Three types of tyrosine hydroxylase-positive CNS neurons distinguished by dopa decarboxylase and VMAT2 co-expression - PubMed (original) (raw)

Three types of tyrosine hydroxylase-positive CNS neurons distinguished by dopa decarboxylase and VMAT2 co-expression

Eberhard Weihe et al. Cell Mol Neurobiol. 2006 Jul-Aug.

Abstract

1. We investigate here for the first time in primate brain the combinatorial expression of the three major functionally relevant proteins for catecholaminergic neurotransmission tyrosine hydroxylase (TH), aromatic acid acid decarboxylase (AADC), and the brain-specific isoform of the vesicular monoamine transporter, VMAT2, using highly specific antibodies and immunofluorescence with confocal microscopy to visualize combinatorial expression of these proteins. 2. In addition to classical TH, AADC, and VMAT2-copositive catecholaminergic neurons, two unique kinds of TH-positive neurons were identified based on co-expression of AADC and VMAT2. 3. TH and AADC co-positive, but VMAT2-negative neurons, are termed "nonexocytotic catecholaminergic TH neurons." These were found in striatum, olfactory bulb, cerebral cortex, area postrema, nucleus tractus solitarius, and in the dorsal motor nucleus of the vagus. 4. TH-positive neurons expressing neither AADC nor VMAT2 are termed "dopaergic TH neurons." We identified these neurons in supraoptic, paraventricular and periventricular hypothalamic nuclei, thalamic paraventicular nucleus, habenula, parabrachial nucleus, cerebral cortex and spinal cord. We were unable to identify any dopaergic (TH-positive, AADC-negative) neurons that expressed VMAT2, suggesting that regulatory mechanisms exist for shutting off VMAT2 expression in neurons that fail to biosynthesize its substrates. 5. In several cases, the corresponding TH phenotypes were identified in the adult rat, suggesting that this rodent is an appropriate experimental model for further investigation of these TH-positive neuronal cell groups in the adult central nervous system. Thus, no examples of TH and VMAT2 co-positive neurons lacking AADC expression were found in rodent adult nervous system. 6. In conclusion, the adult mammalian nervous system contains in addition to classical catecholaminergic neurons, cells that can synthesize dopamine, but cannot transport and store it in synaptic vesicles, and neurons that can synthesize only L-dopa and lack VMAT2 expression. The presence of these additional populations of TH-positive neurons in the adult primate CNS has implications for functional catecholamine neurotransmission, its derangement in disease and drug abuse, and its rescue by gene therapeutic maneuvers in neurodegenerative diseases such as Parkinson's disease.

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Figures

Fig. 1

Coexpression of VMAT2 and catecholamine synthesizing enzymes in classical catecholaminergic cell groups of rhesus monkey brain. Each horizontal panel (row) represents a single co-stained section analyzed by confocal microscopy. (A) Dopaminergic TH-positive neurons and processes of the substantia nigra pars compacta co-stain for AADC and VMAT2 (arrow heads). Note that VMAT2 staining in neuronal processes and fibers is comparatively weak and absent from some TH-positive fiber profiles. VMAT2-immunoreactivity appears granular and is asymmetrically concentrated in the perinuclear space while TH-positive staining comprises the entire cell bodies (lower panel). Note VMAT2-positive varicose fiber profiles lacking TH (arrows in lower panel). Bars are 30 _μ_m. (B) Noradrenergic TH-positive neurons and processes of the locus coeruleus co-stain for AADC, DBH, and VMAT2 (arrow heads). Note two small AADC-positive cell profiles that lack TH (arrows). VMAT2-positive/TH-negative puncta are intermingled between TH-positive/VMAT2-positive neuronal cell bodies and processes (high magnification in lower panel). The VMAT2-positive/TH-negative puncta presumably represent serotonergic input. The upper three panels are adjacent sections showing the same blood vessel (asterisks). Note staining of portions or all of the region of the nucleus in some AADC-positive cells, which can be attributed to superimposition of positive staining in cytoplasm underlying or overlaying the nucleus in these 7–10 _μ_m sections. Bars are 30 _μ_m.

Fig. 1

Fig. 2

Absence of VMAT2 expression from dopaminergic TH-positive neurons in rhesus monkey ol-factory bulb. Horizontal panels (rows) represent single co-stained sections adjacent to each other analyzed by confocal microscopy. TH-positive neuronal and cell fiber profiles co-express AADC, but lack VMAT2 (arrows). Note VMAT2-positive/TH-negative puncta which presumably represent serotonergic input. Bars are 30 _μ_m.

Fig. 3

Heterogeneous phenotypes of presumed dopaminergic neurons in rhesus monkey area postrema (AP) and nucleus of the solitary tract (NTS). Each horizontal panel (row) represents a single co-stained section analyzed by confocal microscopy. (A) The majority of TH-positive neurons of the AP coexpress AADC (double arrow heads in upper panel), but none of them coexpresses VMAT2 (arrows in lower panel). Note occurrence of both AADC-positive/TH-negative (arrow head) and TH-positive/AADC-negative (arrow) neurons (upper panel). VMAT2-positive/TH-positive and VMAT2-positive/TH-negative puncta are encountered. Bars are 30 _μ_m. (B) TH-positive neurons in the NTS coexpress AADC (arrows in upper panel), but lack VMAT2 (arrows in lower panel). In addition, AADC-positive/TH-negative neurons (arrow heads in upper panel) and VMAT2-positive/TH-negative neurons and fibers (arrow heads in lower panel) are encountered. Upper and lower panels are from adjacent sections. Asterisks label the same blood vessel profile. As in Fig. 1, staining in the vicinity of the nucleus in some cells is attributable to overlaying or underlying positively stained cytoplasm for the soluble enzyme AADC. Bars are 100 _μ_m.

