Integrated Effects of Neonatal Ventral Hippocampal Lesions and Impoverished Social-Environmental Rearing on Endophenotypes of Mental Illness and Addiction Vulnerability

A wide range of mental illnesses show high rates of addiction comorbidities regardless of their genetic, neurodevelopmental, and/or adverse-environmental etiologies. Understanding how the spectrum of mental illnesses produce addiction vulnerability will be key to discovering more effective preventions and integrated treatments for adults with addiction and dual diagnosis comorbidities. A population of 131 rats containing a spectrum of etiological mental illness models and degrees of severity was experimentally generated by crossing neonatal ventral hippocampal lesions (NVHL; n = 68) or controls (SHAM-operated; n = 63) with adolescent rearing in environmentally/socially enriched (ENR; n = 66) or impoverished (IMP; n = 65) conditions. This population was divided into 2 experiments: first, examining NVHL and IMP effects on novelty and mild stress-induced locomotion across 3 adolescent ages; second, looking at initial cocaine reactivity and long-term cocaine behavioral sensitization in adulthood. NVHL and IMP-environmental conditions independently produced remarkably similar and robustly significant abnormalities of hyperreactivity to novelty, mild stress, and long-term cocaine sensitization. The combined NVHL-IMP groups showed the most severe phenotypes across the board, so that the mental illness and addiction vulnerability phenotypes increased together in severity in a consistent stepwise progression from the healthiest rats to those with the greatest loading of etiological models. These findings add weight to our understanding of mental illness and addiction vulnerability as brain disorders that are biologically and developmentally unified in ways that transcend etiological causes, and yet co-intensify with increased loading of etiological conditions. Combining neurodevelopmental and adverse-environmental models of mental illness may provide an approach to identifying and therapeutically targeting cortical-striatal-limbic network mechanisms that generate addiction and dual diagnosis diseases.

Ketamine: Leading us into the future for development of antidepressants

Numerous randomized double-blind clinical trials have consistently shown that that a single intravenous administration of a subanesthetic dose of ketamine to treatment-resistant depressed patients significantly improved depressive symptomatology rapidly, within two hours, with the effect lasting up to seven days. Despite its very promising effects, ketamine has long been associated with potential for abuse as it can cause psychotropic side effects, such as hallucinations, false beliefs, and severe impairments in judgment and other cognitive processes. Consequently, within the last two decades preclinical research has been carried out aimed at understanding its mechanisms of action and the brain circuits involved in ketamine's antidepressant effects, both of which are discussed in this review. Furthermore, with the hippocampus being a key target for ketamine's beneficial antidepressant effects, we and others have begun to examine behavioral and neurochemical effects of drugs that act selectively on the hippocampus due to the preferential location of their receptor targets. Such drugs are negative allosteric modulators (NAMs) and positive allosteric modulator (PAM) of the α5-GABA_A receptor. Such compounds are discussed within the framework of how lessons learned with ketamine point to novel classes of drugs, targeting the GABAergic system, that can recapitulate the antidepressant effects of ketamine without its adverse effects.

Anxiety-like behavior induced by salicylate depends on age and can be prevented by a single dose of 5-MeO-DMT

Salicylate intoxication is a cause of tinnitus and comorbidly associated with anxiety in humans. In a previous work, we showed that salicylate induces anxiety-like behavior and hippocampal type 2 theta oscillations (theta2) in mice. Here we investigate if the anxiogenic effect of salicylate is dependent on age and previous tinnitus experience. We also tested whether a single dose of DMT can prevent this effect. Using microwire electrode arrays, we recorded local field potential in young (4-5- month-old) and old (11-13-month-old) mice to study the electrophysiological effect of tinnitus in the ventral hippocampus (vHipp) and medial prefrontal cortex (mPFC) in an open field arena and elevated plus maze 1h after salicylate (300mg/kg) injection. We found that anxiety-like behavior and increase in theta2 oscillations (4-6 Hz), following salicylate pre-treatment, only occurs in young (normal hearing) mice. We also show that theta2 and slow gamma oscillations increase in the vHipp and mPFC in a complementary manner during anxiety tests in the presence of salicylate. Finally, we show that pre-treating mice with a single dose of the hallucinogenic 5-MeO-DMT prevents anxiety-like behavior and the increase in theta2 and slow gamma oscillations after salicylate injection in normal hearing young mice. This work further support the hypothesis that anxiety-like behavior after salicylate injection is triggered by tinnitus and require normal hearing. Moreover, our results show that hallucinogenic compounds can be effective in treating tinnitus-related anxiety.

Vortioxetine reverses medial prefrontal cortex-mediated cognitive deficits in male rats induced by castration as a model of androgen deprivation therapy for prostate cancer

RATIONALE

Androgen deprivation therapy (ADT) is an effective treatment for prostate cancer, but induces profound cognitive impairment. Little research has addressed mechanisms underlying these deficits or potential treatments. This is an unmet need to improve quality of life for prostate cancer survivors.

OBJECTIVES

We investigated mechanisms of cognitive impairment after ADT in rats and potential utility of the multimodal serotonin-targeting drug, vortioxetine, to improve the impairment, as vortioxetine has specific efficacy against cognitive impairment in depression.

METHODS

Male Sprague-Dawley rats were surgically castrated. Vortioxetine (28 mg/kg/day) was administered in the diet. The attentional set-shifting test was used to assess medial prefrontal cortex (mPFC) executive function. Afferent-evoked field potentials were recorded in the mPFC of anesthetized rats after stimulating the ventral hippocampus (vHipp) or medial dorsal thalamus (MDT). Gene expression changes were assessed by microarray. Effects of vortioxetine on growth of prostate cancer cells were assessed in vitro.

RESULTS

ADT impaired cognitive set shifting and attenuated responses evoked in the mPFC by the vHipp afferent, but not the MDT. Both the cognitive impairment and attenuated vHipp-evoked responses were reversed by chronic vortioxetine treatment. Preliminary investigation of gene expression in the mPFC indicates that factors involved in neuronal plasticity and synaptic transmission were down-regulated by castration and up-regulated by vortioxetine in castrated animals. Vortioxetine neither altered the growth of prostate cancer cells in vitro nor interfered with the antiproliferative effects of the androgen antagonist, enzalutamide.

CONCLUSIONS

These results suggest that vortioxetine may be useful in mitigating cognitive impairment associated with ADT for prostate cancer.

