Misassembly of full-length Disrupted-in-Schizophrenia 1 protein is linked to altered dopamine homeostasis and behavioral deficits.

Disrupted-in-schizophrenia 1 (DISC1) is a mental illness gene first identified in a Scottish pedigree. So far, DISC1-dependent phenotypes in animal models have been confined to expressing mutant DISC1. Here we investigated how pathology of full-length DISC1 protein could be a major mechanism in sporadic mental illness. We demonstrate that a novel transgenic rat model, modestly overexpressing the full-length DISC1 transgene, showed phenotypes consistent with a significant role of DISC1 misassembly in mental illness. The tgDISC1 rat displayed mainly perinuclear DISC1 aggregates in neurons. Furthermore, the tgDISC1 rat showed a robust signature of behavioral phenotypes that includes amphetamine supersensitivity, hyperexploratory behavior and rotarod deficits, all pointing to changes in dopamine (DA) neurotransmission. To understand the etiology of the behavioral deficits, we undertook a series of molecular studies in the dorsal striatum of tgDISC1 rats. We observed an 80% increase in high-affinity DA D2 receptors, an increased translocation of the dopamine transporter to the plasma membrane and a corresponding increase in DA inflow as observed by cyclic voltammetry. A reciprocal relationship between DISC1 protein assembly and DA homeostasis was corroborated by in vitro studies. Elevated cytosolic dopamine caused an increase in DISC1 multimerization, insolubility and complexing with the dopamine transporter, suggesting a physiological mechanism linking DISC1 assembly and dopamine homeostasis. DISC1 protein pathology and its interaction with dopamine homeostasis is a novel cellular mechanism that is relevant for behavioral control and may have a role in mental illness.

Serotonergic interaction between medial prefrontal cortex and mesotelencephalic DA system underlies cognitive and affective deficits in hemiparkinsonian rats.

Parkinson's disease (PD) patients not only exhibit motor impairments, but also characteristic deficits in cognitive and affective functions. Such functions have consistently been associated with the medial prefrontal cortex (mPFC). To determine whether there is an interaction between the midbrain dopamine system (MDS) and the mPFC underlying the cognitive and emotional deficits seen in rats, we administered a disconnection procedure of these structures by applying lesions to the mPFC (N-methyl-d-aspartic acid (NMDA)) and the medial forebrain bundle (6-hydroxydopamine (6-OHDA)) either in the same or opposite hemispheres. The results indicate a functional interaction of the MDS and the mPFC: Disconnection effects on behavior were observed with respect to memory-, anxiety- and depression-related behaviors. A disconnection of the mPFC and MDS had promnestic, antidepressant- and anxiolytic-like effects. In order to determine whether this circuit between the mPFC and MDS involves serotonergic mechanisms, we also utilized serotonin-specific disconnections of the mPFC by applying the 5-HT-specific agent 5,7-dihydroxytryptamine (5,7-DHT) into the mPFC and 6-OHDA into the medial forebrain bundle, again either in the same or opposite hemispheres. The behavioral effects observed here resembled those incurred by the unspecific disconnection of the mPFC, demonstrating a significant contribution of serotonergic mechanisms to the interplay between the MDS and the mPFC. Taken together, these experiments provide evidence for an interaction of the MDS and the mPFC in the control of cognitive and affective processes known to be impaired in PD and point toward a prominent involvement of the serotonergic system. A disconnection of the mPFC and the MDS had promnestic, antidepressant- and anxiolytic-like behavioral effects. These findings may impact therapeutic approaches in the treatment of cognitive and neuropsychiatric symptoms seen in PD.

Dopamine in the nucleus accumbens core, but not shell, increases during signaled food reward and decreases during delayed extinction.

