Monoaminergic regulation of Sonic hedgehog signaling cascade expression in the adult rat hippocampus

Monoamines are implicated in the modulation of adult hippocampal neurogenesis in depression models and following chronic antidepressant treatment. Given the key role of Sonic hedgehog (Shh) in adult neurogenesis, we examined whether monoaminergic perturbations regulate the expression of Shh or its co-receptors Smoothened (Smo) and Patched (Ptc). Combined depletion of both serotonin and norepinephrine with para-chlorophenylalanine (PCPA) resulted in a significant decrease in Smo and Ptc mRNA within the dentate gyrus subfield of the hippocampus. However, selective depletion of serotonin, using the serotonergic neurotoxin 5,7-dihyrdroxytryptamine (5,7-DHT), or norepinephrine, using the noradrenergic neurotoxin DSP-4, did not alter expression of Shh and its co-receptors, Smo and Ptc. Acute treatment with the monoamine releasing agent, para-chloroamphetamine (PCA) significantly upregulated Smo mRNA within the dentate gyrus. However, acute or chronic treatment with pharmacological antidepressants that modulate monoaminergic neurotransmission did not regulate Shh cascade expression. These results indicate that robust changes in monoamine levels can regulate the expression of the Shh signaling cascade in the adult rodent brain.     

Changes in serotonin contents in brain affect metabolic heat production of rabbits in cold.

Elevating serotonin (5-HT) contents in brain with 5-hydroxytryptophan (5-HTP) reduced rectal temperature (Tre) in rabbits after peripheral decarboxylase inhibition with the aromatic-L-amino-acid decarboxylase inhibitor R04-4602 at two ambient temperatures (Ta), 2 and 22 degrees C. The hypothermia was brought about by both an increase in respiratory evaporative heat loss (Eres) and a decrease in metabolic rate (MR) in the cold. At a Ta of 22 degrees C, the hypothermia was achieved solely due to an increase in heat loss. Depleting brain contents of 5-HT with intraventricular, 5,7-dihydroxytryptamine (5,7-DHT) produced an increased Eres and ear blood flow even at Ta of 2 degrees C. Also, MR increased at all but the Ta of 32 degrees C. However, depleting the central and peripheral contents of 5-HT with p-chlorophenylalanine (pCPA) produced lower MR accompanied by lower Eres in the cold compared to the untreated control. Both groups of pCPA-treated and 5,7-DHT-treated animals maintained their Tre within normal limits. The data suggest that changes in 5-HT content in brain affects the MR of rabbits in the cold. Elevating brain content of 5-HT tends to depress the MR response to cold, while depleting brain content of 5-HT tends to enhance the MR response to cold.     

Effect of serotonin depletion on the neuronal,endocrine and behavioural responses to corticotropin-releasing factor in the rat

Interactions between serotonin and corticotropin-releasing factor (CRF) have been demonstrated by various studies in different parts of the brain. Both are activated by stressful stimuli. Additionally, serotoninergic fibres directly synapse with the parvocellular division of the paraventricular nucleus (PVN) that mainly synthesize CRF. The functional impact of this serotonin-CRF interaction on CRF-induced responses remains unclear. CRF infusion into the brain evokes a specific pattern of behavioural, endocrine and neuronal changes that resemble those following various forms of stress. The aim of the present study was to investigate the effects of serotonin depletion on acute CRF-induced c-fos expression, corticosterone levels and behavioural responses. Lateral ventricular (i.c.v.) infusion of CRF (250 pmol) resulted in a significant increase in grooming, corticosterone and c-fos mRNA in the PVN. Adequate and specific depletion of serotonin using 5,7-DHT did not alter these CRF-induced changes. These data suggest that acute responses induced by i.c.v. CRF are independent of basal levels of serotonin.     

