Cannabidiol in the dorsal hippocampus attenuates emotional and cognitive impairments related to neuropathic pain: Role of prelimbic neocortex-hippocampal connections.

BACKGROUND AND PURPOSE: Chronic neuropathic pain (NP) is commonly associated with cognitive and emotional impairments. Cannabidiol (CBD) presents a broad spectrum of action with a potential analgesic effect. This work investigates the CBD effect on comorbidity between chronic NP, depression, and memory impairment. EXPERIMENTAL APPROACH: The connection between the neocortex and the hippocampus was investigated with biotinylated dextran amine (BDA) deposits in the prelimbic cortex (PrL). Wistar rats were submitted to chronic constriction injury (CCI) of the sciatic nerve and CA1 treatment with CBD (15, 30, 60 nmol). KEY RESULTS: BDA-labeled were found in CA1 and dentate gyrus. CCI-induced mechanical and cold allodynia increased c-Fos protein expression in the PrL and CA1. The number of astrocytes in PrL and CA1 increased, and the number of neuroblasts decreased in CA1. The CCI animals showed increasing depressive-like behaviors, such as memory impairment. CBD (60 nmol) treatment decreased mechanical and cold allodynia, attenuated depressive-associated behaviors, and improved memory performance. Cobalt chloride (CoCl2: 1 nM), WAY-100635 (0.37 nmol), and AM251 (100 nmol) intra-PrL reversed the CBD (60 nmol) effect intra-CA1, both in nociceptive, cognitive, and depressive behaviors. CONCLUSION: CBD represents a promising therapeutic perspective in the pharmacological treatment of chronic NP and associated comorbidities such as depression and memory impairments. The CBD effects possibly recruit the CA1-PrL pathway, inducing neuroplasticity. CBD acute treatment into the CA1 produces functional and molecular morphological improvements.

Alpha1- and Beta-norepinephrinergic receptors of dorsomedial and ventromedial hypothalamic nuclei modulate panic attack-like defensive behaviour elicited by diencephalic GABAergic neurotransmission disinhibition.

Gamma-aminobutyric acid (GABA) disinhibition in medial hypothalamus (MH) nuclei of rats elicits some defensive reactions that are considered panic attack-like behaviours. Recent evidence showed that the norepinephrine-mediated system modulates fear-related defensive behaviours organised by MH neurons at least in part via noradrenergic receptors recruitment on midbrain tegmentum. However, it is unknown whether noradrenergic receptors of the MH also modulate the panic attack-like reactions. The aim of this work was to investigate the distribution of noradrenergic receptors in MH, and the effects of either α1-, α2- or ß-noradrenergic receptors blockade in the MH on defensive behaviours elaborated by hypothalamic nuclei. Defensive behaviours were evaluated after the microinjection of the selective GABAA receptor antagonist bicuculline into the MH that was preceded by microinjection of either WB4101, RX821002, propranolol (α1-, α2- and ß-noradrenergic receptor selective antagonists, respectively), or physiological saline into the MH of male Wistar rats. The α1-, α2- and ß-noradrenergic receptors were found in neuronal perikarya of all MH nuclei, and the α2-noradrenergic receptor were also found on glial cells mainly situated in the ventrolateral division of the ventromedial hypothalamic nucleus. The α1- and ß-noradrenergic receptors blockade in the MH decreased defensive attention and escape reactions elicited by the intra-MH microinjections of bicuculline. These findings suggest that, despite the profuse distributions of α1-, α2- and ß-noradrenergic receptors in the MH, both α1- and ß-noradrenergic receptor- rather than α2-noradrenergic receptor-signalling in MH are critical for the neuromodulation of panic-like behaviour.

Neostriatum neuronal TRPV1-signalling mediates striatal anandamide at high concentration facilitatory influence on neostriato-nigral dishinhibitory GABAergic connections.

