Journal
JOURNAL OF NEUROSCIENCE
Volume 20, Issue 14, Pages 5374-5381Publisher
SOC NEUROSCIENCE
DOI: 10.1523/JNEUROSCI.20-14-05374.2000
Keywords
startle; superior colliculus; bicuculline; muscimol; SKF 82958; D-1 receptor
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Funding
- NIMH NIH HHS [MH47840, R37 MH047840, MH57250, MH00004, R01 MH057250, R01 MH047840] Funding Source: Medline
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GABA transmission in the deep layers of the superior colliculus/deep mesencephalic reticular formation (deep SC/Me) mediates several motor responses, including those expressed after systemic administration of dopamine agonists. In the present study we examined the role of the deep SC/Me in the modulation of the acoustic startle reflex and its enhancement by the dopamine D-1 agonist SKF 82958. Rats were implanted with bilateral cannulas into the deep SC/Me or superficial layers of the SC (super SC) and 1 week later were infused with various compounds. The GABA(A) antagonist bicuculline (0, 5, and 10 ng) produced a dose- and time-dependent enhancement of startle after infusion into the deep SC/Me, but not the super SC. Infusion of the GABA(A) agonist muscimol (0.1 mu g) into the deep SC/Me, but not the super SC, blocked the enhancement of startle by systemic SKF 82958 (1 mg/kg) but had no effect on baseline startle by itself. This effect was not produced by infusion of the D-1 antagonist SCH 23390 (1 mu g) or the glutamate antagonist NBQX (0.1 mu g). Deposits of FluoroGold into the deep SC/Me, combined with immunohistochemistry for glutamic acid decarboxylase (GAD), confirmed a direct GABAergic input from the substantia nigra pars reticulata (SNr) to the deep SC/Me. These results suggest that GABA tone in the deep SC/Me modulates the expression of startle as well as the enhancement of startle by dopamine D-1 agonists. On the basis of these data and previous work, we have proposed a striatonigral-tectal-reticular neural pathway mediating the effects of dopamine D-1 agonists on startle.
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