Increased behavioural response to intrathecal serotonin after lesion of serotonergic pathways with 5,7-dihydroxytryptamine seems not to be due to depletion of serotonin

The behavioural response to intrathecal i.th. serotonin (5-HT) was examined in mice pretreated with the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) or the 5-HT synthesis inhibitor p-chlorophenylalanine (PCPA) which produce similar extensive depletion of central 5-HT levels. Intrathecal 5-HT (0.4 micrograms) elicited a behavioural response consisting of reciprocal hindlimb scratching and biting or licking of the hindquarters indicative of nociceptive stimulation. The response to i.th. 5-HT was markedly increased 5 days after intracerebroventricular (i.c.v.) injection of 5,7-DHT (80 micrograms base per mouse). On the other hand, 24 h after the last pretreatment injection of PCPA (400 mg kg-1 for 6 consecutive days), the response to i.th. 5-HT was unaltered. These results indicate that i.c.v. 5,7-DHT produces supersensitivity to 5-HT. Since PCPA failed to alter the effect of 5-HT, the supersensitivity seems not to be due to depletion of 5-HT levels after the lesion.     

Increased expression of preproneuropeptide Y and preprosomatostatin mRNA in striatum after selective serotoninergic lesions in rats

The levels of neuropeptide Y and somatostatin may change when serotoninergic neurotransmission is altered in different brain regions. To assess whether serotonin regulates the synthesis of these peptides, we measured the levels of preproneuropeptide Y (ppNPY) and preprosomatostatin (ppSOM) mRNA in different brain regions after intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT), a selective serotonin neurotoxin. The mRNA of these peptides significantly increased in the striatum but not in hippocampus and frontal cortex. It thus appears that serotonin has an inhibitory effect on the biosynthesis of neuropeptide Y and somatostatin in striatum whereas it probably acts by stimulating the release of these peptides in hippocampus and frontal cortex.     

Reduction of somatostatin receptors in rat hippocampus by treatment with 5,7-dihydroxytryptamine.

Several lines of evidence suggest that somatostatin (SS) may interact with serotonergic neurons in the central nervous system. To assess whether SS acts presynaptically on serotonin (5-hydroxytryptamine, (5-HT)) neurons, SS receptors were measured in membranes from the hippocampus, a brain region that receives dense serotonergic innervation and has a high number of SS receptors in control and 5,7-dihydroxytryptamine (5,7-DHT)-treated rats, at 1 and 3 weeks after injection. Intracerebroventricular (i.c.v.) injection of the 5-HT-specific neurotoxin 5,7-DHT (11 micrograms (free base) dissolved in 10 microliters of isotonic saline containing 0.01% ascorbic acid) produced a 70% reduction in hippocampal 5-HT content at 3 weeks after injection but not at 1 week. This change was associated with a significant decrease in SS receptor density in rat hippocampus only at 3 weeks following the injection, without influencing the apparent affinity of the receptors at any time. Administration of 5,7-DHT did not affect somatostatin-like immunoreactivity (SSLI) levels at both times studied. These results suggest that some of the hippocampal SS receptors may be localized presynaptically on the serotonergic nerve terminals.     

Similarities between aberrant serotonergic fibers in the aged and 5,7-DHT denervated young adult rat brain

Summary Recent morphological observations have suggested neurotransmitter specific degeneration of amongst others, the serotonergic system in the aged rat brain. However, morphological studies can only give a static picture of the events that take place over a period of several months. In the present study we used an experimental model in which degeneration of the serotonergic system in the young adult rat brain was produced on a short time scale. Morphological changes were studied 2 h and 1 or 14 days after intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT). Nonspecific damage and severe depletion of serotonergic fibers was observed in the immediate surroundings of the injection site, representing the effects of high local concentrations of 5,7-DHT. Sometime after injection swollen varicosities and dilated non-varicose fibers were observed. Fourteen days after the 5,7-DHT treatment cluster-like fibers appeared. It is argued that these swollen and crumpled fiber knots are slowly degenerating fibers. A comparison is made with the abnormal serotonergic fibers in the aged rat brain and it is concluded that these aged abnormal fibers represent axonal degeneration of the serotonergic system in the senescent rat brain.This work was supported by MEDIGON grant no. 900-552-072     

Injections of beta-noradrenergic substances in the flocculus of rabbits affect adaptation of the VOR gain

