Repeated pre-trial and post-trial low and high dose apomorphine treatments induce comparable inhibitory/excitatory sensitization and conditioned drug effects

Psychostimulant induced behavioral sensitization: The contribution of drug stimuli to context and Pavlovian conditioned stimuli

The drug induced enhancement of behavioral stimulation effects with repeated drug treatments is frequently context specific implicating associative processes. Attempts to label these effects as Pavlovian conditioned drug responses have generally been dismissed as it has frequently been demonstrated that the test environment cues alone are insufficient to elicit the sensitized drug response. In this paper evidence will be presented showing that the sensitized drug response can in fact be elicited by test environment cues in a non-drug test. The key reason test environment cues alone are an inadequate conditioned stimulus to elicit the sensitized drug response with commonly used behavioral sensitization protocols is because drug stimulus cues of the drug used to induce behavioral sensitization are conflated with the test environment cues so that the conditioned stimulus has been transformed into a compound conditioned stimulus comprised of the test environment cues co-mingled with the drug stimulus cues In this paper we will present evidence that shows that modifications in the drug testing protocol such as placement of the subject into the test environment immediately after drug administration so that the test environment cues precede the onset of the drug response creates the opportunity for a Pavlovian test environment/drug response association. Also, the use of posttest drug administration can enable the test environment stimulus trace to be selectively paired with the drug response and acquire conditioned stimulus properties and become sufficient to elicit the sensitized behavioral drug response. From a Pavlovian conditioning perspective, repeated pairing of the drug with the test environment enables the conditioned drug response test response to add to the unconditioned drug response to generate a behavioral sensitization effect. Critically, the context needs to be recognized as a conditioned stimulus composite comprised of the test environment cues coupled with the drug generated stimulus cues.

Ankk1 Loss of Function Disrupts Dopaminergic Pathways in Zebrafish

Ankyrin repeat and kinase domain containing 1 (ANKK1) is a member of the receptor-interacting protein serine/threonine kinase family, known to be involved in cell proliferation, differentiation and activation of transcription factors. Genetic variation within the ANKK1 locus is suggested to play a role in vulnerability to addictions. However, ANKK1 mechanism of action is still poorly understood. It has been suggested that ANKK1 may affect the development and/or functioning of dopaminergic pathways. To test this hypothesis, we generated a CRISPR-Cas9 loss of function ankk1 zebrafish line causing a 27 bp insertion that disrupts the ankk1 sequence introducing an early stop codon. We found that ankk1 transcript levels were significantly lower in ankk1 mutant (ankk127ins) fish compared to their wild type (ankk1+/+) siblings. In ankk1+/+ adult zebrafish brain, ankk1 protein was detected in isocortex, hippocampus, basolateral amygdala, mesencephalon, and cerebellum, resembling the mammalian distribution pattern. In contrast, ankk1 protein was reduced in the brain of ankk127ins/27ins fish. Quantitative polymerase chain reaction analysis revealed an increase in expression of drd2b mRNA in ankk127ins at both larval and adult stages. In ankk1+/+ adult zebrafish brain, drd2 protein was detected in cerebral cortex, cerebellum, hippocampus, and caudate homolog regions, resembling the pattern in humans. In contrast, drd2 expression was reduced in cortical regions of ankk127ins/27ins being predominantly found in the hindbrain. No differences in the number of cell bodies or axonal projections detected by anti-tyrosine hydroxylase immunostaining on 3 days post fertilization (dpf) larvae were found. Behavioral analysis revealed altered sensitivity to effects of both amisulpride and apomorphine on locomotion and startle habituation, consistent with a broad loss of both pre and post synaptic receptors. Ankk127ins mutants showed reduced sensitivity to the effect of the selective dopamine receptor antagonist amisulpride on locomotor responses to acoustic startle and were differentially sensitive to the effects of the non-selective dopamine agonist apomorphine on both locomotion and habituation. Taken together, our findings strengthen the hypothesis of a functional relationship between ANKK1 and DRD2, supporting a role for ANKK1 in the maintenance and/or functioning of dopaminergic pathways. Further work is needed to disentangle ANKK1’s role at different developmental stages.

A new method to study learning and memory using spontaneous locomotor activity in an open-field arena

BACKGROUND

Reduced locomotion with repeated exposure to a novel environment is often used as a measure of the basic adaptive learning process of habituation. While this is a well-established and reliable measure of habituation, it is not useful for the investigation of neurobiological changes before and after habituation because of the uncontrolled differential activity levels in a novel versus habituated environment. In this study we report a behavioral method that uses spontaneous locomotion to measure habituation, in which the total spontaneous locomotion in an initially novel environment does not change with repeated testing but, the ratio of central to peripheral activity does change and is indicative of habituation. The test sessions are brief (5 min) and the locomotion is measured in 2 separate zones. The peripheral zone comprises 8/9 of the test arena and the central zone 1/9 of the arena.

