Behavioral characteristics of rat lines selected for differential hypothermic responses to cholinergic or serotonergic agonists

The present review will describe the formation of two pharmacologically selected lines of rats, their behavioral phenotypes, their responses to select drugs, their possible neurochemical correlates, and their use to detect the therapeutic potential of antidepressant drugs. The Flinders Line rats were established at Flinders University in Australia by selectively breeding for differential responses to an anticholinesterase agent from outbred Sprague-Dawley (SD) rats; the Flinders Sensitive Line (FSL) rats were more sensitive to the hypothermic and behavioral suppressing effects of this agent than the Flinders Resistant Line (FRL) rats. The 8-OH-DPAT line rats were established at the University of North Carolina at Chapel Hill by selectively breeding for differential hypothermic responses to the 5-HT_1A receptor agonist, 8-OH-DPAT; the high DPAT sensitive (HDS) line rats were more sensitive to the hypothermic effects of 8-OH-DPAT than the low DPAT sensitive (LDS) line rats. Studies of these two pairs of lines have indicated that the FSL and HDS rats are both more susceptible to stress-induced behavioral disturbances. Their usefulness in detecting potential antidepressant drugs and the relationship between mood disorders and drug abuse will be discussed.     

Serotonin produces an enhanced outward current recorded at rat dorsal lateral septal neurons from the Flinders Sensitive Line of rats,a genetically-selected animal model of depression

Abnormalities in serotonin (5-HT), serotonin receptors, and serotonergic neurons have been reported in studies of brains from patients diagnosed clinically with depression. In this study, we examined a known cellular function of 5-HT(1A) receptor activation in dorsolateral septal nucleus (DLSN) neurons, namely, a concentration dependent 5-HT-induced outward current, and compared basic neuronal membrane properties and activities of DLSN neurons from two known genetic lines of rats. As compared to "control" rats (Flinders Resistant Line, FRL), DLSN neurons from Flinders Sensitive Line of rats (FSL) did not exhibit significant differences in resting membrane potential, membrane input resistance, or changes in typical spontaneous inhibitory or excitatory post-synaptic currents. FSL-rats exhibit a depressive phenotype and have been suggested to be rats with a genetic susceptibility to exhibit depressive behaviors. Exogenous application of 5-HT resulted in expected concentration-dependent outward currents; however, the amplitudes of these currents were enhanced significantly in 50% of DLSN neurons recorded from FSL rats compared to similar results recorded from FRL rats. Our results suggest that within a particular population of DLSN neurons from rats exhibiting a known phenotype of depression a post-synaptic 5-HT(1A) receptor is functionally hyper-responsive compared to controls.     

Galanin receptors and their second messengers in the lumbar dorsal spinal cord.

The ligand binding properties of galanin receptors were examined in crude synaptosomal fraction preparations of lumbar dorsal spinal cord, using chloramin-T mono-iodinated porcine Tyr26 galanin as ligand. The equilibrium binding of [125I]galanin showed the presence of a single population of high-affinity binding sites with KD = 0.6 +/- 0.2 nM in a concentration of 55 +/- 15 fmol mg-1 protein (Bmax). The N-terminal fragments galanin (1-16) and galanin (1-12) fully displaced specific [125I]galanin binding from membranes with IC50 values 6 nM and 4 microM, respectively. The C-terminal fragment galanin (17-29) did not displace [125I]galanin when applied in the concentration range 10(-11)-10(-4) M. GTP inhibited the specific binding of [125I] galanin in a concentration dependent manner, with 54% inhibition at 1 mM, suggesting that the galanin receptor found in lumbar dorsal spinal cord is G-protein coupled. Second messenger systems, through which the galanin receptor in lumbar dorsal spinal cord may exert its effect, were also studied. A galanin (10 microM) produced inhibition (58%) of the depolarization induced cGMP increase was found, whereas galanin (10 microM) did not inhibit the noradrenalin (100 microM) activated cAMP synthesis or phosphoinositide turnover in tissue slices of the spinal cord. Bilateral transection of the sciatic nerve at midthigh level 14 days prior to the binding experiment was performed, a treatment which is known to cause a dramatic increase of galanin-like immunoreactivity in the superficial layers of the dorsal spinal cord, dorsal root ganglion and in galanin mRNA levels, but no significant effect on Bmax or KD of the galanin receptor was found.     