Noradrenaline (NA) has been implicated as a neuromodulator in plasticity, presumably facilitating adaptive processes. Recent experiments by others have suggested a modulatory role of NA in adaptive changes in the vestibulo-ocular reflex (VOR). These experiments showed that general depletion of brain NA resulted in a decreased ability to produce adaptive changes in the VOR gain. In order to identify the specific brain region responsible for these effects, as well as the nature of the adrenoceptors involved, we injected beta-adrenergic substances bilaterally into the flocculus of rabbits. The flocculus is known to receive noradrenergic afferents and, moreover, ablation of the flocculus interferes strongly with the normal adaptive changes in the VOR gain. We injected the beta-agonist isoproterenol and the beta-antagonist sotalol, and compared the adaptive capacity of the rabbits after these injections to that in a situation without injection. The rabbit was oscillated in a direction opposite to the direction of motion of the platform on which the rabbit was mounted, a condition which normally results in an increase in the VOR gain, measured either in light or in darkness. Injection of the beta-agonist did not greatly affect the adaptation of the VOR measured in the light. In darkness, the increase in gain after the injection of isoproterenol was larger than in the non-injection experiments in 9 out of 10 rabbits. The beta-antagonist sotalol reduced the adaptation of the VOR gain significantly in the light, as well as in darkness. In a control condition without pressure for adaptation (only intermittent testing of the VOR gain over a period of 2.5 h), the gain of the VOR either remained unaffected or was only slightly affected by similar injections of beta-adrenergic agents in individual rabbits. For the group as a whole, these effects were insignificant. We conclude from these results that noradrenergic systems facilitate the adaptation of the VOR gain to retinal slip in rabbits, without affecting the VOR gain directly. At least part of this influence is exerted through beta-receptors located in the cerebellar flocculus.     

Adaptive modification of the rabbit's horizontal vestibulo-ocular reflex during sustained vestibular and optokinetic stimulation

Summary Adaptability of the horizontal vestibulo-ocular reflex (HVOR) and the optokinetic response (OKR) was examined in alert albino rabbits during sustained runs lasting 5–12 h under four different stimulus conditions. (1) Sinusoidal rotation of the rabbit in darkness by 5 ° at 1/10 Hz, or (2) sinusoidal movement of a vertical slit light by 2.5 ° or 5 ° at 1/10 Hz around the optical axis of the stationary rabbit, affected the gain of neither the HVOR nor the OKR. (3) Combination of the stimulus as in (1) with the stationary slit light increased the gain of the HVOR gradually. A plateau at about 140% of the initial control was reached in 5 h. (4) Combination of the stimulus as in (1) with the slit light movement by 10 ° in phase with the turntable decreased the HVOR gain gradually, a plateau being obtained at about 70 % of the initial control in 5 h. Changes of the HVOR gain induced in conditions (3) and (4) were not frequency-specific and accompanied by no significant modification of either the gain or phase of the OKR or the linear property of HVOR-OKR interaction. A small but significant change of the HVOR phase was also detected under the condition (3) but not (4).On leave from Nencki Institute of Experimental Biology, Warsaw (from Jan. 1977 to Jan. 1978) and supported by a Polish-Japanese Cultural Relations Program Fellowship     

The effect of amphetamine analogs on cleaved microtubule-associated protein-tau formation in the rat brain

The present study quantified the cleaved form of the microtubule-associated protein tau (cleaved MAP-tau, C-tau), a previously demonstrated marker of CNS toxicity, following the administration of monoamine-depleting regimens of the psychostimulant drugs amphetamine (AMPH), methamphetamine (METH), +/-3,4-methylenedioxymethamphetamine (MDMA), or para-methoxyamphetamine (PMA) in an attempt to further characterize psychostimulant-induced toxicity. A dopamine (DA)-depleting regimen of AMPH produced an increase in C-tau immunoreactivity in the striatum, while a DA- and serotonin (5-HT)-depleting regimen of METH produced an increase in the number of C-tau immunoreactive cells in the striatum and CA2/CA3 and dentate gyrus regions of the hippocampus. MDMA and PMA, two psychostimulant drugs that produce selective 5-HT depletion in the striatum, had no effect on C-tau immunoreactivity in the striatum or hippocampus. Furthermore, 5,7-dihydroxytryptamine (5,7-DHT), an established 5-HT selective neurotoxin, did not produce an increase in C-tau immunoreactivity. Dual fluorescent immunocytochemistry with antibodies to glial fibrillary acidic protein (GFAP) and C-tau indicated that C-tau immunoreactivity was present in astrocytes, not neurons, suggesting that increased C-tau may be an alternative indicator of reactive gliosis. The present results are consistent with previous findings that the DA-depleting psychostimulants AMPH and METH produce reactive gliosis whereas the 5-HT-depleting drugs MDMA and PMA, as well as the known 5-HT selective neurotoxin 5,7-DHT, do not produce an appreciable glial response.     