Brain-Derived Neurotrophic Factor in the Nucleus Accumbens Mediates Individual Differences in Behavioral Responses to a Natural, Social Reward

BDNF-oxytocin interactions in the brain are implicated in mammalian maternal behavior. We found that BDNF gene expression is increased in the hippocampus of rat mothers that show increased pup licking/grooming (high LG mothers) compared to low LG mothers. High LG mothers also showed increased BDNF protein levels in the nucleus accumbens (nAcc). Immunoneutralization of BDNF in the nAcc eliminated the differences in pup LG between high and low LG mothers. Oxytocin antagonist in the ventral hippocampus significantly decreased the frequency of maternal LG behavior. Oxytocin antagonist significantly prevented the oxytocin-induced BDNF gene expression in primary hippocampal cell cultures. We suggest that oxytocin-induced regulation of BDNF in the nAcc provides a neuroendocrine basis for both individual differences in maternal behavior and resilience to the stress of reproduction in female mammals.

Perineuronal Nets, Inhibitory Interneurons, and Anxiety-Related Ventral Hippocampal Neuronal Oscillations Are Altered by Early Life Adversity

BACKGROUND

In humans, accumulated adverse experiences during childhood increase the risk of anxiety disorders and attention-deficit/hyperactivity disorder. In rodents, the ventral hippocampus (vHIP) is associated with anxiety regulation, and lesions in this region alter both anxiety-like behavior and activity levels. Neuronal oscillations in the vHIP of the theta frequency range (4-12 Hz) have been implicated in anxious states and derive in part from the activity of inhibitory interneurons in the hippocampus, some of which are enwrapped with perineuronal nets (PNNs), extracellular matrix structures known to regulate plasticity. We sought to investigate the associations among early life stress-induced anxiety and hyperactivity with vHIP neuronal oscillations, inhibitory interneurons, and PNNs in mice.

METHODS

We used repeated maternal separation with early weaning (MSEW) to model accumulated early life adversity in mouse offspring and studied the underlying cellular and electrophysiological changes in the vHIP that are associated with excessive anxiety and hyperactivity.

RESULTS

We found increased anxiety-like behavior and activity levels in MSEW adult males, along with increased theta power and enhanced theta-gamma coupling in the vHIP. MSEW mice showed reduced intensity of parvalbumin as well as increased PNN intensity around parvalbumin-positive interneurons in the vHIP. We further observed that MSEW increased orthodenticle homeobox protein 2, a transcription factor promoting PNN development, in the choroid plexus, where it is produced, as well as in parvalbumin-positive interneurons, where it is sequestered.

CONCLUSIONS

These findings raise the possibility of causal links among parvalbumin-positive interneurons, PNNs, orthodenticle homeobox protein 2, and MSEW-induced anxiety and hyperactivity.

Pathway specific activation of ventral hippocampal cells projecting to the prelimbic cortex diminishes fear renewal

The ability to learn that a stimulus no longer signals danger is known as extinction. A major characteristic of extinction is that it is context-dependent, which means that fear reduction only occurs in the same context as extinction training. In other contexts, there is re-emergence of fear, known as contextual renewal. The ability to properly extinguish fear memories and generalize safety associations to multiple contexts provides therapeutic potential, but little is known about the specific neural pathways that mediate fear renewal and extinction generalization. The ventral hippocampus (VH) is thought to provide a contextual gating mechanism that determines whether fear or safety is expressed in particular contexts through its projections to areas of the fear circuit, including the infralimbic (IL) and prelimbic (PL) cortices. Moreover, VH principal cells fire in large, overlapping regions of the environment, a characteristic that is ideal to support generalization; yet it is unclear how different projection cells mediate this process. Using a pathway-specific (intersectional) chemogenetic approach, we demonstrate that selective activation of VH cells projecting to PL attenuates fear renewal without affecting fear expression. These results have implications for anxiety disorders since they uncover a neural pathway associated with extinction generalization.

Ventral hippocampal overexpression of Cannabinoid Receptor Interacting Protein 1 (CNRIP1) produces a schizophrenia-like phenotype in the rat

Adolescent cannabis use has been implicated as a risk factor for schizophrenia; however, it is neither necessary nor sufficient. Previous studies examining this association have focused primarily on the role of the cannabinoid receptor 1 (CB1R) with relatively little known about a key regulatory protein, the cannabinoid receptor interacting protein 1 (CNRIP1). CNRIP1 is an intracellular protein that interacts with the C-terminal tail of CB1R and regulates its intrinsic activity. Previous studies have demonstrated aberrant CNRIP1 DNA promoter methylation in post-mortem in human patients with schizophrenia, and we have recently reported decreased methylation of the CNRIP1 DNA promoter in the ventral hippocampus (vHipp) of a rodent model of schizophrenia susceptibility. To examine whether augmented CNRIP1 expression could contribute to the pathology of schizophrenia, we performed viral-mediated overexpression of CNRIP1 in the vHipp of Sprague Dawley rats. We then tested these rats for behavioral correlates of schizophrenia symptoms, followed by electrophysiology to determine the effects on the dopamine system, known to underlie psychosis. Here, we report that overexpression of vHipp CNRIP1 induces impairments in latent inhibition and social interaction, similar to those observed in individuals with schizophrenia and in rodent models of the disease. Furthermore, rats overexpressing vHipp CNRIP1 displayed a significant increase in ventral tegmental area (VTA) dopamine neuron population activity, a putative correlate of psychosis. These data provide evidence that alterations in CNRIP1 may contribute to the pathophysiology of schizophrenia, as overexpression is sufficient to produce neurophysiological and behavioral correlates consistently observed in rodent models of the disease.

Endocannabinoid interactions in the regulation of acquisition of contextual conditioned fear

Endocannabinoids (eCBs) anandamide (AEA) and 2-arachidonoylglycerol (2-AG) were shown to be involved in the basis of trauma-induced behavioral changes, particularly contextual conditioned fear, however, their ligand-specific effects and possible interactions are poorly understood. Here we assessed specific eCB effects and interactions on acquisition of contextual conditioned fear employing electric footshocks in a rat model. We selectively increased eCB levels by pharmacological blockade of the degrading enzymes of AEA by URB597 and 2-AG by JZL184 before traumatization either systemically or locally in relevant brain areas, the prelimbic cortex (PrL), ventral hippocampus (vHC) and basolateral amygdala (BLA). Following traumatization, a series of contextual reminders were conducted during which conditioned fear was assessed. While systemic URB597-treatment during traumatization only slightly enhanced the acquisition of contextual conditioned fear, administration of the compound in the PrL and vHC led to the acquisition of stable, lasting conditioned fear, resistant to extinction. These effects of URB597 were blocked by simultaneous administration of JZL184. Similar treatment effects did not occur in the BLA. Treatment effects were not secondary to alterations in locomotor activity or nociception. Our findings suggest that AEA and 2-AG functionally interact in the regulation of acquisition of contextual conditioned fear. AEA signaling in the PrL and vHC is a crucial promoter of fear acquisition while 2-AG potentially modulates this effect. The lack of eCB effects in the BLA suggests functional specificity of eCBs at distinct brain sites.

