Calretinin-expressing islet cells are a source of pre- and post-synaptic inhibition of non-peptidergic nociceptor input to the mouse spinal cord

Unmyelinated non-peptidergic nociceptors (NP afferents) arborise in lamina II of the spinal cord and receive GABAergic axoaxonic synapses, which mediate presynaptic inhibition. However, until now the source of this axoaxonic synaptic input was not known. Here we provide evidence that it originates from a population of inhibitory calretinin-expressing interneurons (iCRs), which correspond to lamina II islet cells. The NP afferents can be assigned to 3 functionally distinct classes (NP1-3). NP1 afferents have been implicated in pathological pain states, while NP2 and NP3 afferents also function as pruritoceptors. Our findings suggest that all 3 of these afferent types innervate iCRs and receive axoaxonic synapses from them, providing feedback inhibition of NP input. The iCRs also form axodendritic synapses, and their targets include cells that are themselves innervated by the NP afferents, thus allowing for feedforward inhibition. The iCRs are therefore ideally placed to control the input from non-peptidergic nociceptors and pruritoceptors to other dorsal horn neurons, and thus represent a potential therapeutic target for the treatment of chronic pain and itch.

Calretinin-expressing islet cells: a source of pre- and post-synaptic inhibition of non-peptidergic nociceptor input to the mouse spinal cord

Unmyelinated non-peptidergic nociceptors (NP afferents) arborise in lamina II of the spinal cord and receive GABAergic axoaxonic synapses, which mediate presynaptic inhibition. However, until now the source of this axoaxonic synaptic input was not known. Here we provide evidence that it originates from a population of inhibitory calretinin-expressing interneurons (iCRs), which correspond to lamina II islet cells. The NP afferents can be assigned to 3 functionally distinct classes (NP1-3). NP1 afferents have been implicated in pathological pain states, while NP2 and NP3 afferents also function as pruritoceptors. Our findings suggest that all 3 of these afferent types innervate iCRs and receive axoaxonic synapses from them, providing feedback inhibition of NP input. The iCRs also form axodendritic synapses, and their targets include cells that are themselves innervated by the NP afferents, thus allowing for feedforward inhibition. The iCRs are therefore ideally placed to control the input from non-peptidergic nociceptors and pruritoceptors to other dorsal horn neurons, and thus represent a potential therapeutic target for the treatment of chronic pain and itch.

Diversity of inhibitory and excitatory parvalbumin interneuron circuits in the dorsal horn

ABSTRACT

Parvalbumin-expressing interneurons (PVINs) in the spinal dorsal horn are found primarily in laminae II inner and III. Inhibitory PVINs play an important role in segregating innocuous tactile input from pain-processing circuits through presynaptic inhibition of myelinated low-threshold mechanoreceptors and postsynaptic inhibition of distinct spinal circuits. By comparison, relatively little is known of the role of excitatory PVINs (ePVINs) in sensory processing. Here, we use neuroanatomical and optogenetic approaches to show that ePVINs comprise a larger proportion of the PVIN population than previously reported and that both ePVIN and inhibitory PVIN populations form synaptic connections among (and between) themselves. We find that these cells contribute to neuronal networks that influence activity within several functionally distinct circuits and that aberrant activity of ePVINs under pathological conditions is well placed to contribute to the development of mechanical hypersensitivity.

Spinoparabrachial projection neurons form distinct classes in the mouse dorsal horn

ABSTRACT

Projection neurons in the spinal dorsal horn relay sensory information to higher brain centres. The activation of these populations is shaped by afferent input from the periphery, descending input from the brain, and input from local interneuron circuits. Much of our recent understanding of dorsal horn circuitry comes from studies in transgenic mice; however, information on projection neurons is still based largely on studies in monkey, cat, and rat. We used viral labelling to identify and record from mouse parabrachial nucleus (PBN) projecting neurons located in the dorsal horn of spinal cord slices. Overall, mouse lamina I spinoparabrachial projection neurons (SPBNs) exhibit many electrophysiological and morphological features that overlap with rat. Unbiased cluster analysis distinguished 4 distinct subpopulations of lamina I SPBNs, based on their electrophysiological properties that may underlie different sensory signalling features in each group. We also provide novel information on SPBNs in the deeper lamina (III-V), which have not been previously studied by patch clamp analysis. These neurons exhibited higher action potential discharge frequencies and received weaker excitatory synaptic input than lamina I SPBNs, suggesting this deeper population produces different sensory codes destined for the PBN. Mouse SPBNs from both regions (laminae I and III-V) were often seen to give off local axon collaterals, and we provide neuroanatomical evidence they contribute to excitatory input to dorsal horn circuits. These data provide novel information to implicate excitatory input from parabrachial projection neuron in dorsal horn circuit activity during processing of nociceptive information, as well as defining deep dorsal horn projection neurons that provide an alternative route by which sensory information can reach the PBN.

