Pheromone-Induced Odor Associative Fear Learning in Rats

Alarm pheromones alert conspecifics to the presence of danger. Can pheromone communication aid in learning specific cues? Such facilitation has an evident evolutionary advantage. We use two associative learning paradigms to test this hypothesis. The first is stressed cage mate-induced conditioning. One pair-housed adult rat received 4 pairings of terpinene + shock over 30 min. Ten minutes after return to the home cage, its companion rat was removed and exposed to terpinene. Single-housed controls were exposed to either terpinene or shock only. Companion rats showed terpinene-specific freezing, which was prevented by β-adrenoceptor blockade. Using Arc to index neuronal activation in response to terpinene re-exposure, stressed cage-mate induced associative learning was measured. Companion rats showed increased neuronal activity in the accessory olfactory bulb, while terpinene + shock-conditioned rats showed increased activity in the main olfactory bulb. Both groups had enhanced activity in the anterior basolateral amygdala and central amygdala. To test involvement of pheromone mediation, in the 2nd paradigm, we paired terpinene with soiled bedding from odor + shock rats or a rat alarm pheromone. Both conditioning increased rats’ freezing to terpinene. Blocking NMDA receptors in the basolateral amygdala prevented odor-specific learning suggesting shock and pheromone-paired pathways converge in the amygdala. An alarm pheromone thus enables cue-specific learning as well as signalling danger

Blocking of orexin receptors in the paraventricular nucleus of the thalamus has no effect on conditioned fear

The paraventricular nucleus of the thalamus (PVT) projects to the central nucleus of the amygdala and recent experimental evidence indicates a role for the PVT in conditioned fear. Furthermore, the PVT contains a high density of orexin receptors and fibers and acute injections of orexin antagonist into the PVT produce anxiolytic effects. The present study was done to determine if administration of a dual orexin receptor antagonist (DORA) in the region of the PVT interfered with the expression of conditioned fear in rats exposed to cued and contextual conditioning paradigms. Infusion of 0.5 µl of the DORA N-biphenyl-2-yl-1-{[(1-methyl-1H-benzimidazol-2yl) sulfanyl] acetyl}-L-prolinamide at a concentration of 0.1, 1.0, and 10 nmol had no effect on the freezing produced by exposing rats to an auditory cue or the context associated with foot shock. In contrast, the 1.0 and 10 nmol doses were anxiolytic in the social interaction test. The results of the present study do not support a role for orexin receptors in the PVT in the expression of learned fear. The finding that the 1.0 and 10 nmol doses of DORA in the PVT region were anxiolytic in the social interaction test is consistent with other studies indicating a role for orexins in the PVT in anxiety-like behaviors

The hypothalamus and periaqueductal gray are the sources of dopamine fibers in the paraventricular nucleus of the thalamus in the rat

The paraventricular nucleus of the thalamus (PVT) sends a very dense projection to the nucleus accumbens. This area of the striatum plays a key role in motivation and recent experimental evidence indicates that the PVT may have a similar function. It is well known that a dopaminergic projection from the ventral tegmental area (VTA) to the nucleus accumbens is a key regulator of motivation and reward-related behavior. Dopamine (DA) fibers have also been localized in the PVT but the source of these fibers in the rat has not been unequivocally identified. The present study was done to re-examine this question. Small iontophoretic injections of cholera toxin B (CTb) were made in the PVT to retrogradely label tyrosine hydroxylase (TH) neurons. Neurons that were double-labeled for TH/CTb were found scattered in DA cell groups of the hypothalamus (ventrorostral A10, A11, A13, A15 DA cell groups) and the midbrain (dorsocaudal A10 embedded in the periaqueductal gray). In contrast, double-labeled neurons were absent in the retrorubral field (A8), substantia nigra (A9) and VTA (A10) of the midbrain. We conclude that DA fibers in the PVT do not originate from VTA but from a heterogeneous population of DA neurons located in the hypothalamus and periaqueductal gray

Changes in emotional behavior produced by orexin microinjections in the paraventricular nucleus of the thalamus