Dopamine D1-like receptors in the dorsomedial prefrontal cortex regulate contextual fear conditioning

RATIONALE

Dopamine D1 receptor (D1R) signalling is involved in contextual fear conditioning. The D1R antagonist SCH23390 impairs the acquisition of contextual fear when administered systemically or infused locally into the dorsal hippocampus or basolateral amygdala.

OBJECTIVES

We determined if state dependency may account for the impairment in contextual fear conditioning caused by systemic SCH23390 administration. We also examined if the dorsomedial prefrontal cortex (dmPFC), nucleus accumbens (NAc), and ventral hippocampus (VH) are involved in mediating the effect of systemic SCH23390 treatment on contextual fear conditioning.

METHODS

In experiment 1, SCH23390 (0.1 mg/kg) or vehicle was given before contextual fear conditioning and/or retrieval. In experiment 2, SCH23390 (2.5 μg/0.5 uL) or vehicle was infused locally into dmPFC, NAc, or VH before contextual fear conditioning, and retrieval was tested drug-free. Freezing was quantified as a measure of contextual fear.

RESULTS

In experiment 1, SCH23390 given before conditioning or before both conditioning and retrieval decreased freezing at retrieval, whereas SCH23390 given only before retrieval had no effect. In experiment 2, SCH23390 infused into dmPFC before conditioning decreased freezing at retrieval, while infusion of SCH23390 into NAc or VH had no effect.

CONCLUSIONS

The results of experiment 1 confirm those of previous studies indicating that D1Rs are required for the acquisition but not retrieval of contextual fear and rule out state dependency as an explanation for these findings. Moreover, the results of experiment 2 provide evidence that dmPFC is also part of the neural circuitry through which D1R signalling regulates contextual fear conditioning.

Cocaine Self-administration Alters Transcriptome-wide Responses in the Brain's Reward Circuitry

BACKGROUND

Global changes in gene expression underlying circuit and behavioral dysregulation associated with cocaine addiction remain incompletely understood. Here, we show how a history of cocaine self-administration (SA) reprograms transcriptome-wide responses throughout the brain's reward circuitry at baseline and in response to context and/or cocaine re-exposure after prolonged withdrawal (WD).

METHODS

We assigned male mice to one of six groups: saline/cocaine SA + 24-hour WD or saline/cocaine SA + 30-day WD + an acute saline/cocaine challenge within the previous drug-paired context. RNA sequencing was conducted on six interconnected brain reward regions. Using pattern analysis of gene expression and factor analysis of behavior, we identified genes that are strongly associated with addiction-related behaviors and uniquely altered by a history of cocaine SA. We then identified potential upstream regulators of these genes.

RESULTS

We focused on three patterns of gene expression that reflect responses to 1) acute cocaine, 2) context re-exposure, and 3) drug + context re-exposure. These patterns revealed region-specific regulation of gene expression. Further analysis revealed that each of these gene expression patterns correlated with an addiction index-a composite score of several addiction-like behaviors during cocaine SA-in a region-specific manner. Cyclic adenosine monophosphate response element binding protein and nuclear receptor families were identified as key upstream regulators of genes associated with such behaviors.

CONCLUSIONS

This comprehensive picture of transcriptome-wide regulation in the brain's reward circuitry by cocaine SA and prolonged WD provides new insight into the molecular basis of cocaine addiction, which will guide future studies of the key molecular pathways involved.

Functional Neurochemistry of the Ventral and Dorsal Hippocampus: Stress, Depression, Dementia and Remote Hippocampal Damage

The hippocampus is not a homogeneous brain area, and the complex organization of this structure underlies its relevance and functional pleiotropism. The new data related to the involvement of the ventral hippocampus in the cognitive function, behavior, stress response and its association with brain pathology, in particular, depression, are analyzed with a focus on neuroplasticity, specializations of the intrinsic neuronal network, corticosteroid signaling through mineralocorticoid and glucocorticoid receptors and neuroinflammation in the hippocampus. The data on the septo-temporal hippicampal gradient are analyzed with particular emphasis on the ventral hippocampus, a region where most important alteration underlying depressive disorders occur. According to the recent data, the existing simple paradigm "learning (dorsal hippocampus) versus emotions (ventral hippocampus)" should be substantially revised and specified. A new hypothesis is suggested on the principal involvement of stress response mechanisms (including interaction of released glucocorticoids with hippocampal receptors and subsequent inflammatory events) in the remote hippocampal damage underlying delayed dementia and depression induced by focal brain damage (e.g. post-stroke and post-traumatic). The translational validity of this hypothesis comprising new approaches in preventing post-stroke and post-trauma depression and dementia can be confirmed in experimental and clinical studies.

Dopamine D1 receptor in the medial prefrontal cortex mediates anxiety-like behaviors induced by blocking glutamatergic activity of the ventral hippocampus in rats

The medial prefrontal cortex (mPFC) receives direct and indirect projections from the ventral hippocampus (VH) and plays an important role in the regulation of anxiety. However, the effect of the mPFC dopamine D₁ receptor on anxiety-like behaviors induced by inhibition of glutamatergic activity in the VH has not been described. Here, we examined the effects of SKF38393, a selective dopamine D₁ receptor agonist, on anxiety-like behaviors induced by NMDA receptor inhibition in the VH and neuron firing activity of mPFC. Injection of MK-801 (6 μg/0.5 μl) into the VH produced anxiety-like behaviors in the elevated plus maze and open field tests, increased the firing activity of pyramidal neurons in the mPFC, and decreased the level of dopamine in the mPFC. Injection of SKF38393 (0.5 μg/0.5 μl) into the mPFC produced anxiolytic effects, and normalized the hyperactive firing activity of mPFC pyramidal neurons induced by MK-801, whereas in both normal and anxiety-like rats caused by MK-801, injection of SKF38393 into the mPFC decreased the firing activity of mPFC interneurons but did not affect the dopamine content in the mPFC. The present data demonstrate that decreased D₁ receptor activation in the mPFC may mediate anxiety-like behaviors induced by inhibition of glutamatergic activity in the VH. The balance of D₁ receptor activity between pyramidal neurons and interneurons is a crucial factor in maintaining normal conditions, and inhibitory glutamatergic activity in the VH induces hyperactivity of mPFC pyramidal neurons through decreases in dopamine release and in the amount of D₁ receptor activation on mPFC pyramidal neurons, which may be a critical factor for anxiety disorders.