Differential brain,but not serum VEGF levels in a genetic rat model of depression

Compared to the classical monoamine hypotheses focus on neuroplasticity is a major new approach in studies of depression and antidepressants. Recent studies have demonstrated that vascular endothelial growth factor (VEGF) is regulated by antidepressant treatment in rodents. However, in depressive patients no significant changes were found in the serum VEGF levels compared to control subjects. To our knowledge, brain and serum VEGF levels have never been reported in parallel for any psychiatric disease model. That prompted us to examine the levels of VEGF in serum, hippocampus, frontal cortex, corpus striatum, and hypothalamus in male Flinders Sensitive Line (FSL) and Flinders Resistant Line (FRL), a genetic rat model of depression. The VEGF levels were identical in the FSL and the FRL rats in serum, corpus striatum, and hypothalamus. In hippocampus and frontal cortex, the VEGF levels were significantly decreased in the FSL rats compared to the FRL rats. The results may add to the hypothesis that altered expression of growth factors/neurotrophic factors are related to the pathophysiology of depression.     

Antidepressant effect of ingested nicotine in female rats of Flinders resistant and sensitive lines.

Both major depression and depressive symptoms are associated with a high rate of nicotine dependence, and a history of major depression has an adverse impact on smoking cessation. The main objective of this study was to investigate whether continuous ingestion of nicotine affects indices of depressive behavior in the rat. We compared cholinergic- and serotonergic-hypersensitive Flinders Sensitive Line rats (FSL), a genetic animal model of depression, with their control counterparts, Flinders Resistant Line rats (FRL). Female rats of both lines were allowed access to a solution of nicotine bitartrate (100 microg/mL) in tap water for 14 days. Subsequent behavioral testing revealed striking effects of continuous ingestion of nicotine on depressive-like behavior of both lines. FSL and FRL rats that ingested nicotine for 14 days displayed less immobility in the 10-min forced-swim test (an index of depressive-like behavior) relative to the animals of both lines that were not exposed to nicotine or exposed to nicotine for shorter periods of time. This finding indicates that ingested nicotine has antidepressant properties that are independent of the genetic difference between FSL and FRL female rats. Animal studies on nicotine ingestion and withdrawal may become an important source of insights into the comorbidity of depression and nicotine self-administration.     

Impaired active avoidance responding in rats selectively bred for increased cholinergic function

It was found that the Flinders Sensitive Line (FSL) of rat, selectively bred for increased cholinergic function, performed poorly in a tone-cued two-way active avoidance task in comparison with the control Flinders Restraint Line (FRL) of rat. These findings are consistent with the suggestion that the FSL rats may be a genetic animal model of depression.     

Nortriptyline mediates behavioral effects without affecting hippocampal cytogenesis in a genetic rat depression model

A prevailing hypothesis is that neurogenesis is reduced in depression and that the common mechanism for antidepressant treatments is to increase it in adult hippocampus. Reduced neurogenesis has been shown in healthy rats exposed to stress, but it has not yet been demonstrated in depressed patients. Emerging studies now indicate that selective serotonin reuptake inhibitors can, exert behavioral effects without affecting neurogenesis in mice. Here we extend our previous findings demonstrating that the number of BrdU positive cells in hippocampus was significantly higher in a rat model of depression, the Flinders Sensitive Line (FSL) compared to the control strain the Flinders Resistant Line (FRL). We also show that chronic treatment with the tricyclic antidepressant nortriptyline exerts behavioral effects in the Porsolt forced swim test without affecting hippocampal cell proliferation in the FSL model. These results strengthen the arguments against hypothesis of neurogenesis being necessary in etiology of depression and as requisite for effects of antidepressants, and illustrate the importance of using a disease model and not healthy animals to assess effects of potential therapies for major depressive disorder.     

