A quantitative in situ hybridization protocol for formalin-fixed paraffin-embedded archival post-mortem human brain tissue

The tuberomamillary nucleus in neuropsychiatric disorders

The tuberomamillary nucleus (TMN) is located within the posterior part of the hypothalamus. The histamine neurons in it synthesize histamine by means of the key enzyme histidine decarboxylase (HDC) and from the TMN, innervate a large number of brain areas, such as the cerebral cortex, hippocampus, amygdala as well as the thalamus, hypothalamus, and basal ganglia. Brain histamine is reduced to an inactivated form, tele-methylhistamine (t-MeHA), by histamine N-methyltransferase (HMT). In total, there are four types of histamine receptors (H_1-4Rs) in the brain, all of which are G-protein coupled. The histaminergic system controls several basal physiological functions, including the sleep-wake cycle, energy and endocrine homeostasis, sensory and motor functions, and cognitive functions such as attention, learning, and memory. Histaminergic dysfunction may contribute to clinical disorders such as Parkinson's disease, Alzheimer's disease, Huntington's disease, narcolepsy type 1, schizophrenia, Tourette syndrome, and autism spectrum disorder. In the current chapter, we focus on the role of the histaminergic system in these neurological/neuropsychiatric disorders. For each disorder, we first discuss human data, including genetic, postmortem brain, and cerebrospinal fluid studies. Then, we try to interpret the human changes by reviewing related animal studies and end by discussing, if present, recent progress in clinical studies on novel histamine-related therapeutic strategies.

Histamine-4 receptor antagonist JNJ7777120 inhibits pro-inflammatory microglia and prevents the progression of Parkinson-like pathology and behaviour in a rat model

The activation of microglial cells is presumed to play a key role in the pathogenesis of Parkinson's disease (PD). The activity of microglia is regulated by the histamine-4 receptor (H₄R), thus providing a novel target that may prevent the progression of PD. However, this putative mechanism has so far not been validated. In our previous study, we found that mRNA expression of H₄R was upregulated in PD patients. In the present study, we validated this possible mechanism using the rotenone-induced PD rat model, in which mRNA expression levels of H₄R-, and microglial markers were significantly increased in the ventral midbrain. Inhibition of H₄R in rotenone-induced PD rat model by infusion of the specific H₄R antagonist JNJ7777120 into the lateral ventricle resulted in blockade of microglial activation. In addition, pharmacological targeting of H₄R in rotenone-lesioned rats resulted in reduced apomorphine-induced rotational behaviour, prevention of dopaminergic neuron degeneration and associated decreases in striatal dopamine levels. These changes were accompanied by a reduction of Lewy body-like neuropathology. Our results provide first proof of the efficacy of an H₄R antagonist in a commonly used PD rat model, and proposes the H₄R as a promising target to clinically tackle microglial activation and thereby the progression of PD.

Changes in Histidine Decarboxylase, Histamine N-Methyltransferase and Histamine Receptors in Neuropsychiatric Disorders

Compared to other monoamine neurotransmitters, information on the association between the histaminergic system and neuropsychiatric disorders is scarce, resulting in a lack of histamine-related treatment for these disorders. The current chapter tries to combine information obtained from genetic studies, neuroimaging, post-mortem human brain studies and cerebrospinal fluid measurements with data from recent clinical trials on histamine receptor agonists and antagonists, with a view to determining the possible role of the histaminergic system in neuropsychiatric disorders and to pave the way for novel histamine-related therapeutic strategies.

In situ hybridization (both radioactive and nonradioactive) and spatiotemporal gene expression analysis

Section in situ hybridization using either radioactive or nonradioactive labeled cDNA probes is an invaluable technique that enables the investigator to detect and localize mRNA expression within tissue sections and cells. Here, we describe the labeling of (35)S-UTP radioactive and nonradioactive digoxigenin probes, preparation of tissue sections, hybridization, and washing of non-hybridized probes, followed by the detection of radioactive signals via dipping in nuclear emulsion and the immunohistochemical and subsequent colorimetric detection of nonradioactive signals.