RATIONALE: Several lines of evidence have demonstrated that the cannabinoid type 1 receptor (CB1) is found in the caudate nucleus and putamen (CPu) in addition to the substantia nigra pars reticulata (SNpr). Here, we investigated the role of endocannabinoid neuromodulation of striato-nigral disinhibitory projections on the activity of nigro-collicular GABAergic pathways that control the expression of unconditioned fear-related behavioural responses elicited by microinjections of the GABAA receptor selective antagonist bicuculline (BIC) in the deep layers of the superior colliculus (dlSC). METHODS: Fluorescent neural tract tracers were deposited in either CPu or in SNpr. Wistar rats received injection of vehicle, anandamide (AEA), either at low (50 pmol) or high (100 pmol) concentrations in CPu followed by bicuculline microinjections in dlSC. RESULTS: Connections between CPu, the SNpr and dlSC were demonstrated. The GABAA receptor blockade in dlSC elicited panic-like behaviour. AEA at the lowest concentration caused a panicolytic-like effect that was antagonised by the CPu pretreatment with AM251 at 100 pmol. AEA at the highest concentration caused a panicogenic-like effect that was antagonised by the CPu pretreatment with 6-iodonordihydrocapsaicin (6-I-CPS) at different concentrations (0.6, 6, 60 nmol). CONCLUSION: These findings suggest that while pre-synaptic CB1-signalling subserves an indirect facilitatory effect of AEA on striato-nigral pathways causing panicolytic-like responses through midbrain tectum enhanced activity, post-synaptic TRPV1-signalling in CPu mediates AEA direct activation of striato-nigral disinhibitory pathways resulting in increasing dlSC neurons activity and a panicogenic-like response. All these actions seem to depend on the interface with the nigro-collicular inhibitory GABAergic pathways.

The modulation of striatonigral and nigrotectal pathways by CB1 signalling in the substantia nigra pars reticulata regulates panic elicited in mice by urutu-cruzeiro lancehead pit vipers.

Cannabinoid receptor type 1 (CB1R) is widely distributed in the substantia nigra pars reticulata (SNpr). However, the role of CB1R at the SNpr level in threatening situations is poorly understood. We investigated the role of CB1R in the SNpr on the expression of fear responses in mice confronted with urutu-cruzeiro pit vipers. First, a bidirectional neurotracer was injected into the SNpr; then, immunostaining of the vesicular GABA transporter was conducted at the levels of the striatum (CPu) and deep layers of the superior colliculus (dlSC). In addition, CB1R immunostaining and GABA labelling were performed in the SNpr. Using a prey-versus-snake paradigm, mice were pretreated with the CB1R antagonist AM251 (100 pmol) and treated with the endocannabinoid anandamide (AEA, 5 pmol) in the SNpr, followed by bicuculline (40 ng) in the dlSC, and were then confronted with a snake. Bidirectional neural tract tracers associated with immunofluorescence showed the GABAergic striatonigral disinhibitory and nigrotectal inhibitory pathways. Furthermore, we showed that CB1R labelling was restricted to axonal fibres surrounding SNpr GABAergic cells. We also demonstrated a decrease in the defensive behaviours of mice treated with AEA in the SNpr, but this effect was blocked by pre-treatment with AM251 in this structure. Taken together, our results show that the panicolytic consequences of the AEA enhancement in the SNpr are signalled by CB1R, suggesting that CB1R localised in axon terminals of CPu GABAergic neurons in the SNpr modulates the activity of the nigrotectal GABAergic pathway during the expression of defensive behaviours in threatening situations.

Photobiomodulation therapy reduces acute pain and inflammation in mice.

Photobiomodulation (PBM) is a therapy suggested for the treatment of pain and inflammation. Different mechanisms have been proposed to explain the analgesic and inflammatory effects of photobiomodulation, but there are still gaps on the mechanisms underlying. The objective was to investigate the analgesic and anti-inflammatory effect of red LED, as well as to investigate the possible mechanism of action in acute nociception models. Radiation was applied with red LED (660 nm, 215 mW, 84.64 mW/cm2, 2.531 J/cm2 (30s); 5.07 J/cm2 (60s) 7.61 J/cm2 (90s) and 10.15 J/cm2 (120 s)). The red LED applied 60 s before the experiments, promoted reduction of the nociceptive neurogenic (1st phase) and inflammatory pain (2nd phase) induced by intraplantar (i.pl.) injection of formalin. This effect duration in the second phase was 180 min after pretreatment of the LED. Red LED also reduced nociception induced by intraperitoneal injection of acetic acid. Furthermore, red LED prevented nociception induced by i.pl. injection of cinnamaldehyde, capsaicin, menthol and acidified saline. It was demonstrate the involvement of glutamatergic system with the reduction the nociception induced by glutamate. The red LED was able to prevent nociception induced by intracellular signaling cascades activators, phorbol 12-myristate 13-acetate (PMA), bradykinin, forskolin and prostaglandin. In addition, red LED, respectively, from 30 to 90s demonstrated an antiedematogenic effect on ear edema and reduction the migration of inflammatory cells induced by single application of croton oil. Thus, the new findings in this study support some underlying mechanism by which red LED phototherapy reduces acute pain. However, need further clarification regarding analgesic and anti-inflammatory effect of the photobiomodulation in preclinical studies.

