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. 2018 Dec 28;160(1):136–150. doi: 10.1097/j.pain.0000000000001386

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Copyright © 2018 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the International Association for the Study of Pain.

This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.

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Figure 1. — Acute and repeated CBD administration on firing activity of DRN 5-HT neurons in naive rats. (A) Representation of coronal sections of the rat brain⁶⁶ with the photomicrograph of the recording site in the DRN. Central gray dorsal (CGD); central gray lateral ventral (CGLV); aqueduct (Aq). The white arrow indicates the site of the electrode recording labeled with pontamine sky blue dye. (B) The typical spike waveform of 5-HT neuron. (C) Acute intravenous (i.v.) CBD administration decreases firing rate of DRN 5-HT neurons (n = 9), prevented by previous i.v. injection of WAY 100635 (WAY, n = 4) and CPZ (n = 4) but not by AM 251 (n = 4). Each point of the line represents mean ± SEM expressed as percentage of baseline before injections of veh, CBD, or antagonists. White arrow indicates the injection of veh, WAY, CPZ, or AM 251, and black arrow indicates the beginning of cumulative CBD injection. (D) WAY, CPZ, and AM 251 do not affect the basal 5-HT firing rate activity. (E-H) Representative firing rate histograms showing the acute response of 5-HT neurons to CBD alone (E) and with previous injection of WAY (F), CPZ (G), and AM 251 (H). Black arrows indicate sequence of a single injection of antagonists and of increasing doses of CBD. The cumulative doses are indicated on top of each arrow. Two-way ANOVA for RM followed by Bonferroni post hoc comparisons. *P < 0.05 and ***P < 0.001 vs veh; P < 0.001 vs CBD. (I) Mean firing DRN 5-HT activity of naive rats treated with veh (65 recorded neurons in 4 rats) or with CBD (5 mg/kg/day, subcutaneously [s.c.], for 7 days) (77 neurons recorded in 4 rats). Each bar represents mean ± SEM and each point represents a single neuron recorded in each group. The Student unpaired 2-tailed t test. ***P < 0.001 vs veh. (J) Simple linear regression analysis showing relationship between degree of suppression of 5-HT firing activity in the DRN and the dose of LSD administered i.v. in naive rats treated for 7 days with vehicle or CBD (5.0 mg/kg/day, s.c.). ANOVA, analysis of variance; CBD, cannabidiol; CPZ, capsazepine; DRN, dorsal raphe nucleus; N.S., not significant; RM, repeated measures.

Inline graphic — Acute and repeated CBD administration on firing activity of DRN 5-HT neurons in naive rats. (A) Representation of coronal sections of the rat brain⁶⁶ with the photomicrograph of the recording site in the DRN. Central gray dorsal (CGD); central gray lateral ventral (CGLV); aqueduct (Aq). The white arrow indicates the site of the electrode recording labeled with pontamine sky blue dye. (B) The typical spike waveform of 5-HT neuron. (C) Acute intravenous (i.v.) CBD administration decreases firing rate of DRN 5-HT neurons (n = 9), prevented by previous i.v. injection of WAY 100635 (WAY, n = 4) and CPZ (n = 4) but not by AM 251 (n = 4). Each point of the line represents mean ± SEM expressed as percentage of baseline before injections of veh, CBD, or antagonists. White arrow indicates the injection of veh, WAY, CPZ, or AM 251, and black arrow indicates the beginning of cumulative CBD injection. (D) WAY, CPZ, and AM 251 do not affect the basal 5-HT firing rate activity. (E-H) Representative firing rate histograms showing the acute response of 5-HT neurons to CBD alone (E) and with previous injection of WAY (F), CPZ (G), and AM 251 (H). Black arrows indicate sequence of a single injection of antagonists and of increasing doses of CBD. The cumulative doses are indicated on top of each arrow. Two-way ANOVA for RM followed by Bonferroni post hoc comparisons. *P < 0.05 and ***P < 0.001 vs veh; P < 0.001 vs CBD. (I) Mean firing DRN 5-HT activity of naive rats treated with veh (65 recorded neurons in 4 rats) or with CBD (5 mg/kg/day, subcutaneously [s.c.], for 7 days) (77 neurons recorded in 4 rats). Each bar represents mean ± SEM and each point represents a single neuron recorded in each group. The Student unpaired 2-tailed t test. ***P < 0.001 vs veh. (J) Simple linear regression analysis showing relationship between degree of suppression of 5-HT firing activity in the DRN and the dose of LSD administered i.v. in naive rats treated for 7 days with vehicle or CBD (5.0 mg/kg/day, s.c.). ANOVA, analysis of variance; CBD, cannabidiol; CPZ, capsazepine; DRN, dorsal raphe nucleus; N.S., not significant; RM, repeated measures.