Astrid Chamson-Reig

Disruption of the Dopamine D2 Receptor Impairs Insulin Secretion and Causes Glucose Intolerance

The relationship between antidopaminergic drugs and glucose has not been extensively studied, even though chronic neuroleptic treatment causes hyperinsulinemia in normal subjects or is associated with diabetes in psychiatric patients. We sought to evaluate dopamine D2 receptor (D2R) participation in pancreatic function. Glucose homeostasis was studied in D2R knockout mice (Drd2(-/-)) mice and in isolated islets from wild-type and Drd2(-/-) mice, using different pharmacological tools. Pancreas immunohistochemistry was performed. Drd2(-/-) male mice exhibited an impairment of insulin response to glucose and high fasting glucose levels and were glucose intolerant. Glucose intolerance resulted from a blunted insulin secretory response, rather than insulin resistance, as shown by glucose-stimulated insulin secretion tests (GSIS) in vivo and in vitro and by a conserved insulin tolerance test in vivo. On the other hand, short-term treatment with cabergoline, a dopamine agonist, resulted in glucose intolerance and decreased insulin response to glucose in wild-type but not in Drd2(-/-) mice; this effect was partially prevented by haloperidol, a D2R antagonist. In vitro results indicated that GSIS was impaired in islets from Drd2(-/-) mice and that only in wild-type islets did dopamine inhibit GSIS, an effect that was blocked by a D2R but not a D1R antagonist. Finally, immunohistochemistry showed a diminished pancreatic beta-cell mass in Drd2(-/-) mice and decreased beta-cell replication in 2-month-old Drd2(-/-) mice. Pancreatic D2Rs inhibit glucose-stimulated insulin release. Lack of dopaminergic inhibition throughout development may exert a gradual deteriorating effect on insulin homeostasis, so that eventually glucose intolerance develops.

Depth of photothermal conversion of gold nanorods embedded in a tissue-like phantom

Gold nanorod (AuNR)-assisted photothermal therapy has emerged as a viable method for selective killing of cancer cells and shows promise for tumor destruction in vivo. This study examined the distribution of AuNR conversion expected to occur during photothermal therapy in vivo. Tissue-like phantoms were prepared with polyethylene glycol AuNRs distributed homogeneously at a concentration representative of a systemic injection. Phantoms were illuminated with a nanosecond pulsed laser (800 nm) at a variety of combinations of pulse energy (12-120 mJ) and pulse count (1-1000). Operating at the American National Standards Institute safety limit for human skin exposure (30 mJ cm(-2)), a diameter of 13 mm and a depth of 7.6 mm of AuNR conversion were observed in the gel phantoms after 1000 laser pulses (100 s exposure). Significant AuNR conversion was measured to a depth of 6 mm after only 100 pulses. Comparison of the measured AuNR conversion distribution with Monte Carlo simulation suggested that the fluence threshold for AuNR conversion estimated from phantom measurements was in the range of 20-43 mJ cm(-2). The results suggest that AuNR-assisted photothermal therapy will be effective for tumors within 10 mm of the illuminated tissue surface.

Transillumination hyperspectral imaging for histopathological examination of excised tissue

Angular domain spectroscopic imaging (ADSI) is a novel technique for the detection and characterization of optical contrast in turbid media based on spectral characteristics. The imaging system employs a silicon micromachined angular filter array to reject scattered light traversing a specimen and an imaging spectrometer to capture and discriminate the largely remaining quasiballistic light based on spatial position and wavelength. The imaging modality results in hyperspectral shadowgrams containing two-dimensional (2D) spatial maps of spectral information. An ADSI system was constructed and its performance was evaluated in the near-infrared region on tissue-mimicking phantoms. Image-based spectral correlation analysis using transmission spectra and first order derivatives revealed that embedded optical targets could be resolved. The hyperspectral images obtained with ADSI were observed to depend on target concentration, target depth, and scattering level of the background medium. A similar analysis on a muscle and tumor sample dissected from a mouse resulted in spatially dependent optical transmission spectra that were distinct, which suggested that ADSI may find utility in classifying tissues in biomedical applications.