Cerebellar nodulectomy impairs spatial memory of vestibular and optokinetic stimulation in rabbits

Natural vestibular and optokinetic stimulation were used to investigate the possible role of the cerebellar nodulus in the regulation and modification of reflexive eye movements in rabbits. The nodulus and folium 9d of the uvula were destroyed by surgical aspiration. Before and after nodulectomy the vertical and horizontal vestibuloocular reflexes (VVOR, HVOR) were measured during sinusoidal vestibular stimulation about the longitudinal (roll) and vertical (yaw) axes. Although the gain of the HVOR (G(HVOR) = peak eye movement velocity/peak head velocity) was not affected by the nodulectomy, the gain of the VVOR (G(VVOR)) was reduced. The gains of the vertical and horizontal optokinetic reflexes (G(VOKR), G(HOKR)) were measured during monocular, sinusoidal optokinetic stimulation (OKS) about the longitudinal and vertical axes. Following nodulectomy, there was no reduction in G(VOKR) or G(HOKR). Long-term binocular OKS was used to generate optokinetic afternystagmus, OKAN II, that lasts for hours. After OKAN II was induced, rabbits were subjected to static pitch and roll, to determine how the plane and velocity of OKAN II is influenced by a changing vestibular environment. During static pitch, OKAN II slow phase remained aligned with earth-horizontal. This was true for normal and nodulectomized rabbits. During static roll, OKAN II remained aligned with earth-horizontal in normal rabbits. During static roll in nodulectomized rabbits, OKAN II slow phase developed a centripetal vertical drift. We examined the suppression and recovery of G(VVOR) following exposure to conflicting vertical OKS for 10-30 min. This vestibular-optokinetic conflict reduced G(VVOR) in both normal and nodulectomized rabbits. The time course of recovery of G(VVOR) after conflicting OKS was the same before and after nodulectomy. In normal rabbits, the head pitch angle, at which peak OKAN II velocity occurred, corresponded to the head pitch angle maintained during long-term OKS. If the head was maintained in a "pitched-up" or "pitched-down" orientation during long-term OKS, the subsequently measured OKAN II peak velocity occurred at the same orientation. This was not true for nodulectomized rabbits, who had OKAN II peak velocities at head pitch angles independent of those maintained during long-term OKS. We conclude that the nodulus participates in the regulation of compensatory reflexive movements. The nodulus also influences "remembered" head position in space derived from previous optokinetic and vestibular stimulation.     

Role of cerebellar flocculus in adaptive interaction between optokinetic eye movement response and vestibulo-ocular reflex in pigmented rabbits

Summary Sustained sinusoidal oscillation of a striped cylindrical screen around a stationary, alert pigmented rabbit with certain parameters (for 4h, 5°, 7.5°, or 10° peak-to-peak, 0.1 or 0.2 Hz) adaptively modified not only the horizontal optokinetic response (HOKR) but also the horizontal vestibulo-ocular reflex (HVOR). The major effects thus obtained during 4 h were an increase in the HOKR gain by 0.23, and that of the HVOR gain by 0.18. Bilateral destruction of floccular Purkinje cells with microinjection of kainic acid abolished these effects on both HOKR and HVOR. Single unit activities of floccular Purkinje cells were recorded from the floccular areas related to horizontal eye movements (H-zone) with local stimulus effects. Most H-zone Purkinje cells normally exhibited modulation of simple spike discharge in phase with screen velocity and out of phase with turntable velocity. Sustained screen oscillation (7.5°, 0.1 Hz) for 1 h increased the simple spike responses not only to screen but also to turntable oscillation. No such changes were observed in other floccular areas. These observations suggest that sustained optokinetic stimulations induce adaptation of HVOR through an interaction of retinal slip and head velocity signals within the flocculus or its related neuronal tissues.     