The human histaminergic system in neuropsychiatric disorders

Histaminergic neurons are exclusively located in the hypothalamic tuberomamillary nucleus, from where they project to many brain areas. The histaminergic system is involved in basic physiological functions, such as the sleep-wake cycle, energy and endocrine homeostasis, sensory and motor functions, cognition, and attention, which are all severely affected in neuropsychiatric disorders. Here, we present recent postmortem findings on the alterations in this system in neuropsychiatric disorders, including Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD), depression, and narcolepsy. In addition, we highlight the need to validate animal models for these diseases and also for Tourette's syndrome (TS) in relation to alterations in the histaminergic system. Moreover, we discuss the potential for, and concerns over, the use of novel histamine 3 receptor (H3R) antagonists/inverse agonists as treatment for such disorders.

Unaltered histaminergic system in depression: a postmortem study

BACKGROUND

Rodent experiments suggested that the neuronal histaminergic system may be involved in symptoms of depression.

METHODS

We determined, therefore, in postmortem tissue of 12 mood disorder patients (8 major depression disorder (MDD) and 4 bipolar disorder (BD)) and 12 well matched controls the expression of the rate-limiting enzyme for histamine production and histidine decarboxylase in the tuberomamillary nucleus (TMN) by quantitative in situ hybridization. In addition we used qPCR to determine the expression of the 4 histamine receptors and of the enzyme breaking down histamine, histamine N-methyltransferase (HMT), in the dorsolateral prefrontal cortex (DLPFC) and anterior cingulated cortex (ACC).

RESULTS

No changes were observed in the expression of these molecules, except for a significant lower HMT mRNA expression in the ACC of MDD subjects.

LIMITATIONS

Several inherent and potentially confounding factors of a postmortem study, such as medication and cause of death, did not seem to affect the conclusions. The group size was relatively small but well documented, both clinically and neuropathologically.

CONCLUSION

Except for a lower HMT mRNA expression in the ACC of MDD subjects, the neuronal histaminergic system did not show significant changes, either in the rate limiting enzyme involved in its production or in its receptors in 2 main projection sites, the ACC/DLPFC.

Neuropeptide alterations in the infundibular nucleus of Huntington's disease patients

Data from transgenic mouse models of Huntington's disease (HD) suggest that dysfunction of the hypothalamic infundibular nucleus (INF) (in rodents, the arcuate nucleus) may contribute to unintended weight loss and insatiable appetite among HD patients. Using post-mortem paraffin-embedded tissue, we assessed the total number of INF neurones by thionin staining and four major regulatory neuropeptides in the INF of HD patients by immunocytochemistry and in situ hybridisation. In HD patients, the total number of neurones in the INF was unchanged compared to control subjects (P = 0.92), whereas it contained over 30% less neuropeptide Y-immunoreactive (IR) neurones (P = 0.016), as well as reduced peptide levels, in fibres to the paraventricular and ventromedial nucleus (P = 0.003, P = 0.005, respectively). Conversely, neuropeptide Y mRNA expression levels were increased three-fold (P = 0.047). No changes were observed in the number of neurones immunoreactive for α-melanocyte-stimulating hormone, agouti-related peptide, and cocaine- and amphetamine-regulated transcript (P ≥ 0.17). Our findings suggest changes in the pathology of the INF neuropeptide Y-expressing neurones in HD patients without changes in other (an)orexigenic neuropeptides and without neuronal cell loss. These findings indicate that unintended weight loss in patients suffering from this disease may be partly a result of neuropeptidergic alterations in the hypothalamic infundibular nucleus.

Diurnal fluctuation in histidine decarboxylase expression, the rate limiting enzyme for histamine production, and its disorder in neurodegenerative diseases

STUDY OBJECTIVES

Neuronal histamine shows diurnal rhythms in rodents and plays a major role in the maintenance of vigilance. No data are available on its diurnal fluctuation in humans, either in health or in neurodegenerative disorders such as Parkinson disease (PD), Alzheimer disease (AD), or Huntington disease (HD), all of which are characterized by sleep-wake disturbances.