Postnatal development of the endocrine pancreas in mice lacking functional GABAB receptors

Adult mice lacking functional GABAB receptors (GABAB1KO) have glucose metabolism alterations. Since GABAB receptors (GABABRs) are expressed in progenitor cells, we evaluated islet development in GABAB1KO mice. Postnatal day 4 (PND4) and adult, male and female, GABAB1KO, and wild-type littermates (WT) were weighed and euthanized, and serum insulin and glucagon was measured. Pancreatic glucagon and insulin content were assessed, and pancreas insulin, glucagon, PCNA, and GAD65/67 were determined by immunohistochemistry. RNA from PND4 pancreata and adult isolated islets was obtained, and Ins1, Ins2, Gcg, Sst, Ppy, Nes, Pdx1, and Gad1 transcription levels were determined by quantitative PCR. The main results were as follows: 1) insulin content was increased in PND4 GABAB1KO females and in both sexes in adult GABAB1KOs; 2) GABAB1KO females had more clusters (<500 μm(2)) and less islets than WT females; 3) cluster proliferation was decreased at PND4 and increased in adult GABAB1KO mice; 4) increased β-area at the expense of the α-cell area was present in GABAB1KO islets; 5) Ins2, Sst, and Ppy transcription were decreased in PND4 GABAB1KO pancreata, adult GABAB1KO female islets showed increased Ins1, Ins2, and Sst expression, Pdx1 was increased in male and female GABAB1KO islets; and 6) GAD65/67 was increased in adult GABAB1KO pancreata. We demonstrate that several islet parameters are altered in GABAB1KO mice, further pinpointing the importance of GABABRs in islet physiology. Some changes persist from neonatal ages to adulthood (e.g., insulin content in GABAB1KO females), whereas other features are differentially regulated according to age (e.g., Ins2 was reduced in PND4, whereas it was upregulated in adult GABAB1KO females).

Hyperspectral optical imaging of tissues using silicon micromachined microchannel arrays

Angular Domain Spectroscopic Imaging (ADSI) is a novel technique for the detection and characterization of optical contrast abnormalities in a turbid medium. The imaging system employs silicon micro-machined angular filtering methodology, which has high angular selectivity for photons exiting the turbid medium. The ADSI system performance was evaluated on tissue samples from a dissected mouse. Images collected with the ADSI displayed differences in image contrast between different tissue types.

Angular domain spectroscopic imaging for breast cancer margin assessment after lumpectomy

Angular Domain Spectroscopic Imaging (ADSI) is a novel technique for the detection and characterization of optical contrast abnormalities in ex-vivo breast tissue samples based on spectral characteristics. The imaging system employs a spatial filter called an angular filter array to reject scattered photons traversing a sample. The system employs an imaging spectrometer to capture and discriminate the largely remaining quasi-ballistic photons based on spatial position and wavelength. Spectral data were obtained from samples obtained from two patients, one sample contained invasive mammary carcinoma, and the other one contained normal fat and fibrous tissue. Principal component analysis using transmission absorption spectra obtained with ADSI was able to differentiate tumor versus normal tissue regions.

Development of a neonatal skull phantom for photoacoustic imaging

Photoacoustic imaging (PAI) has been proposed as a non-invasive technique for the diagnosis and monitoring of disorders in the neonatal brain. However, PAI of the brain through the intact skull is challenging due to reflection and attenuation of photoacoustic pressure waves by the skull bone. The objective of this work was to develop a phantom for testing the potential limits the skull bone places on PAI of the neonatal brain. Our approach was to make acoustic measurements on materials designed to mimic the neonatal skull bone and construct a semi-realistic phantom. A water tank and two ultrasound transducers were utilized to measure the ultrasound insertion loss (100 kHz to 5MHz) of several materials. Cured mixtures of epoxy and titanium dioxide powder provided the closest acoustic match to neonatal skull bone. Specifically, a 1.4-mm thick sample composed of 50% (by mass) titanium dioxide powder and 50% epoxy was closest to neonatal skull bone in terms of acoustic insertion loss. A hemispherical skull phantom (1.4 mm skull thickness) was made by curing the epoxy/titanium dioxide powder mixture inside a mold. The mold was constructed using 3D prototyping techniques and was based on the hairless head of a realistic infant doll. The head was scanned to generate a 3D model, which in turn was used to build a 3D CAD version of the mold. The mold was CNC machined from two solid blocks of Teflon®. The neonatal skull phantom will enable the study of the propagation of photoacoustic pressure waves under a variety of experimental conditions.