Abnormalities in behaviour, histology and prefrontal cortical gene expression profiles relevant to schizophrenia in embryonic day 17 MAM-Exposed C57BL/6 mice

Gestational and perinatal disruption of neural development increases the risk of developing schizophrenia (SCZ) later in life. Embryonic day 17 (E17) methylazoxymethanol (MAM) treatment leads to histological, physiological and behavioural abnormalities in post-puberty rats that model the neuropathological and cognitive deficits reported in SCZ patients. However, the validity of E17 MAM-exposed mice to model SCZ has not been explored. Here we treated E17 C57BL/6 mouse dams with various dosages of MAM. We found that this mouse strain was more vulnerable to MAM treatment than rats and there were gender differences in behavioural abnormalities, histological changes and prefrontal cortical gene expression profiles in MAM (7.5 mg/kg)-exposed mice. Both male and female MAM-exposed mice had deficits in prepulse inhibition. Female MAM-exposed mice exhibited mildly increased spontaneous locomotion activity and social recognition deficits, while male mice were normal. Consistently, only female MAM-exposed mice exhibited reduced brain weight, decreased size of prefrontal cortex (PFC) and enlarged lateral ventricles. Transcriptome analysis of the PFC revealed that there were more differentially expressed genes in female MAM-exposed mice than those in male mice. Moreover, expression of Pvalb, Arc and genes in their association networks were downregulated in the PFC of female MAM-exposed mice. These results indicate that E17 MAM-exposure in C57BL/6 mice leads to behavioural changes that model certain deficits reported in SCZ patients. MAM-exposed female mice may be used to study gene expression changes, inhibitory neural circuit dysfunction and glutamatergic synaptic plasticity deficits with a possible relation to those in the brains of SCZ patients.

Rats with ventral hippocampal damage are impaired at various forms of learning including conditioned inhibition, spatial navigation, and discriminative fear conditioning to similar contexts

The ventral hippocampus (vHPC) has been implicated in learning and memory functions that seem to differ from its dorsal counterpart. The goal of this series of experiments was to provide further insight into the functional contributions of the vHPC. Our previous work implicated the vHPC in spatial learning, inhibitory learning, and fear conditioning to context. However, the specific role of vHPC on these different forms of learning are not clear. Accordingly, we assessed the effects of neurotoxic lesions of the ventral hippocampus on retention of a conditioned inhibitory association, early versus late spatial navigation in the water task, and discriminative fear conditioning to context under high ambiguity conditions. The results showed that the vHPC was necessary for the expression of conditioned inhibition, early spatial learning, and discriminative fear conditioning to context when the paired and unpaired contexts have high cue overlap. We argue that this pattern of effects, combined with previous work, suggests a key role for vHPC in the utilization of broad contextual representations for inhibition and discriminative memory in high ambiguity conditions.

Disruption of medial septum and diagonal bands of Broca cholinergic projections to the ventral hippocampus disrupt auditory fear memory

In classical fear conditioning, a neutral conditioned stimulus (CS) is paired with an aversive unconditioned stimulus (US), which leads to a fear memory. If the CS is repeatedly presented without the US after fear conditioning, the formation of an extinction memory occurs, which inhibits fear memory expression. A previous study has demonstrated that selective cholinergic lesions in the medial septum and vertical limb of the diagonal bands of Broca (MS/vDBB) prior to fear and extinction learning disrupt contextual fear memory discrimination and acquisition of extinction memory. MS/vDBB cholinergic neurons project to a number of substrates that are critical for fear and extinction memory. However, it is currently unknown which of these efferent projections are critical for contextual fear memory discrimination and extinction memory. To address this, we induced cholinergic lesions in efferent targets of MS/vDBB cholinergic neurons. These included the dorsal hippocampus (dHipp), ventral hippocampus (vHipp), medial prefrontal cortex (mPFC), and in the mPFC and dHipp combined. None of these lesion groups exhibited deficits in contextual fear memory discrimination or extinction memory. However, vHipp cholinergic lesions disrupted auditory fear memory. Because MS/vDBB cholinergic neurons are the sole source of acetylcholine in the vHipp, these results suggest that MS/vDBB cholinergic input to the vHipp is critical for auditory fear memory. Taken together with previous findings, the results of this study suggest that MS/vDBB cholinergic neurons are critical for fear and extinction memory, though further research is needed to elucidate the role of MS/vDBB cholinergic neurons in these types of emotional memory.

Intra-hippocampal D-cycloserine rescues decreased social memory, spatial learning reversal, and synaptophysin levels in aged rats

RATIONALE

Aging is characterized by a decrease in N-methyl-D-aspartate receptors (NMDARs) in the hippocampus, which might be one of the factors involved in the age-dependent cognitive decline. D-Cycloserine (DCS), a partial agonist of the NMDAR glycine recognition site, could improve memory deficits associated to neurodegenerative disorders and cognitive deficits observed in normal aging.

OBJECTIVES AND METHODS

The aim of the present study was to explore whether DCS would reverse age-dependent memory deficits and decreases in NMDA receptor subunits (GluN1, GluN2A, and GluN2B) and the presynaptic protein synaptophysin in Wistar rats. We investigated the effects of pre-training infusions of DCS (10 μg/hemisphere) in the ventral hippocampus on two hippocampal-dependent learning tasks, the social transmission of food preference (STFP), and the Morris water maze (MWM).

RESULTS

The results revealed that infusions of DCS administered before the acquisition sessions rescued deficits in the STFP retention and MWM reversal learning in old rats. DCS also significantly increased the hippocampal levels of synaptophysin in old rats, which correlated with STFP and MWM performance in all tests. Moreover, although the levels of the GluN1 subunit correlated with the MWM acquisition and reversal, DCS did not enhance the expression of such synaptic protein.

CONCLUSIONS

The present behavioral results support the role of DCS as a cognitive enhancer and suggest that enhancing the function of NMDARs and synaptic plasticity in the hippocampus may be related to improvement in social memory and spatial learning reversal in aged animals.

Interaction of basolateral amygdala, ventral hippocampus and medial prefrontal cortex regulates the consolidation and extinction of social fear

Background

Following a social defeat, the balanced establishment and extinction of aversive information is a beneficial strategy for individual survival. Abnormal establishment or extinction is implicated in the development of mental disorders. This study investigated the time course of the establishment and extinction of aversive information from acute social defeat and the temporal responsiveness of the basolateral amygdala (BLA), ventral hippocampus (vHIP) and medial prefrontal cortex (mPFC) in this process.

Methods

Mouse models of acute social defeat were established by using the resident–intruder paradigm. To evaluate the engram of social defeat, the intruder mice were placed into the novel context at designated time to test the social behavior. Furthermore, responses of BLA, vHIP and mPFC were investigated by analyzing the expression of immediate early genes, such as zif268, arc, and c-fos.

Results

The results showed after an aggressive attack, aversive memory was maintained for approximately 7 days before gradually diminishing. The establishment and maintenance of aversive stimulation were consistently accompanied by BLA activity. By contrast, vHIP and mPFC response was inhibited from this process. Additionally, injecting muscimol (Mus), a GABA receptor agonist, into the BLA alleviated the freezing behavior and social fear and avoidance. Simultaneously, Mus treatment decreased the zif268 and arc expression in BLA, but it increased their expression in vHIP.