UNLABELLED: Microdialysis studies in rat have generally shown that appetitive stimuli release dopamine (DA) in the nucleus accumbens (NAc) shell and core. Here we examined the release of DA in the NAc during delivery of reward (food) and during extinction of food reward in the freely moving animal by use of in vivo microdialysis and HPLC. Fifty-two male Wistar rats were trained to receive food reward associated with appearance of cue-lights in a Skinner-box during in vivo microdialysis. Different behavioral protocols were used to assess the effects of extinction on DA and its metabolites. Results Exp. 1: (a) During a 20-min period of cued reward delivery, DA increased significantly in the NAc core, but not shell subregion; (b) for the next 60min period half of the rats underwent immediate extinction (with the CS light presented during non-reward) and the other half did not undergo extinction to the cue lights (CS was not presented during non-reward). DA remained significantly increased in both groups, providing no evidence for a decrease in DA during extinction in either NAc core or shell regions. (c) In half of the animals of the group that was not subjected to extinction, the cue lights were turned on for 30min, thus, initiating extinction to cue CS at a 1h delay from the period of reward. In this group DA in the NAc core, but not shell, significantly decreased. Behavioral analysis showed that while grooming is an indicator of extinction-induced behavior, glances toward the cue-lights (sign tracking) are an index of resistance to extinction. Results Exp. 2: (a) As in Exp. 1, during a 30-min period of cued reward delivery, DA levels again increased significantly in the NAc core but not in the NAc shell. (b) When extinction (the absence of reward with the cue lights presented) was administered 24h after the last reward session, DA again significantly decreased in the NAc core, but not in the NAc shell. CONCLUSIONS: (a) These results confirm the importance of DA release in the NAc for reward-related states, with DA increasing in the core, but not shell subregion. (b) They provide first evidence that during the withholding of expected reward, DA decreases in the NAc core, but not shell region. (c) This decrease in DA appears only after a delay between delivery of reward and extinction likely due to it being masked by persisting DA release. We hypothesize the decrease in extinction-induced release of DA in the NAc core to be a marker for the despair/depression that is known to accompany the failure to obtain expected rewards/reinforcers.

Time-dependent bidirectional effects of chronic caffeine on functional recovery of the dorsal light reflex after hemilabyrinthectomy in the goldfish Carassius auratus.

Caffeine works through a variety of complex mechanisms to exert an often bidirectional set of functional and structural neurological changes in vertebrates. We investigated the effects of chronic caffeine exposure on functional recovery of the dorsal light reflex (DLR) in hemilabyrinthectomized common goldfish, Carassius auratus. In this lesion model, the unilateral removal of the vestibular organs results in a temporary loss of gravitationally modulated postural control which is quantifiable via the DLR. We compared the functional recovery over 24 days of post-surgery goldfish continuously held in a caffeine solution of 2.5mg/L (n=10), 5.0mg/L (n=10), 10.0mg/L (n=11), or 0.0mg/L control (n=9). Comparison to a sham surgery group (n=11) indicated statistically significant changes in the DLR of all hemilabyrinthectomized fish on day 1. The control group recovered over the study period and approached, but did not reach sham surgery DLR. Although the caffeine-treated fishes appeared to initiate some postural recovery within the first 2 weeks, beginning on day 10, all caffeine groups diverged from the control group with a deterioration of postural control. All three caffeine groups were significantly deficient in comparison with the control on days 10-24. These results suggest that caffeine exposure can at first be benign, but that high dosage or prolonged exposure hinders functional recovery.

Immunization with DISC1 protein in an animal model of ADHD influences behavior and excitatory amino acids in prefrontal cortex and striatum.

