Tamás Ollmann

The role of neurotensin in passive avoidance learning in the rat central nucleus of amygdala

Tridecapeptide neurotensin (NT) acts as a neurotransmitter and/or neuromodulator and plays a role in learning and reinforcement. The central nucleus of amygdala (CeA), which is relatively rich in NT and neurotensin-1 receptors (NTS1), participates in the regulation of memory and learning mechanisms. The aim of this study was to examine the possible effect of NT and NTS1 antagonist (ANT) on passive avoidance learning after their microinjection into the CeA of male wistar rats. NT significantly increased the latency time. Effect of NT was blocked by ANT pretreatment. ANT in itself had no effect. Our results show that in the rat CeA NT facilitates passive avoidance learning via NTS1.

Effects of neurotensin in amygdaloid spatial learning mechanisms

Neurotensin (NT) acts as a neurotransmitter and/or neuromodulator and plays a role in learning and reward related processes. The central nucleus of amygdala (CeA) participates in the regulation of memory and learning mechanisms. In Morris water maze test, rats were microinjected with NT or neurotensin receptor-1 (NTS1) antagonist SR 48692 (ANT). NT significantly reduced the escape latency. Effect of NT was blocked by ANT pretreatment. Our results show that in the rat CeA NT facilitates spatial learning. We clarified that NTS1s are involved in this action.

Microinjection of RFRP-1 in the central nucleus of amygdala decreases food intake in the rat

Several members of the RFamide peptide family are known to have role in the regulation of feeding. For example, neuropeptide FF and prolactin-releasing peptide cause anorexigenic, while 26RFa and QRFP result in orexigenic effects in rodents. I.c.v. microinjection of neuropeptide RFRP-1 significantly reduced food and water intake in chicks. However, feeding related effects of RFRP-1 have not been studied in mammals yet. The central part of amygdala (CeA) is essentially involved in the regulation of feeding and body weight. RFRP-1 positive nerve cells were detected in the rat hypothalamus and RFRP-1 immunoreactive fibers were identified in the CeA. RFRP analogs bind with relatively high affinity to the NPFF1 and NPFF2 receptors (NPFF-R). RFRP-1 has potent activity for NPFF1. Significant expression of NPFF1 was detected in the CeA. To evaluate the role of RFRP-1 in feeding regulation rats were microinjected with different doses of RFRP-1 and their food intake were quantified over a 60min period. Liquid food intake of male Wistar rats was measured after bilateral intraamygdaloid administration of RFRP-1 (25, 50 or 100ng/side, RFRP-1 dissolved in 0.15M sterile NaCl/0.4μl, respectively). The 50ng dose of RFRP-1 microinjections resulted in significant decrease of food intake. The 25 and 100ng had no effect. Action of 50ng (37.8pmol) RFRP-1 was eliminated by 20ng (41.4pmol) RF9 NPFF-R antagonist pretreatment. In open-field test 50ng RFRP-1 did not modify spontaneous locomotor activity and general behavior of animals did not change. Our results are the first reporting that RFRP-1 injected to the CeA result in a decrease of liquid food consumption. This is a receptor-linked effect because it was eliminated by a NPFF-R selective antagonist.

Positive reinforcing effect of oxytocin microinjection in the rat central nucleus of amygdala

Neuropeptide oxytocin (OT) receives increasing attention since, it plays a role in various behaviors including anxiety, drug addiction, learning, social recognition, empathy, pair bonding and decreased aggression. The central nucleus of the amygdala (CeA), part of the limbic system, plays an important role in learning, memory, anxiety and reinforcing mechanisms. CeA was shown to be rich in OT-receptors (OTR). The aim of our study was to examine the possible effects of OT and OTR antagonist in the CeA on reinforcement using the conditioned place preference test and on anxiety using the elevated plus maze test. Male Wistar rats were microinjected bilaterally with 10 ng OT or 100 ng OT (Sigma: O6379, injected in volume of 0.4μl) or 10ng OTR antagonist (Sigma: L-2540) alone, or OTR antagonist 15 min prior 10 ng OT treatment or vehicle solution into the CeA. Rats receiving 10 ng OT spent significantly more time in the treatment quadrant during the test session, while 100 ng OT treatment produced no effect. Prior treatment with the non-peptide OTR antagonist blocked the effects of OT. The antagonist in itself did not influence the place preference. The elevated plus maze test revealed that 10 ng OT significantly increased the time spent in the open arms. OTR antagonist pre-treatment could inhibit this effect and the antagonist in itself did not affect the time spent in the open arms. Our results show that in the rat CeA OT has dose-dependent, positive reinforcing and anxiolytic effects, via OTR demonstrated by the blocking effects of selective OTR antagonist.

