Elsevier

Neuroscience

Volume 76, Issue 3, 11 December 1996, Pages 715-724
Neuroscience

The basolateral amygdala regulates sensorimotor gating of acoustic startle in the rat

https://doi.org/10.1016/S0306-4522(96)00218-7Get rights and content

Abstract

The acoustic startle reflex is a co-ordinated contraction of the skeletal musculature in response to a sudden, intense sound. One form of startle plasticity, “prepulse inhibition”, is the normal suppression of the startle reflex when the intense startling stimulus is immediately preceded by a weak pre-stimulus. Prepulse inhibition is utilized as an operational measure of sensorimotor gating, and is significantly impaired in several neuropsychiatric disorders that are characterized by symptoms associated with central inhibitory deficits. In rats, prepulse inhibition is disrupted by central dopamine activation or by manipulations of limbic cortical structures including the prefrontal cortex and hippocampus. In the present study, we assessed prepulse inhibition in rats after surgical and pharmacologic manipulations of the basolateral amygdala. Quinolinic acid lesions of the basolateral amygdala significantly reduced prepulse inhibition without significantly changing startle amplitude. These lesions also blocked fear-potentiated startle, which is known to be regulated by the basolateral amygdala. The prepulse inhibition-disruptive effects of basolateral amygdala lesions were not reversed by systemic injection of the dopamine antagonist haloperidol at doses that totally restored prepulse inhibition in apomorphine-treated rats. In other studies, intra-amygdala infusion of the competitive N-methyl-d-aspartate antagonist dl-2-amino-5-phosphonovaleric acid (0, 0.15, 1.5, 4.5 μg) dose-dependently reduced prepulse inhibition.

These data suggest that the basolateral amygdala regulates sensorimotor gating by mechanisms that are independent of central dopamine hyperactivity.

Section snippets

Animals

Male Sprague–Dawley rats (225–250 g) were housed in groups of two to three and maintained on a reversed 12 h:12 h light/dark schedule (lights off at 07.00) with food and water provided continuously. Behavioral testing occurred between 09.00 and 15.00, during the dark phase, when acoustic startle is most robust and least variable.[9]Rats were handled individually within three days of arrival. All surgery occurred between seven and 14 days after shipment arrival, using Equithesin anesthesia and a

Experiment 1: effects of quinolinic acid lesions of the basolateral amygdala on prepulse inhibition and fear-potentiated startle

This experiment was designed to evaluate the effects of quinolinic acid lesions of the BLA on sensorimotor gating and fear-potentiated startle. The effects of BLA lesions on PPI are seen in Fig. 1. PPI was significantly reduced after quinolinic acid lesions of the BLA. A two-way ANOVA using treatment (lesion group, n=14; sham group, n=15) as the between-subject factor with repeated measures on prepulse intensity revealed a significant effect of treatment (F1,27=37.66, P<0.001), a significant

Discussion

In the present study, cell-specific lesions of the BLA reduced PPI and fear-potentiated startle. This finding is consistent with a recent report that was published during the period of review of the present paper.[11]The PPI-disruptive effects of BLA lesions were not mediated via increased forebrain DA transmission at D2 receptors, since they were not opposed by DA D2 receptor blockade. NMDA-substrates in the BLA appear to critically regulate PPI, since intra-BLA infusion of the NMDA antagonist

Unlinked reference

[13]

Acknowledgements

These studies were supported by NIMH Awards MH-48381 and MH-42228, by funding from Sandoz Pharmaceuticals, and by an award from the Alfred P. Sloan Foundation (NRS). Fang-Jung Wan was supported by the National Defense Medical Center, Taipei, Taiwan, ROC. Excellent technical assistance was provided by Ms Pamela Auerbach and Mr Navid Taaid.

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