Lipopolysaccharide and cyclic AMP regulation of CB(2) cannabinoid receptor levels in rat brain and mouse RAW 264.7 macrophages.

CB(2) cannabinoid receptors exist in immune cells including macrophages. Affinity-purified antibodies against the CB(2) receptor identified a 45 kDa protein in rat brain, human tonsil and rat and mouse microglia, but not mouse N18TG2 neuroblastoma cells. Intracerebroventricular lipopolysaccharide (LPS) increased immunoreactive CB(2) receptors in brain membranes detected by Western blot. LPS increased immunodetectable CB(2) receptors in cultured RAW 264.7 macrophages, and this was partially attenuated by cyclohexamide or the protein kinase A and C inhibitors H8 and bis-indolylmaleimide. Forskolin or dibutyryl cyclic AMP increased CB(2) receptor immunoreactivity, suggesting the involvement of the cyclic AMP-protein kinase A-Cyclic AMP response element pathway in the regulation of CB(2) receptor levels.

Vulnerabilities of ventral mesencephalic neurons projecting to the nucleus accumbens following infusions of 6-hydroxydopamine into the medial forebrain bundle in the rat.

The terminal arbors of dopaminergic projections in the nucleus accumbens (Acb) core degenerate more rapidly, completely and permanently in a variety of neurotoxic circumstances than do those in the medial shell. It is unknown if this always reflects purely losses of the distal parts of axons from the core (as proposed in methamphetamine intoxication), or whether, in some circumstances, the disproportionate loss of core axons may also stem from an intrinsic vulnerability to degeneration of core-projecting neuronal perikarya. Experiments described here addressed this issue in the following manner. Three days after Fluoro-Gold (FG), a retrogradely transported tracer, had been iontophoresed selectively into the core or medial shell of male Sprague-Dawley rats, each received an infusion of saline vehicle containing or lacking 6-hydroxydopamine (6-OHDA) in the ipsilateral medial forebrain bundle (MFB). Twenty-one days later the brains were processed to exhibit ventral mesencephalic neurons containing FG. Application of an unbiased sampling method revealed substantially greater losses of FG labeled neurons relative to controls in rats that had received 6-OHDA lesions and deposition of FG in the Acb core as compared to the medial shell. Of the few core-projecting neurons that remained in the ventral mesencephalon after these lesions, 54% did not co-localize tyrosine hydroxylase immunoreactivity (TH-ir) and, thus, were not expected to degenerate. The capacity to selectively remove core-projecting dopaminergic neurons may be useful in the determination of molecular correlates of vulnerability and resistance to neurotoxicity and to possibly test the role of the core in reinforcement paradigms.

Neurotoxicity of MAO metabolites of catecholamine neurotransmitters: role in neurodegenerative diseases.

The monoamine oxidase (MAO) metabolites of norepinephrine (NE) or epinephrine (EPI) and of dopamine (DA) are 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL) and 3,4-dihydroxyphenylacetaldehyde (DOPAL), respectively. The toxicity of these catecholamine (CA) MAO metabolites was predicted over 50 years ago. However, until our recent chemical synthesis of these CA aldehyde metabolites, the hypothesis about their toxicity could not be tested. The present paper reviews recent knowledge gained about these compounds. Topics to be reviewed include: chemical synthesis and properties of DOPEGAL and DOPAL; in vitro and in vivo toxicity of CA aldehydes; subcellular mechanisms of toxicity; free radical formation by DOPEGAL versus DOPAL; mechanisms of accumulation of CA aldehydes in Alzheimer's disease (AD) and Parkinson's disease (PD) and potential therapeutic targets in Alzheimer's disease and Parkinson's disease.

3,4-Dihydroxyphenylacetaldehyde is the toxic dopamine metabolite in vivo: implications for Parkinson's disease pathogenesis.

