Abstract
The cerebellum receives dopaminergic innervation and expresses the five types of described dopaminergic receptors. The cerebellar function involves both motor movement and cognition, but the role of cerebellar dopaminergic system on these processes remain unclear. The present study explores the behavioral responses to intracerebellar microinjection of dopaminergic agents in motor and emotional memory. For this, naïve Swiss mice had their cerebellar vermis implanted with a guide canula, received a intravermis microinjection of Dopamine, D1-like antagonist SCH-23390 or D2-like antagonist Eticlopride, and underwent a behavioral analysis of motor learning (by a Rotarod and balance beam learning protocol) or aversive memory acquisition (by the inhibitory avoidance task). The mixed-effects analysis was used to evaluate groups performance, followed by Tukey’s post hoc when appropriated. In this study, Dopamine, SCH-23390 and Eticlopride at the doses used did not affected motor control and motor learning. In addition, the administration of Dopamine and SCH-233390 had no effects on emotional memory acquisition, but the animals that received the highest dose of Eticlopride had an improvement in aversive memory acquisition, shown by a suppression of its innate preference for the dark compartment of the inhibitory avoidance apparatus following an exposure to a foot shock. We propose that cerebellar dopaminergic D2 receptors seem to participate on the modulation of aversive memory processes, without influencing motor performance at the doses used in this study.
Highlights
Dopamine is a biogenic amine derived from hydroxylation and decarboxylation of tyrosine (Rodwell, 2003), and its most prominent neuronal portion is located in the ventral midbrain, sending projections to multiple areas of the central nervous system (CNS) (Chinta and Andersen, 2005)
There was no difference for the crossing latency among the groups that received Dopamine in different doses and the control group (F3,38 = 2.35; p = 0.09), which indicates that the microinjection in the cerebellar vermis of Dopamine in the doses 0.29, 0.86, and 1.5 nmol/0.1 ul had no significant behavioral effects on the emotional memory acquisition in mice in this study (Table 2 and Figure 3)
We found that mice that received an intracerebellar microinjection of the D2-like antagonist Eticlopride at dose 2.65 nmol/0.1 ul had an improvement in aversive emotional memory, by a suppression of its innate preference for the dark compartment of the inhibitory avoidance apparatus following an exposure to a foot shock
Summary
Dopamine is a biogenic amine derived from hydroxylation and decarboxylation of tyrosine (Rodwell, 2003), and its most prominent neuronal portion is located in the ventral midbrain, sending projections to multiple areas of the central nervous system (CNS) (Chinta and Andersen, 2005). There are five characterized types of dopaminergic receptors (D1, D2, D3, D4, and D5), which are classified into two subgroups, according to its structural and functional similarities: Intracerebellar Dopaminergic Agents and Memory. The dopaminergic system is known to play a role in learning and memory processes in the prefrontal cortex (PFC) (Puig et al, 2014), anterior cingulate cortex, basolateral amygdala (Zheng et al, 2008), and hippocampus (Hamilton et al, 2010). Despite the dopaminergic innervation (Panagopoulos et al, 1991) and expression of the five types of dopaminergic receptors in the cerebellum (Barili et al, 2000) its role on modulation of motor and emotional mnemonic processes is unclear
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