Dopamine-glutamate neuron projections to the nucleus accumbens medial shell and behavioral switching.

Dopamine (DA) neuron projections to the striatum are functionally heterogeneous with diverse behavioral roles. We focus here on DA neuron projections to the nucleus accumbens (NAc) medial Shell, their distinct anatomical and functional connections, and discuss their role in motivated behavior. We first review rodent studies showing that a subpopulation of DA neurons in the medial ventral tegmental area (VTA) project to the NAc medial Shell. Using a combinatorial strategy, we show that the majority of DA neurons projecting to the NAc Shell express vesicular glutamate transporter 2 (VGLUT2) making them capable of glutamate co-transmission (DA-GLU neurons). In the NAc dorsal medial Shell, all of the DA neuron terminals arise from DA-GLU neurons, while in the lateral NAc Shell, DA neuron terminals arise from both DA-GLU neurons and DA-only neurons, without VGLUT2. DA-GLU neurons make excitatory connections to the three major cells types, spiny projection neurons, fast-spiking interneuron and cholinergic interneurons (ChIs). The strongest DA-GLU neuron excitatory connections are to ChIs. Photostimulation of DA-GLU neuron terminals in the slice drives ChIs to burst fire. Finally, we review studies that address specially the behavioral function of this subpopulation of DA neurons in extinction learning and latent inhibition. Taking into account findings from anatomical and functional connectome studies, we propose that DA-GLU neuron connections to ChIs in the medial Shell play a crucial role in switching behavioral responses under circumstances of altered cue-reinforcer contingencies.

Rapid optical control of nociception with an ion-channel photoswitch.

Local anesthetics effectively suppress pain sensation, but most of these compounds act nonselectively, inhibiting activity of all neurons. Moreover, their actions abate slowly, preventing precise spatial and temporal control of nociception. We developed a photoisomerizable molecule, quaternary ammonium-azobenzene-quaternary ammonium (QAQ), that enables rapid and selective optical control of nociception. QAQ is membrane-impermeant and has no effect on most cells, but it infiltrates pain-sensing neurons through endogenous ion channels that are activated by noxious stimuli, primarily TRPV1. After QAQ accumulates intracellularly, it blocks voltage-gated ion channels in the trans form but not the cis form. QAQ enables reversible optical silencing of mouse nociceptive neuron firing without exogenous gene expression and can serve as a light-sensitive analgesic in rats in vivo. Because intracellular QAQ accumulation is a consequence of nociceptive ion-channel activity, QAQ-mediated photosensitization is a platform for understanding signaling mechanisms in acute and chronic pain.

Effects of prolonged hypobaric hypoxia on carotid nerve endings and glomus cells. Changes in intercellular coupling.

Carotid bodies were removed from anesthetized rats kept under normobaric (640 Torr) and hypobaric conditions (380 Torr for 2-3 weeks). Slices (100-150 microm) of the organ were viewed under an inverted microscope for simultaneous stimulation and recording of coupled glomus cells and carotid nerve endings. The latter were identified by their more negative Em, high input resistance (Ro) and time-dependent rectification in response to negative current pulses. Also, when nerve endings had an Em more negative than -40 mV showed spontaneous activity in the form of mini-receptor potentials (mrps). Glomus cells had less negative Em and lower Ro. Prolonged hypobaric hypoxia did not change the Em of nerve endings and glomus cells. However, in both structures, Ro increased. Also, the mrps became smaller and occurred less frequently. Intercellular coupling was recognized when currents applied to one cell spread to adjoining ones. In the case of glomus cells (GC/GC coupling), it was mostly resistive and bidirectional. Coupling between nerve endings and glomus cells was more complex, When a glomus cell was stimulated, current spread to the nerve ending (GC/NE coupling) was similar in magnitude (2-3%) to coupling between GCs. However, when NE was stimulated current spread to GC (NE/GC coupling) was minimal (less than 0.1%) and transient (capacitive). Nerve endings were also bidirectionally and capacitively coupled (NE/NE coupling) with a median of 2,8%. Intracellularly injected Lucifer Yellow or Alexa 488 diffused to neighboring structures. Prolonged hypobaric hypoxia significantly tightened coupling modes GC/NE, NE/GC, and NE/NE but reduced GC/GC coupling. Tighter coupling was accompanied by lower coupling resistance, and the opposite occurred when intercellular coupling decreased. Increased GC/NE and reduced GC/GC coupling during hypobaric hypoxia may be partly responsible for the increased reactivity of these receptors under this condition.

