Distribution of type 1 cannabinoid receptor-expressing neurons in the septal-hypothalamic region of the mouse: colocalization with GABAergic and glutamatergic markers

Characterization of Sonic Hedgehog transcripts in the adult mouse brain: co-expression with neuronal and oligodendroglial markers

In the adult mammalian brain, astrocytes are proposed to be the major Sonic Hedgehog (Shh)-responsive cells. However, the sources of the Shh molecule mediating activation of the pathway are still poorly characterized. The present work investigates the distribution and phenotype of cells expressing Shh mRNA in the adult mouse brain. Using single-molecule fluorescent in situ hybridization (smfISH), we report much broader expression of Shh transcripts in almost all brain regions than originally reported. We identify Shh mRNA in HuC/D+ neuronal populations, including GABAergic (glutamic acid decarboxylase 67, Gad67), cholinergic (choline acetyltransferase, ChAT), dopaminergic (tyrosine hydroxylase, TH), nitrergic (neuronal nitric oxide synthase, nNOS), and in a small population of oligodendroglial cells expressing Sox10 and Olig2 mRNA transcription factors. Further analysis of Shh mRNA in cerebral cortical and hypothalamic neurons suggests that Shh is also expressed by glutamatergic neurons. Interestingly, we did not observe substantial Desert Hedgehog and Indian Hedgehog mRNA signals, nor Shh signals in S100β+ astrocytes and Iba1+ microglial cells. Collectively, the present work provides the most robust central map of Shh-expressing cells to date and underscores the importance of nitrergic neurons in regulating Shh availability to brain cells. Thus, our study provides a framework for future experiments aimed at better understanding of the functions of Shh signaling in the brain in normal and pathological states, and the characterization of novel regulatory mechanisms of the signaling pathway.

A Cannabinoid Receptor 1 Agonist Reduces Light-induced Phase Delays in Male But Not Female Mice

Animals adapt to a changing environment by synchronizing their circadian rhythms to different stimuli, the strongest and most reliable being the daily light-dark cycle. Photic information reaches the central circadian pacemaker, the suprachiasmatic nucleus (SCN), which drives rhythms in physiology and behavior throughout the brain and body. The endocannabinoid system (ECS) is a neuromodulatory system that is present within the SCN, including the primary receptor, cannabinoid receptor 1 (CB1). Exogenous cannabinoids that target CB1 inhibit the phase-shifting effects of light in hamsters, mice, and rats. Furthermore, there is evidence in cultured microglial cells that cannabidiol (CBD), a constituent of Cannabis sativa, alters core circadian clock genes, while the CB1 agonist delta-9-tetrahydrocannabinol (THC) does not. The CB1 agonist studies were conducted using male animals only, but cannabinoids exhibit sex-dependent effects in various aspects of physiology and behavior. In addition, the effects of CBD on circadian behavioral rhythms have yet to be investigated. Therefore, we decided to test the effects of acute injections of CBD or the CB1 agonist CP 55,940 on light-induced phase delays in male and female C57BL/6J mice. Animals received a single injection at circadian time (CT) 15.5, followed by a 10-min light or dark (sham) pulse at CT 16. Running-wheel activity was monitored to determine activity levels and the behavioral phase shifts from different treatments. We observed a sex difference in the magnitude of phase delay size in response to CP 55,940 administration. Males had attenuated phase delays with increasing doses of CP 55,940, while females did not differ from control. Various doses of CBD had no effect on the phase-delaying effects of light in either sex. Our results show a sex difference in the gating of photic phase shifts by CB1 activation.

Expression of type one cannabinoid receptor in different subpopulation of kisspeptin neurons and kisspeptin afferents to GnRH neurons in female mice

The endocannabinoids have been shown to target the afferents of hypothalamic neurons via cannabinoid 1 receptor (CB1) and thereby to influence their excitability at various physiological and/or pathological processes. Kisspeptin (KP) neurons form afferents of multiple neuroendocrine cells and influence their activity via signaling through a variation of co-expressed classical neurotransmitters and neuropeptides. The differential potency of endocannabinoids to influence the release of classical transmitters or neuropeptides, and the ovarian cycle-dependent functioning of the endocannabinoid signaling in the gonadotropin-releasing hormone (GnRH) neurons initiated us to study whether (a) the different subpopulations of KP neurons express CB1 mRNAs, (b) the expression is influenced by estrogen, and (c) CB1-immunoreactivity is present in the KP afferents to GnRH neurons. The aim of the study was to investigate the site- and cell-specific expression of CB1 in female mice using multiple labeling in situ hybridization and immunofluorescent histochemical techniques. The results support that CB1 mRNAs are expressed by both the GABAergic and glutamatergic subpopulations of KP neurons, the receptor protein is detectable in two-thirds of the KP afferents to GnRH neurons, and the expression of CB1 mRNA shows an estrogen-dependency. The applied estrogen-treatment, known to induce proestrus, reduced the level of CB1 transcripts in the rostral periventricular area of the third ventricle and arcuate nucleus, and differently influenced its co-localization with vesicular GABA transporter or vesicular glutamate transporter-2 in KP neurons. This indicates a gonadal cycle-dependent role of endocannabinoid signaling in the neuronal circuits involving KP neurons.

