a relatively selective effect on sympathetic nerve terminals. The selectivity of this action appears to be related to its accumulation within noradrenergic neurons by uptake-1 transport mechanisms. Once inside the neuron, 6-OHDA is bound in a granular storage pool and can be released by nerve stimulation, thus acting as a false neurotransmitter. In sufficiently high amounts, apparently more related to the concentration in the cytoplasmic pool, 6-OHDA generates highly reactive products, suggested to be peroxides, superoxides, hydroxyindoles, and quinones. These products react nonspecifically with neuronal structures and eventually destroy the neuron. MAO appears to be important in the metabolism of the 6-OHDA molecule and this enzyme, as well as granule storage, may serve as protective mechanisms. The actual subcellular component most altered by 6-OHDA, and most involved with maintaining neuronal function, is not known. However, the endoplasmic reticulum, outer limiting membrane, nucleus, mitochondrion and other structures have been suggested as sites for the primary lesion, and 6-OHDA has been shown in vitro to uncouple oxidative phosphorylation in mitochondria. During the process of degeneration the nerves first lose their ability to conduct action potentials, NE stores become depleted and sympathomimetic responses may be observed. Uptake mechanisms become incapacitated and the nerve membrane ultimately is phagocytized, as evidenced by the intense neuroglia reaction. Accompanying the loss in the adrenergic nerve active amine uptake mechanism is the appearance of presynaptic supersensitivity at a host of sites. Development of postsynaptic supersensitivity has been suggested to occur with time in certain structures. In the peripheral nervous system the terminals regenerate, and it has been observed that functional activity is restored at early times, when the amine levels are still reduced and while the terminal network is far from being fully regenerated. In the peripheral nervous system, 6-OHDA alters noradrenergic terminals to various degrees in different end organs. Time-course studies, following various routes of administration, have determined the threshold for terminal destruction in various organs of several species. In general, the increasing order for threshold of the destructive action of 6-OHDA in various end organs is cardiac ventricles 〉 salivary glands 〉 whole heart 〉 iris 〉 nictitating membrane 〉 spleen 〉 atria 〉 blood vessels 〉 vas deferens 〉 sympathetic ganglia 〉 adrenal glands. In regard to the adrenals it bears mentioning that they apparently are unaffected by direct 6-OHDA action, but respond to diminished sympathetic function by compensatorily increasing CA turnover. Terminals in all organs studied regenerate at a steady rate. In the CNS of mature animals 6-OHDA produces marked alterations of both noradrenergic and dopaminergic neurons after injection into the parenchyma of the brain or into one of the brain cavities. Early studies showed that 6-OHDA in moderate doses could deplete the brain of NE in the absence of ultrastructural damage. Also, DA stores are initially increased after 6-OHDA and are depleted only as a consequence of damage to dopaminergic neurons. The regional effects of 6-OHDA on noradrenergic neurons in the brain vary according to the parameter under study. Different regional variations are found when either NE content, NE uptake or tyrosine hydroxylase activity is measured. The degeneration of the central noradrenergic neurons occurs in different phases, classified as primary and secondary degeneration. The primary phase is related to the direct destructive action of 6-OHDA on the neuron and occurs in about the first 48 hours after treatment. The secondary phase occurs over a period of weeks and appears to be the result of retrograde degenerative events subsequent to terminal or axonal damage. Higher doses of 6-OHDA produce less of a specific effect, as is the case with any other pharmacological agent. Damage extends to noncatecholamine-containing neurons, and may even include non-neuronal cells. Possibly related to this type of unspecific damage is the observed depletion of 5-hydroxytryptamine in certain brain regions of different species. However, in reasonable amounts, 