Intraamygdaloid microinjection of RFamide-related peptide-3 decreases food intake in rats

Some members of the RFamide peptide family are associated with feeding in rodents. For example, neuropeptide FF and prolactin-releasing peptide cause anorexigenic, while 26RFa and QRFP result in orexigenic effects. I.c.v. microinjection of RFamide-related peptide-3 (RFRP-3) facilitates feeding. Feeding related effects of RFRP-3, however, have not been studied after direct brain microinjections in rats. The central part of amygdala (CeA) is essentially involved in the regulation of feeding and body weight. RFRP-3 positive nerve cells were detected in the rat hypothalamus and RFRP-3 immunoreactive fibers were identified in the CeA. RFRP analogs bind with relatively high affinity to the NPFF1 and NPFF2 receptors (NPFF-R). RFRP-3 has potent activity for NPFF-1 that is expressed in the CeA. To evaluate the role of RFRP-3 in feeding regulation rats were microinjected with different doses of RFRP-3 and their food intake were quantified over a 60 min period. Liquid food intake of male Wistar rats was measured after bilateral intraamygdalar administration of RFRP-3 (25, 50, 100 or 200 ng/side, RFRP-3 dissolved in 0.15M sterile NaCl/0.4 μl, respectively). The 50 ng and 100 ng doses of RFRP-3 microinjections resulted in significant decrease of food intake. Twenty-five and 200 ng had no effect. Food intake decreasing effect of RFRP-3 was eliminated by NPFF-R antagonist RF9 pretreatment. In open-field test effective doses of RFRP-3 did not modify spontaneous locomotor activity and general behavior of animals did not change. Our results are the first reporting that RFRP-3 injected to the CeA resulted in a decrease of liquid food consumption. This is a receptor-linked effect because it was eliminated by NPFF-R antagonist.

Role of D1 dopamine receptors of the ventral pallidum in inhibitory avoidance learning.

The mesolimbic dopaminergic system (MLDS) originating from the ventral tegmental area has important role in the regulation of motivation, learning and memory. The ventral pallidum (VP), innervated by the MLDS, is involved in the regulation of adaptive behavior, but its exact role is not known in inhibitory avoidance learning. The VP contains both D1 and D2 dopamine receptors, but the density of the former subtype is more excessive. Therefore, in our present experiments, the role of D1 dopamine receptors of the VP in one trial step-through inhibitory avoidance paradigm was investigated. In the conditioning trial, animals were shocked 3 times with 0.5 mA current for 1s, and subsequently were microinjected bilaterally with D1 dopamine receptor agonist SKF38393 into the VP in three doses (0.1 μg, 1.0 μg or 5.0 μg in 0.4 μl saline). To clarify whether the agonist effect was specific, we also applied the D1 dopamine receptor antagonist SCH23390 (5.0 μg in 0.4 μl saline) 15 min prior the agonist treatment. The D1 dopamine receptor agonist, in a dose-dependent manner, significantly increased the step-through latency during the test trials: retention was significant relative to the controls even after 2 weeks of conditioning. The D1 dopamine receptor antagonist SCH23390 pretreatment eliminated SKF38393 effects in the ventral pallidum. Our results show that D1 dopamine receptor mediated mechanisms in the VP facilitate learning and memory in inhibitory avoidance paradigm and this facilitation is specific because it can be eliminated by D1 dopamine receptor antagonist.

Positive reinforcing effect of neurotensin microinjection into the ventral pallidum in conditioned place preference test

The ventral pallidum (VP) is innervated by the mesolimbic dopaminergic system and it has a key role in motivation, reward, and memory processes. Neurotensin (NT) is an important neuromodulator which has been shown to modulate reinforcement in the ventral tegmental area, in the ventral mesencephalic region and in the central nucleus of amygdala. Neurotensin receptor 1 (NTR1) has already been detected in the VP in abundance, but its role in rewarding and reinforcing processes is not fully understood yet. In our present experiments, the effects of NT on positive reinforcement were investigated in the VP. In conditioned place preference (CPP) test, male Wistar rats were microinjected bilaterally with 100 ng or 250 ng NT in the volume of 0.4 μl. In other groups of animals, 35 ng NTR1 antagonist SR 48692 was applied by itself, or microinjected 15 min before 100 ng NT treatment. One hundred ng dose of NT induced CPP, whereas animals injected with 250 ng NT did not exhibit significant differences from the vehicle group. Antagonist pretreatment inhibited the effect of NT, while the antagonist applied by itself had no effect. Our results show that NT injected into the VP is involved in positive reinforcement. This effect is specific to NTR1 receptors because the development of CPP can be prevented by specific antagonist.

