The effects of chronic administration of established and putative antipsychotics on natural prepulse inhibition deficits in Brattleboro rats.

We previously reported that vasopressin deficient Brattleboro (BRAT) rats exhibit deficits in prepulse inhibition (PPI) of the startle reflex that are consistent with PPI deficits exhibited by patients with schizophrenia and other neuropsychiatric disorders. Preliminary evidence indicates that this may be the basis of a predictive model for antipsychotic drug efficacy. Here we report the effects of acute and chronic administration of established and putative antipsychotics on these PPI deficits. BRAT rats, compared to their derivative strain, Long Evans rats, exhibited significantly decreased PPI and startle habituation consistent with patients with schizophrenia and other neuropsychiatric disorders. The second generation antipsychotics, risperidone and clozapine as well as a neurotensin agonist (PD149163) increased BRAT rat PPI, whereas saline, the typical antipsychotic, haloperidol, and a vasopressin analog (1-desamino-D-arginine vasopressin) did not. Similar to their effects in humans, chronic administration of antipsychotic drugs produced stronger effects than acute administration. These results further support the BRAT rat as a model of sensorimotor gating deficits with predictive validity for antipsychotics. The model appears to be able to differentiate first generation from second generation antipsychotics, identify putative antipsychotics with novel mechanisms (i.e., peptides) and reasonably model the therapeutic time course of antipsychotic drugs in humans.

The effects of cross-fostering on inherent sensorimotor gating deficits exhibited by Brattleboro rats.

Prepulse inhibition (PPI) of the startle reflex is an operational measure of sensorimotor gating, a process critical to normal cognitive function. Researchers (D. Feifel & K. Priebe, 2001) have identified PPI deficits in the Brattleboro rat, a genetically vasopressin-deficient strain that is derived from the Long Evans rat. The absence of vasopressin, a neuropeptide involved in affiliative behaviors, may adversely affect the rearing of offspring by Brattleboro dams, perhaps accounting for their attenuated PPI. Cross-fostering of Long Evans and Brattleboro pups did not alter the PPI deficits in Brattleboro rats. However, the magnitude and habituation of the startle response, which normally differs between Brattleboro and Long Evans rats, was not different in cross-fostered rats. The authors' results indicated that abnormal rearing by Brattleboro dams may contribute to the startle magnitude and habituation abnormalities in Brattleboro Rats but not to their PPI deficits, suggesting that their sensorimotor gating deficits result from their genetic deviation from Long Evans rats.

Maternal influences on adult stress and anxiety-like behavior in C57BL/6J and BALB/cJ mice: a cross-fostering study.

The quality of maternal care during early life has a dramatic impact on later stress reactivity and anxiety. Two inbred mouse strains, C57BL/6J and BALB/cJ, differ in levels of maternal care, stress reactivity, and anxiety-like behavior in adulthood. However, the relative contribution of early environmental factors and genetic predisposition to differences in these strains is not known. Maternal care, plasma corticosterone levels, emotionality, and hippocampal and paraventricular nucleus (PVN) glucocorticoid receptor mRNA levels were measured in adult C57BL/6J and BALB/cJ mice. Litters were then cross-fostered and anxiety-like behavior and stress reactivity was assessed in adulthood. Significantly less maternal care and elevated stress-induced corticosterone and emotionality was observed in BALB/cJ compared to C57BL/6J mice. Yet, no strain differences were found in hippocampal or paraventricular nucleus glucocorticoid receptor mRNA levels. Cross-fostering did alter anxiety-like behavior and basal corticosterone levels, which suggests that while genetic differences account for some of the variations between these two strains early rearing conditions also contribute.

Sensorimotor gating effects produced by repeated dopamine agonists in a paradigm favoring environmental conditioning.

RATIONALE: It is not known whether dopamine agonist-induced disruption of prepulse inhibition (PPI) can be conditioned to the environment, a phenomenon established for dopamine agonist-induced locomotor activation and other behaviors. Furthermore, the literature is contradictory regarding whether PPI disruption, like locomotor activity, can become sensitized after repeated dopamine agonist administration. Differences in methodology (e.g. drug-environment pairing) may have contributed to these contradictory findings. OBJECTIVES: In a series of studies, we investigated whether dopamine agonist-induced disruption of PPI could be conditioned and whether repeated administration of dopamine agonists, in a paradigm favorable to conditioning, would produce sensitization to dopamine agonist-induced disruption of PPI. METHODS: One group of rats were administered subcutaneous apomorphine (0.5 mg/kg) daily for 7 (experiment 1) or 5 (experiment 3) consecutive days contingent with startle testing (in testing rooms, immediately before test sessions). A second group received the same apomorphine dose daily in a manner non-contingent with behavioral testing (in home cages after test sessions). The following day, all rats received vehicle injections contingent with the test environment to assess for environmental conditioning (vehicle challenge day). The next day, all animals received a challenge of apomorphine (0.5 mg/kg) contingent with the test environment to assess the contribution of drug-environment pairing on changes observed in apomorphine-induced disruption of PPI (apmorphine challenge day). PPI was measured immediately after drug injections in the test environment. A separate study (experiment 2) tested amphetamine (3.0 mg/kg) using a similar methodology. In a fourth study, rats were pretreated with haloperidol (1.0 mg/kg) or saline prior to receiving daily apomorphine to see if haloperidol could modify the changes in PPI produced by repeated apomorphine administration. RESULTS: On the vehicle challenge day, PPI exhibited by the rats that received daily apomorphine contingent with the testing environment did not differ from the group that received vehicle contingent with the testing environment. However, animals receiving apomorphine contingent with testing exhibited partial tolerance to its PPI effects during the conditioning period. The PPI exhibited by both groups did not differ significantly on the apomorphine-challenge day. Amphetamine produced a complete tolerance to its PPI effects by day 3. Haloperidol pretreatment blocked the PPI tolerance produced by repeated apomorphine injections. CONCLUSIONS: These results suggest: 1) unlike locomotion, PPI disruption induced by apomorphine cannot be conditioned to the environment; 2) unlike locomotion, repeated adminstration of dopamine agonists produce tolerance, rather than sensitization, to PPI; 3) environmental factors do not seem to be critical for PPI tolerance; and 4) dopamine receptors mediate PPI tolerance to apomorphine.