The paraventricular nucleus of the midline thalamus (PVT) innervates areas of the extended amygdala known to play a key role in the expression of emotional behaviors. In this study, microinjections of orexins (hypocretins), which have excitatory actions on neurons in the PVT, in the midline thalamus were used to investigate if the PVT modulates the expression of emotional behavior in the open field. First, the approach-avoidance tendency (number and duration of visit to the center area) associated with novelty was examined in orexin treated rats before and after placing a novel object in the center of the open field. Second, the expression of ethological behaviors (rearing, locomotion, freezing, and grooming) in the open field was used to determine the effects of orexins on emotionality. Microinjections of orexin-A (OXA) or orexin-B (OXB) in the PVT decreased exploration of the center area and the novel object indicating that the center area and the object had more aversive properties in orexin treated rats. Both OXA and OXB microinjections in the PVT increased the expression of freezing and grooming behaviors which are indicative of a negative emotional state. The results indicate that microinjections of orexins in the PVT made the test situation more aversive and produced avoidance behaviors. This suggests that orexins may act at the PVT to modulate behaviors associated with a negative emotional state. (C) 2010 Elsevier Inc. All rights reserved

Orexin-A acts on the paraventricular nucleus of the midline thalamus to inhibit locomotor activity in rats

Orexins (hypocretins) are novel peptides that have been shown to play a role in control of behavioral arousal. The paraventricular nucleus of the midline thalamus (PVT) is one area of the brain that is the most densely innervated by orexin fibers. In addition, the PVT sends a dense projection to the nucleus accumbens an area, of the striatum involved in the regulation of locomotion. This study was done to determine the effect of microinjections of orexin-A (OXA) or the orexin receptor antagonist SB334867 in the PVT oil locomotor activity (LA) in morphine-naive and morphine-sensitized rats. Microinjections of OXA (3 mu g/500 nl) in or near the PVT inhibited LA in rats tested in a novel and familiar environment as well as in rats expressing behavioral sensitization to repeated injections of morphine. In contrast, microinjections of SB334867 had no effect on LA in any of the test situations. Using an approach involving experimenter based analysis of ethological behaviors; we found that microinjections of OXA in the midline thalamus decreased LA while at the same time increasing the expression of grooming and freezing. These results suggest that OXA can act on the PVT and the midline thalamus to produce arousal independent of LA.Orexins (hypocretins) are novel peptides that have been shown to play a role in control of behavioral arousal. The paraventricular nucleus of the midline thalamus (PVT) is one area of the brain that is the most densely innervated by orexin fibers. In addition, the PVT sends a dense projection to the nucleus accumbens an area, of the striatum involved in the regulation of locomotion. This study was done to determine the effect of microinjections of orexin-A (OXA) or the orexin receptor antagonist SB334867 in the PVT oil locomotor activity (LA) in morphine-naive and morphine-sensitized rats. Microinjections of OXA (3 mu g/500 nl) in or near the PVT inhibited LA in rats tested in a novel and familiar environment as well as in rats expressing behavioral sensitization to repeated injections of morphine. In contrast, microinjections of SB334867 had no effect on LA in any of the test situations. Using an approach involving experimenter based analysis of ethological behaviors; we found that microinjections of OXA in the midline thalamus decreased LA while at the same time increasing the expression of grooming and freezing. These results suggest that OXA can act on the PVT and the midline thalamus to produce arousal independent of LA. (C) 2009 Elsevier Inc. All rights reserved

Blocking of orexin receptors in the paraventricular nucleus of the thalamus has no effect on the expression of conditioned fear in rats

