Amygdala dopamine receptors are required for the destabilization of a reconsolidating appetitive memory

Disrupting maladaptive memories may provide a novel form of treatment for neuropsychiatric disorders, but little is known about the neurochemical mechanisms underlying the induction of lability, or destabilization, of a retrieved consolidated memory. Destabilization has been theoretically linked to the violation of expectations during memory retrieval, which, in turn, has been suggested to correlate with prediction error (PE). It is well-established that PE correlates with dopaminergic signaling in limbic forebrain structures that are critical for emotional learning. The basolateral amygdala is a key neural substrate for the reconsolidation of pavlovian reward-related memories, but the involvement of dopaminergic mechanisms in inducing lability of amygdala-dependent memories has not been investigated. Therefore, we tested the hypothesis that dopaminergic signaling within the basolateral amygdala is required for the destabilization of appetitive pavlovian memories by investigating the effects dopaminergic and protein synthesis manipulations on appetitive memory reconsolidation in rats. Intra-amygdala administration of either the D1-selective dopamine receptor antagonist SCH23390 or the D2-selective dopamine receptor antagonist raclopride prevented memory destabilization at retrieval, thereby protecting the memory from the effects of an amnestic agent, the protein synthesis inhibitor anisomycin. These data show that dopaminergic transmission within the basolateral amygdala is required for memory labilization during appetitive memory reconsolidation

Western blot analysis of Kv 2.1 and Kv4.2 subunit expression in cerebral cortex and hippocampus.

<p>Representative immunoblot of cerebral cortex and hippocampus enriched membrane proteins (50 µg/lane) from (Ctr), Aβ_25–35, Aβ_25–35+SP and SP treated rats. Protein markers are shown at right (in kDa). The immunoreactive signals for <b>a</b>) Kv2.1 and <b>b</b>) Kv4.2 were quantified and normalized against β-actin and expressed as a percentage of control (CTR). Data represent mean (±SEM) from 3 independent experiments. Statistically significant differences were calculated by one-way analysis of variance (ANOVA) for repeated measures followed by Tukey's test for multiple comparisons (**p<0.01 versus Ctr value).</p

Immunofluorescence analysis of Kv1.4 subunit expression in hippocampus and cerebral cortex.

<p>Upper panel. Representative immunofluorescence photomicrographs showing Kv1.4 expression in <b>a</b>) hippocampus and <b>b</b>) frontal cortex after memory tests in the four experimental treatments: Control (Saline), Aβ_25–35-i.c.v. treated rats (Abeta), Aβ_25–35-i.c.v. and SP-i.p. treated rats (Abeta+SP), SP-i.p. treated rats (SP). Brain sections were labeled with the neuronal marker NeuN (green) and with the anti Kv1.4 antibody (red). As shown by the merge channel all neurons are Kv1.4 positive. Note the diffuse increase in Kv1.4 fluorescence intensity in the Abeta group and the decrease in the Abeta+SP group compared to the Control. Scale bar: a) 20 µm; b) 60 µm. Lower panel. Histograms showing image analysis performed on neuronal cytoplasm (first row) and the surrounding neuropil (second row). The indexes used were: total fluorescence intensity, vesicles diameters, and vesicles fluorescence intensity. Data represent means (±S.E.M.) obtained from three independent experiments. Statistically significant differences were calculated by one-way analysis of variance (ANOVA) for repeated measures followed by Tukey's test for multiple comparisons (**p<0.01 versus Saline; #p<0.05, ##p<0.01 versus Aβ_25–35treatment).</p

SP reduced Aβ25–35-induced overexpression of Kv1.4 subunit in rat hippocampal neurons.