The Disrupted-in-schizophrenia 1 (DISC1) gene is involved in vulnerability to neuropsychiatric disorders. Naples high-excitability (NHE) rat model neuropsychiatric problems characterized by an unbalanced mesocortical dopamine system. Here, we assessed behavioral and neurochemical effects of immunization against multimeric rat DISC1 protein in adult NHE rats, an animal model of attention-deficit hyperactivity disorder and their Random-Bred (NRB) controls. Males of both lines received subcutaneous injections of vehicle (PB), adjuvant only (AD) or recombinant rat DISC1 protein purified from E. coli, suspended in AD (anti-DISC1) at age of 30, 45 and 60 postnatal days (pnd). At 75 pnd, the rats were exposed to a Làt maze and 2 days later to an Olton eight-arm radial maze, and horizontal (HA) and vertical activities (VA) were monitored. Non-selective (NSA) and selective spatial attention (SSA) were monitored in the Làt and in the Olton maze by duration of rearings and working memory, respectively. Post mortem neurochemistry in the prefrontal cortex (PFc), dorsal (DS) and ventral (VS) striatum of L-Glutamate, L-Aspartate and L-Leucine was performed. All immunized rats showed a clear humoral IgM (but not IgG) immune response against the immunogen, indicating that immunological self-tolerance to DISC1 can be overcome by immunization. NHE rats exhibited a higher unspecific IgM response to adjuvant, indicating an immunological abnormality. The sole anti-DISC1 immunization-specific behavioral in the NHE rats was an increased horizontal activity in the Làt maze. Adjuvant treatment increased vertical activity in both lines, but in the NRB controls it increased rearing and decreased horizontal activity. Liquid chromatography/tandem mass spectrometry analysis of soluble or membrane-trapped neurotransmitters aspartate, glutamate and leucine revealed increased soluble aspartate levels in the ventral striatum of NRB controls after anti-DISC1 immunization. Immune activation by adjuvant independent of simultaneous DISC1 immunization led to other specific changes in NHE and control NRB rats. In DISC1-immunized NHE rats, horizontal activity in Lat maze correlated with membrane-trapped glutamate in PFc and in the NRB rats, duration of rearing in Olton maze correlated with membrane-trapped glutamate in PFc and aspartate in dorsal striatum. In addition to non-specific immune activation (by AD), the postnatal anti-DISC1 immune treatment led to behavioral changes related to mechanisms of activity and attention and had influenced amino acids and synaptic markers in striatum and neocortex in the adult NHE as well as control animals.

Intranasal dopamine treatment reinstates object-place memory in aged rats.

Following oral or IV administration, dopamine (DA) cannot cross the blood-brain barrier to a significant extent, but can enter the brain when administered via the nasal passages. Intranasal administration of DA was shown to increase extracellular DA in the striatum, to have antidepressant action and to improve attention and working memory in rats. Here we show that aged (22-24 months old) rats are deficient in an object-place learning task, but that this learning/memory is intact and comparable with that of adult rats upon pre-trial administration of 0.3 mg/kg DA gel into the nasal passages. This result raises the possibility of the therapeutic application of intranasal DA treatment for age-related cognitive disorders.

Prepuberal intranasal dopamine treatment in an animal model of ADHD ameliorates deficient spatial attention, working memory, amino acid transmitters and synaptic markers in prefrontal cortex, ventral and dorsal striatum.