Brain serotonin depletion impairs short-term memory, but not long-term memory in rats

Intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT) (150 microg; 4.5 microl/ventricle), a serotonergic neurotoxin, significantly decreased spontaneous alternation in Y-maze task and working memory in radial 8 arm-maze task, suggesting effects on short-term memory, without affecting long-term memory, explored by reference memory in radial 8 arm-maze task and step-through latency in multi-trial passive avoidance task. Parachlorophenylalanine (PCPA) (3 days treatment 200 microg, i.c.v.), a serotonin synthesis inhibitor, did not impair step-through-latency in multi-trial passive avoidance task, suggesting no effects on long-term memory. These results suggest that serotonin, among other neurotransmitters, play an important role in cognitive functions, especially short-term memory.     

Specific effects of unilateral lesions in the flocculus upon eye movements in albino rabbits

Summary The horizontal vestibulo-ocular reflex (HVOR) and optokinetic response (OKR) were examined in alert albino rabbits following unilateral flocculectomy. Chemical flocculectomy with local application of kainic acid was used to avoid the retrograde degeneration of inferior olive neurons that accompanies surgical flocculectomy. Effects of chemical flocculectomy, however, were identical to those of surgical flocculectomy. The following functional deficiencies were observed in the movements of the ipsilateral eye: (1) reduction of the HVOR gain; (2) increased lag of the HVOR phase; (3) increased non-linearity of the relationship between the HVOR gain and the amplitude of turntable rotation; (4) decreased OKR gain; (5) delay with increased variation in the OKR phase; (6) impairment of rapid visual-vestibular interaction; (7) loss of the adaptation of the HVOR. Only a transient depression of the HVOR gain was seen in the contralateral eye. Control experiments with lesions in the paraflocculus, nodulus, and uvula, or lobules VI and VII, revealed no such deficiencies, except that lesions in the nodulus and uvula produced marked advancement of the HVOR phase. The effects of flocculectomy are consistent with present knowledge of both neuronal circuitry and activity of the rabbit flocculus.Abbreviations and Definitions iHVOR and iOKR HVOR and OKR in the eye ipsilateral to flocculectomy - cHVOR and cOKR HVOR and OKR in the eye contralateral to flocculectomy - HVOR gain amplitude ratio of eye movement in darkness to turntable rotation - OKR gain amplitude ratio of eye movement to light slit movement - HVOR phase defined as 0 ° when the eye movement is shifted 180 ° with respect to the rotation of the turntable - OKR phase defined as 0 ° when the eye movement is shifted 0 ° with respect to light slit movement Supported by a grant from the Japanese Ministry of Education, Science, and Culture (544021)On leave from Nencki Institute of Experimental Biology (Warsaw) and supported by a Polish-Japanese Cultural Relations Program Fellowship (January 1977 through January 1978, and April 1979 through October 1979)     

Effect of brain 5-hydroxytryptamine alterations on reflex bradycardia in rats.

The vasopressor and bradycardia responses to an intravenous dose of epinephrine were assessed in saline-controlled, 5-hydroxytryptamine-(5-HT) depleted, and 5-HT-potentiated rats. Regardless of the previous treatment epinephrine produced an insignificant change in the basal levels of mean arterial pressure and heart rate. However, brain serotonin alteration did produce some influences on the reflex bradycardia in response to an elevation in arterial pressure. Elevating 5-HT contents in brain with 5-hydroxytryptophan (5-HTP) after peripheral decarboxylase inhibition with Ro 4-4602 produced a significant reduction in reflex bradycardia compared to the controls. In contrast, depleting 5-HT contents in brain with either p-chlorophenylalanine (PCPA) or 5,7-dihydroxytryptamine (5,7-DHT) led to an enhancement of epinephrine-induced bradycardia. Moreover, the enhanced reflex bradycardia induced by PCPA treatment was readily blocked by the replacement of the depleted brain 5-HT with 5-HTP and Ro 4-4602. The results suggest that serotoninergic systems play a role in the elaboration or modulation of reflex bradycardia. Specifically, 5-HT appears to inhibit reflex bradycardia since its depletion facilitated and its elevation inhibited reflex bradycardia.     