Conclusion

Our data support and extend earlier findings that implicate BLA, vHIP and mPFC in social defeat. The time courses of the establishment and extinction of social defeat are particularly consistent with the contrasting BLA and vHIP responses involved in this process.

Electronic supplementary material

The online version of this article (10.1186/s12993-018-0139-6) contains supplementary material, which is available to authorized users.

Behavioral sensitization induced by dorsal periaqueductal gray electrical stimulation is counteracted by NK1 receptor antagonism in the ventral hippocampus and central nucleus of the amygdala

A single threatening experience may change the behavior of an animal in a long-lasting way and elicit generalized behavioral responses to a novel threatening situation that is unrelated to the original aversive experience. Electrical stimulation (ES) of the dorsal periaqueductal gray (dPAG) produces a range of defensive reactions, characterized by freezing, escape, and post-stimulation freezing (PSF). The latter reflects the processing of ascending aversive information to prosencephalic structures, including the central nucleus of the amygdala (CeA), which allows the animal to evaluate the consequences of the aversive situation. This process is modulated by substance P (SP) and its preferred receptor, neurokinin 1 (NK1). The ventral hippocampus (VH) has been associated with the processing of aversive information and expression of emotional reactions with negative valence, but the participation of the VH in the expression of these defensive responses has not been investigated. The VH is rich in NK1 receptor expression and has a high density of SP-containing fibers. The present study examined the role of NK1 receptors in the VH in the expression of defensive responses and behavioral sensitization that were induced by dPAG-ES. Rats were implanted with an electrode in the dPAG for ES, and a cannula was implanted in the VH or CeA for injections of vehicle (phosphate-buffered saline) or the NK1 receptor antagonist spantide (100 pmol/0.2 μL. Spantide reduced the duration of PSF that was evoked by dPAG-ES, without changing the aversive freezing or escape thresholds. One and 7 days later, exploratory behavior was evaluated in independent groups of rats in the elevated plus maze (EPM). dPAG-ES in rats that received vehicle caused higher aversion to the open arms of the EPM compared with rats that did not receive dPAG stimulation at both time intervals. Injections of spantide in the VH or CeA prevented the proaversive effects of dPAG-ES in the EPM only 1 day later. These findings suggest that NK1 receptors are activated in both the VH and CeA during the processing of aversive information that derives from dPAG-ES. As previously shown for the CeA, SP/NK1 receptors in the VH are recruited during PSF that is evoked by dPAG-ES, suggesting that a 24-h time window is susceptible to interventions with NK1 antagonists that block the passage of aversive information from the dPAG to higher brain areas.

The vagus nerve modulates BDNF expression and neurogenesis in the hippocampus

Accumulating evidence suggests that certain gut microbiota have antidepressant-like behavioural effects and that the microbiota can regulate neurogenesis and the expression of brain-derived neurotrophic factor (BDNF) in the hippocampus. The precise mechanisms underlying these effects are not yet clear. However, the vagus nerve is one of the primary bidirectional routes of communication between the gut and the brain and thus may represent a candidate mechanism. Yet, relatively little is known about the direct influence of vagus nerve activity on hippocampal function and plasticity. Thus, the aim of the present study was to determine whether constitutive vagus nerve activity contributes to the regulation of neurogenesis and BDNF mRNA expression in the hippocampus. To this end, we examined the impact of subdiaphragmatic vagotomy in adult mice on these parameters. We found that vagotomy decreased BDNF mRNA in all areas of the hippocampus. Vagotomy also reduced the proliferation and survival of newly born cells and decreased the number of immature neurons, particularly those with a more complex dendritic morphology. Taken together, these findings suggest that vagal nerve activity influences neurogenesis and BDNF mRNA expression in the adult hippocampus.

Hippocampus ghrelin receptor signaling promotes socially-mediated learned food preference

Social cues are potent regulators of feeding behavior, yet the neurobiological mechanisms through which social cues influence food intake are poorly understood. Here we investigate the hypothesis that the appetite-promoting gut-derived hormone, ghrelin, signals in the hippocampus to promote learned social aspects of feeding behavior. We utilized a procedure known as 'social transmission of food preference' (STFP) in which rats ('Observers') experience a social interaction with another rat ('Demonstrators') that recently consumed flavored/scented chow. STFP learning in Observer rats is indicated by a significant preference for the Demonstrator paired flavor of chow vs. a novel unpaired flavor of chow in a subsequent consumption choice test. Our results show that relative to vehicle treatment, ghrelin targeted to the ventral CA1 subregion of the hippocampus (vHP) enhanced STFP learning in rats. Additionally, STFP was impaired following peripheral injections of l-cysteine that reduce circulating ghrelin levels, suggesting that vHP ghrelin-mediated effects on STFP require peripheral ghrelin release. Finally, the endogenous relevance of vHP ghrelin receptor (GHSR-1A) signaling in STFP is supported by our data showing that STFP learning was eliminated following targeted viral vector RNA interference-mediated knockdown of vHP GHSR-1A mRNA. Control experiments indicate that vHP ghrelin-mediated STFP effects are not secondary to altered social exploration and food intake, nor to altered food preference learning based on nonsocial olfactory cues. Overall these data reveal a novel neurobiological system that promotes conditioned, social aspects of feeding behavior.

The Avian Hippocampal Formation and the Stress Response

Though widely studied for its function in memory and navigation, the hippocampal formation (HF) in mammals also plays an important role in regulating the stress response. If this is an ancestral feature of the hippocampus, then it is likely that the avian HF plays a similar role. Indeed, the avian HF strongly expresses both mineralocorticoid and glucocorticoid receptors, and has indirect projections to the paraventricular nucleus of the hypothalamus, which controls the hypothalamic-pituitary-adrenal (HPA) axis. Hippocampal lesions increase HPA activity, while electrical stimulation suppresses it. In addition, adult hippocampal neurogenesis in birds is reduced in response to different acute and chronic stressors, as it is in mammals. Because the mammalian hippocampus is functionally specialized along its septotemporal axis, with the temporal pole playing a more important role in the stress response, the hypothesis is put forward that a similar functional specialization exists in birds along the rostrocaudal hippocampal axis. Some, though not all, of the evidence supports a rostrocaudal functional gradient. The evidence for whether this is equivalent to the mammalian septotemporal organization is currently ambiguous at best and needs to be more extensively investigated.

