Scintillation characteristics of the EJ-299-02H scintillator.

A study of the dead layer thickness and quenching factor of a plastic scintillator for use in ultracold neutron (UCN) experiments is described. Alpha spectroscopy was used to determine the thickness of a thin surface dead layer to be 630 ± 110 nm. The relative light outputs from the decay of 241Am and Compton scattering of electrons were used to extract Birks' law coefficient, yielding a kB value of 0.087 ± 0.003 mm/MeV, consistent with some previous reports for other polystyrene-based scintillators. The results from these measurements are incorporated into the simulation to show that an energy threshold of (∼9 keV) can be achieved for the UCNProBe experiment. This low threshold enables high beta particle detection efficiency and the indirect measurement of UCN. The ability to make the scintillator deuterated, accompanied by its relatively thin dead layer, gives rise to unique applications in a wide range of UCN experiments, where it can be used to trap UCN and detect charged particles in situ.

Ultracold neutron properties of the Eljen-299-02D deuterated scintillator.

In this paper, we report studies of the Fermi potential and loss per bounce of ultracold neutrons (UCNs) on a deuterated scintillator (Eljen-299-02D). These UCN properties of the scintillator enable its use in a wide variety of applications in fundamental neutron research.

Orbitomedial prefrontal cortical projections to distinct longitudinal columns of the periaqueductal gray in the rat.

We utilised retrograde and anterograde tracing procedures to study the origin and termination of prefrontal cortical (PFC) projections to the periaqueductal gray (PAG) in the rat. A previous study, in the primate, had demonstrated that distinct subgroups of PFC areas project to specific PAG columns. Retrograde tracing experiments revealed that projections to dorsolateral (dlPAG) and ventrolateral (vlPAG) periaqueductal gray columns arose from medial PFC, specifically prelimbic, infralimbic, and anterior cingulate cortices. Injections made in the vlPAG also labeled cells in medial, ventral, and dorsolateral orbital cortex and dorsal and posterior agranular insular cortex. Other orbital and insular regions, including lateral and ventrolateral orbital, ventral agranular insular, and dysgranular and granular insular cortex did not give rise to appreciable projections to the PAG. Anterograde tracing experiments revealed that the projections to different PAG columns arose from specific PFC areas. Projections from the caudodorsal medial PFC (caudal prelimbic and anterior cingulate cortices) terminated predominantly in dlPAG, whereas projections from the rostroventral medial PFC (rostral prelimbic cortex) innervated predominantly the vlPAG. As well, consistent with the retrograde data, projections arising from select orbital and agranular insular cortical areas terminated selectively in the vlPAG. The results indicate: (1) that rat orbital and medial PFC possesses an organisation broadly similar to that of the primate; and (2) that subdivisions within the rat orbital and medial PFC can be recognised on the basis of projections to distinct PAG columns.

Orbitomedial prefrontal cortical projections to hypothalamus in the rat.

A previous study in the rat revealed that distinct orbital and medial prefrontal cortical (OMPFC) areas projected to specific columns of the midbrain periaqueductal gray region (PAG). This study used anterograde tracing techniques to define projections to the hypothalamus arising from the same OMPFC regions. In addition, injections of anterograde and retrograde tracers were made into different PAG columns to examine connections between hypothalamic regions and PAG columns projected upon by the same OMPFC regions. The most extensive patterns of hypothalamic termination were seen after injection of anterograde tracer in prelimbic and infralimbic (PL/IL) and the ventral and medial orbital (VO/MO) cortices. Projections from rostral PL/IL and VO/MO targeted the rostrocaudal extent of the lateral hypothalamus, as well as lateral perifornical, and dorsal and posterior hypothalamic areas. Projections arising from caudal PL/IL terminated within the dorsal hypothalamus, including the dorsomedial nucleus and dorsal and posterior hypothalamic areas. There were also projections to medial perifornical and lateral hypothalamic areas. In contrast, it was found that anterior cingulate (AC), dorsolateral orbital (DLO), and agranular insular (AId) cortices projected to distinct and restricted hypothalamic regions. Projections arising from AC terminated within dorsal and posterior hypothalamic areas, whereas DLO and AId projected to the lateral hypothalamus. The same OMPFC regions also projected indirectly, by means of specific PAG columns, to many of the same hypothalamic fields. In the context of our previous findings, these data indicate that, in both rat and macaque, parallel but distinct circuits interconnect OMPFC areas with specific hypothalamic regions, as well as PAG columns.

A calbindin immunoreactive "deep pain' recipient thalamic nucleus in the rat.

The ventrolateral periaqueductal gray (vlPAG) is the only brain region known to receive convergent deep noxious inputs and to mediate the reactions characteristic of deep pain. Injections of biotinylated dextran into the vlPAG of the rat revealed a strong projection to a discrete, calbindin terminal-immunoreactive region of the caudal ventromedial nucleus (VMc) of the thalamus. This nucleus appears homologous to the calbindin-positive, pain- and temperature-specific-posterior ventromedial thalamic region of primates. We suggest that the vlPAG to VMc projection represents an important new route via which deep noxious inputs reach thalamus. As the rat is the species of choice in most experimental studies of pain, the functional-anatomical definition of this projection should further investigation of the thalamic representation of deep pain.