RESULTS/COMPARISON WITH EXISTING METHODS

In contrast to methods that use between-session reductions in locomotion to assess habituation, this method employs brief test sessions in which overall activity between sessions does not change, but the distribution of locomotion in the periphery versus the central zone of the arena does change. The brevity of the test session also enables us to utilize post-trial drug treatment protocols to impact memory consolidation.

CONCLUSIONS

The progressive change in the central/peripheral activity ratio with repeated testing can be determined independently of total activity and provides a habituation acquisition function that permits the measurement of neurobiological changes without the complication of effects related to changes in locomotor activity per se. The present report also presents evidence that this method can be used with post-trial drug treatment protocols to study the learning and memory effects of the post-trial treatments without the use of explicit rewards and punishments.

Increased emissions of 50-kHz ultrasonic vocalizations in hemiparkinsonian rats repeatedly treated with dopaminomimetic drugs: A potential preclinical model for studying the affective properties of dopamine replacement therapy in Parkinson's disease

Dopamine replacement therapy used in Parkinson's disease (PD) may induce alterations in the emotional state that can underlie the manifestation of iatrogenic psychiatric-like disturbances. The preclinical investigation of these disturbances is limited, also because few reliable paradigms are available to study the affective properties of dopaminomimetic drugs in parkinsonian animals. To provide a relevant experimental tool in this respect, we evaluated whether dopaminomimetic drugs modified the emission of 50-kHz ultrasonic vocalizations (USVs), a behavioral marker of positive affect, in rats bearing a unilateral lesion with 6-hydroxydopamine in the medial forebrain bundle. Apomorphine (2 or 4 mg/kg, i.p.), L-3,4-dihydroxyphenilalanine (L-DOPA, 6 or 12 mg/kg, i.p.), or pramipexole (2 or 4 mg/kg, i.p.) were administered in a test cage (× 5 administrations) on alternate days. Seven days after treatment discontinuation, rats were re-exposed to the test cage to measure conditioned calling behavior and thereafter received a drug challenge. Hemiparkinsonian rats treated with either apomorphine or L-DOPA, but not pramipexole, markedly vocalized during repeated treatment and after challenge, and showed conditioned calling behavior. Moreover, apomorphine, L-DOPA and pramipexole elicited different patterns of 50-kHz USV emissions and rotational behavior, indicating that calling behavior in hemiparkinsonian rats treated with dopaminomimetic drugs is not a byproduct of motor activation. Taken together, these results suggest that measuring 50-kHz USV emissions may be a relevant experimental tool for studying how dopaminomimetic drugs modify the affective state in parkinsonian rats, with possible implications for the preclinical investigation of iatrogenic psychiatric-like disturbances in PD.

Morphine administered post-trial induces potent morphine conditioned effects if the context is novel but not if the context is familiar

Morphine administered shortly after exposure to a novel environment induces potent locomotor stimulant conditioning. Environmental novelty is important as pre-exposure (PE) to a stimulus can attenuate the capacity to acquire conditioned stimulus (CS). Here, the importance of environmental novelty for the efficacy of an open-field to become a CS for elicitation of a morphine conditioned response was assessed by comparing the effects of morphine administered post-trial following a 5 min exposure to a novel environment versus a PE environment. Four groups of rats (2 vehicle and 2 morphine groups) were used. Two groups received ten daily 5 min non-drug PEs to an open-field arena and the other two groups were not pre-exposed to the environment. Subsequently, all groups received post-trial injections of either vehicle or morphine immediately after each of five daily 5 min sessions in the open-field. Importantly, on the first day of testing prior to the first post-test morphine administration, the locomotor activity of the novel and PE groups was not different. Over the 5 post-trial morphine treatments, the activity of the PE morphine group, the PE vehicle and the novel environment vehicle groups did not change and were equivalent. In contrast, in the novel environment morphine group, a conditioned hyper-activity response increased with repeated post-trial morphine treatments. For the morphine group it is suggested that the novel environment initiated a post-trial stimulus trace that occurred in temporal contiguity with the post-trial drug response and enabled the trace to become a CS for the morphine unconditioned response. In contrast, PE induced a latent inhibition effect in the PE morphine group, thus the post-trial CS trace was insufficient to become associated to the morphine response and no conditioning occurred. In addition to conventional drug induced Pavlovian delay conditioning, the findings are suggestive of drug induced Pavlovian trace conditioning.