Potential for photoacoustic imaging of the neonatal brain

Photoacoustic imaging (PAI) has been proposed as a non-invasive technique for imaging neonatal brain injury. Since PAI combines many of the merits of both optical and ultrasound imaging, images with high contrast, high resolution, and a greater penetration depth can be obtained when compared to more traditional optical methods. However, due to the strong attenuation and reflection of photoacoustic pressure waves at the skull bone, PAI of the brain is much more challenging than traditional methods (e.g. near infrared spectroscopy) for optical interrogation of the neonatal brain. To evaluate the potential limits the skull places on 3D PAI of the neonatal brain, we constructed a neonatal skull phantom (1.4-mm thick) with a mixture of epoxy and titanium dioxide powder that provided acoustic insertion loss (1-5MHz) similar to human infant skull bone. The phantom was molded into a realistic infant skull shape by means of a CNCmachined mold that was based upon a 3D CAD model. To evaluate the effect of the skull bone on PAI, a photoacoustic point source was raster scanned within the phantom brain cavity to capture the imaging operator of the 3D PAI system (128 ultrasound transducers in a hemispherical arrangement) with and without the intervening skull phantom. The resultant imaging operators were compared to determine the effect of the skull layer on the PA signals in terms of amplitude loss and time delay.

Angle-resolved spectroscopy: a tissue-mimicking phantom study

The Radial Angular Filter Array (RAFA) is a novel optical filter consisting of a radially-distributed series of micromachined channels with a focal length of a few millimeters. The RAFA filters photons passing through the focal point according to the propagation direction and has proven to be capable of collecting the angular distribution and the spectral information of photons simultaneously and non-invasively, which allows angle-resolved spectroscopic measurement of a turbid medium. To explore the feasibility of using this device to characterize the optical abnormalities in human tissues, we tested the performance of an angle-resolved RAFA-based spectroscopy system to detect absorption targets embedded within a tissue-mimicking phantom. The body of the phantom was made of 0.1% IntralipidTM/agarose gel (7 mm in thickness) and the targets were spherical (1.5 mm in radius) and contained 10 μM Indocyanine Green (ICG). The illumination source was a broadband near infrared (NIR) collimated beam. Photons were angularly filtered by the RAFA and spectrally resolved by a pushbroom spectrometer. The experimental results confirmed that the RAFA preferentially filtered photons that carried absorption and scattering information of the embedded targets.

Deep illumination angular domain spectroscopic imaging: tissue-mimicking phantom study

The angular filter array (AFA) is a silicon micro-machined optical collimator, which only accepts photons propagating within a narrow solid angle. It can be used to select photons exiting an imaging sample along a specific direction. This paper describes a novel Angular Domain Spectroscopic Imaging (ADSI) technique that utilizes deep illumination from the front surface of the sample and a camera with an AFA to image features embedded inside a turbid medium. This approach permitted spectroscopic imaging of turbid samples too thick to be imaged in a trans-illumination setup. The tissue-mimicking test phantom contained three groups of Indocyanine Green doped inclusions at depths from 1 to 3 mm embedded within an IntralipidTM/agarose gel. The sample was scanned across the AFA and the intensity of the back scattered light along the direction normal to the surface was acquired as a function of location and wavelength. The resultant spectral images were captured and analyzed. The experiments demonstrated that ADSI could detect subsurface features that differed in wavelength-dependent absorption and/or scattering properties from the surrounding medium with the deep illumination configuration. Deep illumination ADSI may be useful as a non-invasive tissue imaging tool.