Inhibition of itch-related responses by selectively ablated serotonergic signals at the rostral ventromedial medulla in mice

Descending control of nociceptive processing in the rostral ventromedial medulla (RVM) has been implicated in the inhibition and facilitation of spinal nociceptive transmission. Here we investigated the contribution of serotonergic (5-HT) pathway at the RVM to pruritic behavior. Selective lesion of the descending serotonergic pathway by intra-RVM injection of focal neurotoxin 5,7-dihydroxytryptamine (2 μg/0.5 μl) attenuated pruritic behavior at the 30-min observation period following an intradermal microinjection of compound 48/80 (100 μg/100 μl) in the nape of the neck. Intradermal microinjection of compound 48/80 resulted in a dramatic increase in itch behavior between naive group and saline group. 5,7-DHT-treated mice showed profound scratching deficits after intradermal injection of compound 48/80. 5,7-DHT treatment resulted in a significant decrease in the number of 5-HT positive neurons in the RVM by using intracisternal injection of the serotonin neurotoxin 5,7-DHT. These findings demonstrate that pruritic behavior is dependent in part on descending facilitation via the RVM, and identify a modulatory role of serotonergic pathway at the RVM for pruritic behavior.     

Behavior of floccular Purkinje cells correlated with adaptation of vestibulo-ocular reflex in pigmented rabbits

Summary The responsiveness of floccular Purkinje cells to head oscillations was examined in alert pigmented rabbits subjected to adaptation of horizontal vestibulo-ocular reflex (HVOR) under three different combinations of turntable and screen oscillations. Purkinje cells involved in the HVOR control (H-zone cells) were identified by local stimulation effects that induced horizontal eye movements. In control states, simple spike discharages of H-zone cells were modulated predominantly out of phase with the velocity of sinusoidal turntable oscillation (0.1 Hz, 5° peak-to-peak). A sustained 180° outphase combination (5° turntable and 5° screen oscillation) was found to increase the average HVOR gain by 0.16, at which point the majority of H-zone cells increased the outphase simple spike modulation. A sustained inphase combination (5° turntable and 5° screen oscillation) decreased the average HVOR gain by 0.09, with the majority of H-zone cells decreasing the outphase simple spike modulation or becoming converted to the inphase modulation. With a vision-reversal combination (5° turntable and 10° screen oscillation), there was no change in the gain of the HVOR, but a moderate advancement in the phase. In this case, H-zone cells showed no appreciable changes in their simple spike modulation. Complex spike discharges of all H-zone cells tested were modulated in response to optokinetic stimuli involved in the combinations of turntable and screen oscillations. These results support the hypothesis that H-zone cells adaptively control HVOR dynamic characteristics through modification of mossy fiber responsiveness to head oscillation under influences of retinal error signals conveyed by climbing fiber afferents.     

Effects of unilateral lesions of the flocculus on optokinetic and vestibuloocular reflexes of the rabbit