Second application of low-energy shock waves has a cumulative effect on free nerve endings.

Some physicians recommend treating tendinopathies with multiple sessions of shock waves. Some evidence, however, suggests shock wave application can induce nerve fiber degeneration. We questioned whether repeated shock wave application provides a cumulative effect on nerve fibers compared with the effect of one application. One thousand shock wave impulses of an energy flux density of 0.08 mJ/mm were applied to the foot pad of 32 rats. After 14 days, 16 rats received a second application. The foot pads were resected on Days 7, 14, 28, and 42. Sections were processed immunohistochemically using antibodies for sensory nerve. We compared the number of epidermal nerve fibers in rats that received one application of shock waves with the fibers in rats that received two applications. During the first 4 weeks, there was nearly complete degeneration of epidermal nerve fibers in both groups. By the end of 6 weeks, reinnervation of the epidermis began in the single-treatment group. Reinnervation occurred slower in the repeated-treatment group. These data show that a second application has a cumulative effect on nerve fibers. Our data suggest multiple applications of low-energy shock waves might a provide longer-lasting antinociceptive effect.

Localization of neurovascular bundles on pelvic CT and evaluation of radiation dose to structures putatively involved in erectile dysfunction after prostate brachytherapy.

PURPOSE: To (a) locate neurovascular bundles (NVB) on pelvic CT and (b) retrospectively evaluate relationships between radiation dose to structures putatively involved in prostate brachytherapy-induced erectile dysfunction (ED) and incidence of postbrachytherapy ED. METHODS AND MATERIALS: (a) Right/left NVB were identified on nine prostate MRIs. Structures visible on MRI and CT were cross-referenced. Cross-sectional area of each NVB was measured. (b) All patients treated with implant alone and whose treatment was planned on Variseed (Varian Medical Systems, Palo Alto, CA), with follow-up of >12 months were included; n = 41. Median follow-up was 20 months. All patients were potent (+/- sildenafil) before implant (erection sufficient for intercourse). The right/left NVB (using results from part "a"), penile bulb, and right/left crus were outlined on postimplant CT. Volumes and doses to these structures were calculated. RESULTS: (a) On prostate MRI, NVB was consistently located where the prostate border bends away from the levator ani, at the gland's smallest radius of curvature. Average area of the circle best encompassing the NVB = 0.27 cm(2); diameter was 0.58 cm. (b) 11 of 41 (27%) patients had ED; 30 of 41 were potent (15 with sildenafil). There was no significant difference between potent/impotent patients in isotope, age, diabetes, hypertension, follow-up, or volume of prostate, bulb, right/left NVB, or right/left crus. There was a relationship between smoking and ED (p = 0.05). There was a relationship between bulb %D90 and ED: >10% 67% (4 of 6) vs. <10% 20% (7 of 35) (p = 0.03), which remained when controlling for smoking. There was no relationship between dose to left NVB and potency. There was paradoxical decreased risk of ED with right NVB %V100 >60% (p = 0.019), and right NVB %D60 >100% (p = 0.003). There was no relationship between dose to right/left crus and ED. CONCLUSIONS: A reliable method for localizing NVB on CT is demonstrated. There is no increased risk of prostate brachytherapy-induced ED with increasing dose to crus or NVB at the doses given in this study. There is a possible dose-response relationship between dose to the bulb and risk of ED.

[Histo-architectonic features of the autonomic nerve terminals and their cellular microenvironment in breast cancer tissues before and after radiotherapy]. / Osobennosti gistoarkhitektoniki vegetativnykh nervnykh terminalei i ikh kletochnogo mikrookruzheniia v tkaniakh raka molochnoi zhelezy do i posle luchevoi terapii.

The difference in the histoarchitectonics of structures of vegetative nervous terminals (VNT) before and after radiotherapy (RT) indicates the existence of VNT fragments sensitive and resistant to radiation damage. Heterogeneity of the local neuromediator background in tumor morphogenesis before and after RT can be clarified through studying the VNT cellular microenvironment.

Short-term histomorphological effects of Er:YAG laser irradiation to rat coronal dentin-pulp complex.

