Hypothalamic cell types and circuits that drive behaviors essential for survival

Cracking the cytoarchitectural organization, activity patterns, and neurotransmitter nature of genetically-distinct cell types in the lateral hypothalamus is fundamental to understanding survival behaviors such as feeding. Here I revealed that chemogenetic inhibition of parvalbumin-positive neurons in the lateral hypothalamus increases food consumption and general arousal in sated mice. Moreover, functional imaging using two-photon fluorescence endomicroscopy exhibited decreased activity of these neurons during food-deprived conditions, suggesting an unprecedented role in encoding for metabolic states. Furthermore, these neurons are fast-spiking similar to canonical inhibitory parvalbumin neurons in the neocortex and hippocampus, but unlike those cells, lateral hypothalamic parvalbumin neurons are excitatory. Finally, sensory detection of food rapidly increases the activity of these neurons

Impaired Retinal Vasoreactivity: An Early Marker of Stroke Risk in Diabetes

Diabetes is a common cause of small vessel disease leading to stroke and vascular dementia. While the function and structure of large cerebral vessels can be easily studied, the brain’s microvasculature remains difficult to assess. Previous studies have demonstrated that structural changes in the retinal vessel architecture predict stroke risk, but these changes occur at late disease stages. Our goal was to examine whether retinal vascular status can predict cerebral small vessel dysfunction during early stages of diabetes. Retinal vasoreactivity and cerebral vascular function were measured in 78 subjects (19 healthy controls, 22 subjects with prediabetes, and 37 with type‐2 diabetes) using a new noninvasive retinal imaging device (Dynamic Vessel Analyzer) and transcranial Doppler studies, respectively. Cerebral blood vessel responsiveness worsened with disease progression of diabetes. Similarly, retinal vascular reactivity was significantly attenuated in subjects with prediabetes and diabetes compared to healthy controls. Subjects with prediabetes and diabetes with impaired cerebral vasoreactivity showed mainly attenuation of the retinal venous flicker response. This is the first study to explore the relationship between retinal and cerebral vascular function in diabetes. Impairment of venous retinal responsiveness may be one of the earliest markers of vascular dysfunction in diabetes possibly indicating subsequent risk of stroke and vascular dementia.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/136050/1/jon12412.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/136050/2/jon12412_am.pd

Comparison of retinal vasodilator and constrictor responses in type 2 diabetes

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93551/1/j.1755-3768.2012.02445.x.pd

Impaired retinal vasodilator responses in prediabetes and type 2 diabetes

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/99677/1/aos12129.pd

Electrophysiological properties and projections of lateral hypothalamic parvalbumin positive neurons.

Cracking the cytoarchitectural organization, activity patterns, and neurotransmitter nature of genetically-distinct cell types in the lateral hypothalamus (LH) is fundamental to develop a mechanistic understanding of how activity dynamics within this brain region are generated and operate together through synaptic connections to regulate circuit function. However, the precise mechanisms through which LH circuits orchestrate such dynamics have remained elusive due to the heterogeneity of the intermingled and functionally distinct cell types in this brain region. Here we reveal that a cell type in the mouse LH identified by the expression of the calcium-binding protein parvalbumin (PVALB; LHPV) is fast-spiking, releases the excitatory neurotransmitter glutamate, and sends long range projections throughout the brain. Thus, our findings challenge long-standing concepts that define neurons with a fast-spiking phenotype as exclusively GABAergic. Furthermore, we provide for the first time a detailed characterization of the electrophysiological properties of these neurons. Our work identifies LHPV neurons as a novel functional component within the LH glutamatergic circuitry

Molecular and electrophysiological characterization of LH^PV neurons.

<p>(A) Detection of <i>Kv3</i>.<i>1</i>, <i>Kv3</i>.<i>2</i>, and <i>Hcn2</i> subunit genes by RT-qPCR analysis after harvesting the cytoplasm from single LH^PV neurons. Representative amplification plot displayed. Note that cells were <i>Pvalb</i>⁺/<i>Vglut2</i>⁺/<i>Vgat</i>⁻. (B) Relative abundance of <i>Kv3</i>.<i>1</i>, <i>Kv3</i>.<i>2</i>, and <i>Hcn2</i> in single LH^PV neurons. Box plots show mean (×), median, quartiles (boxes), and s.e.m. (whiskers). Cycle threshold (Ct), relative abundance values, and sample sizes are explained in Methods. (C) Representative firing pattern of a fast-spiking LH^PV neuron that displays spike frequency accommodation and amplitude attenuation during large depolarizing current injections (500 pA, 500 ms pulses). Note decreases in firing frequency and amplitude during the last 100 ms of the pulse. Dotted line denotes resting membrane potential (V_rmp = –63 mV). (D) Firing rate of LH^PV neurons in response to current injection (<i>I–f</i> curves) during 500 ms pulses. The red/gray dots show the average firing rate of the LH^PV neurons and the standard deviation is indicated by the black vertical bar (<i>n</i> = 34).</p