The Effect of Cannabinoids on the Brain's Circadian Clock

The circadian rhythm is without a doubt the main element influencing the way human lead their lives. Emerging evidence indicate that cannabinoids affect these routines by regulating neuronal firing within the suprachiasmatic nucleus, the master circadian pacemaker in the brain. These actions of cannabinoids on the brain's clock may also underlie time-wraps commonly experienced by marijuana users.

Endocannabinoid signaling in hypothalamic circuits regulates arousal from general anesthesia in mice

Consciousness can be defined by two major attributes: awareness of environment and self, and arousal, which reflects the level of awareness. The return of arousal after general anesthesia presents an experimental tool for probing the neural mechanisms that control consciousness. Here we have identified that systemic or intracerebral injection of the cannabinoid CB1 receptor (CB1R) antagonist AM281 into the dorsomedial nucleus of the hypothalamus (DMH) - but not the adjacent perifornical area (Pef) or the ventrolateral preoptic nucleus of the hypothalamus (VLPO) - accelerates arousal in mice recovering from general anesthesia. Anesthetics selectively activated endocannabinoid (eCB) signaling at DMH glutamatergic but not GABAergic synapses, leading to suppression of both glutamatergic DMH-Pef and GABAergic DMH-VLPO projections. Deletion of CB1R from widespread cerebral cortical or prefrontal cortical (PFC) glutamatergic neurons, including those innervating the DMH, mimicked the arousal-accelerating effects of AM281. In contrast, CB1R deletion from brain GABAergic neurons or hypothalamic glutamatergic neurons did not affect recovery time from anesthesia. Inactivation of PFC-DMH, DMH-VLPO, or DMH-Pef projections blocked AM281-accelerated arousal, whereas activation of these projections mimicked the effects of AM281. We propose that decreased eCB signaling at glutamatergic terminals of the PFC-DMH projection accelerates arousal from general anesthesia through enhancement of the excitatory DMH-Pef projection, the inhibitory DMH-VLPO projection, or both.

Neural correlates of interactions between cannabidiol and Δ(9) -tetrahydrocannabinol in mice: implications for medical cannabis

BACKGROUND AND PURPOSE

It has been proposed that medicinal strains of cannabis and therapeutic preparations would be safer with a more balanced concentration ratio of Δ(9) -tetrahydrocannabinol (THC) to cannabidiol (CBD), as CBD reduces the adverse psychotropic effects of THC. However, our understanding of CBD and THC interactions is limited and the brain circuitry mediating interactions between CBD and THC are unknown. The aim of this study was to investigate whether CBD modulated the functional effects and c-Fos expression induced by THC, using a 1:1 dose ratio that approximates therapeutic strains of cannabis and nabiximols.

EXPERIMENTAL APPROACH

Male C57BL/6 mice were treated with vehicle, CBD, THC or a combination of CBD and THC (10 mg·kg(-1) i.p. for both cannabinoids) to examine effects on locomotor activity, anxiety-related behaviour, body temperature and brain c-Fos expression (a marker of neuronal activation).

KEY RESULTS

CBD potentiated THC-induced locomotor suppression but reduced the hypothermic and anxiogenic effects of THC. CBD alone had no effect on these measures. THC increased brain activation as measured by c-Fos expression in 11 of the 35 brain regions studied. CBD co-administration suppressed THC-induced c-Fos expression in six of these brain regions. This effect was most pronounced in the medial preoptic nucleus and lateral periaqueductal gray. Treatment with CBD alone diminished c-Fos expression only in the central nucleus of the amygdala compared with vehicle.

CONCLUSIONS AND IMPLICATIONS

These data confirm that CBD modulated the pharmacological actions of THC and provide new information regarding brain regions involved in the interaction between CBD and THC.