OBJECTIVE: The objective of the study was to examine the morphological changes of neural elements in dentin-pulp complex ultrastructurally after Er:YAG laser irradiation and elucidate the mechanism of pain reduction in cavity ablation. STUDY DESIGN: The Er:YAG laser was applied at occlusal surfaces of upper and lower first molar cusps of 6 rats, and shallow cavities were ablated. The dentin and pulps were examined with light and electron microscopes at 6 hours after the irradiation. Teeth, without laser irradiation, from three rats were used as controls. RESULTS: Disruption of nerve terminals in the dentinal tubules, degeneration of nerve terminals between odontoblasts, and disruption of the myelin sheath in the pulp core were demonstrated with electron microscope. CONCLUSION: Some Er:YAG laser beams could penetrate to deeper areas than ablated area, and damage of nerve fibers and terminals might be a mechanism of pain reduction in cavity ablation with Er:YAG laser.

Involvement of primary afferent nerves after abdominal irradiation: consequences on ileal contractile activity and inflammatory mediator release in the rat.

In this study we analyzed the role of substance P (SP) from afferent nerves in ileum contractibility and in the release of inflammatory mediators (neurotensin, Il-1beta, and TNF-alpha) in ileal mucosa and muscularis layers after a 10-Gy gamma-irradiation of the abdomen. Six hours after irradiation, SP concentrations were lower than in control rats, and 3 days after irradiation SP-induced contractile activity was higher. Irradiation significantly increased the levels of neurotensin, Il-1beta, and TNF-alpha in both layers. Pretreatment with capsaicin depleted afferent nerve endings of SP and reduced SP levels by about 50%. Capsaicin treatment reduced SP concentrations further, beyond the levels due to irradiation, thereby suggesting that all sources of SP are affected by irradiation. Capsaicin treatment prevented the irradiation from affecting SP-induced contractile response or increasing neurotensin levels. This finding suggests that SP released by afferent nerve endings controls these functions. Proinflammatory cytokine release was not reduced by capsaicin treatment.

Staurosporine blocks evoked release of FM1-43 but not acetylcholine from frog motor nerve terminals.

The protein kinase inhibitor staurosporine inhibited, and often abolished, activity-dependent destaining of frog motor nerve terminals that had been preloaded with the fluorescent dye FM1-43. Staurosporine did not, however, block synaptic transmission; staurosporine treated muscles twitched in response to nerve stimulation, and the amplitudes of evoked end plate potentials were reduced only slightly, and in some cases not at all. The blockade of FM1-43 destaining was not reversed by washing, although treatment with black widow spider venom caused complete destaining. Nerve terminal pretreated with staurosporine could subsequently be stained with FM1-43 (and then destained by black widow spider venom). Thus, staurosporine blocked destaining but not staining of nerve terminals. Staurosporine treatment had little effect on the ultra-structure of resting terminals, the main difference we noted being a somewhat closer packing of synaptic vesicles after exposure to staurosporine. However, staurosporine blocked completely the ultrastructural changes produced by prolonged nerve stimulation, such as depletion of synaptic vesicles, appearance of intraterminal cisternae, and the uptake of horseradish peroxidase. The effects of staurosporine were not mimicked by KN-62, H7, calmidozolium, or trifluoroperazine. These and other observations are consistent with, but do not prove the hypothesis that, after exposure to staurosporine, the exocytotic fusion pore behaved like a valve, letting FM1-43 in, but not out, as if staurosporine interfered with the postexocytotic collapse of synaptic vesicles into the surface membrane.

[The biochemical changes in the brain synaptosomes during the gamma irradiation of mice at a low dose with different intensities]. / Biokhimicheskie izmeneniia v sinaptosomakh golovnogo mozga pri gamma-obluchenii myshei maloi dozoi s raznoi intensivnost'iu.

Some characteristics of mice brain nerve-endings' lipid phase were studied (total lipids, total and individual phospholipids and cholesterol contents, their ratios, lipid peroxidation level, rigidity index) after single low dose, whole body gamma-irradiation (15 cGy) with dose intensities of 0.01, 0.25, 9.0 cGy/min. Some markedly expressed alterations were found out in those parameters. Brain membranes functioning also changed significantly as it was judged by membrane-bound acetylcholinesterase activity. All the changes revealed complicated dependence both on dose intensity and on time period after irradiation. The ranges of the observed changes suppose CNS state to have been modified by low dose irradiation including CNS sensibility to external psycho- and neurotrophic factors.

Merkel cells are not the mechanosensory transducers in the touch dome of the rat.