Projection Neuron Axon Collaterals in the Dorsal Horn: Placing a New Player in Spinal Cord Pain Processing

The pain experience depends on the relay of nociceptive signals from the spinal cord dorsal horn to higher brain centers. This function is ultimately achieved by the output of a small population of highly specialized neurons called projection neurons (PNs). Like output neurons in other central nervous system (CNS) regions, PNs are invested with a substantial axon collateral system that ramifies extensively within local circuits. These axon collaterals are widely distributed within and between spinal cord segments. Anatomical data on PN axon collaterals have existed since the time of Cajal, however, their function in spinal pain signaling remains unclear and is absent from current models of spinal pain processing. Despite these omissions, some insight on the potential role of PN axon collaterals can be drawn from axon collateral systems of principal or output neurons in other CNS regions, such as the hippocampus, amygdala, olfactory cortex, and ventral horn of the spinal cord. The connectivity and actions of axon collaterals in these systems have been well-defined and used to confirm crucial roles in memory, fear, olfaction, and movement control, respectively. We review this information here and propose a framework for characterizing PN axon collateral function in the dorsal horn. We highlight that experimental approaches traditionally used to delineate axon collateral function in other CNS regions are not easily applied to PNs because of their scarcity relative to spinal interneurons (INs), and the lack of cellular organization in the dorsal horn. Finally, we emphasize how the rapid development of techniques such as viral expression of optogenetic or chemogenetic probes can overcome these challenges and allow characterization of PN axon collateral function. Obtaining detailed information of this type is a necessary first step for incorporation of PN collateral system function into models of spinal sensory processing.

Functional and Molecular Analysis of Proprioceptive Sensory Neuron Excitability in Mice

Neurons located in dorsal root ganglia (DRG) are crucial for transmitting peripheral sensations such as proprioception, touch, temperature, and nociception to the spinal cord before propagating these signals to higher brain structures. To date, difficulty in identifying modality-specific DRG neurons has limited our ability to study specific populations in detail. As the calcium-binding protein parvalbumin (PV) is a neurochemical marker for proprioceptive DRG cells we used a transgenic mouse line expressing green fluorescent protein (GFP) in PV positive DRGs, to study the functional and molecular properties of putative proprioceptive neurons. Immunolabeled DRGs showed a 100% overlap between GFP positive (GFP+) and PV positive cells, confirming the PVeGFP mouse accurately labeled PV neurons. Targeted patch-clamp recording from isolated GFP+ and GFP negative (GFP−) neurons showed the passive membrane properties of the two groups were similar, however, their active properties differed markedly. All GFP+ neurons fired a single spike in response to sustained current injection and their action potentials (APs) had faster rise times, lower thresholds and shorter half widths. A hyperpolarization-activated current (I_h) was observed in all GFP+ neurons but was infrequently noted in the GFP− population (100% vs. 11%). For GFP+ neurons, I_h activation rates varied markedly, suggesting differences in the underlying hyperpolarization-activated cyclic nucleotide-gated channel (HCN) subunit expression responsible for the current kinetics. Furthermore, quantitative polymerase chain reaction (qPCR) showed the HCN subunits 2, 1, and 4 mRNA (in that order) was more abundant in GFP+ neurons, while HCN 3 was more highly expressed in GFP− neurons. Likewise, immunolabeling confirmed HCN 1, 2, and 4 protein expression in GFP+ neurons. In summary, certain functional properties of GFP+ and GFP− cells differ markedly, providing evidence for modality-specific signaling between the two groups. However, the GFP+ DRG population demonstrates considerable internal heterogeneity when hyperpolarization-activated cyclic nucleotide-gated channel (HCN channel) properties and subunit expression are considered. We propose this heterogeneity reflects the existence of different peripheral receptors such as tendon organs, muscle spindles or mechanoreceptors in the putative proprioceptive neuron population.