Oral treatment with essential oil of Hyptis spicigera Lam. (Lamiaceae) reduces acute pain and inflammation in mice: Potential interactions with transient receptor potential (TRP) ion channels.

ETHNOPHARMACOLOGICAL RELEVANCE: The genus Hyptis comprehends almost 400 species widespread in tropical and temperate regions of America. The use of Hyptis spicigera Lam. (Lamiaceae) is reported in traditional medicine due to its gastroprotective, anti-inflammatory and analgesic properties. AIM OF THE STUDY: The rationale of this study was to investigate the potential use of the essential oil of H. spicigera (EOHs) as analgesic. MATERIAL AND METHODS: The antinociceptive effect of EOHs was verified analyzing acute nocifensive behavior of mice induced by chemical noxious stimuli [i.e., formalin and transient receptor potential (TRP) channels agonists]. We also verified the effects of EOHs on locomotor activity and motor performance in mice. Finally, we investigate the involvement of central afferent C-fibers with EOHs analgesic effect. RESULTS: EOHs presented antinociceptive effect at 300 and 1000mg/kg on formalin-induced pain behavior model, presenting 50% and 72% of inhibition during the first phase (ED50 =292mg/kg), and 85% and 100% during de second phase (ED50 =205mg/kg), respectively. Temperature of the hind paw was reduced by EOHs treatment in a dose-dependent manner; oedema was diminished only by EOHs 1000mg/kg. EOHs does not impaired locomotor activity or motor performance. For mice injected with capsaicin, a TRPV1 activator, EOHs (1000mg/kg, ED50 =660mg/kg) showed decreased (63%) nociceptive behavior. When injected with cinnamaldehyde (TRPA1 activator), mice treated with EOHs showed 23%, 43% and 66% inhibition on nociceptive behavior (100, 300 and 1000mg/kg, respectively; ED50 402mg/kg). When mice were injected with menthol (TRPM8 activator), EOHs showed 29%, 59% and 98% inhibition of nociceptive behavior (100, 300 and 1000mg/kg, respectively; with ED50 =198mg/kg. Finally, when desensitized mice were injected with menthol, EOHs (300mg/kg) does not show antinociceptive effect. CONCLUSIONS: This study demonstrated the efficacy of EOHs on experimental models of nociception. We have found the involvement of TRP channels V1, A1 and M8 with EOHs activity, which was remarkably potent and efficient in inhibiting pain evoked by menthol, a TRPM8 channel activator. TRPM8 channels from TRPV1+ C-fibers, but not TRPM8+ C-fibers nor TRPM8+ Aδ mechanosensory fibers, mediate EOHs analgesic effects.

Light-Emitting Diode Phototherapy Reduces Nocifensive Behavior Induced by Thermal and Chemical Noxious Stimuli in Mice: Evidence for the Involvement of Capsaicin-Sensitive Central Afferent Fibers.