Positive reinforcing effects of RFamide-related peptide-1 in the rat central nucleus of amygdala

The amygdaloid body (AMY) plays an important role in memory, learning and reward-related processes. RFamide-related peptide-1 (RFRP-1) immunoreactive fibers and NPFF1 receptors were identified in the AMY, and previously we verified that neuropeptide RFRP-1 infused into the central nucleus of AMY (CeA) caused food intake decrease. The aim of the present study was to examine the possible rewarding or aversive effects of RFRP-1 in the CeA. In conditioned place preference, test male Wistar rats were microinjected bilaterally with 50 or 100ng RFRP-1 in volume of 0.4μl. In other groups of animals, 20ng NPFF receptor antagonist RF9 was applied or the antagonist was used 15min before 50ng RFRP-1 treatment. Fifty nanograms of RFRP-1 had positive reinforcing properties, while 100ng RFRP-1 had no effect. Prior treatment with NPFF receptor antagonist RF9 could block the rewarding effects of RFRP-1, while the antagonist applied alone did not influence the behavior of rats in place preference paradigm. Our results show that RFRP-1 and NPFF-1 receptors play important roles in the amygdaloid rewarding-reinforcing mechanisms.

Effects of ventral pallidal D1 dopamine receptor activation on memory consolidation in morris water maze test

In the present experiments, in adult male Wistar rats, the effect of microinjection of the D1 dopamine receptor agonist SKF38393 into the ventral pallidum on memory consolidation, as well as on resistance of the resulting memory trace against extinction were investigated in Morris water maze test. SKF38393 was applied in three doses (0.1, 1.0 or 5.0μg in 0.4μl physiological saline, respectively). To clarify whether the effect of the agonist was specific, in a separate group of animals, the D1 dopamine receptor antagonist SCH23390 (5.0μg in 0.4μl physiological saline) was administered 15min prior to 1.0μg agonist treatment. In another group of animals, the same dose of antagonist was applied by itself. The two lower doses (0.1 and 1.0μg) of the agonist accelerated memory consolidation relative to controls and increased the stability of the consolidated memory trace against extinction. Antagonist pretreatment eliminated the effects of the agonist, thus confirming that the effect was selectively specific to D1 dopamine receptors. Our findings indicate that the ventral pallidal D1 dopamine receptors are intimately involved in the control of the consolidation processes of spatial memory.

Substance P and neurotensin in the limbic system: Their roles in reinforcement and memory consolidation

HIGHLIGHTSSP and NT have rewarding effects in various limbic structures.SP and NT facilitate memory consolidation.These effects are mediated mainly by NK1 SP and NTS1 NT receptors.SP and NT influence synaptic plasticity via modulation of DA and ACh systems. ABSTRACT Substance P (SP) and neurotensin (NT) are neuropeptides isolated in the periphery and in the central nervous system. They are involved in various regulatory processes in the gastrointestinal tract, in the circulatory and respiratory systems, kidney and endocrine system. In addition to the peripheral effects, SP and NT act as neurotransmitters and neuromodulators in the central nervous system, regulating various behavioural actions, such as general and motor activity, pain, food and water intake, anxiety, reward/reinforcement and memory consolidation. In the limbic system SPergic and NTergic pathways, terminals and related receptors have been identified. According to several data of literature and to our recently published results, SP and NT have rewarding/reinforcing effects and facilitate memory consolidation in various limbic regions. In this report evidences are provided about the interaction of these neuropeptides with dopaminergic and acetylcholinergic systems. A hypothesis is presented that rewarding/reinforcing effects of SP and NT develop by modulating the mesencephalic dopaminergic system, while their mnemonic effects are mediated via the mesencephalic dopaminergic and the basal forebrain cholinergic systems.