The Quinpirole Hypolocomotive Effects are Strain and Route of Administration Dependent in SHR and SLA16 Isogenic Rats

The SHR and SLA16 inbred strains present behavioral differences in anxiety/emotionality that could be under the influence of dopaminergic neurotransmission. In order to investigate the role of D2 receptors in modulating such differences, an agonist (quinpirole) and an antagonist (haloperidol) of this receptor were administered, either via systemic injection (IP), or microinjected into the ventral area of the hippocampus (vHIP). Quinpirole and haloperidol IP decreased locomotor activity, only in SLA16 rats in the open-field (OF), and in both strains in the elevated plus-maze (EPM). Quinpirole also increased the preference for the aversive areas of the EPM. Quinpirole vHIP decreased locomotor activity in both strains. Haloperidol vHIP did not elicit behavioural changes and no differences in the levels of D2 receptors and of dopamine transporter in the hippocampus were found. Results indicate that systemic activation/blocking of D2 receptors caused a strain-dependent hypolocomotion, whereas activation of D2 receptors in the vHIP, but not D2 receptor antagonism, regardless of dose, decreased general locomotor activity in the two strains. Therefore, we suggest that genomic differences in the chromosome 4 can influence the locomotor activity regulated by the D2 dopaminergic receptor, especially in the vHIP.

The effect of hippocampal NMDA receptor blockade by MK-801 on cued fear extinction

Extinction of conditioned fear has been suggested to be a new form of learning instead of erasure of what was originally learned, and the process is NMDA (N-methyl d-aspartate) receptor (NMDAR) dependent. Most of studies have so far revealed the important roles of NMDARs in the amygdala and medial prefrontal cortex (mPFC) in cued fear extinction. Although the ventral hippocampus has intimately reciprocal connections with the amygdala and mPFC, the role of its NMDARs in cued fear extinction remains unclear. The present experiment explored the issue by bilateral pre-extinction microinjection of the noncompetitive NMDAR antagonist MK-801 into the ventral hippocampus. Four groups of rats were given habituation, tone cued fear conditioning, fear extinction training and extinction test. Prior to extinction training, rats received bilateral infusions of either MK-801 (1.5, 3, or 6μg/0.5μl) or saline. Our results showed that MK-801 reduced freezing on the first trial of extinction training with no impact on within-session acquisition of extinction, and that the lower doses of MK-801 resulted in increased freezing on the extinction retrieval test. These findings suggest that ventral hippocampal NMDARs are necessary for the consolidation of tone cued fear extinction.

Hippocampus Contributions to Food Intake Control: Mnemonic, Neuroanatomical, and Endocrine Mechanisms

Food intake is a complex behavior that can occur or cease to occur for a multitude of reasons. Decisions about where, when, what, and how much to eat are not merely reflexive responses to food-relevant stimuli or to changes in energy status. Rather, feeding behavior is modulated by various contextual factors and by previous experiences. The data reviewed here support the perspective that neurons in multiple hippocampal subregions constitute an important neural substrate linking the external context, the internal context, and mnemonic and cognitive information to control both appetitive and ingestive behavior. Feeding behavior is heavily influenced by hippocampal-dependent mnemonic functions, including episodic meal-related memories and conditional learned associations between food-related stimuli and postingestive consequences. These mnemonic processes are undoubtedly influenced by both external and internal factors relating to food availability, location, and physiological energy status. The afferent and efferent neuroanatomical connectivity of the subregions of the hippocampus is reviewed with regard to the integration of visuospatial and olfactory sensory information (the external context) with endocrine and gastrointestinal interoceptive stimuli (the internal context). Also discussed are recent findings demonstrating that peripherally derived endocrine signals act on receptors in hippocampal neurons to reduce (leptin, glucagon-like peptide-1) or increase (ghrelin) food intake and learned food reward-driven responding, thereby highlighting endocrine and neuropeptidergic signaling in hippocampal neurons as a novel substrate of importance in the higher-order regulation of feeding behavior.

Hemi-ovariectomies promote a decrease in the dendritic lengths of CA1 and CA3 neurons: A dimorphic effect of the cerebral hemispheres

Certain structures of the central nervous system (CNS) are morphologically and functionally related to the ovaries. Ovariectomy has been used to study the functional role of the ovaries in the CNS, as well as the role of the CNS on the reproductive system. In the present study, the effects of left and right hemi-ovariectomy on the morphology of pyramidal neurons from the CA1 and CA3 regions of the ventral hippocampus were studied. During the estrus phase, female Long-Evans rats underwent either left and right hemi-ovariectomies or left and right sham surgeries. Three estrous cycles later, the animals were sacrificed, and their brains were processed in Golgi-Cox stain and analyzed by the Sholl method to calculate the dendritic length of the CA1 and CA3 neurons of the left and right hemispheres. The results indicate that the dendritic lengths of the basilar and apical arbors of the CA1 neurons from the left hemisphere were shorter after both left and right hemi-ovariectomy, while the CA1 neurons from the right hemisphere were not affected by either procedure. However, the basilar dendritic arbors of the CA3 neurons from both hemispheres were affected by right hemi-ovariectomy. The spine density only decreased in the apical arbors in the CA3 neurons from the left hemisphere of rats that underwent right hemi-ovariectomy. This study's results indicate that hemi-ovariectomy in adult rats changes in the morphology of the CA1 and CA3 pyramidal neurons in the ventral hippocampus and that there are dimorphic responses between the hemispheres.

Left-right functional asymmetry of ventral hippocampus depends on aversiveness of situations

Many studies suggest that animals exhibit lateralized behaviors during aversive situations, and almost all animals exhibit right hemisphere-dominant behaviors associated with fear or anxiety. However, which brain structure in each hemisphere underlies such lateralized function is unclear. In this study, we focused on the hippocampus and investigated the effects of bilateral and unilateral lesions of the ventral hippocampus (VH) on anxiety-like behavior using the successive alleys test. We also examined the expression of c-fos in the VH, which was induced by an aversive situation. Results revealed that consistent right VH dominance trended with the anxiety level. Weaker anxiety induced both right and left VH functions, whereas stronger anxiety induced right VH function. From these results, we conclude that animals are able to adaptively regulate their behaviors to avoid aversive stimuli by changing the functional dominance of their left and right VH.

Cell-based therapies for the treatment of schizophrenia

Schizophrenia is a devastating psychiatric disorder characterized by positive, negative and cognitive symptoms. While aberrant dopamine system function is typically associated with the positive symptoms of the disease, it is thought that this is secondary to pathology in afferent regions. Indeed, schizophrenia patients show dysregulated activity in the hippocampus and prefrontal cortex, two regions known to regulate dopamine neuron activity. These deficits in hippocampal and prefrontal cortical function are thought to result, in part, from reductions in inhibitory interneuron function in these brain regions. Therefore, it has been hypothesized that restoring interneuron function in the hippocampus and/or prefrontal cortex may be an effective treatment strategy for schizophrenia. In this article, we will discuss the evidence for interneuron pathology in schizophrenia and review recent advances in our understanding of interneuron development. Finally, we will explore how these advances have allowed us to test the therapeutic value of interneuron transplants in multiple preclinical models of schizophrenia. This article is part of a Special Issue entitled SI:StemsCellsinPsychiatry.

