In vivo histamine voltammetry in the mouse premammillary nucleus

Abstract

Histamine plays a major role in the mediation of allergic reactions such as peripheral inflammation. This classical monoamine is also a neurotransmitter involved in the central nervous system but its role in this context is poorly understood. Studying histamine neurotransmission is important due to its implications in many neurological disorders. The sensitivity, selectivity and high temporal resolution of fast scan cyclic voltammetry (FSCV) offer many advantages for studying electroactive neurotransmitters. Histamine has previously been studied with FSCV; however, the lack of a robust Faradaic electrochemical signal makes it difficult to selectively identify histamine in complex media, as found in vivo. In this work, we optimize an electrochemical waveform that provides a stimulation-locked and unique electrochemical signal towards histamine. We describe in vitro waveform optimization and a novel in vivo physiological model for stimulating histamine release in the mouse premammillary nucleus via stimulation of the medial forebrain bundle. We demonstrate that a robust signal can be used to effectively identify histamine and characterize its in vivo kinetics.

Fig. 1

(A) Color plots for FIA of (i) 20 μM histamine, (ii) 10 μM adeno-sine. (B) CVs extracted from the vertical dashed lines from (i) and (ii).

Fig. 2

(A) The schematic diagram of the experimental setup used for potentiometric experiments. (B) The experimental potentiometric data for five consecutive injections of histamine (200 μM) on CFM. (C) Langmuir isotherm for histamine adsorption on CFMs in Tris buffer.

Fig. 3

(A & C) Color plots for FIA of 20 μM histamine with the serotonin and HSW waveforms respectively. CVs extracted from vertical dashed lines are shown on the right. (B) Current vs. time traces from the horizontal dashed lines from color plots. (D) (i) Calibration curve, (ii) linear dynamic range (n = 4 ± SEM). (E) Stability of CFM over 50 consecutive injections of 10 μM histamine (n = 4 ± SEM).

Fig. 4

CVs for 20 μM histamine, 100 nM dopamine, 10 nM serotonin and 1 μM adenosine with in vitro FIA using HSW on CFMs. Vertical dashed lines indicate potential positions of peaks.

Fig. 5

(A) A representative color plot of the histamine signal in PM upon MFB stimulation. (B) A representative in vitro color plot of histamine (20 μM) using FIA. (C) [Histamine] vs. time extracted from the horizontal dashed line from the color plot (A). (D) Normalized CVs of in vivo and in vitro (5 μM histamine) signals taken from vertical dashed lines.

Fig. 6

(A) The positions of electrodes (stimulation and CFM) in mouse brain. (B & D) Representative color plots of stimulated release of histamine using HSW – before and after tacrine (2 mg kg⁻¹) and thioperamide (20 mg kg⁻¹). (C & E) Concentration vs. time traces extracted from the horizontal dashed line from B & D respectively, (n = 5 ± SEM). The 2 s stimulation starting at 5 s is shown by the blue bar.