Area-specific analysis of the distribution of hypothalamic neurons projecting to the rat ventral tegmental area, with special reference to the GABAergic and glutamatergic efferents

The ventral tegmental area (VTA) is a main regulator of reward and integrates a wide scale of hormonal and neuronal information. Feeding-, energy expenditure-, stress, adaptation- and reproduction-related hypothalamic signals are processed in the VTA and influence the reward processes. However, the neuroanatomical origin and chemical phenotype of neurons mediating these signals to the VTA have not been fully characterized. In this study we have systematically mapped hypothalamic neurons that project to the VTA using the retrograde tracer Choleratoxin B subunit (CTB) and analyzed their putative gamma-aminobutyric acid (GABA) and/or glutamate character with in situ hybridization in male rats. 23.93 ± 3.91% of hypothalamic neurons projecting to the VTA was found in preoptic and 76.27 ± 4.88% in anterior, tuberal and mammillary hypothalamic regions. Nearly half of the retrogradely-labeled neurons in the preoptic, and more than one third in the anterior, tuberal and mammillary hypothalamus appeared in medially located regions. The analyses of vesicular glutamate transporter 2 (VGLUT2) and glutamate decarboxylase 65 (GAD65) mRNA expression revealed both amino acid markers in different subsets of retrogradely-labeled hypothalamic neurons, typically with the predominance of the glutamatergic marker VGLUT2. About one tenth of CTB-IR neurons were GAD65-positive even in hypothalamic nuclei expressing primarily VGLUT2. Some regions were populated mostly by GAD65 mRNA-containing retrogradely-labeled neurons. These included the perifornical part of the lateral hypothalamus where 58.63 ± 19.04% of CTB-IR neurons were GABAergic. These results indicate that both the medial and lateral nuclear compartments of the hypothalamus provide substantial input to the VTA. Furthermore, colocalization studies revealed that these projections not only use glutamate but also GABA for neurotransmission. These GABAergic afferents may underlie important inhibitory mechanism to fine-tune the reward value of specific signals in the VTA.

Metabotropic glutamate receptor 3 is downregulated and its expression is shifted from neurons to astrocytes in the mouse lateral septum during the postpartum period

The inhibitory metabotropic glutamate receptor 3 (mGluR3) plays diverse and complex roles in brain function, including synaptic plasticity and neurotransmission. We recently found that mGluR3 is downregulated in the lateral septum (LS) of postpartum females using microarray and qPCR analysis. In this study, we used double fluorescence immunohistochemical approaches to characterize mGluR3 changes in LS of the postpartum brain. The number of mGluR3-immunoractive cells was significantly reduced in the dorsal (LSD) and intermediate (LSI) but not ventral (LSV) parts of the LS in postpartum versus virgin females. mGluR3 immunoreactivity in the LS was found predominantly in neurons (~70%), with a smaller portion (~20%-30%) in astrocytes. Colocalization analysis revealed a reduced mGluR3 expression in neurons but an increased astrocytic localization in postpartum LSI. This change in the pattern of expression suggests that mGluR3 expression is shifted from neurons to astrocytes in postpartum LS, and the decrease in mGluR3 is neuron-specific. Because mGluR3 is inhibitory and negatively regulates glutamate and GABA release, decreases in neuronal expression would increase glutamate and GABA signaling. Given our recent finding that ~90% of LS neurons are GABAergic, the present data suggest that decreases in mGluR3 are a mechanism for elevated GABA in LS in the postpartum state.

The hypothalamic ventral premammillary nucleus: A key site in leptin's regulation of reproduction

Reproduction is an energy-expensive process that relies on indicators of energy availability to adjust its proper functioning. The adipokine leptin provides one such metabolic signal, with leptin receptor-expressing neurons at sites widespread within the CNS, including regions associated with the neuroendocrine reproductive axis. One substantial population lies within the hypothalamic ventral premammillary nucleus (PMv), a region itself linked to reproductive control, which may provide a strategic site for the integration of energy availability, sensory and gonadal cues. Here we review our current understanding of leptin and PMv regulation of reproduction, including emerging details about intracellular mechanisms of leptin action at this site.