The identity of the mechanosensory transducing elements in the vertebrate touch receptors that contain Merkel cell-neurite complexes is unknown. The Merkel cells, however, have long been the favoured candidates. We have now selectively eliminated the Merkel cells from rat touch domes by first loading them with quinacrine, and then irradiating the domes with near-UV light. Mechanical stimulation of these domes revealed a range of mechanosensory function, evaluated qualitatively, that varied from non-responsive to normal. Since irradiation eliminated the quinacrine fluorescence, the status of the Merkel cells was evaluated by EM. In both responsive and unresponsive domes fixed for EM immediately following irradiation, the Merkel cells and associated nerve endings appeared to be normal. After 2 or more days, even in domes that continued to be normally responsive, there was a striking reduction in the normal complement of about 90 Merkel cells, and most of the remaining Merkel cells appeared to be degenerating. However, numerous 'isolated' (Merkel cell-free) nerve endings remained in the basal epidermis. A few of these nerve endings showed signs of damage, but in the non-responsive domes abnormal nerve endings were routinely observed. The EM studies did not exclude the possibility that a few surviving innervated Merkel cells, or even one such, had escaped detection and were responsible for a persisting mechanosensitivity. To resolve this issue a mechanical stimulating technique with a spatial resolution of 55 microns was used to map the mechanosensory profile of a single responsive dome irradiated 2.75 days earlier. This dome was then serially sectioned for EM study. Only seven Merkel cells had survived which appeared to be both viable and innervated, but almost all of the tested sites were normally responsive. When the correlation was made, seven of these sites were located 55-100 microns away from the nearest surviving Merkel cell, four were 110-165 microns away, and three were more than 165 microns away. Even when allowance is made for errors in the positioning of the stimulus, the responses at the last seven sites cannot be attributed to the presence of underlying Merkel cells. We conclude that mechanosensory transduction within touch domes is not a function of the Merkel cells, but must reside in the associated nerve endings.

Laser irradiation abates neuronal responses to nociceptive stimulation of rat-paw skin.

The effects of diode laser irradiation on peripheral nerves was examined by monitoring neuronal discharges elicited by application of various stimuli to the hind-paw skin of rats. Neuronal discharges elicited by brush, pinch, cold, and/or heat stimulation, as well as chemical stimulation by injection of turpentine (0.1 ml, SC) were recorded from L5 dorsal roots in urethane-anesthetized rats. Diode laser irradiation (830 nm, 40 mW, 3 min, continuous wave) of the saphenous nerve exposed from the muscle of the lower leg significantly inhibited neuronal discharges elicited by pinch (68.4 +/- 6.5%), cold (45.4 +/- 9.2%), and heat stimulation (49.2 +/- 11.3%). Neuronal discharges induced by brush stimulation (104.3 +/- 4.7%) were not affected by laser irradiation. Injection of turpentine, a chemical irritant, into the hind-paw skin (0.1 ml, SC) elicited neuronal discharges in the ipsilateral dorsal root, and these discharges were significantly inhibited or abolished by laser irradiation. In 6- to 7-week-old rats treated neonatally with capsaicin (10 mg/kg, SC), injection of turpentine into the hind-paw skin did not elicit neuronal discharges and laser irradiation did not affect the background discharges. These data suggest that laser irradiation may selectively inhibit nociceptive neuronal activities.

[The effect of ionizing radiation at superhigh doses on the processes of dopamine release and reuptake by nerve endings in different sections of the brain]. / Vliianie ioniziruiushchego izlucheniia v sverkhvysokikh dozakh na protsessy vysvobozhdeniia i obratnogo zakhvata dofamina nervnymi terminaliami razlichnykh otdelov golovnogo mozga.

Rats exposed to fast 24 MeV electrons (100 Gy) at the state of early transient incapacity (ETI) exhibited active release and reuptake of dopamine in nerve terminals of the striatum. No changes in the indices under study were found in rats exposed to 25 Gy radiation that did not cause the ETI development. The in vitro irradiation of the isolated synaptosomes (100 Gy) inhibited dopamine reuptake and increased the number of sites of 3H-spiperone binding to D2-receptors in a membrane fraction isolated from the striatum.

[Status of neurocytes of the arcuate and suprachiasmatic nuclei of the hypothalamus and median eminence in rats exposed to prolonged internal irradiation]. / Sostoianie neirotsitov arkuatnogo i suprakhiazmaticheskogo iader gipotalamusa i sredinnogo vozysheniia u krys v usloviiakh dlitel'nogo vnutrennego oblucheniia.