Reduced primary antibody responses in a genetic animal model of depression

OBJECTIVE: Clinical depression is associated with multiple abnormalities of immune function, including reduced virus-specific responses. This study tested the hypothesis that the Flinders Sensitive Line (FSL) rat, a promising genetic animal model of depression, would exhibit reductions in antigen-specific primary antibody responses to immunization. METHODS: FSL (N = 13) and control Flinders Resistant Line (FRL; N = 14) rats were immunized with the protein antigen keyhole limpet hemocyanin (KLH; 300 microg/kg), and KLH-specific immunoglobulin (Ig)M, IgG, IgG1, and IgG2a responses were measured before and 3, 5, 7, 11, and 14 days after immunization. In separate experiments, production of interferon-gamma (IFN-gamma) by cells from naive and KLH-immunized animals was measured in vitro to determine whether strain differences in antibody production might be associated with differential production of this regulatory cytokine. RESULTS: KLH-specific production of IgM (p <.01) and IgG2a (p <.05) was significantly reduced in the FSL rats compared with the FRL controls. There were no strain differences in IgG or IgG1 production. Although IFN-gamma production between the two strains was similar in naive animals, cells from KLH-immunized FSL rats produced significantly less IFN-gamma when stimulated with KLH in vitro than cells from KLH-immunized FRL controls (p =.01). CONCLUSIONS: This study extends previous reports of altered immune function in the FSL rats to include reduced in vivo antigen-specific antibody responses. Moreover, diminished production of IFN-gamma by KLH-primed lymphocytes may contribute to lower antibody production in these animals. Collectively, these data suggest deficiencies in type 1 T-helper cell-mediated immunity in the FSL rats.     

Alterations in beta adrenergic and muscarinic receptors in aged rat heart. Effects of chronic administration of propranolol and atropine.

The cardiac responses to sympathetic and vagal stimulations are attenuated with ageing. To understand these findings, the densities of beta adrenergic (beta R) and muscarinic (MR) receptors in the left ventricles have been quantitated in parallel in male Wistar rats (4- and 24-month-old) using [125I]iodocyanopindolol and [3H]quinuclidinyl benzilate as specific radioligands. The homologous regulation of these receptor densities was also explored after a 7-day continuous infusion of propranolol or atropine. As compared to young rats, the beta R and MR densities in aged animals were decreased (from 31 +/- 2 to 23 +/- 2 fmol/mg protein, P less than 0.05 for beta R; from 104 +/- 7 to 54 +/- 3 fmol/mg protein, P less than 0.001 for MR) but the diminution in MR was more pronounced (-48%) than that in beta R (-26%), resulting in a drop in the beta R/MR ratio. Continuous infusion of propranolol or atropine up-regulated the beta R and MR densities (respectively +50%, P less than 0.01 and +33%, P less than 0.05) in aged but not in young adult rats. We therefore conclude: (i) that the diminution of the cardiac response to the sympathetic and vagal stimulations during ageing may be partly explained by a decrease in the corresponding receptor density; (ii) these changes are reversible and the density of these two groups of receptors can return to adult control values by chronic administration of the appropriate antagonist.     

Galanin receptors and their second messengers in the lumbar dorsal spinal cord

The ligand binding properties of galanin receptors were examined in crude synaptosomal fraction preparations of lumbar dorsal spinal cord, using chloramin-T mono-iodinated porcine Tyr²⁶ galanin as ligand. The equilibrium binding of [¹²⁵I]galanin showed the presence of a single population of high-affinity binding sites with K_D= 0.6±0.2 nM in a concentration of 55±15 fmol mg^-1 protein (B_max. The N-terminal fragments galanin (1–16) and galanin (1–12) fully displaced specific [¹²⁵1]galanin binding from membranes with IC₅₀ values 6 nM and 4 μM, respectively. The C-terminal fragment galanin (17–29) did not displace [¹²⁵I]galanin when applied in the concentration range 10^-11–10^-4 M. GTP inhibited the specific binding of [¹²⁵I] galanin in a concentration dependent manner, with 54% inhibition at 1 mM, suggesting that the galanin receptor found in lumbar dorsal spinal cord is G-protein coupled. Second messenger systems, through which the galanin receptor in lumbar dorsal spinal cord may exert its effect, were also studied. A galanin (10,μm) produced inhibition (58%) of the depolarization induced cGMP increase was found, whereas galanin (10 μM) did not inhibit the noradrenalin (100 μM) activated CAMP synthesis or phosphoinositide turnover in tissue slices of the spinal cord. Bilateral transection of the sciatic nerve at midthigh level 14 days prior to the binding experiment was performed, a treatment which is known to cause a dramatic increase of galanin-like immunoreactivity in the superficial layers of the dorsal spinal cord, dorsal root ganglion and in galanin mRNA levels, but no significant effect on B_max or K_D of the galanin receptor was found.     