Cannabinoid Transmission in the Hippocampus Activates Nucleus Accumbens Neurons and Modulates Reward and Aversion-Related Emotional Salience

BACKGROUND

Cannabinoid receptor transmission strongly influences emotional processing, and disturbances in cannabinoid signaling are associated with various neuropsychiatric disorders. The mammalian ventral hippocampus (vHipp) is a critical neural region controlling mesolimbic activity via glutamatergic projections to the nucleus accumbens. Furthermore, vHipp abnormalities are linked to schizophrenia-related psychopathology. Nevertheless, the mechanisms by which intra-vHipp cannabinoid signaling may modulate mesolimbic activity states and emotional processing are not currently understood.

METHODS

Using an integrative combination of in vivo electrophysiological recordings and behavioral pharmacologic assays in rats, we tested whether activation of cannabinoid type 1 receptors (CB1R) in the vHipp may modulate neuronal activity in the shell subregion of the nucleus accumbens (NASh). We next examined how vHipp CB1R signaling may control the salience of rewarding or aversive emotional memory formation and social interaction/recognition behaviors via intra-NASh glutamatergic transmission.

RESULTS

We demonstrate for the first time that vHipp CB1R transmission can potently modulate NASh neuronal activity and can differentially control the formation of context-dependent and context-independent forms of rewarding or aversion-related emotional associative memories. In addition, we found that activation of vHipp CB1R transmission strongly disrupts normal social behavior and cognition. Finally, we report that these behavioral effects are dependent upon intra-NASh alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid/N-methyl-D-aspartate receptor transmission.

CONCLUSIONS

Together, these findings demonstrate a critical role for hippocampal cannabinoid signaling in the modulation of mesolimbic neuronal activity states and suggest that dysregulation of CB1R transmission in the vHipp→NASh circuit may underlie hippocampal-mediated affective and social behavioral disturbances present in neuropsychiatric disorders.

Amphetamine withdrawal differentially affects hippocampal and peripheral corticosterone levels in response to stress

Amphetamine withdrawal is associated with heightened anxiety-like behavior, which is directly driven by blunted stress-induced glucocorticoid receptor-dependent serotonin release in the ventral hippocampus. This suggests that glucocorticoid availability in the ventral hippocampus during stress may be reduced during amphetamine withdrawal. Therefore, we tested whether amphetamine withdrawal alters either peripheral or hippocampal corticosterone stress responses. Adult male rats received amphetamine (2.5mg/kg, ip) or saline for 14 days followed by 2 weeks of withdrawal. Contrary to our prediction, microdialysis samples from freely-moving rats revealed that restraint stress-induced corticosterone levels in the ventral hippocampus are enhanced by amphetamine withdrawal relative to controls. In separate groups of rats, plasma corticosterone levels increased immediately after 20min of restraint and decreased to below stress-naïve levels after 1h, indicating negative feedback regulation of corticosterone following stress. However, plasma corticosterone responses were similar in amphetamine-withdrawn and control rats. Neither amphetamine nor stress exposure significantly altered protein expression or enzyme activity of the steroidogenic enzymes 11β-hydroxysteroid dehydrogenase (11β-HSD1) or hexose-6-phosphate dehydrogenase (H6PD) in the ventral hippocampus. Our findings demonstrate for the first time that amphetamine withdrawal potentiates stress-induced corticosterone in the ventral hippocampus, which may contribute to increased behavioral stress sensitivity previously observed during amphetamine withdrawal. However, this is not mediated by either changes in plasma corticosterone or hippocampal steroidogenic enzymes. Establishing enhanced ventral hippocampal corticosterone as a direct cause of greater stress sensitivity may identify the glucocorticoid system as a novel target for treating behavioral symptoms of amphetamine withdrawal.

Effects of Dopamine and Serotonin Systems on Modulating Neural Oscillations in Hippocampus-Prefrontal Cortex Pathway in Rats

Theta and gamma oscillations are believed to play an important role in cognition and memory, and their phase coupling facilitates the information transmission in hippocampal-cortex network. In a rat model of chronic stress, the phase coupling of both theta and gamma oscillations between ventral hippocampal CA1 (vCA1) and medial prefrontal cortex (mPFC) was found to be disrupted, which was associated with the impaired synaptic plasticity in the pathway. However, little was known about the mechanisms underlying the process. In order to address this issue, both dopamine and serotonin as monoaminergic neurotransmitters were involved in this study, since they were crucial factors in pathological basis of depressive disorder. Local field potentials (LFPs) were recorded simultaneously at both vCA1 and mPFC regions under anesthesia, before and after the injection of dopamine D1 receptor antagonist and 5-HT1A receptor agonist, respectively. The results showed that the blockage of D1 receptor could lead to depression-like decrement on theta phase coupling. In addition, the activation of 5-HT1A receptor enhanced vCA1-mPFC coupling on gamma oscillations, and attenuated CA1 theta-fast gamma cross frequency coupling. These data suggest that the theta phase coupling between vCA1 and mPFC may be modulated by dopamine system that is an underlying mechanism of the cognitive dysfunction in depression. Besides, the serotonergic system is probably involved in the regulation of gamma oscillations coupling in vCA1-mPFC network.

Activation of presynaptic oxytocin receptors enhances glutamate release in the ventral hippocampus of prenatally restraint stressed rats

Oxytocin receptors are known to modulate synaptic transmission and network activity in the hippocampus, but their precise function has been only partially elucidated. Here, we have found that activation of presynaptic oxytocin receptor with the potent agonist, carbetocin, enhanced depolarization-evoked glutamate release in the ventral hippocampus with no effect on GABA release. This evidence paved the way for examining the effect of carbetocin treatment in "prenatally restraint stressed" (PRS) rats, i.e., the offspring of dams exposed to repeated episodes of restraint stress during pregnancy. Adult PRS rats exhibit an anxious/depressive-like phenotype associated with an abnormal glucocorticoid feedback regulation of the hypothalamus-pituitary-adrenal (HPA) axis, and, remarkably, with a reduced depolarization-evoked glutamate release in the ventral hippocampus. Chronic systemic treatment with carbetocin (1mg/kg, i.p., once a day for 2-3 weeks) in PRS rats corrected the defect in glutamate release, anxiety- and depressive-like behavior, and abnormalities in social behavior, in the HPA response to stress, and in the expression of stress-related genes in the hippocampus and amygdala. Of note, carbetocin treatment had no effect on these behavioral and neuroendocrine parameters in prenatally unstressed (control) rats, with the exception of a reduced expression of the oxytocin receptor gene in the amygdala. These findings disclose a novel function of oxytocin receptors in the hippocampus, and encourage the use of oxytocin receptor agonists in the treatment of stress-related psychiatric disorders in adult life.

