scholarly journals Programming of Dopaminergic Neurons by Neonatal Sex Hormone Exposure: Effects on Dopamine Content and Tyrosine Hydroxylase Expression in Adult Male Rats

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Pedro Espinosa ◽  
Roxana A. Silva ◽  
Nicole K. Sanguinetti ◽  
Francisca C. Venegas ◽  
Raul Riquelme ◽  
...  
Keyword(s):  
Nucleus Accumbens ◽  
Tyrosine Hydroxylase ◽  
Substantia Nigra ◽  
Ventral Tegmental Area ◽  
Dopaminergic Neurons ◽  
Dopamine Release ◽  
Male Rats ◽  
Midbrain Dopaminergic Neurons ◽  
Dopamine Content ◽  
Ventral Tegmental

We sought to determine the long-term changes produced by neonatal sex hormone administration on the functioning of midbrain dopaminergic neurons in adult male rats. Sprague-Dawley rats were injected subcutaneously at postnatal day 1 and were assigned to the following experimental groups: TP (testosterone propionate of 1.0 mg/50 μL); DHT (dihydrotestosterone of 1.0 mg/50 μL); EV (estradiol valerate of 0.1 mg/50 μL); and control (sesame oil of 50 μL). At postnatal day 60, neurochemical studies were performed to determine dopamine content in substantia nigra-ventral tegmental area and dopamine release in nucleus accumbens. Molecular (mRNA expression of tyrosine hydroxylase) and cellular (tyrosine hydroxylase immunoreactivity) studies were also performed. We found increased dopamine content in substantia nigra-ventral tegmental area of TP and EV rats, in addition to increased dopamine release in nucleus accumbens. However, neonatal exposure to DHT, a nonaromatizable androgen, did not affect midbrain dopaminergic neurons. Correspondingly, compared to control rats, levels of tyrosine hydroxylase mRNA and protein were significantly increased in TP and EV rats but not in DHT rats, as determined by qPCR and immunohistochemistry, respectively. Our results suggest an estrogenic mechanism involving increased tyrosine hydroxylase expression, either by direct estrogenic action or by aromatization of testosterone to estradiol in substantia nigra-ventral tegmental area.

Cardiovascular depressor responses to stimulation of substantia nigra and ventral tegmental area

1997 ◽  
Vol 273 (6) ◽  
pp. H2549-H2557 ◽  
Author(s):  
Gilbert J. Kirouac ◽  
John Ciriello
Keyword(s):  
Substantia Nigra ◽  
Ventral Tegmental Area ◽  
Intravenous Administration ◽  
Dopaminergic Neurons ◽  
Cardiovascular Responses ◽  
Receptor Blocker ◽  
Transitional Region ◽  
Pars Lateralis ◽  
Ventral Tegmental ◽  
Stimulation Of

Experiments were done in α-chloralose-anesthetized, paralyzed, and artificially ventilated rats to investigate the effect ofl-glutamate (Glu) stimulation of the substantia nigra (SN) and ventral tegmental area (VTA) on arterial pressure (AP) and heart rate (HR). Glu stimulation of the SN pars compacta (SNC) elicited decreases in both mean AP (MAP; −18.9 ± 1.3 mmHg; n = 52) and HR (−26.1 ± 1.6 beats/min; n = 46) at 81% of the sites stimulated. On the other hand, stimulation of the SN pars lateralis or pars reticulata did not elicit cardiovascular responses. Stimulation of the adjacent VTA region elicited similar decreases in MAP (−18.0 ± 2.6 mmHg; n = 20) and HR (−25.4 ± 3.8 beats/min; n = 17) at ∼74% of the sites stimulated. Intravenous administration of the dopamine D2-receptor antagonist raclopride significantly attenuated both the MAP (70%) and the HR (54%) responses elicited by stimulation of the transitional region where the SNC merges with the lateral VTA (SNC-VTA region). Intravenous administration of the muscarinic receptor blocker atropine methyl bromide had no effect on the magnitude of the MAP and HR responses to stimulation of the SNC-VTA region, whereas administration of the nicotinic receptor blocker hexamethonium bromide significantly attenuated both the depressor and the bradycardic responses. These data suggest that dopaminergic neurons in the SNC-VTA region activate a central pathway that exerts cardiovascular depressor effects that are mediated by the inhibition of sympathetic vasoconstrictor fibers to the vasculature and cardioacceleratory fibers to the heart.