Altered [3H]imipramine and 5-HT2 but not [3H]paroxetine binding sites in platelets from depressed patients.

BACKGROUND: Serotonergic system alterations were studied in 51 depressed patients classified according to DSM-III-R criteria for major depression with melancholia compared to 31 healthy controls. METHOD: [3H]Imipramine and [3H]paroxetine binding sites and the 5HT2 receptor were simultaneously determined in blood platelet membranes. RESULTS: A significantly lower maximum binding in [3H]imipramine binding was observed in depressed patients compared to controls (1134+/-74 vs. 1712+/-106 fmol/mg protein, P<0.0001) without changes in the equilibrium dissociation constant (1.10+0.05 vs. 1.25-/+0.09 nM). [3H]Paroxetine binding did not differ between the two groups (Bmax, 1441+/-55 vs. 1280+/-81 fmol/mg protein; Kd, 0.060+/-0.002 vs. 0.062+/-0.002 nM). The K(d) value of 5HT2 binding was lower in depressed patients than controls (0.95+/-0.04 vs. 1.15+/-0.09 nM, P<0.039) without changes in maximum binding (140+/-11 vs. 127+/-14 fmol/mg protein). CONCLUSIONS: Taken together, these results suggest that [3H]imipramine and 5HT2 receptors may be good biological markers for serotonergic dysfunction in depressive disorders.     

Periodic abstinence enhances nociception without significantly altering the antinociceptive efficacy of spinal morphine in the rat

Affective disorders are more common in women. The forced swim test acts like a depressive stimulus. Hippocampus and frontal cortex 5-HT_1A receptors of female and male Wistar rats subjected to the forced swim test were compared with a sham group. The forced swim test diminishes (P<0.05) the hippocampus ³H-8OH-DPAT bound in the female rats (184±16 fmol/mg protein) with respect to the male rats (309±41 fmol/mg protein) and to the female sham rats (255±20 fmol/mg protein). The forced swim test increases the frontal cortex 5-HT_1A receptors in the female rats with respect to the female sham group (40.4±5 versus 24.7±4 fmol/mg protein, P<0.05). An increased sensibility of the 5-HT_1A receptors to depressive-stimulus may be one mechanism underlying the higher prevalence of depression in female.     

Effects of thyroid hormones on cardiac hypertrophy and beta-adrenergic receptors during aging

Administration of thyroxine daily at a dosage of 6.4 mu g/g body weight stimulates cardiac hypertrophy in both 9--13-month-old (mature, n = 34) and 22--24-month-old (senescent, n = 45) Wistar rats. The increase due to thyroxine as well as the time course of the effect do not change with age, although ventricular wet weight to tibial length ratios are higher in senescent animals at 0, 3, and 7 days of treatment (senescent controls = 0.331; senescent hypertrophied = 0.395; mature controls = 0.295; mature hypertrophied = 0.336). Hypertrophy is maximal after 3 days. beta-Adrenergic receptor levels as measured by stereospecific binding of dihydroalprenolol in mature rats are increased about two-fold after 7 days of thyroxine treatment (mature controls = 35 +/- 3 fmol/mg protein, mature treated = 65 +/- 6 fmol/mg protein). Although both stimulated and control values do not differ significantly between mature and senescent groups (senescent controls = 45 +/- 4 fmol/mg protein, senescent treated = 56 +/- 9 fmol/mg protein), the effect of thyroxine on senescent hearts is not statistically significant. In addition, 3-day levels do not increase over 0-day controls at either age. No significant differences in either beta-adrenergic receptor concentrations or affinities between age groups are observed at 0, 3, and 7 days of treatment. However, senescent membrane preparations contain 33% more sialic acid (a rough plasma membrane marker) per unit of protein than mature preparations. Thus, the beta-adrenergic receptor density per unit of sialic acid may be reduced very slightly in the senescent hearts.     

