GABAergic Neurons that Contain Neuropeptide Y Selectively Target Cells with the Neurokinin 1 Receptor in Laminae III and IV of the Rat Spinal Cord

Abstract

Neuropeptide Y (NPY) is contained in a population of GABAergic interneurons in the spinal dorsal horn and, when administered intrathecally, can produce analgesia. We previously identified a strong monosynaptic link between substance P-containing primary afferents and cells in lamina III or IV with the neurokinin 1 (NK1) receptor. Because some of these cells belong to the spinothalamic tract, they are likely to have an important role in pain mechanisms.In this study, we used confocal microscopy to examine the input to lamina III/IV NK1 receptor-immunoreactive neurons from NPY-containing axons. All of the cells studied received a dense innervation from NPY-immunoreactive axons, and electron microscopy revealed that synapses were often present at points of contact. Most NPY-immunoreactive boutons were also GABAergic, which supports the suggestion that they are derived from local neurons. The association between NPYcontaining axons and NK1 receptor-immunoreactive neurons was specific, because postsynaptic dorsal column neurons (which were located in laminae III-V but did not possess NK1 receptors) and lamina I neurons with the NK1 receptor received significantly fewer contacts from NPY-immunoreactive axons. In addition, the NK1 receptor-immunoreactive lamina III/IV cells received few contacts from nitric oxide synthase-containing axons (which belong to a different population of GABAergic dorsal horn neurons). The NPY-containing axons appeared to be targeted to the NK1 receptor-immunoreactive neurons themselves rather than to their associated substance P-immunoreactive inputs.The dense innervation of these cells by NPY-containing axons suggests that they may possess receptors for NPY and that activation of these receptors may contribute to NPY-mediated analgesia.

Loss of Neurons from Laminas I-III of the Spinal Dorsal Horn Is Not Required for Development of Tactile Allodynia in the Spared Nerve Injury Model of Neuropathic Pain

“…To investigate neuronal packing density in the dorsal horn after SNI, sections from the caudal half of the L4 spinal segment from operated animals that survived 28 d (SNI, n ϭ 6; sham operated, n ϭ 6) were incubated in monoclonal antibody against neuronal-specific nuclear protein (NeuN) (1:1000; Chemicon, Chandlers Ford, UK) and guinea pig antiserum against the neurokinin 1 (NK1) receptor (Polgár et al, 1999) (1:1000; this was used to define the lamina I/II border; see below), and then in the following secondary antibodies: anti-mouse IgG conjugated to cyanine 5.18 (Cy5) and anti-guinea pig IgG conjugated to Alexa 488. Sections were then stained with propidium iodide (1% in PBS; Sigma, Poole, UK) in the presence of RNase (10 mg/ml; Sigma) to reveal cell nuclei (Todd et al, 1998).…”

Long-term potentiation of glycinergic synapses triggered by interleukin 1β

“…Dorsal horn functional circuitry is incompletely mapped out, but lamina II GABAergic interneurons are ideally located to gate the flow of nociceptive information from the periphery to supraspinal areas. Previous studies have shown that these interneurons receive both highthreshold and low-threshold primary afferent input (67), and innervate NK1R-expressing projection neurons (21,68), therefore being positioned to provide inhibitory control over dorsal horn nociceptive circuitry. We hypothesize that IL-1β released from microglia or astrocytes rapidly potentiates glycinergic synapses on GABAergic lamina II interneurons that normally inhibit the passage of nociceptive signals to the brain; after inflammation, the nociception-transmitting neurons will in turn be rapidly disinhibited via this mechanism, enhancing the perceived pain and contributing to hyperalgesia and allodynia (44).…”

Inhibition of Inflammatory Pain by Activating B-Type Natriuretic Peptide Signal Pathway in Nociceptive Sensory Neurons

“…Moreover, low levels of galanin, neurotensin, and neuropeptide Y are expressed in DRG neurons under normal circumstance, in addition to their expression in the spinal dorsal horn neurons (Todd et al, 1994;Simmons et al, 1995;X. Zhang et al, , 1998Polgar et al, 1999). These neuropeptides are also involved in the modulation of DRG neuron activity (X.…”