6-OHDA will destroy catecholaminergic neurons with a high degree of selectivity. The histochemical method shows that 6-OHDA brings about alterations in the appearance of CA-containing nerves, similar to those observed after axonal section or ligation. Nerve terminal varicosities decrease in number, the nerve network stains less intensely, and finally, the number of terminal processes decreases. After a low dose of 6-OHDA the fluorescence intensity of nerves can be restored by subsequent treatment with a CA. However, after a high dose of 6-OHDA nerves are not unmasked by CA treatment, indicating that the initial depletion is followed by actual destruction. Correlations have been shown between histochemical alterations and reductions in endogenous CA levels, CA-uptake capacity, and endogenous DBH and T-OH activity. Electron microscopic studies have provided the ultimate confirmation of nerve terminal destruction. While the terminal network is undergoing these functional changes, the axonal processes become highly fluorescent, swollen and highly irregular in appearance. Evidence to date indicates that axoplasmic flow is impeded, so that NE, being transported down the axon, accumulates in a retrograde manner. The above alterations are seen in both noradrenergic and dopaminergic neurons. In newborn mice and rats, 6-OHDA causes extensive damage of sympathetic postganglionic neurons, and the destructive lesion includes the entire neuron. Ganglia at prevertebral and paravertebral sites are destroyed and subsequent development is impaired throughout adulthood. As a consequence, numerous end organs normally innervated by sympathetic fibers, show a reduction of NE content due to the loss of the nerve network. In addition, central noradrenergic neurons are damaged, since 6-OHDA has the capacty of passing through the unfully-developed blood-brain barrier of the neonates. The pattern of this chemical lesion is different from that observed in mature animals. Numerous behavioral parameters are altered by 6-OHDA. Initial behavioral changes are likely to result from NE or DA release from central CA-containing neurons after treatment with 6-OHDA, while more permanent alterations appear to be a better reflection of central neuronal destruction. Immediately after injection 6-OHDA decreases food and water consumption, lowers body temperature, and decreases locomotion More permanent effects are manifested by altered sleep patterns, increased irritability and aggression, and altered operant activity. Numerous studies have been performed to characterize the observed alterations to a specific region in the brain and also to the specific neurohumor involved. Studies with 6-OHDOPA indicate that it is metabolically decarboxylated to 6-OHDA, which then destroys CA-containing neurons. It appears to be useful for selective destruction of noradrenergic neurons. One distinct advantage of 6-OHDOPA is its ability to cross the blood-brain barrier, so that both central and peripheral noradrenergic neurons may be destroyed after a single dose. Although 6-OHDOPA is far less potent than 6-OHDA in mature animals, the central neurotoxic actions in neonates are quite similar. However, unlike 6-OHDA, 6-OHDOPA does not appear to produce permanent alterations of all adrenergic neurons. Thus, as the animals develop one may be able to study the effects of centrally impaired noradrenergic development in the absence of peripheral effects. The limited studies to date indicate that 6-OHDOPA produces alterations in behavior that are similar to those produced by 6-OHDA. Studies with 6-OHDA have illustrated the utility of this compound in investigating the function of both noradrenergic and dopaminergic neurons. Much has been learned about basic functional processes, such as uptake and storage mechanisms, axoplasmic transport, and the influence of central regulation of ongoing noradrenergic nerve development and function. It is now more meaningful to attempt to characterize the role of noradrenergic and dopaminergic neurons in different types of behavior. The search for other neurotoxic agents continues and perhaps others will be found with more desirable actions. However, the studies with 6-OHDA have provided new insights into innumerable areas of neuroscience.

