Stress-induced attenuation of acoustic startle in low-saccharin-consuming rats

Abstract

Both heightened and attenuated stress reactivity from prior stress also have been documented in other mammals (Koolhaas et al., 2006). Milder stressors tend to attenuate later stress responses, whereas trauma tends to enhance them. However, the same stressor can affect various stress response systems differently (e.g. sympathetic versus hypothalamic-pituitary-adrenal activity, Schommer et al., 2003). Futhermore, situational and dispositional variables moderate the impact of prior stress on subsequent vulnerability (e.g., Gunnar and Vasquez, 2006; Moore et al., 2006). A useful paradigm for studying sequential stress effects in laboratory rats centers on modulation of acoustic startle amplitude. Startle is a defensive reflex, and startle testing after earlier stress constitutes a mild stressor reexposure (Commissaris et al., 2004; Cranney, 1988). Prior experimental stress, such as inescapable shock, usually sensitizes startle. Sensitization has been observed seconds (Pilz et al., 1999), minutes (Davis, 1989), and days (Servatius et al., 1995) after shock. As stressor severity increases, sensitization emerges later and lasts longer. Sensitization emerges a few minutes after ten 0.5-s, 0.6-mA footshocks and is gone within 40 min; at 1.0 or 1.4 mA, sensitization emerges in 20-30 min and is robust at 40 min (Davis, 1989). Sensitization is detectable a week after one session of forty 3-s, 2-mA tailshocks, but not until 10 days after three sessions (Servatius et al., 1995; see also Matuszewich et al., 2007). The degree to which shock sensitizes startle also varies among rats. Sprague-Dawley rats sensitize more than Wistars (Pilz et al., 1999; also see, Faraday, 2002). Using startle nonhabituation after shock as a PTSD model, Garrick et al. (2001) observed nonhabituation only in rats with low baseline startle amplitudes. Milde et al. (2003) also found sensitization after shock in a subset of rats, those with low plasma corticosterone (CORT). Compared to sensitization, stress-induced startle attenuation seems rarer and more circumscribed. Beck and Servatius (2005, 2006) observed attenuation 2 h after shock but not after restraint, and only in intact females, concluding that attenuation depends on nociception and ovarian hormones. However, Conti and Printz (2003) observed attenuated startle 24 h after restraint in males of some rat strains. Stress-attenuated startle appears to be a potentially important phenomenon in need of further study. Accounting for individual differences in stress-induced changes in startle requires approaches in which dispositional variables are well characterized. Selective breeding is such an approach: Lines are developed on a clearly operationalized phenotype, after which phenotypic correlates and functional relationships are examined. For example, Roman low (RLA) and high (RHA) avoidance rats are

Only susceptible rats exposed to a model of PTSD exhibit reactivity to trauma-related cues and other symptoms: An effect abolished by a single amphetamine injection

“…The literature generally reports increases in ASR [1,12,17] due to increases in arousal. However, as mentioned in our previous paper [6], decreases in ASR after PTSD have been reported both in human [26,27] and rats [28,29], and it has been shown that stress may affect the startle amplitude with either an increase or decrease, depending on experimental conditions [30]. So the important point is to show that SPS is able to alter the arousal of traumatized rats.…”

Peritraumatic startle response predicts the vulnerability to develop PTSD-like behaviors in rats: a model for peritraumatic dissociation

“…In rats, the startle amplitude increased after mild footshocks, while it began to negatively correlate with the shock intensity when the shock current increased to a certain level (Davis and Astrachan, 1978), and severe stress decreased the startle response (Gonzales et al, 2008). These results suggested that the ASR attenuation is a unique phenomenon after intense stress, which may protect individuals from disruptive influences of subsequent abrupt stimuli.…”

“…Plasma corticosterone level in rodents or cortisol release in humans was negatively correlated with ASR (Miller and Gronfier, 2006; Gonzales et al, 2008; Miller et al, 2009), and oral hydrocortisone could inhibit fear potentiated startle (Miller et al, 2011). These results indicated that the elevated cortisol or corticosterone level is one of the reason on startle attenuation immediate after severe stress.…”

Sweet Success, Bitter Defeat: A Taste Phenotype Predicts Social Status in Selectively Bred Rats

“…[29]), yielded the usual hyperstartle in LoS rats, t (68) = 2.89, P  = .005. A two-bottle water vs. saccharin test conducted after the conclusion of the study confirmed the selection phenotype, t (68) = 16.83, P <.001.…”

“…After a 3-min habituation period, 30 startle trials occurred on a 10-sec fixed-time schedule. Full-body startle reflex amplitude was recorded from a digital display (arbitrary units; see [29] for additional details). Reduction to 92% of free-feeding bodyweight through chow rationing began after startle testing.…”