Intranasal application of dopamine (IN-DA) has been shown to increase motor activity and to release DA in the ventral (VS) and dorsal striatum (DS) of rats. The aim of the present study was to assess the effects of IN-DA treatment on parameters of DA and excitatory amino acid (EAA) function in prepuberal rats of the Naples high-excitability (NHE) line, an animal model for attention-deficit hyperactivity disorder (ADHD) and normal random bred (NRB) controls. NHE and NRB rats were daily administered IN-DA (0.075, 0.15, 0.30 mg/kg) or vehicle for 15 days from postnatal days 28-42 and subsequently tested in the Làt maze and in the Eight-arm radial Olton maze. Soluble and membrane-trapped L-glutamate (L-Glu) and L-aspartate (L-Asp) levels as well as NMDAR1 subunit protein levels were determined after sacrifice in IN-DA- and vehicle-treated NHE and NRB rats in prefrontal cortex (PFc), DS and VS. Moreover, DA transporter (DAT) protein and tyrosine hydroxylase (TH) levels were assessed in PFc, DS, VS and mesencephalon (MES) and in ventral tegmental area (VTA) and substantia nigra, respectively. In NHE rats, IN-DA (0.30 mg/kg) decreased horizontal activity and increased nonselective attention relative to vehicle, whereas the lower dose (0.15 mg/kg) increased selective spatial attention. In NHE rats, basal levels of soluble EAAs were reduced in PFc and DS relative to NRB controls, while membrane-trapped EAAs were elevated in VS. Moreover, basal NMDAR1 subunit protein levels were increased in PFc, DS and VS relative to NRB controls. In addition, DAT protein levels were elevated in PFc and VS relative to NRB controls. IN-DA led to a number of changes of EAA, NMDAR1 subunit protein, TH and DAT protein levels in PFc, DS, VS, MES and VTA, in both NHE and NRB rats with significant differences between lines. Our findings indicate that the NHE rat model of ADHD may be characterized by (1) prefrontal and striatal DAT hyperfunction, indicative of DA hyperactivty, and (2) prefrontal and striatal NMDA receptor hyperfunction indicative of net EAA hyperactivty. IN-DA had ameliorative effects on activity level, attention, and working memory, which are likely to be associated with DA action at inhibitory D2 autoreceptors, leading to a reduction in striatal DA hyperactivity and, possibly, DA action on striatal EAA levels, resulting in a decrease of striatal EAA hyperfunction (with persistence of prefrontal EAA hyperfunction). Previous studies on IN-DA treatment in rodents have indicated antidepressant, anxiolytic and anti-parkinsonian effects in relation to enhanced central DAergic activity. Our present results strengthen the prospects of potential therapeutic applications of intranasal  DA by indicating an enhancement of selective attention and working memory in a deficit model.

Distance from source of reward as a marker for extinction-induced "despair": modulation by the antidepressants clomipramine and citalopram.

Despair-related withdrawal behaviors are common symptoms of major depression (MD) and can be ascribed to a loss or absence of former rewarding events. Extinction of negatively reinforced escape behavior in the Morris Water Maze has been shown to induce despair-like behavior. A new animal model of depressive-like behavior is based on the extinction of positively reinforced behavior, which was shown to induce spatial avoidance of the former source of reward and biting of the operandum. Treatment with antidepressants attenuated these extinction-induced behaviors, suggesting that they reflect a depressive-like state. Here we present a methodological variation of this depression model. We employed an elongated operant chamber rather than a two-compartment procedure with the intent to establish a flowing gradient of withdrawal from the source of reward, rather than an all-or-none binary measure. Furthermore, instead of employing extinction of lever-pressing behavior, we applied a cued fixed-time food-delivery schedule. Sixty adult male Wistar rats (n=12/group) were trained to receive a food reward after appearance of a cue-light (fixed interval 90s) in an elongated Skinner-box of 72 cm length. Prior to extinction, the animals were treated for 9 days with either 7.5 or 10mg/kg of the tricyclic antidepressant clomipramine, 7.5 or 10mg/kg of the selective serotonin reuptake inhibitor (SSRI) citalopram or vehicle. Subsequent testing in an open field was carried out to investigate potential effects of the antidepressants on locomotor- and anxiety-like behavior. An overall increase in distance from the feeder and biting behavior was found over the course of the extinction trials. Both, citalopram and clomipramine decreased the distance from the pellet feeder during the initial extinction trials compared to the vehicle-treated group. The attenuation of withdrawal behavior by the antidepressants supports the hypothesis that avoidance/withdrawal behavior during extinction trials can serve as a marker for extinction-induced depression and suggests the utility of this paradigm as a rodent model of depression.

Antidepressants reduce extinction-induced withdrawal and biting behaviors: a model for depressive-like behavior.