Electrophysiological properties of LH^PV neurons.

<p>Electrophysiological properties of LH^PV neurons.</p

Axonal projections of LH^PV neurons.

<p>(A) Schematic and representative image depicting a bilateral injection of the Cre recombinase-dependent viral vector for anterograde tracing (rAAV2/9-hEf1α-DIO-synaptophysin-mCherry) into the lateral hypothalamus (LH) of a <i>Pvalb</i>^{<i>IREScre</i>} mouse. Scale bar 500 μm. Representative images of projections to (B) the lateral habenula (LHb), (C) the submedius thalamic nucleus (Sub), (D) the parafascicular thalamic nucleus (PF) surrounding the fasciculus retroflexus (fr), (E) the posterior hypothalamus (PH), (F) the retromamillary nucleus (RMM), (G) the periaqueductal gray (PAG), and (H) the reticulotegmental nucleus of the pons (RtTg). (B-D-E-F) Scale bars (low magnification), 200 μm; Scale bars (high magnification), 25 μm (C-G-H) Scale bars (low magnification), 100 μm; Scale bars (high magnification), 25 μm. (<i>n</i> = 3 mice). Schematic images modified from Franklin KBJ & Paxinos G (2013) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198991#pone.0198991.ref027" target="_blank">27</a>].</p

LH^PV neurons are <i>Vglut2</i>-positive and release glutamate.

<p>(A) Traces of excitatory postsynaptic currents (EPSCs; gray) evoked by photostimulation (1 ms light pulses) of LH^PV-ChR2⁺ neurons before and after bath application of DNQX and APV (black trace; AMPA-R and NMDA-R antagonists). Red and black traces are the average of ten consecutive sweeps. LH neuron was held at −70 mV. Note schematic of ChR2-assisted circuit mapping (inset; upper left) from LH^PV-ChR2⁺ neuron (red) onto a postsynaptic lateral hypothalamic neuron (gray) as well as arrow indicating the recorded postsynaptic LH neuron (inset; bottom right) filled with biocytin (green) surrounded by ChR2:tdTomato-expressing LH^PV dendrites/axons (red). Scale bar, 50 μm. (B-C) Coronal sections showing that parvalbumin immunoreactive cells (brown; left panel) mainly colocalize with <i>Vglut2</i> mRNA (95%; green grain aggregates; right panel) but not with <i>Vgat</i> mRNA (5%; green grain aggregates; right panel). Scale bars, 50 μm. (D) Fluorescent <i>in situ</i> hybridization assay for <i>Vgat</i> (green), <i>Vglut2</i> (white), and <i>Pvalb</i> (red) with DAPI (blue) counterstain. <i>Pvalb</i> mRNA was predominantly detected in neurons that express <i>Vglut2</i> (95% <i>Pvalb</i>⁺<i>/Vglut2</i>⁺; 5% <i>Pvalb</i>⁺<i>/Vgat</i>⁺) Scale bar, 50 μm.</p

LH^PV neurons exhibit fast-spiking characteristics.

<p>(A) Immunohistochemical identification of parvalbumin-expressing neurons in a horizontal section of the mouse LH. Dotted lines highlight a cluster of immuno-positive LH^PV neurons (green). Scale bar, 200 μm. (B) Representative traces and firing pattern of a fast-spiking LH^PV neuron in response to step hyperpolarizing (bottom traces; from −100 to 0 pA) and depolarizing current injections (upper traces; 900 pA) during a 500 ms pulse. Resting membrane potential (V_rmp = −66 mV) and maximal firing frequency 264 Hz. Abbreviations, fornix (f), optic tract (opt), lateral mammillary nucleus (LM), lateral (L), medial (M), rostral (R), and caudal (C).</p