Distinct glutamatergic and GABAergic subsets of hypothalamic pro-opiomelanocortin neurons revealed by in situ hybridization in male rats and mice

Pro-opiomelanocortin (POMC) and agouti-related protein (AGRP) neurons in the hypothalamus regulate various aspects of energy homeostasis and metabolism. POMC and AGRP neurons, respectively, agonize and antagonize melanocortin receptors on their common downstream neurons. However, it is unknown whether they also reciprocally stimulate and inhibit the same neurons by amino acid transmitters. Whereas AGRP neurons are mostly GABAergic, surprisingly, only a small population of POMC neurons has been found to be glutamatergic, and a significantly larger subpopulation to be GABAergic. To further examine amino acid phenotypes of POMC neurons, we studied mRNA expression for the glutamatergic marker, type 2 vesicular glutamate transporter (VGLUT2), and the GABA synthetic enzyme, glutamic acid decarboxylase 67 (GAD67), in POMC neurons of both rats and mice by using in situ hybridization techniques. In rats, approximately 58% of POMC neurons were labeled for VGLUT2 and 37% for GAD67 mRNA. In mice, approximately 43% of POMC neurons contained VGLUT2, and 54% contained GAD67 mRNA. In both species, a prominent mediolateral distribution pattern was observed at rostral and mid levels of the POMC cell group with VGLUT2-POMC neurons dominating in lateral portions and GAD67-POMC neurons in medial portions. These data demonstrate that both glutamatergic and GABAergic cells are present in comparably significant numbers among POMC neurons. Their glutamatergic or GABAergic phenotype may represent a major functional division within the POMC cell group.

Mechanisms underlying current and future anti-obesity drugs

Regulation of body weight is organized by distributed brain circuits that use a variety of neuropeptides and transmitters, and that are responsive to endocrine and metabolic signals. Targeting of these circuits with novel pharmaceutical drugs would be helpful additions to lifestyle interventions for the treatment of obesity. The recent FDA approval of two anti-obesity drugs holds promise in a field in which previous drugs were removed from clinical use because of unacceptable psychiatric and cardiovascular side effects. Here, the modes of action of anti-obesity drugs are reviewed.

Cannabinoid modulation of midbrain urocortin 1 neurones during acute and chronic stress

Neurones in the centrally projecting Edinger-Westphal nucleus (EWcp) are the main site of urocortin 1 (Ucn1) synthesis in the mammalian brain, and are assumed to play a role in the stress response of the animal. Because endocannabinoid signalling has also been strongly implicated in stress, we hypothesised that endocannabinoids may modulate the functioning of the urocortinergic EWcp. First, using in situ hybridisation, we demonstrated cannabinoid receptor 1 (CB1R) mRNA expression in mouse EWcp-neurones that were Ucn1-negative. Dual- and triple-label immunocytochemistry revealed the presence of CB1R in several GABA-immunopositive fibres juxtaposed to EWcp-Ucn1 neurones. To test functional aspects of such an anatomical constellation, we compared acute (1 h of restraint) and chronic (14 days of chronic mild stress) stress-induced changes in wild-type (WT) and CB1R knockout (CB1R-KO) mice. Acute and especially chronic stress resulted in an increase in Ucn1 content of the EWcp, which was attenuated in CB1R-KO mice. CB1R-KO mice had higher basal and chronic stress-induced adrenocorticotrophin and corticosterone levels and were more anxious on the elevated plus-maze versus WT. Collectively, our results show for the first time EWcp-Ucn1 neurones are putatively innervated by endocannabinoid sensitive, inhibitory, GABAergic afferents. In addition, we provide novel evidence that the absence of the CB1 receptor alters the Ucn1 mRNA and peptide levels in EWcp neurones, concomitant with an augmented stress response and increased anxiety-like behaviour.

Cannabinoid-1 receptors in the mouse ventral pallidum are targeted to axonal profiles expressing functionally opposed opioid peptides and contacting N-acylphosphatidylethanolamine-hydrolyzing phospholipase D terminals

