Differential expression of nitric oxide in serotonergic projection neurons: Neurochemical identification of dorsal raphe inputs to rodent trigeminal somatosensory targets

Abstract

The dorsal raphe (DR) is invested with nitric oxide synthase (NOS)-expressing profiles. To characterize the connections of NO-containing cells and further assess neurochemical relationships maintained by DR, the transmitter identity of the raphe projection to the trigeminal somatosensory system was examined. Rats were injected with retrograde tracer into vibrissae-related target areas or with anterograde tracer into DR. NADPH-diaphorase (NADPHd) histochemistry or NOS-immunostaining was combined with serotonin (5HT)- or serotonin transporter (SERT)-immunolabeling to examine: 1) the presence of NO in 5HT-containing axons from DR; 2) the distribution of NO-containing fibers with respect to other nitrergic profiles in the somatosensory system; and 3) the propensity for individual projection neurons in specific subdivisions of DR to colocalize 5HT and NO. Results confirm that "barrel-like" patches can be identified in several adult trigeminal relay nuclei by NADPHd histochemistry and demonstrate that fibers from DR contain 5HT and NO. Observations include a high percentage of cortical midline projection neurons which contained NADPHd (70-80%) and coexpressed 5HT. In contrast, approximately 40% of retrogradely labeled DR-thalamus cells in the lateral wing demonstrated NADPHd or 5HT expression, but not both in the same neuron. Colocalization of NADPHd and 5HT within individual DR projection neurons indicates that: i) DR is a source of nitrergic input to trigeminal structures, and ii) NO and 5HT may be simultaneously released to influence information-processing within somatosensory targets. Disparities in NADPHd expression between retrogradely labeled DR neuronal subpopulations further suggest functional differences in the impact of NO on cortical and subcortical targets.

NMDA Receptor-Dependent Regulation of Axonal and Dendritic Branching

“…To our knowledge, none of these molecules are known to be specifically expressed by PrV barrelette neurons. NO synthase distribution in the rat brainstem trigeminal complex does not correspond to the thalamic projection (barrelette) neurons (Dohrn et al, 1994), and nicotinamide adenine dinucleotide phosphate-diaphorase-positive elements seen in the PrV are of dorsal raphe origin (Simpson et al, 2003). BDNF expression in the developing mouse PrV has not been detailed, although a subset of trigeminal ganglion cells are endowed with tyrosine kinase receptor B and depend on survival for BDNF (Ernfors et al, 1994).…”

Modulation of Serotonergic Neurotransmission by Nitric Oxide

“…Recently, it has been recognized that there is significant morphological and functional overlap between 5-HT and nitric oxide (NO). Immunohistochemical studies, for example, have provided evidence for the co-localization of NO synthase (NOS) and 5-HT in dorsal raphe projections to the trigeminal somatosensory system in rats (Simpson et al 2003). Co-localization of 5-HT and NOS has also been reported in other vertebrate species (e.g., Dun et al 1994;Johnson and Ma 1993;Leger et al 1998;Maqbool et al 1995;Wang et al 1995;Wotherspoon et al 1994).…”

Selective anterograde tracing of nonserotonergic projections from dorsal raphe nucleus to the basal forebrain and extended amygdala

“…Experiments combining retrograde tracing with serotonin (5-HT) immunostaining have established that many nonserotonergic DRN neurons project extrinsically (Beitz et al, 1986;Ma et al, 1991;Petrov et al, 1992Petrov et al, , 1994 Van Bockstaele et al, 1993;Kirifides et al, 2001;Kim et al, 2004;Halberstadt and Balaban, 2006a). Nonserotonergic DRN projections are neurochemically heterogeneous, and may contain a number of transmitter substances, including glutamate (Schwarz and Schwarz, 1992;Kiss et al, 2002), dopamine (Pohle et al, 1984;Descarries et al, 1986;Yoshida et al, 1989;Stratford and Wirtshafter, 1990;Hasue and Shammah-Lagnado, 2002), GABA (Nanopoulos et al, 1982;Stamp and Semba, 1995;Ford et al, 1995;Jankowski and Sesack, 2002), nitric oxide (Xu and Hokfelt, 1997;Simpson et al, 2003), and neuropeptides such as vasoactive intestinal polypeptide (VIP) (Petit et al, 1995;Kozicz et al, 1998) and cholecystokinin Seroogy and Fallon, 1989).…”

“…Experiments combining retrograde tracing with serotonin (5-HT) immunostaining have established that many nonserotonergic DRN neurons project extrinsically (Beitz et al, 1986;Ma et al, 1991;Petrov et al, 1992Petrov et al, , 1994 Van Bockstaele et al, 1993;Kirifides et al, 2001;Kim et al, 2004;Halberstadt and Balaban, 2006a). Nonserotonergic DRN projections are neurochemically heterogeneous, and may contain a number of transmitter substances, including glutamate (Schwarz and Schwarz, 1992;Kiss et al, 2002), dopamine (Pohle et al, 1984;Descarries et al, 1986;Yoshida et al, 1989;Stratford and Wirtshafter, 1990;Hasue and Shammah-Lagnado, 2002), GABA (Nanopoulos et al, 1982;Stamp and Semba, 1995;Ford et al, 1995;Jankowski and Sesack, 2002), nitric oxide (Xu and Hokfelt, 1997;Simpson et al, 2003), and neuropeptides such as vasoactive intestinal polypeptide (VIP) (Petit et al, 1995;Kozicz et al, 1998) and cholecystokinin Seroogy and Fallon, 1989).Although it is likely that non-5-HT DRN projections influence processing in target regions (Weiss and Pellet, 1982;Hajés-Korcsok and Sharp, 2002), very little is known about the anatomical organization of this pathway. Anterograde tracing studies with Phaseolus vulgaris leucoagglutinin (PHA-L) or biotinylated dextran amine (BDA) have demonstrated that regions of the basal forebrain are heavily targeted by DRN projections (Vertes, 1991;Sim and Joseph, 1993;Morin and Meyer-Bernstein, 1999), and retrograde tracing has confirmed that this projection arises, in part, from nonserotonergic neurons (Descarries et al, 1986;Semba et al, 1988;Stratford and Wirtshafter, 1990;…”