The withholding of expected rewards results in extinction of behavior and, hypothetically, to depression-like symptoms. In a test of this hypothesis, we examined the effects of extinction of food-reinforced lever-pressing on collateral behaviors that might be indices of depression. Operant extinction is known to be aversive to the organism and results in avoidance behavior. We hypothesized that avoidance of, or withdrawal from, the former source of reward may serve as a marker for "despair." Adult male Wistar rats (n=6-7 animals per group) were exposed to a Skinner box attached to a second compartment of the same size, providing opportunity for the animals to leave the operant chamber and to enter the "withdrawal" compartment. The animals spent a portion of the time during the extinction trials in this second chamber. To assess the predictive validity of this behavior as a potential marker of "despair," we tested the effects of chronic administration of two common antidepressant drugs on this measure. The tricyclic antidepressant imipramine (20 mg/kg) as well as the selective serotonin reuptake inhibitor citalopram (20 mg/kg) reduced the number of entries and time spent in the withdrawal compartment. We propose that entries into and time spent in the withdrawal compartment may operationalize "avoidance," a core symptom of major depression. Rearing as well as biting behaviors during the extinction trials were also attenuated by the antidepressant treatment. These results lend support to the hypothesis that extinction of positively reinforced operants evokes behaviors that reflect elements of "despair/depression" because these behaviors are modulated by antidepressant treatment. The avoidance of the operant chamber as a consequence of extinction, together with rearing and biting behaviors, may serve as useful measures for the testing of antidepressant treatments.

Behavioral alterations and changes in Ca/calmodulin kinase II levels in the striatum of connexin36 deficient mice.

Gap junctions (GJ) are intercellular channels which directly connect the cytoplasm of adjacent cells. GJ allow direct cell-to-cell communication via the diffusion of ions, metabolites and second messengers such as IP(3). The connexin36 (Cx36) protein has been detected in GJ between interneurons of the hippocampus, cerebral cortex, striatum, amygdala, the inferior olive, cerebellum and other brain structures, such as the olfactory bulb. Cx36 knockout (Cx36 KO) mice display changes in synchronous network oscillations in the hippocampus, neocortex and inferior olive and exhibit impaired spatial alternation and one-trial object recognition in a Y-maze. Here, we further characterized the behavioral changes induced by Cx36 deficiency in the mouse by using different behavioral measures and experimental procedures. Additionally, we examined the effects of Cx36 deficiency on acetylcholine esterase (AChE) activity and calcium calmodulin kinase II alpha (CaMKII) protein levels in the striatum. The homozygous Cx36 KO mice displayed increased locomotion and running speed in the open-field, reduced object exploration and impaired one-trial object-place recognition. Furthermore, they exhibited more anxiety-like behavior as compared to the heterozygous controls in the light-dark box. Homozygous Cx36 KO mice exhibited reduced CaMKII levels in the striatum as compared to the heterozygous mice. AChE activity in the striatum was not significantly different between groups. The present results suggest that Cx36 deficiency in the mouse leads to reduced CaMKII levels in the striatum and behavioral changes in open-field activity, anxiety-related behavior in the light-dark box and one-trial object-place recognition.

The grid-walking test: assessment of sensorimotor deficits after moderate or severe dopamine depletion by 6-hydroxydopamine lesions in the dorsal striatum and medial forebrain bundle.

The present study aims to evaluate the applicability of the grid-walking test in rats with moderate or severe dopamine-depletion incurred by unilateral nigro-striatal 6-hydroxydopamine (6-OHDA) lesions. Striatum samples were analyzed by high pressure liquid chromatography coupled to electrochemical detection (HPLC-EC) after behavioral testing. In Experiment 1, 2 weeks after the injection of 6-OHDA into the medial forebrain bundle, adult Wistar rats were divided into an l-3,4-dihydroxyphenylalanine (L-dopa) and a vehicle treatment group and their behaviors on the grid were compared. The severely lesioned animals (mean dopamine depletion of 92%) did not exhibit behavioral asymmetry in the number of contralateral foot-slips. However, L-dopa administration selectively reduced the number of foot-slips of the contralateral forelimb when compared with the vehicle group. In Experiment 2, 6-OHDA was injected into the dorsal striatum and foot-slips on the grid were analyzed 4, 9 and 13 days following the lesion. The rats with moderate dopamine-depletion (mean depletion of 54%) exhibited more contralateral forelimb-slips on all testing days. Compared with naive rats, hemiparkinsonian rats also showed more forelimb-slips. These results suggest that the grid-walking test should be a powerful and sensitive behavioral assay for sensory-motor deficits in rat models of nigro-striatal dopamine lesions.