Transgenic Cross-Referencing of Inhibitory and Excitatory Interneuron Populations to Dissect Neuronal Heterogeneity in the Dorsal Horn

The superficial dorsal horn (SDH, LI-II) of the spinal cord receives and processes multimodal sensory information from skin, muscle, joints, and viscera then relay it to the brain. Neurons within the SDH fall into two broad categories, projection neurons and interneurons. The later can be further subdivided into excitatory and inhibitory types. Traditionally, interneurons within the SDH have been divided into overlapping groups according to their neurochemical, morphological and electrophysiological properties. Recent clustering analyses, based on molecular transcript profiles of cells and nuclei, have predicted many more functional groups of interneurons than expected using traditional approaches. In this study, we used electrophysiological and morphological data obtained from genetically-identified excitatory (vGLUT2) and inhibitory (vGAT) interneurons in transgenic mice to cluster cells into groups sharing common characteristics and subsequently determined how many clusters can be assigned by combinations of these properties. Consistent with previous reports, we show differences exist between excitatory and inhibitory interneurons in terms of their excitability, nature of the ongoing excitatory drive, action potential (AP) properties, sub-threshold current kinetics, and morphology. The resulting clusters based on statistical and unbiased assortment of these data fell well short of the numbers of molecularly predicted clusters. There was no clear characteristic that in isolation defined a population, rather multiple variables were needed to predict cluster membership. Importantly though, our analysis highlighted the appropriateness of using transgenic lines as tools to functionally subdivide both excitatory and inhibitory interneuron populations.

Calretinin positive neurons form an excitatory amplifier network in the spinal cord dorsal horn

Nociceptive information is relayed through the spinal cord dorsal horn, a critical area in sensory processing. The neuronal circuits in this region that underpin sensory perception must be clarified to better understand how dysfunction can lead to pathological pain. This study used an optogenetic approach to selectively activate spinal interneurons that express the calcium-binding protein calretinin (CR). We show that these interneurons form an interconnected network that can initiate and sustain enhanced excitatory signaling, and directly relay signals to lamina I projection neurons. Photoactivation of CR interneurons in vivo resulted in a significant nocifensive behavior that was morphine sensitive, caused a conditioned place aversion, and was enhanced by spared nerve injury. Furthermore, halorhodopsin-mediated inhibition of these interneurons elevated sensory thresholds. Our results suggest that dorsal horn circuits that involve excitatory CR neurons are important for the generation and amplification of pain and identify these interneurons as a future analgesic target.

A quantitative analysis of tumour characteristics in breast cancer patients with extranodal extension in non-sentinel nodes

BACKGROUND

The presence of extranodal extension (ENE) is well documented as a predictor of non-sentinel lymph node (NSLN) metastasis. The ACOSOG Z0011 trial (2011) concluded that patients who satisfy criteria including the absence of sentinel lymph node (SLN) ENE can forgo axillary clearance (AC). Currently there are no studies analysing the rate of ENE in NSLN metastasis in which the sentinel node was positive but had no ENE. Determining this incidence will help determine if current paradigms are resulting in residual ENE in NSLN metastasis by forgoing AC based on the Z0011 trial..

METHODS

This study determined incidence of ENE at NSLN metastasis in patients with a positive SLN biopsy without ENE in 162 symptomatic breast cancer patients who underwent AC between 2009 and 2014 at Cork University Hospital Breast Cancer Service, a teaching hospital of University College Cork.

RESULTS

Of 965 sentinel node biopsies performed 251 were identified as SLN positive, 162 (64.5%) underwent further AC. Of the 162 patients, 56.8% (92/162) were positive for ENE at SLN, of these 57.6% (53/92) had NSLN metastasis versus 17.1% (12/70) in the ENE-negative group (χ² test; P < 0.001). On adjusted analysis, ENE at the SLN was a significant predictor of NSLN metastasis (odds ratio [OR] 8.63; 95% confidence interval [CI] 3.26-22.86; P < 0.001). The incidence of NSLN-ENE in patients without SLN-ENE was 1/70 (1.4%) compared with 33.7% (31/92) in patients who had ENE at the SLN (χ² test; P < 0.001).

CONCLUSION

ENE at the SLN is an independent predictor of NSLN involvement; its absence significantly reduces the likelihood of ENE in NSLN metastasis..

When pathological and radiological correlation is achieved, excision of fibroadenoma with lobular neoplasia on core biopsy is not warranted

BACKGROUND

The diagnosis and management of lobular neoplasia (LN) including lobular carcinoma in situ (LCIS) and atypical lobular hyperplasia (ALH) remains controversial. Current management options after a core needle biopsy (CNB) with lobular neoplasia (LN) incorporating both ALH and LCIS include excision biopsy or careful clinical and radiologic follow up.

METHODS

A retrospective analysis of the surgical database at Cork University Hospital was performed to identify all core needle biopsies from January 1st 2010 to 31st December 2013 with a diagnosis of FA who subsequently underwent surgical excision biopsy. All cases with associated LN including ALH and classical LCIS were selected. We excluded cases with coexistent ductal carcinoma in situ (DCIS), invasive carcinoma, LN associated with necrosis, pleomorphic lobular carcinoma in situ (PLCIS) or lesions which would require excision in their own right (papilloma, radial scar, atypical ductal hyperplasia (ADH) or flat epithelial atypia (FEA)). Cases in which the radiologic targeted mass was discordant with a diagnosis of FA were also excluded.