Local circuit neurons immunoreactive for calretinin, calbindin D-28k or parvalbumin in monkey prefrontal cortex: distribution and morphology.

Abstract: In the cerebral cortex, local circuit neurons provide critical inhibitory control over the activity of pyramidal neurons, the major class of excitatory efferent cortical cells. The calciumbinding proteins, calretinin, calbindin, and parvalbumin, are expressed in a variety of cortical local circuit neurons. However, in the primate prefrontal cortex, relatively little is known, especially with regard to calretinin, about the specific classes or distribution of local circuit neurons that contain these calcium-binding proteins. In this study, we used immunohistochemical techniques to characterize and compare the morphological features and distribution in macaque monkey prefrontal cortex of local circuit neurons that contain each of these calcium-binding proteins. On the basis of the axonal features of the labeled neurons, and correlations with previous Golgi studies, calretinin appeared to be present in double-bouquet neurons, calbindin in neurogliaform neurons and Martinotti cells, and parvalbumin in chandelier and wide arbor (basket) neurons. Calretinin was also found in other cell populations, such as a distinctive group of large neurons in the infragranular layers, but it was not possible to assign these neurons to a known cell class. In addition, although the animals studied were adults, immunoreactivity for both calretinin and calbindin was found in Cajal-Retzius neurons of layer I. Dual labeling studies confirmed that with the exception of the Cajal-Retzius neurons, each calcium-binding protein was expressed in separate populations of prefrontal cortical neurons. Comparisons of the laminar distributions of the labeled neurons also indicated that these calcium-binding proteins were segregated into discrete neuronal populations. Calretinin-positive neurons were present in greatest density in deep layer I and layer II, calbindin-immuno-reactive cells were most dense in layers II-superficial III, and parvalbumin-containing neurons were present in greatest density in the middle cortical layers. In addition, the relative density of calretinin-labeled neurons was approximately twice that of the calbindin- and parvalbumin-positive neurons. However, within each group of labeled neurons, their laminar distribution and relative density did not differ substantially across regions of the prefrontal cortex. These findings demonstrate that calretinin, calbindin, and parvalbumin are markers of separate populations of local circuit neurons in monkey prefrontal cortex, and that they may be useful tools in unraveling the intrinsic inhibitory circuitry of the primate prefrontal cortex in both normal and disease states.

Establishment of a noradrenergic clonal line of rat adrenal pheochromocytoma cells which respond to nerve growth factor.

Abstract: A single cell clonal line which responds reversibly to nerve growth factor (NGF) has been established from a transplantable rat adrenal pheochromocytoma. This line, designated PC12, has a homogeneous and near-diploid chromosome number of 40. By 1 week's exposure to NGF, PC12 cells cease to multiply and begin to extend branching varicose processes similar to those produced by sympathetic neurons in primary cell culture. By several weeks of exposure to NGF, the PC12 processes reach 500-1000 mum in length. Removal of NGF is followed by degeneration of processes within 24 hr and by resumption of cell multiplication within 72 hr. PC12 cells grown with or without NGF contain dense core chromaffin-like granules up to 350 nm in diameter. The NGF-treated cells also contain small vesicles which accumulate in process varicosities and endings. PC12 cells synthesize and store the catecholamine neurotransmitters dopamine and norepinephrine. The levels (per mg of protein) of catecholamines and of the their synthetic enzymes in PC12 cells are comparable to or higher than those found in rat adrenals. NGF-treatment of PC12 cells results in no change in the levels of catecholamines or of their synthetic enzymes when expressed on a per cell basis, but does result in a 4- to 6-fold decrease in levels when expressed on a per mg of protein basis. PC12 cells do not synthesize epinephrine and cannot be induced to do so by treatment with dexamethasone. The PC12 cell line should be a useful model system for neurobiological and neurochemical studies.

The hypocretins: Hypothalamus-specific peptides with neuroexcitatory activity

Abstract: We describe a hypothalamus-specific mRNA that encodes preprohypocretin, the putative precursor of a pair of peptides that share substantial amino acid identities with the gut hormone secretin. The hypocretin (Hcrt) protein products are restricted to neuronal cell bodies of the dorsal and lateral hypothalamic areas. The fibers of these neurons are widespread throughout the posterior hypothalamus and project to multiple targets in other areas, including brainstem and thalamus. Hcrt immunoreactivity is associated with large granular vesicles at synapses. One of the Hcrt peptides was excitatory when applied to cultured, synaptically coupled hypothalamic neurons, but not hippocampal neurons. These observations suggest that the hypocretins function within the CNS as neurotransmitters.