Distribution of NADPH Diaphorase-Exhibiting Primary Afferent Neurons in the Trigeminal Ganglion and Mesencephalic Trigeminal Nucleus of the Rabbit

Abstract

1. Nitric oxide (NO) is highly reactive gaseous molecule to which many physiological and pathological functions have been attributed in the central (CNS) and peripheral (PNS) nervous system. The present investigation was undertaken to map the distribution pattern of the enzyme responsible for the synthesis of NO, nitric oxide synthase (NOS), and especially its neuronal isoform (nNOS) in the population of primary afferent neurons of the trigeminal ganglion (TG) and mesencephalic trigeminal nucleus (MTN) of the rabbit. 2. In order to identify neuronal structures expressing nNOS we applied histochemistry to its specific histochemical marker nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd). 3. We found noticeable amount of NADPHd-exhibiting primary afferent neurons in TG of the rabbit under physiological conditions. The intensity of the histochemical reaction was highly variable reaching the maximum in the subpopulation of small-to-medium-sized neurons. The large-sized neurons were only weakly stained or actually did not posses any NADPHd-activity. In addition, NADPHd-positive nerve fibers were detected between clusters of the ganglionic cells and in the peripheral branches of the trigeminal nerve (TN). NADPHd-exhibiting MTN neurons were noticed in the whole rostrocaudal extent of the nucleus even though some differences were found concerning the ratio of NADPHd-positive versus NADPHd-negative cell bodies. Similarly, we observed striking diversity in the intensity of NADPHd histochemical reaction in the subpopulations of small-, medium-, and large-sized MTN neurons. 4. The predominant localization of NADPHd in the subpopulation of small-to-medium-sized TG neurons which are generally considered to be nociceptive suggests that NO probably takes part in the modulation of nociceptive inputs from the head and face. Furthermore, we tentatively assume that NADPHd-exhibiting MTN neurons probably participate in transmission and modulation of the proprioceptive impulses from muscle spindles of the masticatory muscles and mechanoreceptors of the periodontal ligaments and thus provide sensory feedback of the masticatory reflex arc.

Expression and colocalization of NADPH-diaphorase and heme oxygenase-2 in trigeminal ganglion and mesencephalic trigeminal nucleus of the rat

“…NADPH-d activity of small to medium-sized TG neurons was more pronounced than large-sized ones. In general, our results of NADPH-d staining are in agreement with those obtained in rat (Alm et al 1995;Stoyanova and Lazarov 2005) and rabbit (Kolesar et al 2006). This contradicted the results of other authors, who report that there are only a few cells positively stained for NADPH-d in TG in rat (Aimi et al 1991).…”

“…We classified NADPH-d and HO-2 stained neurons by size as small (\30/20 lm), medium (30-40/20-30 lm), and large ([40/30 lm) in TG and MTN, respectively. The relative staining densities of semiquantitative analysis of the five categories of trigeminal primary afferent neurons were evaluated by Kolesar's method (Kolesar et al 2006), which is from (-) to (+++), (i.e. -= lack of staining; ± = very weak staining; + = weak; ++ = moderate; +++ = intense staining).…”

“…Previous studies have demonstrated the expression of NADPH-d/nNOS in the primary afferent trigeminal neurons of mammalian (Stoyanova and Lazarov 2005;Kolesar et al 2006) and other species (Bruning et al 1994). The information about the distribution pattern of HO-2 is limited in TG and MTN (Vollerthun et al 1996;Atsumi et al 2000).…”

Sensory and Signaling Mechanisms of Bradykinin, Eicosanoids, Platelet-Activating Factor, and Nitric Oxide in Peripheral Nociceptors

“…nNOS-like immunoreactivity was shown in small and medium-sized rat, mouse, monkey, and human DRG neurons, and its colocalization with CGRP, SP, TRPV1, and PKG was also revealed (3,66,461,513,590,670,708,718,747,795). NOS expression was also detected in small and medium-sized neurons of the rat, cat, and rabbit trigeminal ganglion (179,371,406,678). In human trigeminal ganglia, nNOS immunorectivity was revealed predominantly in large neurons with practically no iNOS staining in any neuronal population (62).…”

Distribution of heme oxygenase-2 and NADPH-diaphorase in the spinal trigeminal nucleus of the rat

“…NADPH-d and HO-2 stained neurons were subsequently categorized by size as small (\85 lm 2 ), medium ([85 lm 2 \ 150 lm 2 ), and large ([150 lm 2 ). The relative staining densities of semiquantitative analysis of labeled neurons were evaluated by Kolesar's method (Kolesar et al 2006). The expression of HO-2 and NADPH-d in the STN was detected to estimate the gray scale of the staining.…”