Characteristics of Electrically Evoked Somatodendritic Dopamine Release in Substantia Nigra and Ventral Tegmental Area In Vitro

1997 ◽  
Vol 77 (2) ◽  
pp. 853-862 ◽  
Author(s):  
M. E. Rice ◽  
S. J. Cragg ◽  
S. A. Greenfield
Keyword(s):  
Electrical Stimulation ◽  
Substantia Nigra ◽  
Ventral Tegmental Area ◽  
Dopamine Release ◽  
Substantia Nigra Pars Compacta ◽  
Frequency Dependent ◽  
Body Regions ◽  
Ventral Tegmental ◽  
Da Release

Rice, M. E., S. J. Cragg, and S. A. Greenfield. Characteristics of electrically evoked somatodendritic dopamine release in substantia nigra and ventral tegmental area in vitro. J. Neurophysiol. 77: 853–862, 1997. Somatodendritic dopamine (DA) release from neurons of the midbrain represents a nonclassical form of neuronal signaling. We assessed characteristics of DA release during electrical stimulation of the substantia nigra pars compacta (SNc) in guinea pig midbrain slices. With the use of parameters optimized for this region, we compared stimulus-induced increases in extracellular DA concentration ([DA]o) in medial and lateral SNc, ventral tegmental area (VTA), and dorsal striatum in vitro. DA release was monitored directly with carbon-fiber microelectrodes and fast-scan cyclic voltammetry. Detection of DA in SNc was confirmed by electrochemical, pharmacological, and anatomic criteria. Voltammograms of the released substance had the same peak potentials as those of DA obtained during in vitro calibration, but different from those of the indoleamine 5-hydroxytryptamine. Similar voltammograms were also obtained in the DA-rich striatum during local electrical stimulation. Contribution from the DA metabolite 3,4-dihydroxyphenylacetic acid to somatodendritic release was negligible, as indicated by the lack of effect of the monoamine oxidase inhibitor pargyline (20 μM) on the signal. Lastly, DA voltammograms could only be elicited in regions that were subsequently determined to be positive for tyrosine hydroxylase immunoreactivity (TH-ir). The frequency dependence of stimulated DA release in SNc was determined over a range of 1–50 Hz, with a constant duration of 10 s. Release was frequency dependent up to 10 Hz, with no further increase at higher frequencies. Stimulation at 10 Hz was used in all subsequent experiments. With this paradigm, DA release in SNc was tetrodotoxin insensitive, but strongly Ca2+ dependent. Stimulated [DA]o in the midbrain was also site specific. At the midcaudal level examined, DA efflux was significantly greater in VTA (1.04 ± 0.05 μM, mean ± SE) than in medial SNc (0.52 ± 0.05 μM), which in turn was higher than in lateral SNc (0.35 ± 0.03 μM). This pattern followed the apparent density of TH-ir, which was also VTA > medial SNc > lateral SNc. This report has introduced a new paradigm for the study of somatodendritic DA release. Voltammetric recording with electrodes of 2–4 μm tip diameter permitted highly localized, direct detection of endogenous DA. The Ca2+ dependence of stimulated release indicated that the process was physiologically relevant. Moreover, the findings that somatodendritic release was frequency dependent across a range characteristic of DA cell firing rates and that stimulated [DA]o varied markedly among DA cell body regions have important implications for how dendritically released DA may function in the physiology and pathophysiology of substantia nigra and VTA.

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