Low-intensity phototherapy using light fonts, like light-emitting diode (LED), in the red to infrared spectrum is a promising alternative for the treatment of pain. However, the underlying mechanisms by which LED phototherapy reduces acute pain are not yet well understood. This study investigated the analgesic effect of multisource LED phototherapy on the acute nocifensive behavior of mice induced by thermal and chemical noxious stimuli. The involvement of central afferent C fibers sensitive to capsaicin in this effect was also investigated. Mice exposed to multisource LED (output power 234, 390, or 780 mW and power density 10.4, 17.3, and 34.6 mW/cm2, respectively, from 10 to 30 min of stimulation with a wavelength of 890 nm) showed rapid and significant reductions in formalin- and acetic acid-induced nocifensive behavior. This effect gradually reduced but remained significant for up to 7 h after LED treatment in the last model used. Moreover, LED (390 mW, 17.3 mW/cm2/20 min) irradiation also reduced nocifensive behavior in mice due to chemical [endogenous (i.e., glutamate, prostaglandins, and bradykinin) or exogenous (i.e., formalin, acetic acid, TRPs and ASIC agonist, and protein kinase A and C activators)] and thermal (hot plate test) stimuli. Finally, ablating central afferent C fibers abolished LED analgesia. These experimental results indicate that LED phototherapy reduces the acute painful behavior of animals caused by chemical and thermal stimuli and that LED analgesia depends on the integrity of central afferent C fibers sensitive to capsaicin. These findings provide new information regarding the underlying mechanism by which LED phototherapy reduces acute pain. Thus, LED phototherapy may be an important tool for the management of acute pain.

Estudo da emissão de luz por diodoinfravermelho na dor neuropática em ratos / Study of infrared light emitting diodes infraredon neuropathic pain in rats

Introdução: A lesão nervosa periférica pode causar alteraçõesfuncionais tanto sensitivas quanto motoras, podendo promoverimportantes comprometimentos, especialmente a dor neuropática.Dentre os vários tratamentos propostos está o emprego da luz monocromáticade baixa intensidade, como o diodo de emissão de luz(LED). Objetivo: Avaliar o efeito analgésico do LED no espectroinfravermelho em modelo experimental de dor neuropática porconstrição do nervo ciático em ratos. Material e métodos: Foramutilizados 24 ratos machos Wistar, randomizados em 4 grupos (n =6). Grupo I: animais neuropáticos e tratados com LED; grupo II:animais neuropáticos e tratados com o LED desligado (placebo);grupo III: animais Sham e tratados com LED; grupo IV: animaisSham e tratados com LED desligado (placebo). Para avaliar a eficáciado tratamento, foram empregados parâmetros de nocicepção comoalodínia mecânica estática, dinâmica e térmica ao frio; hiperalgesiatérmica ao calor e nocicepção espontânea. Resultados: Os animaisneuropáticos desenvolveram alodínia e hiperalgesia ao estímulomecânico, térmico e nocicepção espontânea em 7 dias (Tempo 0)contados a partir da indução da neuropatia, mantendo essas manifestaçõesaté o 14º dia. Conclusão: O tratamento contínuo com LED noespectro infravermelho promoveu efeito analgésico em um modeloexperimental de dor neuropática em ratos. Os resultados obtidosneste estudo sugerem que esse recurso físico pode ser utilizado notratamento de pacientes com dor neuropática.

Introduction: The peripheral nerve injury can cause sensory andmotor functional changes, promoting important damages, especiallyneuropathic pain. The use of monochromatic light of low intensity,such as light-emitting diode (LED) is among different treatmentsoptions. Objective: This study proposes an evaluation of analgesiceffect of LED in the infrared spectrum in experimental model ofneuropathic pain induced by constriction of the sciatic nerve in rats.Methods: We used 24 male Wistar rats randomized into 4 groups (n= 6). Group I: neuropathic animals, treated with LED; group II:neuropathic animals, treated with LED (placebo); group III: Shamanimals treated with LED, group IV: Sham animals treated withLED turned off (placebo). We used nociception parameters suchas static mechanical allodynia, thermal (cold) dynamics, thermal(heat) hyperalgesia and spontaneous nociceptive in order to evaluatetreatment efficacy. Results: All animals developed neuropathicallodynia and hyperalgesia to mechanical stimulation, thermal andspontaneous nociception in 7 days (time 0), starting on inductionof neuropathy, maintaining these conditions until the 14th day.Conclusion: Continuous LED treatment with infrared spectrumpromotes analgesic effect in experimental model of neuropathic painin rats. The results of this study suggest that this treatment may beused to treat patients with neuropathic pain.