The horizontal optokinetic reflex (HOKR) and the horizontal vestibuloocular reflex (HVOR) were tested in 21 rabbits before and after unilateral lesions were made in the left cerebellar flocculus. The immediate effect, observed within 15 min following placement of a floccular lesion, was a conjugate nystagmus with the slow phase toward the side opposite to the lesion when the animal was placed in total darkness. This spontaneous nystagmus lasted from several hours to two days depending on the extent of damage to the flocculus. It was reversed in sign if the subjacent vestibular nuclei or vestibular nerve were damaged by the operation, and it was totally absent if the unilateral floccular lesions were made in rabbits that had been bilaterally labyrinthectomized. The spontaneous drift of the eyes observed immediately postoperatively caused a bias in measurement of the HVOR that was dependent on the frequency of vestibular stimulation. When measured 50 days postoperatively the HVOR had a normal gain and normal bias. When measured 50 days postoperatively the monocular HOKR (posteroanterior stimulation of the left eye) was significantly reduced in gain at stimulus velocities below 5 degrees/s. A quantitative anatomical analysis of the degeneration of inferior olivary neurons caused by lesions of the flocculus demonstrated contralateral cell loss of as much as 65% of the dorsal cap neuronal population. These data reveal a permanent deficit in the HOKR, but not the HVOR, following unilateral floccular lesions and are consistent with the idea that the flocculus contributes to the regulation of the low-velocity eye movements through the inhibitory modulation of the activity of the subjacent vestibular nuclei.     

Development of circadian rhythms in rats with lesions of serotonergic system

In order to assess the role of the serotonergic system in the development of overt circadian rhythms in the rat, serotonin neurons in the brain were destroyed either by thermocoagulation of the median raphe (MRL) or by an intracerebroventricular injection of the neurotoxin, 5,7-dihydroxytryptamine (DHT). The reductions in serotonin content induced by two manipulations with MRL and DHT were 41% and 100% in the striatum, 40% and 66% in the hypothalamus, and 62% and 88% in the hippocampus, respectively. Neither manipulation eliminated the expression of circadian rhythms in corticosterone (CS) secretion, locomotor activity and drinking behavior, and changed the phase relationship in the overt CS rhythm. Also, 5,7-DHT treatments did not significantly affect the free-running period in locomotor activity. However, the emergence of CS circadian rhythm was delayed for one week in both MRL and DHT groups compared to the intact control ones. These results suggested that a serotonergic system would not be essential for the generation of the endogenous rhythm and the photoentrainment of overt circadian rhythms, but seems to participate in the only development of CS rhythms during the early stage of life.     

Antinociceptive effects of neurotropin in a rat model of central neuropathic pain: DSP-4 induced noradrenergic lesion

Neurotropin is a nonprotein extract isolated from inflamed skin of rabbits inoculated with vaccinia virus, and used for treatment of neuropathic pain. In the present study, we have determined whether neurotropin could exert antinociceptive action using the central neuropathic pain model that we recently established. Rats were randomly allocated to 3 groups: Sham group (n = 20), DSP-4 [N-(-2-chloroethyl)-N-ethyl-2-bromobenzylamine] group (50 mg/kg ip, n = 18), and DSP-4 + 5,7-DHT [5,7-dihydroxytryptamine] group (ip DSP-4 50 mg/kg + icv 5,7-DHT 200 μg, n = 18). In Sham, DSP-4 and DSP-4 + 5,7-DHT groups, the effects of ip neurotropin (100 NU/Kg) on hot-plate latency in rats with no lesion, noradrenergic neuron depletion and both noradrenergic and serotonergic neuronal depletion were studied, respectively. Rats in each group were subdivided equally to 2 subgroups: saline and neurotropin. After completion of the hot-plate tests, each rat was decapitated, the cerebral cortex was dissected from its internal structure for measurement of norepinephrine contents. Hot-plate latency significantly decreased by ∼40% 10 days after ip DSP-4 or after ip DSP-4 and 5,7-DHT. Norepinephrine contents in DSP-4 treated rats (55.6 ± 6.3 ng/ng tissue) and DSP-4 + 5,7-DHT treated rats (35.3 ± 6.3 ng/ng tissue) were significantly lower than those in intact rats (131.6 ± 5.7 ng/ng tissue, p < 0.01). Neurotropin significantly increased the area under the curve (AUC) of the hot-plate latency in the DSP-4 and DSP-4 + 5,7-DHT groups but not in the Sham group. There was a significant correlation between AUC and norepinephrine contents in saline subgroup (p < 0.01, r = 0.597) but not in neurotropin subgroup in DSP-4 group. Neurotropin exerted an antinociceptive effect in DSP-4 induced central neuropathic pain. The present data suggest neuronal pathways other than descending inhibitory noradrenergic and serotonergic systems may be involved in neurotropin mediated antinociception.