Fig. 3

Fig. 4

Absence of VMAT2 from intrinsic TH-positive dopaminergic neurons of rhesus monkey striatum. Each horizontal panel (row) represents a single co-stained section analyzed by confocal microscopy. Adjacent sections show a TH-positive neuron costaining for AADC (upper panel), but lacking VMAT2 (lower panel) (arrows). Note that the vast majority of TH-positive dopaminergic input from the substantia nigra co-stains for AADC and VMAT2 (arrow heads). The AADC-positive/TH-negative and VMAT2-positive/TH-negative fibers/puncta are presumed to represent serotonergic input to the striatum (double arrow heads). Bars are 30 _μ_m.

Fig. 5

DOPAergic neurons in rhesus monkey lateral parabrachial nucleus and spinal cord. Horizontal panels (rows) represent single co-stained sections adjacent to each other analyzed by confocal microscopy. (A) TH-positive neurons in the lateral parabrachial nucleus are negative for AADC and VMAT2 (arrows). In addition to some TH-positive/AADC-positive and TH-positive/VMAT2-positive varicose fibers and puncta, AADC-positive/TH-negative and VMAT2-positive/TH-negative fibers and puncta are present (presumed serotonergic input). Asterisks label profiles of the same blood vessel. Bars are 30 _μ_m. (B) TH-positive neurons in the intermediolateral cell column of the thoracic spinal cord lack AADC and VMAT2 (arrows). AADC-positive varicose fibers containing TH (double arrow heads in middle panel) and lacking TH (arrow heads in middle panel) are present. VMAT2-positive varicose fibers/puncta containing TH (double arrow heads in lower panel) and lacking TH (arrow heads in lower panel) are encountered. Note also TH-positive fibers lacking VMAT2 (uppermost arrow in lower panel). Bars are 30 _μ_m.

Fig. 5

Fig. 6

DOPAergic neurons in the rat habenular nucleus. Horizontal panels (rows) represent single co-stained sections adjacent to each other analyzed by confocal microscopy. TH-positive neurons lack AADC (arrows in upper panel) and VMAT2 (arrows in lower panel). Some TH-positive varicose fibers costain for AADC (double arrow heads in upper panel). Presumed serotonergic AADC-positive fibers lack TH (arrow head in upper panel). Presumed serotonergic VMAT2-positive fibers lack TH (arrow head in lower panel). Bars are 30 _μ_m.

Fig. 7

Absence of AADC and VMAT2 from TH-positive neurons in rat supraoptic nucleus (SON). Horizontal panels (rows) represent single co-stained sections adjacent to each other analyzed by confocal microscopy. TH-positive neurons in the SON lack AADC (arrows in upper panel) and VMAT2 (arrows in middle panel). AADC-positive neurons dorsal to the SON and fibers in the SON are TH-negative (arrow heads in upper panel). AADC-positive neurons dorsal to the SON also lack VMAT2 (arrows in lower panel). Note VMAT2-positive/TH-positive fibers (double arrow heads in middle panel) and VMAT2-positive/TH-negative fibers (arrow heads in middle panel) in the SON. Some VMAT2-positive fibers in and at the dorsal border of the SON are AADC- (arrow heads in lower panel) and TH-negative (arrow heads in middle panel) and are presumed to represent histaminergic input to the SON region. Bars are 100 _μ_m.

Fig. 8

Heterogeneous phenotypes of TH + neurons in the rhesus monkey periventricular hypothalamus. Horizontal panels (rows) represent single co-stained sections analyzed by confocal microscopy. Upper panel: TH-positive neurons coexpressing AADC (double arrow heads) and TH-positive/AADC-negative neurons (arrows) are present. Note AADC-positive/TH-negative fiber (arrow head). Lower panel: TH-positive neurons lack VMAT2 (arrows). Note VMAT2-positive/TH-positive and VMAT2-positive/TH-negative puncta. Occasional immunopositivity in the region of the nucleus for the cytoplasmic antigen AADC is attributed to superimposition of cytoplasm above or below the nucleus in these sections. Bars are 30 _μ_m.

Fig. 9

Heterogeneous phenotypes of TH-positive neurons in the rhesus monkey paraventricular thalamic nucleus. Horizontal panels (rows) represent single co-stained section adjacent to each other analyzed by confocal microscopy. AADC and VMAT2 are absent from TH-positive neurons (arrows in upper and lower panels, respectively). Note AADC-positive/TH-negative fibers (arrow heads in upper panel) and VMAT2-positive/TH-negative fibers (arrow heads in lower panel) as well as VMAT2-positive/TH-positive fibers (double arrow heads in lower panel). Asterisks label third ventricle. Bars are 50 _μ_m.

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Three types of tyrosine hydroxylase-positive CNS neurons distinguished by dopa decarboxylase and VMAT2 co-expression - PubMed (original) (raw)