Chronic progesterone treatment of male rats with unilateral 6-hydroxydopamine lesion of the dorsal striatum exacerbates [corrected] parkinsonian symptoms.

Progesterone (PROG) shows neuroprotective effects in numerous lesion models, including a mouse model of Parkinson's disease (PD) induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). However, the possible beneficial effects of PROG on the behavioral and neurochemical impairments incurred in the hemiparkinsonian 6-hydroxydopamine (6-OHDA) model have not been investigated. Vehicle or PROG (4 mg/kg or 8 mg/kg) was daily applied over 13 days after unilateral injection of 6-OHDA into the dorsal striatum of male rats. Turning behavior, foot slips on a horizontal grid, and forelimb use during rearing in a cylinder were observed on days 4, 5, 9, 10, 13, and 14 postlesion, and then the brain samples were analyzed by HPLC-EC. Chronic 8 mg/kg of PROG administration increased the DOPAC/dopamine (DA) ratio in the lesioned striatum, ipsiversive turnings, and the number of hind limb slips and decreased the symmetrical use of forelimbs. Thus, contrary to hypothesis, the chronic treatment with PROG exasperated rather than alleviated the motor impairments in the hemiparkinsonian rats. Because previous studies with the MPTP model had shown protective effects when PROG treatment was administrated before the lesion, our results do not rule out such potential neuroprotective action with prelesion PROG treatment. However, our results raise the question of possible negative interactions between PROG and parkinsonian symptoms in males.

Time-dependent in-vivo effects of interleukin-2 on neurotransmitters in various cortices: relationships with depressive-related and anxiety-like behaviour.

We investigated the impact of systemically injected IL-2 (2.5 µg/kg, i.p.) on serotonergic and dopaminergic neurotransmission in various cortical areas by in-vivo microdialysis. IL-2 lastingly reduced extracellular 5-HT levels in the medial prefrontal (-75%), occipital (-70%), and temporal cortices (-45%), whereas dopamine was only moderately reduced in the medial prefrontal cortex. Based on the serotonergic time profile, we conducted further experiments to test for acute and delayed (2 h post injection) depressive-related effects of systemic IL-2 (0-5.0 µg/kg) in a forced swim test and delayed effects on anxiety-like behaviour in the elevated plus-maze. IL-2 had dose-dependent effects on depressive-related behaviour after delayed but not acute testing, but no effects on anxiety-like behaviour.

Neurokinin3-R agonism in aged rats has anxiolytic-, antidepressant-, and promnestic-like effects and stimulates ACh release in frontal cortex, amygdala and hippocampus.

Neurokinin-3 receptors (NK(3)-R) are localized in brain regions which have been implicated in processes governing learning and memory as well as emotionality. The effects of acute subcutaneous (s.c.) senktide (0.2 and 0.4 mg/kg), a NK(3)-R agonist, were tested in aged (23-25 month old) Wistar rats: (a) in an episodic-like memory test, using an object discrimination task (this is the first study to test for deficits in episodic-like memory in aged rats, since appropriate tests have only recently became available); (b) on parameters of anxiety in an open field test, (c) on indices of depression in the forced swimming test and (d) on the activity of cholinergic neurons of the basal forebrain, using in vivo microdialysis and HPLC. Neither the saline-, nor senktide-treated aged animals, exhibited episodic-like memory. However, the senktide-, but not the vehicle-treated group, exhibited object memory for spatial displacement, a component of episodic memory. Senktide injection also had anxiolytic- and antidepressant-like effects. Furthermore, the active doses of senktide on behavior increased ACh levels in the frontal cortex, amygdala and hippocampus, suggesting a relationship between its cholinergic and behavioral actions. The results indicate cholinergic modulation by the NK(3)-R in conjunction with a role in the processing of memory and emotional responses in the aged rat.