大鼠中缝背核一氧化氮合酶神经元投射纤维在大脑皮质微血管的分布

目的：研究通过损毁脑干中缝背核(DR)，探讨中缝背核NOS阳性神经元是否投射分布于大脑皮质微血管。方法：将16只SD雄性成年大鼠分为实验组与对照组。对实验组大鼠中缝背核微量注射喹啉酸，饲养1w，灌注固定，然后将大脑及脑干作冠状冰冻切片，NADPH—d组化染色。结果：实验组大鼠的中缝背核被有效损毁，其NOS阳性神经元的数量减少了59．1％(P＜0．001)。额、顶叶皮质NOS阳性纤维终末减少了32．1％(P＜0．05)，其中附着于皮质微血管的NOS阳性纤维终未了减少了37．8％(P＜0．01)。而枕额叶皮质NOS阳性纤维终末也减少了32．8％(P＜0．05)，其中附着于皮质微血管的阳性纤维终末减少了39．4％(P＜0．01)。结论：位于中缝背核的NOS阳性神经元投射分布于大脑皮质微血管，可能参与大脑皮质血流量的调节。     

Enkephalinergic inhibition of raphe pallidus inputs to rat hypoglossal motoneurones in vitro

Hypoglossal motoneurones play a major role in maintaining the patency of the upper airways and in determining airways resistance. These neurones receive inputs from many different regions of the neuroaxis including the caudal raphe nuclei. Whilst we have previously shown that glutamate is utilised in projections from one of these caudal raphe nuclei, the raphe pallidus, to hypoglossal motoneurones, these raphe pallidus-hypoglossal projections also contain multiple co-localised neuropeptides, including a population that are immunopositive for enkephalin. The role of enkephalin in the control of hypoglossal motoneurones is unknown. Therefore the aim of these studies was to determine whether enkephalins modulate caudal raphe glutamatergic inputs to hypoglossal motoneurones. Whole cell recordings were made from rat hypoglossal motoneurones in vitro, with glutamate-mediated excitatory postsynaptic currents (EPSCs) evoked in these neurones following electrical stimulation within the raphe pallidus. Superfusion of enkephalin significantly decreased the amplitude of these raphe pallidus evoked EPSCs (56.1+/-29% of control, P<0.001), an action that was mirrored by the tau-opioid receptor agonist, [D-Ala, N-Me-Phe, Gly-ol]-enkephalin acetate (DAMGO;53.8+/-26%, P<0.01), but not by the delta-opioid receptor agonist, [D-Pen]-enkephalin (DPDPE). Enkephalin also increased the amplitude ratio (1.57+/-0.36 vs. 1.14+/-0.27, P<0.01) of pairs of evoked EPSCs (paired pulse ratio), decreased the frequency (P<0.0001) but not the amplitude of miniature EPSCs, whilst having no effect on the inward current evoked by glutamate applied directly to the postsynaptic cell (97.8+/-2.2% of control, P=n.s.). Likewise, DAMGO also increased the paired pulse ratio (1.62+/-0.35 vs. 1.31+/-0.14, P<0.05) and decreased the frequency of miniature EPSCs (P<0.0001). Together, these data suggest that enkephalin acts at tau-opioid receptors located on the presynaptic terminals of raphe pallidus inputs to hypoglossal motoneurones to significantly decrease glutamate release from these projections.     