The paraventricular nucleus of the thalamus (PVT) projects to the central nucleus of the amygdala and recent experimental evidence indicates a role for the PVT in conditioned fear. Furthermore, the PVT contains a high density of orexin receptors and fibers and acute injections of orexin antagonist into the PVT produce anxiolytic effects. The present study was done to determine if administration of a dual orexin receptor antagonist (DORA) in the region of the PVT interferes with the expression of conditioned fear in rats exposed to cued and contextual conditioning paradigms. Infusion of 0.5 mu l of the DORA N-biphenyl-2-yl-1-[(1-methyl-1H-benzimidazol-2yl) sulfanyl] acetyl-L-prolinamide at a concentration of 0.1, 1.0, and 10 nmol had no effect on the freezing produced by exposing rats to an auditory cue or the context associated with foot shock. In contrast, the 1.0 and 10 nmol doses were anxiolytic in the social interaction test. The results of the present study do not support a role for orexin receptors in the PVT in the expression of learned fear. The finding that the 1.0 and 10 nmol doses of DORA in the PVT region were anxiolytic in the social interaction test is consistent with other studies indicating a role for orexins in the PVT in anxiety-like behaviors

A projection from the paraventricular nucleus of the thalamus to the shell of the nucleus accumbens contributes to footshock stress-induced social avoidance

The paraventricular nucleus of the thalamus (PVT) is an area of the dorsal midline thalamus that contributes to footshock induced anxiety. The PVT sends a dense projection to the shell of the nucleus accumbens (NAcSh) and the present study explored if this projection is involved in the behavioral changes produced by a single exposure of rats to inescapable footshocks. The inhibitory Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) hM4Di was transduced in PVT neurons that project to the NAcSh. Rats were exposed to an episode of moderately intense footshock (1.5 mA x 2 s x 5) and assigned to either high-responder (HR) or low-responder groups (LR) according to their level of fear generalization 24 h later. The effect of chemogenetic inhibition of the PVT-NAcSh projection on anxietyand fear-like behaviors was assessed at approximately 2 weeks post-footshock. HR showed a higher level of social avoidance compared to non-shocked animals and LR. The elevated level of social avoidance was attenuated in the HR treated with the hM4Di agonist clozapine (0.01 mg/kg, i.p.) or clozapine N-oxide (CNO) administrations in the NAcSh while avoidance of open spaces and contextual fear expression were not affected. Analysis of protein product of the early to immediate gene cfos indicated that these effects were mediated by dynorphin neurons in the NAcSh. This study provides evidence for a role of a projection from the PVT to the NAcSh in stress-induced social avoidance independent of anxiety to non-social stimuli and contextual fear mechanisms.</p

Extensive divergence of projections to the forebrain from neurons in the paraventricular nucleus of the thalamus

Neurons in the paraventricular nucleus of the thalamus (PVT) respond to emotionally salient events and project densely to subcortical regions known to mediate adaptive behavioral responses. The areas of the forebrain most densely innervated by the PVT include striatal-like subcortical regions that consist of the shell of the nucleus accumbens (NAcSh), the dorsolateral region of the bed nucleus of the stria terminalis (BSTDL) and the lateral-capsular division of the central nucleus of the amygdala (CeL). A recent tracing experiment demonstrated that the PVT is composed of two intermixed populations of neurons that primarily project to either the dorsomedial (dmNAcSh) or ventromedial region of the NAcSh (vmNAcSh) with many of the vmNAcSh projecting neurons providing collateral innervation of the BSTDL and CeL. The present study used triple injections of the retrograde tracer cholera toxin B to provide a detailed map of the location of PVT neurons that provide collaterals to the vmNAcSh, BSTDL and CeL. These neurons were intermixed throughout the PVT and did not form uniquely localized subpopulations. An intersectional viral anterograde tracing approach was used to demonstrate that regardless of its presumed target of innervation (dmNAcSh, vmNAcSh, BSTDL, or CeL), most neurons in the PVT provide collateral innervation to a common set of forebrain regions. The paper shows that PVT-dmNAcSh projecting neurons provide the most divergent projection system and that these neurons express the immediate early gene product cFos following an aversive incident. We propose that the PVT may regulate a broad range of responses to physiological and psychological challenges by simultaneously influencing functionally diverse regions of the forebrain that include the cortex, striatal-like regions in the basal forebrain and a number of hypothalamic nuclei.</p