Facilitation of short-term memory by histaminergic neurons in the nucleus accumbens is independent of cholinergic and glutamatergic transmission

Brain mapping: topography of neurons and their transmitters involved in various brain functions

Use of the demanding techniques microdialysis or push-pull superfusion makes it possible to identify neurons in distinct brain areas involved in central control of peripheral functions, thus enabling brain mapping. Investigations with the push-pull superfusion technique have shown that mainly catecholaminergic neurons of the posterior and anterior hypothalamus, the locus coeruleus, and the nucleus of the solitary tract are of crucial importance for blood pressure regulation. Experimentally induced blood pressure changes also modify the release of histamine, glutamate, and taurine in the posterior hypothalamus and of serotonin in the locus coeruleus. Furthermore, histaminergic neurons of the nucleus accumbens are involved in memory, serotonergic neurons of the locus coeruleus in response to noxious stimuli, while nitric oxide of striatum has been implicated in neurotoxicity elicited by amphetamines. The involvement of several neurons in one brain function is discussed.

Brain histamine modulates recognition memory: possible implications in major cognitive disorders

Several behavioural tests have been developed to study and measure emotionally charged or emotionally neutral memories and how these may be affected by pharmacological, dietary or environmental manipulations. In this review, we describe the experimental paradigms used in preclinical studies to unravel the brain circuits involved in the recognition and memorization of environmentally salient stimuli devoid of strong emotional value. In particular, we focus on the modulatory role of the brain histaminergic system in the elaboration of recognition memory that is based on the judgement of the prior occurrence of an event, and it is believed to be a critical component of human declarative memory. The review also addresses questions that may help improve the treatment of impaired declarative memory described in several affective and neuropsychiatric disorders such as ADHD, Alzheimer's disease and major neurocognitive disorder. LINKED ARTICLES: This article is part of a themed section on New Uses for 21st Century. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.3/issuetoc.

Embryonic exposure to valproic acid affects the histaminergic system and the social behaviour of adult zebrafish (Danio rerio)

BACKGROUND AND PURPOSE

Histamine modulates several behaviours and physiological functions, and its deficiency is associated with neuropsychiatric disorders. Gestational intake of valproic acid (VPA) is linked to autism spectrum disorder (ASD), characterized by impaired sociability and stereotypies. VPA effects on the neurochemistry and functional morphology of the histaminergic system in ASD are unclear. Zebrafish are highly social, and given the similarities between zebrafish and human neurotransmitter systems, we have studied the effects of VPA on histamine in zebrafish.

EXPERIMENTAL APPROACH

Histaminergic, dopaminergic and noradrenergic systems of larval and adult zebrafish exposed to VPA from the end of gastrulation until neural tube formation were studied using HPLC, quantitative PCR, immunocytochemistry and in situ hybridization. Sociability, dark-flash response and locomotion were also studied.

KEY RESULTS

Zebrafish larvae exposed to VPA showed decreased locomotion and an abnormal dark-flash response. Additionally, a reduced number of histaminergic neurons, low histamine and altered mRNA expression of key genes of the monoaminergic systems were also detected. The reduced mRNA expression of genes of the studied systems persisted until adulthood. Furthermore, adult VPA-exposed animals presented lower brain levels of noradrenaline and 3,4-dihydroxyphenylacetic acid, along with impaired sociability.

CONCLUSIONS AND IMPLICATIONS

VPA exposure in early development causes molecular and neurochemical alterations in zebrafish, which persist into adulthood and accompany impaired sociability. These findings will highlight the possible involvement of the histaminergic system in outcomes related to neuropsychiatric disorders. Furthermore, it supports zebrafish as a tool to investigate mechanisms underlying these disorders.

Use of Push-Pull Superfusion Technique for Identifying Neurotransmitters Involved in Brain Functions: Achievements and Perspectives

The push-pull superfusion technique (PPST) is a procedure for in vivo examination of transmitter release in distinct brain areas. This technique allows to investigate dynamics of transmitter release both under normal and experimentally evoked conditions. The PPST can be modified so that it is possible to determine release of endogenous transmitters simultaneously with electroencephalogram (EEG) recordings, recordings of evoked potentials or the on-line determination of endogenous nitric oxide (NO) released into the synaptic cleft. Because of the good time resolution, the method provides further the possibility to modify the collection periods of superfusates depending on the neuronal function that is analyzed. For instance, investigation of central cardiovascular control, behavioral tasks or mnemonic processes requires very short collection periods, because changes in transmitter release occur within seconds. Even more important is the time resolution when rates of transmitter release are correlated with evoked extracellular potentials or EEG recordings. This review provides an overview of the different devices which might be combined with the PPST and perspectives for future work.

Origin of endogenous nitric oxide released in the nucleus accumbens under real-time in vivo conditions

AIMS

Nitric oxide (NO), is a simple but multifarious molecule. It is implicated in physiological and pathological processes within the striatum, mainly in the nucleus accumbens (NAc). The aim of the present study was to determine the origin of NO in the NAc of anaesthetized rats by applying various compounds known to modulate the release of NO when applied either systemically or locally.

MAIN METHODS

Real-time monitoring of NO was carried out by introducing an amperometric NO sensor into the outer tubing of a push-pull cannula. For local application of substances, the push-pull superfusion technique was used.

KEY FINDINGS

An overdose of urethane (i.p.) or superfusion of the NAc with tetrodotoxin (TTX) led to a fall of NO release in the NAc. The NO synthase (NOS) inhibitors 7-nitroindazolmonosodiumsalt (7-NINA, neuronal NOS selective) and N-nitro-L-arginine (L-NNA, NOS selective) decreased release of NO when applied i.p. or locally. Superfusion of the NAc with N-methyl-D-aspartate (NMDA) elicited a dose dependent increase of NO release.

SIGNIFICANCE

Combination of an amperometric NO sensor for real-time monitoring of NO release with the push-pull superfusion technique showed that NO released in the NAc is, at least to a great extent, of neuronal origin. The enhanced release of NO elicited by locally applied NMDA demonstrates that activation of NMDA receptors facilitates NO synthesis, thus underlining the functionality of NO targets within the NAc.