DESIGN

Quantitative in situ hybridization was used to study the mRNA expression of histidine decarboxylase (HDC), the key enzyme of histamine production in the tuberomammillary nucleus (TMN) in postmortem human hypothalamic tissue, obtained from 33 controls and 31 patients with a neurodegenerative disease-PD (n = 15), AD (n = 9), and HD (n = 8)-and covering the full 24-h cycle with respect to clock time of death.

RESULTS

HDC-mRNA levels in controls were found to be significantly higher during the daytime than at night (e.g., 08:01-20:00 versus 20:01-08:00, P = 0.004). This day-night fluctuation was markedly different in patients with neurodegenerative diseases.

CONCLUSION

The diurnal fluctuation of HDC-mRNA expression in human TMN supports a role for neuronal histamine in regulating day-night rhythms. Future studies should investigate histamine rhythm abnormalities in neurodegenerative disorders.

CITATION

Shan L; Hofman MA; van Wamelen DJ; Van Someren EJW; Bao AM; Swaab DF. Diurnal fluctuation in histidine decarboxylase expression, the rate limiting enzyme for histamine production, and its disorder in neurodegenerative diseases.

Paraventricular nucleus neuropeptide expression in Huntington's disease patients

Neuroendocrine, metabolic and autonomic nervous system dysfunctions are prevalent among patients with Huntington's disease (HD) and may underlie symptoms such as depression, weight loss and autonomic failure. Using post-mortem paraffin-embedded tissue, we assessed the integrity of the major neuropeptide populations in the paraventricular nucleus (PVN)-the hypothalamic neuroendocrine and autonomic integration center-in HD patients. The number corticotropin-releasing hormone, cocaine- and amphetamine-regulated transcript, arginine vasopressin and oxytocin immunoreactive (ir) neurons did not differ between HD patients and control subjects. However, the significant positive correlation between arginine vasopressin and oxytocin ir neurons in control subjects (P = 0.036) was absent in patients. Corticotropin-releasing hormone mRNA levels were 68% higher in HD patients (P = 0.046). Thyrotropin-releasing hormone mRNA levels did not differ between HD patients and control subjects, although a negative correlation with disease duration was present in the former (P = 0.036). These findings indicate that the PVN is largely unaffected in HD patients. However, our findings suggest that hypothalamic-pituitary-thyroid axis activity may alter during the course of the disease and that autonomic nervous system dysfunction might partly arise from an imbalance between arginine vasopressin and oxytocin neurons in the PVN.

Functional increase of brain histaminergic signaling in Huntington's disease

To evaluate whether central histaminergic signaling in Huntington's disease (HD) patients is affected, we assessed mRNA levels of histidine decarboxylase (HDC), volume of and neuron number in the hypothalamic tuberomamillary nucleus (TMN) (HD n = 8, controls n = 8). In addition, we assessed histamine N-methyltransferase (HMT) and histamine receptor (H(1) R, H(2) R and H(3) R) mRNA levels in the inferior frontal gyrus (IFG) (n = 9 and 9) and caudate nucleus (CN) (n = 6 and 6) by real-time polymerase chain reaction. In HD patients, TMN volume and neuronal number was unaltered (P = 0.72, P = 0.25). The levels of HDC mRNA (P = 0.046), IFG HMT (P < 0.001), H(1) R (P < 0.001) and H(3) R mRNA levels (P = 0.011) were increased, while CN H(2) R and H(3) R mRNA levels were decreased (P = 0.041, P = 0.009). In HD patients, we observed a positive correlation between IFG H(3) R mRNA levels and CAG repeat length (P = 0.024) and negative correlations between age at onset of disease and IFG HMT (P = 0.015) and H(1) R (P = 0.021) mRNA levels. These findings indicate a functional increase in brain histaminergic signaling in HD, and provide a rationale for the use of histamine receptor antagonists.