<p><b>a</b>) Example of Western blot obtained from hippocampal cultures exposed to 20 µM Aβ_25–35 (Aβ alone or in the presence of SP (100 nM) and analyzed 48 h later using a polyclonal antibody against Kv1.4 subunit. The same blots were stripped and reprobed with an antibody against β-actin as internal control (lower panels). Quantitative analysis is depicted below the blots and was determined by band densitometry analysis considering the values found in CTR cells as 100. Data represent means (±S.E.M.) obtained from 4 independent experiments run in duplicate. (**p<0.001 versus CTR, #p<0.05 versus Aβ_25–35 treatment). <b>b</b>) Representative immunofluorescence photomicrographs showing Kv1.4 expression in primary hippocampal cultures. Note the increase in immunofluorescence in the Aβ_25–35 neurons, as compared to control neurons, reversed by SP treatment. Images were obtained from three independent experiments. Scale bar: 20 µm.</p

Data_Sheet_1_Reduction of inflammation and mitochondrial degeneration in mutant SOD1 mice through inhibition of voltage-gated potassium channel Kv1.3.PDF

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with no effective therapy, causing progressive loss of motor neurons in the spinal cord, brainstem, and motor cortex. Regardless of its genetic or sporadic origin, there is currently no cure for ALS or therapy that can reverse or control its progression. In the present study, taking advantage of a human superoxide dismutase-1 mutant (hSOD1-G93A) mouse that recapitulates key pathological features of human ALS, we investigated the possible role of voltage-gated potassium channel Kv1.3 in disease progression. We found that chronic administration of the brain-penetrant Kv1.3 inhibitor, PAP-1 (40 mg/Kg), in early symptomatic mice (i) improves motor deficits and prolongs survival of diseased mice (ii) reduces astrocyte reactivity, microglial Kv1.3 expression, and serum pro-inflammatory soluble factors (iii) improves structural mitochondrial deficits in motor neuron mitochondria (iv) restores mitochondrial respiratory dysfunction. Taken together, these findings underscore the potential significance of Kv1.3 activity as a contributing factor to the metabolic disturbances observed in ALS. Consequently, targeting Kv1.3 presents a promising avenue for modulating disease progression, shedding new light on potential therapeutic strategies for ALS.</p

Western blot analysis of Kv1.4 subunit expression in hippocampus and cerebral cortex.

<p>Representative immunoblot of (<b>a</b>) hippocampus and (<b>b</b>) cerebral cortex enriched membrane proteins (50 µg/lane) from (Ctr), Aβ_25–35, Aβ_25–35+SP and SP treated rats. Protein markers are shown at right (in kDa). The immunoreactive signals at 97 and 110 kDa were quantified and normalized against β-actin and expressed as a percentage of the control (Ctr). Data represent mean (±SEM) from 5 independent experiments. Statistically significant differences were calculated by one-way analysis of variance (ANOVA) for repeated measures followed by Tukey's test for multiple comparisons (**p<0.01 versus Ctr value; #p<0.05 versus Aβ_25–35 treatment).</p

Neuroprotective effects of SP on memory impairments induced by intracerebroventricular injection of Aβ25–35.

<p>(a) Timeline and experimental design. All animals received an infusion (i.c.v.) of Aβ_25–35 (2 µg/µl; 10 µL injection volume) or its vehicle (PBS 10 µL injection volume) and daily treated (7 days) with SP (50 µg/ml/Kg, i.p.) or its vehicle (saline solution 0.9%, i.p.). On the 31^st day after surgery rats were given a daily training session of 4 trials for 3 consecutive days (days 31^st–33^rd). On the 34^th day after surgery the retention of the spatial training was assessed during a 1 min probe trial. On the 35^th day after surgery rats were given a daily training session of 5 trials for 4 consecutive days (days 35^th–38^th). (b) Mean (±S.E.M.) distance traveled to the escape platform on 4 trials of 3 consecutive days of acquisition learning sessions. (c) Time spent (mean ±S.E.M.) during the 1-minute probe trial in the target quadrant and (d) illustrative paths of all animals for the probe test session. (e) Mean (±S.E.M.) distance traveled to the escape platform on 4 trials of 4 consecutive days of the reversal learning sessions (the hidden platform were relocated in a new position each day). * p<0.05 Aβ_25–35/Sal <i>vs</i> PBS/Sal; # p<0.05 Aβ_25–35/Sal <i>vs</i> PBS/SP; $ p<0.05 Aβ_25–35/Sal <i>vs</i> Aβ_25–35/SP. PBS/Sal, n = 10; PBS/SP, n = 10; Aβ_25–35/Sal n = 12; Aβ_25–35/SP, n = 10.</p