RESULTS

2878 consecutive CNB with a diagnosis of FA were identified. 25 cases had a diagnosis of concomitant ALH or classical LCIS. Our study cohort consisted of 21 women with a mean age 53 years (age range 41-70 years). The core biopsy diagnosis was of LCIS and FA in 16 cases and ALH and FA in 5 cases. On excision biopsy, a FA was confirmed in all 21 cases. In addition to the FA, residual LCIS was present in 14 cases with residual ALH in 2 cases. One of the twenty-one cases (4.8%) was upgraded to invasive ductal carcinoma on excision.

Automated Cellient(™) cytoblocks: better, stronger, faster?

OBJECTIVE

Cytoblocks (CBs), or cell blocks, provide additional morphological detail and a platform for immunocytochemistry (ICC) in cytopathology. The Cellient(™) system produces CBs in 45 minutes using methanol fixation, compared with traditional CBs, which require overnight formalin fixation. This study compares Cellient and traditional CB methods in terms of cellularity, morphology and immunoreactivity, evaluates the potential to add formalin fixation to the Cellient method for ICC studies and determines the optimal sectioning depth for maximal cellularity in Cellient CBs.

METHODS

One hundred and sixty CBs were prepared from 40 cytology samples (32 malignant, eight benign) using four processing methods: (A) traditional; (B) Cellient (methanol fixation); (C) Cellient using additional formalin fixation for 30 minutes; (D) Cellient using additional formalin fixation for 60 minutes. Haematoxylin and eosin-stained sections were assessed for cellularity and morphology. ICC was assessed on 14 cases with a panel of antibodies. Three additional Cellient samples were serially sectioned to determine the optimal sectioning depth. Scoring was performed by two independent, blinded reviewers.

RESULTS

For malignant cases, morphology was superior with Cellient relative to traditional CBs (P < 0.001). Cellularity was comparable across all methods. ICC was excellent in all groups and the addition of formalin at any stage during the Cellient process did not influence the staining quality. Serial sectioning through Cellient CBs showed optimum cellularity at 30-40 μm with at least 27 sections obtainable.

CONCLUSIONS

Cellient CBs provide superior morphology to traditional CBs and, if required, formalin fixation may be added to the Cellient process for ICC. Optimal Cellient CB cellularity is achieved at 30-40 μm, which will impact on the handling of cases in daily practice.

Hepatic metastases from an unknown primary neoplasm (UPN): survival, prognostic indicators and value of extensive investigations

AIM

The objectives of this study were to identify prognostic features for patients with hepatic metastases and unknown primary neoplasms (UPN), determine the common primary tumours, assess the value of diagnostic tests in finding these tumours, and evaluate the impact of therapy and knowledge of the primary tumour on patient survival.

MATERIALS AND METHODS

Eighty-eight patients with UPN and liver biopsy proven hepatic metastases over a 10-year period were reviewed (M:F, 58:30; age range 27-91 years, median 64.5 years). Histopathology, diagnostic investigations and success at identifying the primary neoplasm were recorded. In addition, in 70 patients with adenocarcinoma histology (M:F, 48:22; age range 27-91 years, median 65 years), treatment and survival data from the date of biopsy were recorded.

RESULTS

The histological spectrum included adenocarcinoma in 70, neuroendocrine in four, squamous cell carcinoma in four, small cell carcinoma in four, carcinoid in two, hepatoma in one and three others. Extensive investigation identified a primary neoplasm in 16/88 patients (18%) including colorectal in six, gastric in two, lung in four, oesophageal in two, prostate in one and carcinoid in one. In the adenocarcinoma group survival data were available for 62/70 patients. Sixteen of 62 patients received active treatment with either surgery, chemotherapy, radiotherapy or a combination protocol. Forty-six of 62 patients received palliative care alone. Median survival for the adenocarcinoma group overall was 49 days. The median survival for treated patients (49 days) versus untreated patients (52 days) was not significantly different (P=0.128). Patients <65 years were more likely to receive active treatment than those >65 years (P=0.006). Age with a hazard ratio (HR) of 1.01 (P=0.178), active treatment (HR=0.65;P=0.194), knowledge of the primary neoplasm (HR=0.60;P=0.213) and male gender (HR=0.88;P=0.642) had no significant effect on survival.

CONCLUSION

Although hepatic metastases are associated with poor prognosis, it is essential that a liver biopsy be performed to obtain a histological diagnosis. Adenocarcinoma metastases carry a dismal prognosis, and no prognostic factors, including knowledge of the primary tumour, are significant for patient survival. Extensive investigation is not warranted in patients with adenocarcinoma liver metastases.