Ultrastructural changes caused by single administration of 75Se-selenomethionine (1.22 X 10(4) Bk/g bw) were studied in neurocytes of the arcuate and suprachiasmatic nuclei of the hypothalamus and medial eminence in random-bred male rats. Within the first three months after administration of the radioactive agent, there was an activation of the synthesis of neurocyte secretion granules and release of their content from nerve terminals into the channel of medial eminence portal capillaries. Afterwards (over 6-12 months) the synthesis of of neurocyte secretion material and the release into medial eminence portal capillaries were suppressed. By the 18th month after 75Se-selenomethionine administration there occurred a relative normalization of the structure and function of neurocytes, and activation of the release of the contents of secretion granules from nerve terminals into the channel of medial eminence portal capillaries.

Biological changes of human cutaneous nerves caused by ultraviolet irradiation: an ultrastructural study.

Three white male volunteers were irradiated by long wave ultraviolet (UV-A) and by solar simulating radiation (SSR). An acute change of cutaneous nerves was found following a single exposure of UV-A irradiation. Non-myelinated Schwann cells and perineural cells in the papillary and reticular dermis were degenerated. Axoplasms appeared to be electron-dense, but were less affected than Schwann cells. After long-term repeated exposure, many free nerve endings were found in the dermo-epidermal junction above the basal lamina and some of them made a terminal enlargement. In one instance an axon made a swelling. Dermal free nerve endings also seemed to be increased in number and some of them were situated immediately beneath the melanocytes which were active in melanogenesis. Multiplication of basal lamina of the Schwann cells and perineural cells was observed. Amorphous material was precipitated around the non-myelinated Schwann cells. After a single exposure of SSR irradiation the degeneration of Schwann cells and axons in the dermo-epidermal junction was less severe than after UV-A and changes were minor in the reticular dermis. After repeated exposure, intra-epidermal proliferation of free nerve endings was detected. Dermal nerves were slightly affected. No intra-epidermal free nerve endings were observed in controls. The intra-epidermal proliferation of free nerve endings was confirmed following repeated UV exposures. Melanocyte-nerve association is suggested to be the cause of stimulating melanocyte activity.

[Effects of the light level and duration of the photoperiod on the retina of albino rats]. / Effets du niveau lumineux et de la durée de la photopériode sur la rétine du rat albinos

Female albino rats were exposed during 3 weeks to various photoperiodic sequences and levels of illumination. As long as the light span of the photoperiod did not exceed 12L-12D, the damaging effects of the light, even when intese (3,000 lx), on the retinal were relatively limited. On the other hand, the 14L-10D photoperiodic regimen that is usually used in standard rat animaleries produced marked degenerative lesions on the photoreceptors under either 1,200 or 3,000 1x. Under lighting schedules of 21L-15D or 28L-20D, the photoreceptors were heavily injured by 1,200 OR 3,000 1X. The degenerative process affected all the photoreceptive cells as well as their various components: rods, cones, nucleus and synaptic endings.

The innervation of hyperplastic epidermis in the mouse: a light microscopic study.

The innervation of the skin of hairless mice has been studied following induction of epidermal hyperplasia by physical and chemical methods. Physical stimuli comprised ultraviolet irradiation, heat, wounding, and friction. Effective chemicals included benzene, carbon tetrachloride, chloroform, creosote, formaldehyde, hexadecane, hydrobromic acid, sodium lauryl sulfate, and turpentine. Epidermal hyperplasia, however produced, was associated with growth of sensory nerve fibers into the outer part of the epidermis. Following a single 10-min exposure to an ultraviolet sunalmp at 40 cm, the nerves extended into the epidermis within 24 hr and disappeared during the second week as the epidermis reverted to its normal thickness. Repeated irradiation (until tumors appeared) was accompanied by persistent hyperplasia and neural invasion. Of 32 papillomas examined, intraepithelial nerves were found in 28. The presence and location of nerves in the tumor epithelium were related to the incorporation of tactile hair disc epithelium. The hyperplastic regenerative epithelium at the margins of skin ulcers were also invaded by nerves which sometimes followed the migrating epithelium across the ulcer floor. Since the regenerative epithelium was not directly treated, it was concluded that the proliferation of nervous tissue in response to skin injury was the result of the hyperplasia per se, regardless of the method used to produce it.