Ventral hippocampal nicotinic acetylcholine receptors mediate stress-induced analgesia in mice

Evidence suggests that various stressful procedures induce an analgesic effect in laboratory animals commonly referred to as stress-induced analgesia (SIA). The aim of the present study was to assess the role of ventral hippocampal (VH) nicotinic acetylcholine receptors (nAChRs) in SIA in adult male NMRI mice. The VHs of animals were bilaterally cannulated and nociceptive threshold was measured using infrared source in a tail-flick apparatus. Acute stress was evoked by placing the animals on an elevated platform for 10, 20 and 30 min. The results showed that exposure to 20 and 30 min acute stress produced analgesia, while exposure to 10 min stress had no effect on the pain response. Intra-VH microinjection of nicotine (0.001-0.1 μg/mouse), 5 min before an ineffective stress (10 min stress), induced analgesia, suggesting the potentiative effect of nicotine on SIA. It is important to note that bilateral intra-VH microinjections of the same doses of nicotine without stress had no effect on the tail-flick test. On the other hand, intra-VH microinjection of mecamylamine (0.5-1 μg/mouse) 5 min before 20-min stress inhibited SIA. However, bilateral intra-VH microinjections of the same doses of mecamylamine without stress had no effect on the tail-flick response. In addition, the microinjection of mecamylamine into the VH reversed the potentiative effect of nicotine on SIA. Taken together, it can be concluded that exposure to acute stress induces SIA in a time-dependent manner and the ventral hippocampal cholinergic system may be involved in SIA via nAChRs.

Coupling of gene expression in medial prefrontal cortex and nucleus accumbens after neonatal ventral hippocampal lesions accompanies deficits in sensorimotor gating and auditory processing in rats

BACKGROUND

After neonatal ventral hippocampal lesions (NVHLs), adult rats exhibit evidence of neural processing deficits relevant to schizophrenia, including reduced prepulse inhibition (PPI) of acoustic startle and impaired sensory processing. In intact rats, the regulation of PPI by the ventral hippocampus (VH) is mediated via interactions with medial prefrontal cortex (mPFC) and nucleus accumbens (NAC). We assessed PPI, auditory-evoked responses and expression of 7 schizophrenia-related genes in mPFC and NAC, in adult rats after sham- or real NVHLs.

METHODS

Male inbred Buffalo (BUF) rat pups (d7; n=36) received either vehicle or ibotenic acid infusion into the VH. PPI and auditory-evoked dentate gyrus local field potentials (LFPs) were measured on d56 and d66, respectively. Brains were processed for RT-PCR measures of mPFC and NAC Comt, Erbb4, Grid2, Ncam1, Slc1a2, Nrg1 and Reln.

RESULTS

NVHL rats exhibited significant deficits in PPI (p=0.005) and LFPs (p<0.015) proportional to lesion size. Sham vs. NVHL rats did not differ in gene expression levels in mPFC or NAC. As we previously reported, multiple gene expression levels were highly correlated within- (mean r's≈0.5), but not across-brain regions (mean r's≈0). However, for three genes--Comt, Slc1a2 and Ncam1--after NVHLs, expression levels became significantly correlated, or "coupled," across the mPFC and NAC (p's<0.03, 0.002 and 0.05, respectively), and the degree of "coupling" increased with VH lesion size.

CONCLUSIONS

After NVHLs that disrupt PPI and auditory processing, specific gene expression levels suggest an abnormal functional coupling of the mPFC and NAC. This model of VH-mPFC-NAC network dysfunction after NVHLs may have implications for understanding the neural basis for PPI- and related sensory processing deficits in schizophrenia patients.

The ventral hippocampus NMDA receptor/nitric oxide/guanylate cyclase pathway modulates cardiovascular responses in rats

The hippocampus is a limbic structure that is involved in the expression of defensive reactions and autonomic changes in rats. The injection of L-glutamate (L-glu) into the ventral hippocampus (VH) decreases blood pressure and heart rate in anesthetized rats. Activation of NMDA receptors in the VH increases the production of nitric oxide (NO), leading to guanylate cyclase activation. The hypothesis of the present study was that a local NMDA receptor-NO-guanylate cyclase interaction mediates the cardiovascular effects of microinjection of L-glu into the VH. Microinjection of increasing doses of L-glu (30, 60 and 200 nmol/200 nL) into the VH of conscious rats caused dose-related pressor and tachycardiac responses. The cardiovascular effects of L-glu were abolished by local pretreatment with: the glutamate receptor antagonist AP-7 (0.4 nmol); the selective neuronal NO synthase (nNOS) inhibitor N(ω)-Propyl-L-arginine (0.04 nmol); the NO scavenger C-PTIO (2 nmol) or the guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolol [4,3-a]quinoxalin-1-one (2 nmol). Moreover, these cardiovascular responses were blocked by intravenous pretreatment with: the ganglionic blocker mecamylamine (2mg/Kg); the nonselective β-adrenergic receptor antagonist propranolol (2mg/Kg); the β1-adrenergic receptor selective antagonist atenolol (1mg/kg). However, pretreatment with the selective α1-adrenergic receptor antagonist prazosin (0,5mg/kg) caused only a small reduction in the pressor response, without affecting the L-glu evoked tachycardia. In conclusion, our results suggest that cardiovascular responses caused by L-glu microinjection into the VH are mediated by NMDA glutamate receptors and involve local nNOS and guanylate cyclase activation. Moreover, these cardiovascular responses are mainly mediated by cardiac sympathetic nervous system activation, with a small involvement of the vascular sympathetic nervous system.

Functional structure of the intermediate and ventral hippocampo-prefrontal pathway in the prefrontal convergent system

The hippocampo-prefrontal pathway is a unique projection that connects distant ends of the cerebral cortex. The direct hippocampo-prefrontal projection arises from the ventral to intermediate third of the hippocampus, but not from the dorsal third. It forms a funnel-shaped structure that collects information from the large hippocampal area and projects it to the prefrontal cortex. The anatomical regional differentiation of the projection has not been described. The hippocampal region is differentiated into structural and behavioural roles. For example, it has been shown that the ventral, but not the dorsal, hippocampus reciprocally connects with the amygdala and influences emotional behaviours. These data imply that hippocampal variation along the dorso-ventral axis is contained within the hippocampo-prefrontal pathway. Here, we present electrophysiological studies that demonstrate regional differences in short- but not long-term plasticity in the intermediate/posterior-dorsal and ventral routes of the hippocampo-prefrontal pathway. Furthermore, behavioural studies revealed that each route appears to play a different role in working memory. These results suggest that hippocampal regional information is processed through different routes, with the integration of individual regulatory functions in the prefrontal convergent system.