The neuropeptide galanin as an in vivo modulator of brain 5-HT1A receptors: possible relevance for affective disorders

The neuropeptide galanin is widely distributed throughout the central nervous system with multiple and diverse biological functions mediated by different receptor subtypes. In the rat, galanin-like immunoreactivity is expressed in a population of 5-hydroxytryptamine (5-HT, serotonin) neurons in the dorsal raphe with extensive projections to the forebrain areas, e.g., hippocampus. This review summarizes results from experimental studies in rodents showing that in vivo galanin is a potent modulator of brain 5-HT transmission, and in particular 5-HT1A receptor-mediated functions. Galanin, given intracerebroventricular (i.c.v.), was demonstrated to have strong inhibitory interactions with 5-HT1A receptor functions, particularly in the dorsal raphe but also in the hippocampus. Since pre- and postsynaptic 5-HT1A receptors in the dorsal raphe and hippocampus are implicated in the action of antidepressant drugs and in depressive disorders, it is suggested that galanin receptors may be an important target for development of novel antidepressant drugs. This view is supported by a recent study in the rat showing that the galanin antagonist M35, given i.c.v., could block the depression-like behavior in the forced swim test induced by galanin, while M35 produced an antidepressant-like effect on its own.     

S-adenosyl-L-methionine prevents 5-HT(1A) receptors up-regulation induced by acute imipramine in the frontal cortex of the rat

S-adenosyl-L-methionine (SAM) has shown efficacy in speeding the onset of the antidepressant effect of imipramine in depressed patients. This effect may be related to their interactions at the serotonin(1A) (5-HT(1A)) receptors. Acute imipramine up-regulated the frontal cortex 5-HT(1A) receptors (B(max), 51.5 +/- 8.4 fmol/mg protein) vs. saline (B(max), 27.5 +/- 5.9 fmol/mg protein), and did not show antidepressant effect. Acute SAM and imipramine+SAM did not modify frontal cortex 5-HT(1A) receptors, and showed antidepressant effects (decrease of the immobility response of 26%, P<0.01; and 47%, P<0.001) vs. saline. All the chronic treatments showed antidepressant effects and up-regulated the hippocampus 5-HT(1A) receptors. SAM prevents the 5-HT(1A) receptor up-regulation induced by acute imipramine in the frontal cortex. This mechanism may contribute to imipramine's antidepressant effect.     

Opiate receptors in the human spinal cord: a detailed anatomical study comparing the autoradiographic localization of [3H]diprenorphine binding sites with the laminar pattern of substance P, myelin and nissl staining

The anatomical localization of opiate receptors in the human spinal cord has been examined in six cases aged 7-41 years using quantitative autoradiographic methods following the incubation of fresh, unfixed cryostat sections with [3H]diprenorphine. In order to precisely localize the distribution of receptors in the spinal cord, the laminar anatomy of the spinal grey was demonstrated at each spinal level examined using 50-microns sections stained for myelin, Nissl substance and substance P. In all cases, autoradiograms demonstrated that opiate receptors were distributed in a similar fashion in the grey matter of the cervical, thoracic, lumbar, sacral and coccygeal regions of the human spinal cord. At all 25 spinal levels examined, opiate receptors were mainly localized within the upper laminae of the dorsal horn (laminae I-III) and within the tract of Lissauer. The highest density of opiate receptors was localized within the inner segment of lamina II where the receptors formed a very dense band lying immediately dorsal to lamina III. The density of receptors in this inner region of lamina II (33 +/- 2 fmol/mg) was more than two-and-one-half times greater than that in the remaining upper laminae which showed moderate receptor densities: lamina I (12 +/- 4 fmol/mg) and outer lamina II (13 +/- 3 fmol/mg) both showed similar receptor densities which were higher than those in lamina III (10 +/- 3 fmol/mg) The tract of Lissauer (11 +/- 2 fmol/mg) also showed a moderate density of opiate receptors which was intermediate between the densities in laminae I/IIo and the density of lamina III. The density of receptors in the remaining laminae of the spinal cord varied from moderately low to virtually zero. Moderately low densities of receptors were found in laminae V, VI, VIII, IX and X with very low levels within laminae IV and VII. In particular, in lamina VII opiate receptors were unable to be detected above normal background levels in the dorsal nucleus of Clarke. These results show that, as in other mammalian species, opiate receptors in the human spinal cord are mainly concentrated in the upper laminae of the dorsal horn and in the tract of Lissauer. The possible role of these receptors in modulating spinal nociceptive information is discussed with respect to previous findings on the relationship of opiate receptors to primary afferent fibres in the spinal cord.     