In Parkinson's disease (PD), there is a highly selective loss of dopamine (DA) neurons in the substantia nigra (SN) greater than in the ventral tegmental area (VTA). The simplest explanation for selective DA neuron loss in PD is that DA is toxic and, because only DA neurons contain significant amounts of DA, this highly localized synthesis of DOPAL accounts for selective vulnerability of DA neurons. However, the large concentrations of DA required to produce in vivo toxicity cast doubt on its role in PD pathogenesis. Alpha-synuclein (alpha-syn) is the major component of the Lewy body, the pathological marker of PD, and is genetically linked to the disease. Recent studies indicate that alpha-syn neurotoxicity is mediated by a free radical generating metabolite of DA. Here we test the hypothesis that 3,4-dihydroxyphenylacetaldehyde (DOPAL), the monamine oxidase metabolite of DA, mediates DA toxicity in vivo. We injected DOPAL, DA and its oxidative, reduced and methylated metabolites into rat SN and VTA. Five days post-surgery, the injection sites were evaluated in Nissl preparations and with tyrosine hydroxylase (for DA neurons), neuronal nuclear antigen (for neurons) and glial fibrillary acidic protein (for astrocytes) immunoreactivities. Lesion size in SN vs. VTA was compared using morphometry. DOPAL at concentrations as low as 100 ng was toxic to DA SN neurons>DA VTA neurons>glia. Neither DA nor its other metabolites showed evidence of neurotoxicity at fivefold higher doses. However, 20 microg of DA produced lesions in the SN and VTA. We conclude that DOPAL is the toxic DA metabolite in vivo. Implications for a unified hypothesis for PD pathogenesis are discussed.

Discrimination of striatopallidum and extended amygdala in the rat: a role for parvalbumin immunoreactive neurons?

Synaptic effects of parvalbumin-immunoreactive (-ir) interneurons (PVs) upon medium spiny neurons may be essential to neural processing in the striatum and, in effect, may serve as an additional feature distinguishing striatum from extended amygdala. The present immunohistochemical study in the rat was done to evaluate the distributions of PVs in the striatum and extended amygdala. Numerous PVs occupy all structures currently regarded as having a striatal composition, including the caudate-putamen, nucleus accumbens, and olfactory tubercle, as well as structures that receive outputs from these, including the globus pallidus, ventral pallidum, entopeduncular nucleus and substantia nigra reticulata. The morphologies of striatal PVs and their distribution were similar to what has been previously reported. In addition, we found that the density of larger neostriatal PVs with extensive and densely immunoreactive dendritic and local axonal arbors is greatest laterally, particularly in striatal districts with slight calbindin-ir, including the striatal patch compartment. In contrast to the situation in striatum, few PVs were observed in the central and medial divisions of the extended amygdala, including the bed nucleus of stria terminalis, interstitial nucleus of the posterior limb of the anterior commissure and central and medial nuclei of the amygdala, or in mesopontine, peribrachial and medullary structures that receive extended amygdala output. The paucity of PVs may be a characteristic feature distinguishing extended amygdala and its projection areas from striatopallidum, as well as the general character of neural processing that occurs in each.

The caudal sublenticular region/anterior amygdaloid area is the only part of the rat forebrain and mesopontine tegmentum occupied by magnocellular cholinergic neurons that receives outputs from the central division of extended amygdala.

Ascending cholinergic projections and the central nucleus of the amygdala (CeA) have both been implicated in attentional and orienting mechanisms leading to adaptive behavioral responses. In view of this, the present study was carried out to identify relevant neuroanatomical relationships in the form of projections from the CeA and a related structure, the dorsolateral divison of the bed nucleus of the stria terminalis (dlBST), to parts of the basal forebrain and mesopontine tegmentum that contain magnocellular cholinergic neurons. The CeA and dlBST are components of the 'central division of extended amygdala'. Following injections of the anterogradely transported compounds, Phaseolus vulgaris-leucoagglutinin or biotinylated dextran amine, into the CeA or dlBST, sections were processed with immunohistochemical reagents to localize the anterograde tracer and choline acetyltransferase (ChAT). The trajectories of efferent projections from CeA and dlBST were qualitatively similar. Few ChAT-immunoreactive (ir) neurons were present within the extended amygdala or regions containing the dense terminations of its efferent projections, with the striking exception of the caudal sublenticular/anterior amygdaloid region. The ChAT-ir neurons there, however, were significantly smaller and weakly ChAT-ir as compared to those located outside of the dense extended amygdaloid terminations. In the mesopontine tegmentum, the robust downstream projection from the extended amygdala was centered medial to ChAT-ir neurons of the pedunculopontine tegmental nucleus. The differentiated character of the relationships between extended amygdala and forebrain and mesopontine districts containing ChAT-ir neurons that give rise to ascending projections may have significant implications for the control of cortical and diencephalic acetylcholine release and accompanying effects on attention, vigilance and locomotor activation.