Neuronal histamine and the interplay of memory, reinforcement and emotions.

The biogenic amine histamine is an important neurotransmitter-neuromodulator in the central nervous system that has been implicated in a variety of biological functions including thermo- and immunoregulation, food intake, seizures, arousal, anxiety, reward and memory. The review of the pertinent literature indicates that the majority of findings are compatible with the appraisal that the inhibition of histaminergic neurotransmission impairs learning and memory formation, decreases cortical activation and arousal, has a suppressive effect on behavioral measures of fear and anxiety, exponentiates the rewarding effects of drugs of abuse and intracranial brain stimulation. In contrast, the stimulation of histaminergic neurotransmission can ameliorate learning and memory impairments that are associated with various experimental deficit models and pathological conditions. Clinical investigations with patients suffering from neurodegenerative diseases such as Alzheimer's and Parkinson's disease demonstrate pathological alterations in the brain's histaminergic system, which, in some cases are correlated with the severity of cognitive deficits. The role of the brain's histamine system in episodic memory formation and the potential of histamine-related drugs to ameliorate cognitive deficits in early stages of neurodegenerative diseases are discussed.

Neurokinin-2 receptor antagonism in medial septum influences temporal-order memory for objects and forebrain cholinergic activity.

UNLABELLED: In the mammalian brain the neurokinin NK(2) receptors are predominantly located in the hippocampus, thalamus, septum and frontal cortex. It has been shown that administration of the NK(2) receptor agonist, neurokinin A (NKA), into the medial septum of rats increases extracellular levels of acetylcholine (ACh) in the hippocampus and that NK(2) receptor antagonism blocks this increase. Therefore, given the prominent role of hippocampal ACh in information processing, we hypothesized that NK(2) receptor antagonism in the medial septum would negatively affect learning and memory via its influence on the cholinergic neurons of the basal forebrain. We investigated the action of local application of the peptidic NK(2) receptor antagonist, Bz-Ala-Ala-D-Trp-Phe-D-Pro-Pro-Nle-NH (1, 10 and 100pmol), into the medial septum on object memory for temporal order and spatial location using an object novelty paradigm. By means of in vivo microdialysis and HPLC analyses, we also examined the influence of NK(2) receptor antagonism in the medial septum on ACh in major cholinergic projection areas of the basal forebrain, namely, hippocampus, frontal cortex and amygdala. RESULTS: Injection of vehicle alone into the medial septum impaired memory for temporal order and spatial location of objects. Application of 1pmol of the NK(2) receptor antagonist partially reversed this deficit by reinstating memory for temporal order. Injection of 10pmol of the NK(2) receptor antagonist into the medial septum decreased levels of ACh in the hippocampus (at 30min post-injection), and frontal cortex (at 30 and 80min post-injection) in comparison to vehicle. However, this apparent decrease was the result of the blockade of a saline-induced increase in ACh levels.

Histamine H1 receptor knockout mice exhibit impaired spatial memory in the eight-arm radial maze.

BACKGROUND AND PURPOSE: In the mammalian brain, histaminergic neurotransmission is mediated by the postsynaptic histamine H1 and H2 receptors and the presynaptic H3 autoreceptor, which also acts as a heteroreceptor. The H1 receptor has been implicated in spatial learning and memory formation. However, pharmacological and lesion studies have revealed conflicting results. To examine the involvement of histamine H1 receptor in spatial reference and working memory formation, H1 receptor knockout mice (KO) were tested in the eight-arm radial maze. Previously, we found that the H1 receptor-KO mice showed reduced emotionality when confronted with spatial novelty. As it is known that emotions can have an impact on spatial learning and memory performance, we also evaluated H1 receptor-KO mice in terms of emotional behaviour in the light-dark box. EXPERIMENTAL APPROACH: Mice lacking the H1 receptor and wild-type mice (WT) were tested for spatial reference and working memory in an eight-arm radial maze with three arms baited and one trial per day. Emotional behaviour was measured using the light-dark test. KEY RESULTS: The H1 receptor-KO mice showed impaired spatial reference and working memory in the radial maze task. No significant differences between H1 receptor-KO and WT mice were observed in the light-dark test. CONCLUSIONS AND IMPLICATIONS: The spatial memory deficits of the H1 receptor-KO mice might be due to the reported changes in cholinergic neurochemical parameters in the frontal cortex and the CA1 subregion of the hippocampus, to impaired synaptic plasticity in the hippocampus, and/or to a dysfunctional brain reward/reinforcement system.