C-fos expression in the spinal cord of rats exhibiting allodynia following contusive spinal cord injury.

Contusive spinal cord injury (SCI) may result in central neuropathic pain marked by allodynia-like features in the dermatomes close to the level of injury. The aim of this study was to compare the laminar distribution of activated neurons (as determined by c-fos immediate early gene expression) in the spinal cord immediately above the level of a SCI in rats with or without allodynia-like features. Non-noxious mechanical stimulation was applied to half the animals in the dermatomes corresponding to the level of injury prior to perfusion. Stimulation resulted in a significant increase in c-fos labelling in all laminae of the spinal dorsal horn in the segment immediately above the level of injury only in allodynia animals. Animals that had allodynia also demonstrated a significant increase in the level of c-fos labelling in lamina III, IV and V of the dorsal horn without stimulation. Thus, allodynia following SCI is associated with significant increases in basal and evoked c-fos expression ("neuronal activity") in response to non-noxious mechanical stimulation. The data also suggest that allodynia-like behaviour following SCI cannot be accounted for solely by changes occurring at a spinal level.

Cardiovascular effects of microinjections of opioid agonists into the 'Depressor Region' of the ventrolateral periaqueductal gray region.

Microinjections of excitatory amino acids made into the ventrolateral midbrain periaqueductal gray of the rat have revealed that neurons in this region integrate a reaction characterised by quiescence, hyporeactivity, hypotension and bradycardia. Microinjections of both excitatory amino acids and opioids into the ventrolateral periaqueductal gray have shown also that it is a key central site mediating analgesia. The effects of injections of opioids into the ventrolateral periaqueductal gray on arterial pressure and heart rate or behaviour are unknown. In this study we first mapped in the rat the extent of the ventrolateral periaqueductal gray hypotensive region as revealed by microinjections of excitatory amino acids. We found that ventrolateral periaqueductal gray depressor region extended more rostrally than previously thought into the tegmentum ventrolateral to the periaqueductal gray. Subsequently we studied for the first time, the effects of microinjections of mu-, delta-, and kappa-opioid agonists made into the ventrolateral periaqueductal grey depressor region. In contrast to the effects of excitatory amino acid injections, microinjections of the mu-opioid agonist ([D-Ala2,N-Me-Phe4,Gly-ol5]enkephalin) evoked hypertension and tachycardia at approximately 50% of sites. Similar to excitatory amino acid injections, microinjections of both the delta-opioid agonist ([D-Pen2,D-Pen5]enkephalin), and the kappa-opioid agonist ((5,7,8)-(+)-N-Methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro[4.5]dec-8-y l]-benzeneacetamide) evoked either a hypotension and bradycardia, or had no effect. These results indicate that different opiate receptor subtypes are present on a distinct population of ventrolateral periaqueductal gray neurons, or at different ventrolateral periaqueductal gray synaptic locations (pre- or post-synaptic).

GABAA receptor subunit mRNA expression in cultured embryonic and adult human dorsal root ganglion neurons.

Previous studies have demonstrated significant pharmacological differences between the GABA(A) receptors expressed by neurons cultured from embryonic and adult human dorsal root ganglia (DRG). GABA(A) receptors of both embryonic and adult neurons are potentiated by diazepam and low concentrations of pentobarbital, and are activated by high concentrations of pentobarbital. However, in contrast to the GABA responses of embryonic neurons, the GABA responses of adult neurons are insensitive to both bicuculline and picrotoxin. We performed RT-PCR using subunit specific primer pairs, followed by Southern blot analysis with a third specific primer, to determine the pattern of subunit mRNA expression in cultures of embryonic and adult human DRG neurons. alpha2 and beta3 mRNA were expressed in all embryonic and adult cultures, while beta2 mRNA was present in all adult cultures but none of the embryonic cultures. Transcripts expressed by at least half of both embryonic and adult cultures were alpha3, alpha5, gamma2S, gamma3, theta, and rho1. Transcripts for gamma1 and delta were expressed in most adult cultures, but only a single embryonic culture. alpha4 mRNA was expressed by a single embryonic culture and pi mRNA was expressed by a single adult culture. We found no evidence for expression of alpha1, alpha6, beta1, gamma2L or rho2 transcripts. Changes in receptor subunit composition may underlie the novel pharmacological properties of GABA(A) receptor responses in adult cells. However, post-translational modification of a known subunit or the expression of a novel subunit may also contribute to the unique pharmacology of these neurons.

Projections from the ventrolateral periaqueductal gray to endocrine regulatory subdivisions of the paraventricular nucleus of the hypothalamus in the rat.

