Iren Belcheva

Asymmetry in behavioral responses to cholecystokinin microinjected into rat nucleus accumbens and amygdala

The behavioral responses of rats to uni- or bilateral microinjections of the octapeptide cholecystokinin (CCK-8) into the left and/or right or both nucleus accumbens (NA) or amygdalae were studied. There were two main findings of effects of microinjections of CCK-8 into NA. First, bilateral injections of CCK-8 into NA dose-dependently decreased the horizontal activity. The second more important finding was that CCK-8 at a specific dose (0.01 micrograms) injected into the right NA increased the number of horizontal movements 6-fold as compared to the injection into the left NA. Neither uni- nor bilateral injections of CCK-8 into NA at all doses used induced changes in the vertical movements. CCK-8 injected into left, right or both amigdalae increased locomotion at the lowest dose (0.01 microgram), while at the high doses (0.5 and 1.0 microgram) it significantly decreased it. The plus-maze test confirmed the anxiogenic effect of CCK-8 (0.01 microgram) injected into amigdalae. CCK-8 exerted a favorable effect on learning and memory (shuttle-box) when injected into the left but not into the right amygdala. Injection of CCK-8 (0.01 micrograms) into left amygdala provoked a 4-fold increase of the number of avoidances as compared to the microinjection into the right amygdala.

Lateralized learning and memory effects of angiotensin II microinjected into the rat CA1 hippocampal area

The effects of angiotensin II (ANG II) microinjected unilaterally (left or right) and bilaterally (left and right) at a dose of 0.5 microg (0.5 nmol) into the CA1 hippocampal area of male Sprague Dowley rats on learning and memory (shuttle box) were studied. Bilateral microinjections of ANG II improved learning, i.e. increased the number of avoidances during the two training days as compared to the respective controls microinjected with saline. ANG II facilitated learning and memory, especially when microinjected into the left CA1 hippocampal area as compared to the respective controls microinjected with saline. Left-side microinjection of ANG II increased the number of avoidances on the first and second training day as compared to the right-side microinjection of ANG II. These findings suggest asymmetric effects of ANG II on cognitive processes in hippocampus.

Hippocampal asymmetry in the behavioral responses to the 5-HT1A receptor agonist 8-OH-DPAT

The present study examined the behavioral responses of rats to unilateral and bilateral injections of the selective serotonin 1A (5-HT1A)-receptor agonist 8-hydroxydipropylaminotetralin hydrobromide (8-OH-DPAT) 1 microgram into the hippocampal CA1 area of male Wistar rats. 8-OH-DPAT increased locomotor activity, which was most pronounced with injections into the left hippocampus. The agonist impaired learning and memory (shuttle-box), especially when injected into the right hippocampus. The elevated plus-maze experiments showed that neither left nor right nor bilateral hippocampal injections of 8-OH-DPAT produced any anxiogenic effect. However, with Vogels conflict test, right injections of 8-OH-DPAT produced anxiety. The present study has revealed hippocampal asymmetry in the behavioral responses to the 5-HT1A-receptor agonist 8-OH-DPAT.

Antinociceptive effect of somatostatin microinjected into caudate putamen.

The effects of somatostatin microinjected bilaterally and unilaterally (left or right) at a dose of 10, 50 and 100 ng into the caudate putamen of male Wistar rats on nociception (analgesy-meter test) were studied. Somatostatin injected into caudate putamen resulted in analgesia. Bilateral microinjections of somatostatin significantly increased the pain threshold in a dose-dependent manner, i.e. somatostatin exerted antinociceptive effect. The pain threshold after left-side microinjections was significantly higher than that after injections into right-side. These findings suggest antinociceptive and asymmetric effects of somatostatin on pain in the caudate putamen.

Behavorial responses to the 5-HT1A receptor antagonist NAN190 injected into rat CA1 hippocampal area

1. Behavioral responses to unilateral and bilateral microinjections of the 5-HT1A receptor antagonist, NAN190 [1-(2-methoxyphenyl)-4-[4-(2-phthalimido) butyl]piperazine hydrobromide] (1 microgram), into the hippocampal CA1 area of male Wistar rats were studied. 2. NAN190 decreased locomotor activity (the number of horizontal and vertical movements). The effect was most pronounced with microinjections of NAN190 into the right hippocampus. 3. Microinjections of NAN190 facilitated learning and memory in shuttle-box testing. 4. Microinjections of NAN190 had an anxiogenic effect in elevated plus-maze experiments and Vogels conflict test. 5. The different behavioral responses to left and right microinjections of NAN190 in some of the behavioral tests suggest functional asymmetry of 5-HT1A receptors in the CA1 hippocampal area.