The role of cortical serotonin in anxiety and locomotor activity in Wistar rats.

The brain's serotonergic system is known to play an important role in the modulation of anxiety. While the role of serotonin (5-HT) in subcortical structures is well investigated, little is known about the function of cortical 5-HT. The present series of studies used local injections of the serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), into the medial prefrontal cortex (mPFC), entorhinal cortex (EC), or occipital cortex (OccC) of rats to chronically reduce 5-HT neurotransmission in these brain areas. The animals were tested for anxiety-like behavior on the elevated plus-maze and open field. An 82% depletion of 5-HT from the mPFC increased anxiety-like behavior, while no general motor effects were evident. In contrast, a 63% 5-HT-depletion of the EC or a 78% 5-HT-depletion of the OccC did not have any effects on emotional or exploratory behaviors. These findings are in line with a proposed role of 5-HT in the mPFC in the modulation of anxiety- and stress-mediated behavior and demonstrate a functional differentiation between different cortical 5-HT projections.

Effects of intranasally applied dopamine on behavioral asymmetries in rats with unilateral 6-hydroxydopamine lesions of the nigro-striatal tract.

Due to its lipophobic properties, dopamine is unable to cross the blood-brain barrier following systemic application. However, recently it has been demonstrated that, when applied directly via the nasal passages in the rat, dopamine exerts neurochemical and behavioural action, including increases of dopamine in striatal subregions, antidepressive-like action, and increased behavioral activity. These effects could potentially be mediated by exogenous dopamine acting as a direct agonist at postsynaptic dopamine receptors. However, it is also possible that intranasally applied dopamine acts indirectly via the modulation of the activity of dopaminergic cell bodies. To approach this question, the present study used rats with unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal tract, as these lesions lead to pharmacologically stimulated behavioural asymmetries which are specific for direct and indirect dopamine agonists. We found that 7 days of repeated treatment with intranasal dopamine induced a sensitization of the turning response to amphetamine, but not to apomorphine. Furthermore, intranasal dopamine dose-dependently increased the use of the forepaw ipsilateral to the 6-OHDA-lesioned side of the brain. These results suggest that intranasally administered dopamine acts via an indirect mechanism of action, putatively by increasing the release of endogenous dopamine in the brain.

Dopaminergic and serotonergic activity in neostriatum and nucleus accumbens enhanced by intranasal administration of testosterone.

Testosterone was administered intranasally in anesthetized male rats, and its effects on the activity of dopaminergic and serotonergic neurons in the neostriatum and nucleus accumbens were assessed by means of microdialysis and HPLC. The treatment (0.5, 1.0 or 2.0 mg/kg of testosterone or vehicle, 10 microl volume) was applied in both nostrils, half (5 microl) into each. Subcutaneous injections of testosterone (2.0, 4.0 or 8.0 mg/kg) or vehicle were tested in other subjects. Samples were collected for 5 h. In the neostriatum, an increase of dopamine occurred after 2.0 mg/kg. Serotonin levels increased after 1.0 mg/kg dose. In the nucleus accumbens, dopamine and serotonin increased after 1.0 mg/kg and 2.0 mg/kg doses. Subcutaneous administration of 8.0 mg/kg testosterone increased dopamine and serotonin in the neostriatum only. We conclude that intranasal administration of testosterone is a more efficacious way for targeting the brain than the subcutaneous route, and may be considered as a means to activate central dopaminergic and serotonergic systems.