The ventrolateral periaqueductal gray (vlPAG) mediates quiescence, hyporeactivity, hypotension and bradycardia, a pattern of response evoked by injury or social defeat. These stimuli also evoke increased levels of vasopressin (VP) and adrenocorticotrophic hormone (ACTH). A key central nervous system (CNS) locus mediating endocrine changes is the paraventricular nucleus of the hypothalamus (PVH). We investigated the extent of vlPAG projections to PVH. Anterograde tracer injections into the vlPAG, revealed 'terminal' label in: (1) the medial, dorsal, anterior and lateral parvicellular divisions, and (2) lateral and medial posterior magnocellular divisions of the PVH. Deposits of the retrograde tracer Fast Blue, verified the projection to the PVH arising from the vlPAG.

Central circuits mediating patterned autonomic activity during active vs. passive emotional coping.

Animals, including humans, react with distinct emotional coping strategies to different sets of environmental demands. These strategies include the capacity to affect appropriate responses to "escapable" or "inescapable" stressors. Active emotional coping strategies--fight or flight--are particularly adaptive if the stress is escapable. On the other hand, passive emotional coping strategies-quiescence, immobility, decreased responsiveness to the environment-are useful when the stress is inescapable. Passive strategies contribute also to facilitating recovery and healing once the stressful event is over. Active vs. passive emotional coping strategies are characterised further by distinct patterns of autonomic change. Active strategies are associated with sympathoexcitation (hypertension, tachycardia), whereas passive strategies are associated with sympathoinhibitory patterns (hypotension, bradycardia). Distinct neural substrates mediating active vs. passive emotional coping have been identified within the longitudinal neuronal columns of the midbrain periaqueductal gray region (PAG). The PAG offers then a potentially useful point of entry for delineating neural circuits mediating the different forms of emotional coping and their associated patterns of autonomic activity. As one example, recent studies of the connections of orbital and medial prefrontal cortical (PFC) fields with specific PAG longitudinal neuronal columns are reviewed. Findings of discrete orbital and medial PFC projections to different PAG columns, and related PFC and PAG columnar connections with specific subregions of the hypothalamus, suggest that distinct but parallel circuits mediate the behavioural strategies and patterns of autonomic activity characteristic of emotional "engagement with" or "disengagement from" the external environment.

Collagen and glycopolymer based hydrogel for potential corneal application.

6-Methacryloyl-alpha-D-galactopyranose (MG) was synthesized, and characterized by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectrometry, and single-crystal X-ray diffraction. A series of interpenetrating polymer network (IPN) hydrogels was fabricated by simultaneously photocuring MG crosslinked by poly(ethylene glycol) diacrylate and chemically crosslinking type I collagen with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide. The successful incorporation of the glycopolymer, polymer MG, into collagen hydrogel was confirmed by FTIR and solid-state (13)C NMR. The optical characteristics of the IPN hydrogels are comparable to those of human corneas. The tensile strength and modulus of the hydrogels are enhanced by incorporation of polymer MG in comparison to that of the control collagen hydrogel. Biodegradation results indicated that polymer MG enhanced the stability of the composite hydrogels against collagenase. In vitro results demonstrated that the IPN hydrogel supported the adhesion and proliferation of human corneal epithelial cells and outperformed human cornea in blocking bacteria adhesion. Taken together, the IPN hydrogel might be a promising material for use in corneal lamellar keratoplasty.

Effects of pyridine ring substitutions on affinity, efficacy, and subtype selectivity of neuronal nicotinic receptor agonist epibatidine.

2'-Pyridine ring substituted analogs of epibatidine were assessed for equilibrium binding affinity, functional potency, and efficacy at rat neuronal nicotinic receptors expressed in Xenopus oocytes. Binding affinities were determined in membrane homogenates from oocytes expressing alpha2beta2, alpha2beta4, alpha3beta2, alpha3beta4, alpha4beta2, or alpha4beta4. Efficacy (relative to acetylcholine) and potency were measured electrophysiologically with oocytes expressing alpha3beta4, alpha4beta2, and alpha4beta4. Hydroxy, dimethylamino, and trifluoromethanesulfonate analogs had affinities too low for accurate measurement. The bromo analog had affinities 4- to 55-fold greater at beta2 than at beta4-containing receptors, modestly greater efficacy at alpha4beta4 than at alpha4beta2, and 5- to 10-fold greater potency at a4beta4 than at alpha3beta4 or alpha4beta2. The fluoro analog displayed affinities 52- to 875-fold greater at beta2- than at beta4-containing receptors, efficacy at alpha4beta4 receptors 3-fold greater than at alpha4beta2 and alpha3beta4, and was equipotent at all receptors tested. The norchloro analog showed affinities 114- to 3500-fold greater at beta2- than at beta4-containing receptors, 2-fold greater efficacy at alpha4beta2 and alpha4beta4 than at alpha3beta4, and 4- to 5-fold greater potency at alpha4beta4 and alpha3beta4 than at alpha4beta2. The amino analog displayed affinities 10- to 115-fold greater at beta2- than at beta4-containing receptors, 3-fold greater efficacy at alpha3beta4 than at alpha4beta2, and 2- to 4-fold greater potency at alpha3beta4 and alpha4beta4 than at alpha4beta2. Although these compounds displayed a variety of differences in affinity, efficacy, and potency, with one exception (binding affinity and functional potency at alpha4beta4 receptors) there were no significant correlations among these properties.