The ventral pallidum (VP) is a major recipient of inhibitory projections from nucleus accumbens (Acb) neurons that differentially express the reward (enkephalin) and aversion (dynorphin)-associated opioid peptides. The cannabinoid-1 receptor (CB1R) is present in Acb neurons expressing each of these peptides, but its location in the VP is not known. To address this question, we used electron microscopic dual immunolabeling of the CB1R and either dynorphin 1-8 (Dyn) or Met(5)-enkephalin (ME) in the VP of C57BL/6J mice, a species in which CB1R gene deletion produces a reward deficit. We also used similar methods to determine the relationship between the CB1R and N-acylphosphatidylethanolamine (NAPE)-hydrolyzing phospholipase D (NAPE-PLD), an anandamide-synthesizing enzyme located presynaptically in other limbic brain regions. CB1R-immunogold was principally localized to cytoplasmic endomembranes and synaptic or extrasynaptic plasma membranes of axonal profiles, but was also affiliated with postsynaptic membrane specializations in dendrites. The axonal profiles included many single CB1R-labeled axon terminals as well as terminals containing CB1R-immunogold and either Dyn or ME immunoreactivity. Dually labeled terminals comprised 26% of all Dyn- and 17% of all ME-labeled axon terminals. Both single- and dual-labeled terminals formed mainly inhibitory-type synapses, but almost 16% of these terminals formed excitatory synapses. Approximately 60% of the CB1R-labeled axonal profiles opposed or converged with axon terminals containing NAPE-PLD immunoreactivity. We conclude that CB1Rs in the mouse VP have subcellular distributions consistent with on demand activation by endocannabinoids that can regulate the release of functionally opposed opioid peptides and also modulate inhibitory and excitatory transmission.

Presynaptic CB(1) cannabinoid receptors control frontocortical serotonin and glutamate release--species differences

Both the serotonergic and endocannabinoid systems modulate frontocortical glutamate release; thus they are well positioned to participate in the pathogenesis of psychiatric disorders. With the help of fluorescent and confocal microscopy, we localized the CB(1) cannabinoid receptor (CB(1)R) in VGLUT1- and 2- (i.e. glutamatergic) and serotonin transporter- (i.e. serotonergic) -positive fibers and nerve terminals in the mouse and rat frontal cortex. CB(1)R activation by the synthetic agonists, WIN55212-2 (1 μM) and R-methanandamide (1 μM) inhibited the simultaneously measured evoked Ca(2+)-dependent release of [(14)C]glutamate and [(3)H]serotonin from frontocortical nerve terminals of Wistar rats, in a fashion sensitive to the CB(1)R antagonists, O-2050 (1 μM) and LY320135 (5 μM). CB(1)R agonists also inhibited the evoked release of [(14)C]glutamate in C57BL/6J mice in a reversible fashion upon washout. Interestingly, the evoked release of [(14)C]glutamate and [(3)H]serotonin was significantly greater in the CB(1)R knockout CD-1 mice. Furthermore, CB(1)R binding experiments revealed similar frontocortical CB(1)R density in the rat and the CD-1 mouse. Still, the evoked release of [(3)H]serotonin was modulated by neither CB(1)R agonists nor antagonists in wild-type CD-1 or C57BL/6J mice. Altogether, this is the first study to demonstrate functional presynaptic CB(1)Rs in frontocortical glutamatergic and serotonergic terminals, revealing species differences.

Glutamatergic and GABAergic innervation of human gonadotropin-releasing hormone-I neurons

Amino acid (aa) neurotransmitters in synaptic afferents to hypothalamic GnRH-I neurons are critically involved in the neuroendocrine control of reproduction. Although in rodents the major aa neurotransmitter in these afferents is γ-aminobutyric acid (GABA), glutamatergic axons also innervate GnRH neurons directly. Our aim with the present study was to address the relative contribution of GABAergic and glutamatergic axons to the afferent control of human GnRH neurons. Formalin-fixed hypothalamic samples were obtained from adult male individuals (n = 8) at autopsies, and their coronal sections processed for dual-label immunohistochemical studies. GABAergic axons were labeled with vesicular inhibitory aa transporter antibodies, whereas glutamatergic axons were detected with antisera against the major vesicular glutamate transporter (VGLUT) isoforms, VGLUT1 and VGLUT2. The relative incidences of GABAergic and glutamatergic axonal appositions to GnRH-immunoreactive neurons were compared quantitatively in two regions, the infundibular and paraventricular nuclei. Results showed that GABAergic axons established the most frequently encountered type of axo-somatic apposition. Glutamatergic contacts occurred in significantly lower numbers, with similar contributions by their VGLUT1 and VGLUT2 subclasses. The innervation pattern was different on GnRH dendrites where the combined incidence of glutamatergic (VGLUT1 + VGLUT2) contacts slightly exceeded that of the GABAergic appositions. We conclude that GABA represents the major aa neurotransmitter in axo-somatic afferents to human GnRH neurons, whereas glutamatergic inputs occur somewhat more frequently than GABAergic inputs on GnRH dendrites. Unlike in rats, the GnRH system of the human receives innervation from the VGLUT1, in addition to the VGLUT2, subclass of glutamatergic neurons.