Haloperidol blocks the acquisition but not the retrieval of a conditioned sensitization to apomorphine

Abstract

The dopamine agonist apomorphine (apo) elicits stereotyped pecking bouts in pigeons, a response which increases with successive apo injections. The present study sought, first, to confirm the hypothesis that this sensitization arises through a Pavlovian conditioning driven by both external and internal cues; and, secondly, to advance the hypothesis that during this learning the dopaminergic activation only initiates a process that probably ends in glutamatergic synapse modifications. The conditioned nature of the sensitization to apo was examined in two separate experiments that compared context contingent and context uncontingent apo treatments. The role of dopaminergic mechanisms in the acquisition, maintenance and retrieval of sensitization-conditioned pecking was examined by administering the dopamine antagonist haloperidol (hal) either before, during or after apo sensitization treatments. A contingency between context and apo was found to be essential for the acquisition and retrieval of apo-sensitized pecking. A pretreatment with hal did not curtail a subsequent sensitization to apo. When hal was co-administrated with apo it suppressed the initial pecking response to apo and blocked the acquisition of sensitized responding. A pecking response normally observed when apo-sensitized pigeons are challenged with saline (sal) in the same cage in which they were sensitized, was also absent. When hal was co-administered with apo after the sensitization was complete this led at first to an only partial apo response suppression. When treated with hal in the same cage, already sensitized pigeons responded much as if they had been challenged with sal. The sensitization induced by apo was thus blocked by hal co-administered during acquisition, but during the maintenance or retrieval phase hal did not impair a previously sensitized responding. It is concluded that when pigeons are sensitized to apo, dopaminergic mechanisms are implicated in initiating the neural modifications that underlie the conditioned sensitization, but that they themselves are not importantly altered.

Sensitization to apomorphine in pigeons

“…Furthermore, according to the data presented in Fig. As this fully concurs with similar findings reported previously (Lindenblatt and Delius, 1987;Wynne and Delius, 1995;Godoy and Delius, 1999;Keller and Delius, 2001;Acerbo et al, 2003a), the CR cage specificity can be considered quite robust. Note, however, that all the pigeons of the present experiment had been presensitized with repeated 0.9 mg/kg apo treatments before being subjected to the first 0.1 mg/kg treatment.…”

“…It is worth pointing out that in both experiments the groups that pecked the least during day 1 of the apo-sensitization procedure also exhibited a lesser response increase until day 6, and also pecked less on day 7 when challenged with saline instead of apo. The present results clearly demonstrated this in Bochum stock pigeons, thus extending equivalent findings with Konstanz stock pigeons (Godoy and Delius, 1999;Acerbo et al, 2003aAcerbo et al, , 2003b. Differences in apo sensitivity have also been found in domestic fowl strains selectively bred for spontaneous high and low frequencies of pecking at cage-mate feathers (allopecking; Van Hierden et al, 2005;Kjaer, 2009).…”

“…Experiments carried out in our laboratory have consistently shown that in pigeons the sensitization, or more precisely the IR, that develops upon repeated administration of apo is strongly cage-environment specific (Experiment 4; Burg et al, 1989;Godoy and Delius, 1999;Keller and Delius, 2001;Acerbo et al, 2003a; cf. also Akins and Geary, 2008, cocaine in quail).…”

“…Note, however, that for the demonstration of cage specificity it is essential that the cages used as controls be physically markedly different from those used for the sensitization procedure to avoid a cross-transfer effect due to simple stimulus generalization (Experiment 6; Godoy and Delius, 1999). Several different control treatments have indicated that the marked context dependency is not due to any simple differential behavioral habituation or sensitization to the experimental cages or procedures (Experiments 4 and 8; Godoy and Delius, 1999;Keller and Delius, 2001;Acerbo et al, 2003a).…”

“…In earlier publications, we have explored several of the variables influencing this spectacular response (Deviche, 1983;Delius, 1985;Delius, 1987, 1988;Burg et al, 1989;Siemann and Delius, 1992a;Delius, 1995, 1996;Godoy and Delius, 1999;Keller and Delius, 2001;Keller et al, 2002;Acerbo et al, 2003aAcerbo et al, , 2003bAcerbo and Delius, 2004). Pecking elicited by apo in birds is an impressive response.…”