In vivo and in vitro effects of peripheral galanin on nociceptive transmission in naive and neuropathic states

Galanin is widely distributed in the nervous system and is consistently upregulated in both dorsal root ganglion and spinal neurones by peripheral nerve injury. This study investigates the peripheral effects of galanin on nociceptive neurones using in vitro and in vivo electrophysiological techniques in naive and neuropathic rats. Using an in vitro skin-nerve preparation recording from single nociceptive fibres, galanin (1 microM) significantly inhibited firing induced by noxious heat in 65% of fibres examined. In the remaining 35% of fibres, galanin (1 microM) induced a facilitation of the responses to noxious heat. To examine the effect of peripheral galanin in vivo, extracellular recordings from convergent dorsal horn neurones were made in anaesthetised naive sham-operated and spinal nerve-ligated (SNL) rats. Injection of galanin (0.1-10 microg) into hindpaw receptive fields inhibited responses to innocuous mechanical, noxious mechanical and noxious heat stimuli in a proportion of neurones in each animal group and facilitated the remaining neurones. However, a higher proportion of neurones (80-90%) was inhibited by peripheral galanin administration in SNL rats compared with naive (45-55%) and sham (70-80%) rats. These results show that galanin can have both excitatory and inhibitory effects on peripheral sensory neurones, perhaps reflecting differential receptor activation, and that the proportion of these receptors may change following peripheral neuropathy.     

Roles of dorsal column pathway and transient receptor potential vanilloid type 1 in augmentation of cerebral blood flow by upper cervical spinal cord stimulation in rats

Clinical and basic studies have indicated that upper cervical spinal cord stimulation (cSCS) significantly increases cerebral blood flow (CBF), but the mechanisms are incompletely understood. This investigation was conducted to differentiate between stimulation of dorsal column fibers and upper cervical spinal cord cell bodies in cSCS-induced increases in CBF and decreases in cerebrovascular resistance (CVR). cSCS (50 Hz, 0.2 ms, 1 min) was applied on the left C1-C2 dorsal column of pentobarbital anesthetized, ventilated and paralyzed male rats. Laser Doppler flowmetry probes were placed bilaterally over the parietal cortex, and arterial pressure was monitored. cSCS at 30%, 60%, and 90% of motor threshold (MT) produced vasodilation bilaterally in cerebral cortices. Subsequently, cSCS was applied at 90% MT, and ipsilateral responses were recorded. Ibotenic acid (0.3 mg/ml, 0.1 ml) placed on dorsal surface of C1-C2 (n=7) to suppress cell body activity, did not affect cSCS-induced %DeltaCBF (42.5+/-8.1% vs. 36.8+/-7.1%, P>0.05) and %DeltaCVR (-19.4+/-4.2% vs. -15.2+/-5.6%, P>0.05). However, bilateral transection of the dorsal column at rostral C1 (n=8) abolished cSCS-induced changes in CBF and CVR. Also, rostral C1 transection (n=7) abolished cSCS-induced changes in CBF and CVR. Resinferatoxin (RTX), an ultrapotent transient receptor potential vanilloid type 1 (TRPV1) agonist, was used to inactivate TRPV1 containing nerve fibers/cell bodies. RTX (2 microg/ml, 0.1 ml) placed on the C1-C2 spinal cord (n=7) did not affect cSCS-induced %DeltaCBF (60.2+/-8.1% vs. 46.3+/-7.7%, P>0.05) and %DeltaCVR (-25.5+/-3.5% vs. -21.4+/-8.9%, P>0.05). However, i.v. RTX (2 microg/kg, n=9) decreased cSCS-induced %DeltaCBF from 65.0+/-9.5% to 27.4+/-7.2% (P<0.05) and %DeltaCVR from -28.0+/-7.6% to -14.8+/-4.2% (P<0.05). These results indicated that cSCS-increases in CBF and decreases in CVR occurred via rostral spinal dorsal column fibers and did not depend upon C1-C2 cell bodies. Also, our results suggested that cerebral but not spinal TRPV1 was involved in cSCS-induced cerebral vasodilation.