Hemispheric asymmetry in behavioral response to D1 and D2 receptor agonists in the nucleus accumbens

The present study examined the locomotor response of rats to unilateral injections of the mixed D1/D2 agonist apomorphine, the D2 agonist quinpirole, and the D1 agonist SKF 38393 into the left or right nucleus accumbens (NA) of male Sprague-Dawley rats. There were 2 main findings. First, unilateral (left or right) injections of apomorphine, quinpirole, or SKF 38393 all provoked locomotor hyperactivity. The second and more important finding was that, at specific dosages, apomorphine and SKF 38393 injections into the right NA produced significantly more locomotor hyperactivity than identical injections into the left NA. These findings suggest the presence of asymmetries in the NA which may involve quantitative differences in the distribution of D1 and D2 receptors.

Hippocampal asymmetry in serotonergic modulation of learning and memory in rats.

The modulation of learning and memory after left or right microinjections of the selective 5-HT1A receptor agonist 8-OH-DPAT and of the 5-HT1A receptor antagonist NAN190 into the hippocampal CA1 area of male Wistar rats was studied. Microinjections of 8-OH-DPAT (1 µg) into the right or left CA1 hippocampal area produced a significant decrease in the number of avoidances in a shuttle box. The impairing effect of 8-OH-DPAT was more pronounced when injected into the right hippocampus compared to the left one. Microinjections of NAN190 (1 µg) into the right or left CA1 hippocampal area produced a significant increase in the number of avoidances in a shuttle box. Right microinjections of NAN190 increased the number of avoidances more strongly than compared to left injections. These effects on learning and memory were more pronounced after injection of either of the serotonergic agents into the right CA1 hippocampal area compared to the left. The stronger memory-modulating effect after injection of 8-OH-DPAT or NAN190 into the right CA1 hippocampal area suggests a rightward bias in the rat.

Behavioral effects of angiotensin II microinjected into CA1 hippocampal area

The behavioral responses of rats to bilateral microinjections of angiotensin II (ATII) at doses of 0.1, 0.5 and 1.0 microg into the hippocampal CA1 area of male Sprague-Dawley rats were studied. ATII affected locomotor activity (the number of horizontal and vertical movements) in a dose-related U-shaped manner. In the elevated plus-maze experiments, ATII at a dose of 0.1 microg microinjected bilaterally into the CA1 hippocampal area increased the number of entries into the open arms, suggesting some anxiolytic effect.

Differential involvement of hippocampal vasoactive intestinal peptide in nociception of rats with a model of depression

The effects of VIP microinjected unilaterally (left or right) into the hippocampal CA1 area at a dose of 10 and 100 ng or bilaterally (10 ng), on nociception of male Wistar rats with a model of depression (bilateral olfactory bulbectomy-OBX) were studied. Nociception was examined applying mechanical pressure on the left hind paw of the rat (analgesy-meter test). It was found that in OBX rats the pain threshold is increased. VIP showed differential effects depending on the side and dose of administration. The pain threshold after left-side microinjections of VIP into the hippocampal CA1 area of OBX rats was significantly higher than that after injections into right-side. There are no significant differences between right-side VIP-treated and OBX rats. Bilateral microinjections of VIP also exerted antinociceptive effect. These findings suggest that the hippocampal lateralized antinociceptive effect of VIP in OBX rats depends on the hemisphere of injection and suggest that VIP-ergic neurons in the hippocampal CA1 area may play differential role in nociception of rats with a model of depression.

Behavioral effects of somatostatin microinjected into caudate putamen.

The present study examined the behavioral responses to bilateral microinjections of somatostatin (SRIF) into caudate putamen of male Wistar rats. SRIF locally administered at doses of 10, 50 and 100 ng/side dose-dependently affected locomotor activity, as reflected in both horizontal and vertical movements. SRIF modulated locomotor activity in a biphasic manner, exerting an inhibitory and a facilitatory effect. In the elevated plus-maze experiments, SRIF at doses of 50 and 100 ng/side microinjected bilaterally into caudate putamen decreased only the total number of entries in the open and closed maze arms, confirming the suppressing effect of SRIF on locomotion at the first 5 min.