Inhibition of medullary raphe serotonergic neurons has age-dependent effects on the CO2 response in newborn piglets.

Medullary raphé serotonergic neurons are chemosensitive in culture and are situated adjacent to blood vessels in the brain stem. Selective lesioning of serotonergic raphé neurons decreases the ventilatory response to systemic CO2 in awake and sleeping adult rats. Abnormalities in the medullary serotonergic system, including the raphé, have been implicated in the sudden infant death syndrome (48). In this study, we ask whether serotonergic neurons in the medullary raphé and extra-raphé regions are involved in the CO2 response in unanesthetized newborn piglets, 3-16 days old. Whole body plethysmography was used to examine the ventilatory response to 5% CO2 before and during focal inhibition of serotonergic neurons by 8-hydroxy-2-di-n-propylaminotetralin (8-OH-DPAT), a 5-HT1A receptor agonist. 8-OH-DPAT (10 or 30 mM in artificial cerebrospinal fluid) decreased the CO2 response in wakefulness in an age-dependent manner, as revealed by a linear regression analysis that showed a significant negative correlation (P < 0.001) between the percent change in the CO2 response and piglet age. Younger piglets showed an exaggerated CO2 response. Control dialysis with artificial cerebrospinal fluid had no significant effect on the CO2 response. Additionally, 8-OH-DPAT increased blood pressure and decreased heart rate independent of age (P < 0.05). Finally, sleep cycling was disrupted by 8-OH-DPAT, such that piglets were awake more and asleep less (P < 0.05). Because of the fragmentary sleep data, it was not possible to examine the CO2 response in sleep. Inhibition of serotonergic medullary raphé and extra-raphé neurons decreases ventilatory CO2 sensitivity and alters cardiovascular variables and sleep cycling, which may contribute to the sudden infant death syndrome.     

CO2 dialysis in nucleus tractus solitarius region of rat increases ventilation in sleep and wakefulness.

To evaluate the function of widely distributed central chemoreceptors during sleep and wakefulness in the rat, we focally stimulate single chemoreceptor sites during naturally occurring sleep-wake cycles by microdialysis of artificial cerebrospinal fluid equilibrated with 25% CO2. In retrotrapezoid nucleus, this increased ventilation (tidal volume) by 24% only in wakefulness (Li A, Randall M, and Nattie E. J Appl Physiol 87: 910-919, 1999). In caudal medullary raphé, it increased ventilation (frequency) by 15-20% only in sleep (Nattie EE and Li A. J Appl Physiol 90: 1247-1257, 2001). Here, in nucleus tractus solitarius (NTS), focal acidification significantly increased ventilation by 11% in sleep and 7% in wakefulness rostrally (n = 5) and by 16% in sleep and 28% in wakefulness caudally (n = 5). The sleep-wake cycle was unaltered. Dialysis with 5% CO2 had no effect. Dialysis with 50% CO2 caudally did not further stimulate ventilation but did disrupt sleep. Central chemoreceptors in the NTS affect breathing in both sleep and wakefulness. The threshold for arousal in caudal NTS is greater than that for the stimulation of breathing.     

Development of a presynaptic 5-HT1A antagonist

A new 5-HT(1A) silent antagonist 14 (5-HT(1A) IC(50)=2.2 nM) antagonizes the effects of agonists on reciprocal forepaw treading behavior, on neuronal firing in the rat dorsal raphé, and on 5-HT(1A) release in the raphé and hippocampus. While 14 alone was inactive in the social interaction paradigm, it completely reversed the social interaction activity of the serotonergic compounds (buspirone, 1, and 2).     

Nucleic acid and protein content of cells of the raphe nuclei of the rat brain when the animals are deprived of the paradoxical sleep phase

A 24 hours paradoxical sleep deprivation (PSD) with rats resulted in lowering the RNA content in neurons and gliocytes of n. raphé dorsalis by 31 and 18%, resp.; the protein content remaining unchanged. A 48 hours PSD reduced RNA and protein contents in neurons by 31%; in gliocytes both these substances being on the control level. In the neurons of n. raphé pontis, by the end of the 1st day of PSD the contents of both RNA and protein were seen reduced by 16 and 28%, resp.; however, by the end of the 2nd day their levels well compared with those in the control rats. There was a phase oscillation of protein content in gliocytes: from - 19%, on the first day of PSD, to +19%, on the 2nd day. There is a great resemblance in response to PSD between the adrenergic nucleus - locus coeruleus - and n. raphé pontis, whereas their responses differ from that of the serotoninergic n. raphé dorsalis.     

Maternal dietary tryptophan deficiency alters cardiorespiratory control in rat pups

Malnutrition during pregnancy adversely affects postnatal forebrain development; its effect upon brain stem development is less certain. To evaluate the role of tryptophan [critical for serotonin (5-HT) synthesis] on brain stem 5-HT and the development of cardiorespiratory function, we fed dams a diet ～45% deficient in tryptophan during gestation and early postnatal life and studied cardiorespiratory variables in the developing pups. Deficient pups were of normal weight at postnatal day (P)5 but weighed less than control pups at P15 and P25 (P < 0.001) and had lower body temperatures at P15 (P < 0.001) and P25 (P < 0.05; females only). Oxygen consumption (Vo(2)) was unaffected. At P15, deficient pups had an altered breathing pattern and slower heart rates. At P25, they had significantly lower ventilation (Ve) and Ve-to-Vo(2) ratios in both air and 7% CO(2). The ventilatory response to CO(2) (% increase in Ve/Vo(2)) was significantly increased at P5 (males) and reduced at P15 and P25 (males and females). Deficient pups had 41-56% less medullary 5-HT (P < 0.01) compared with control pups, without a difference in 5-HT neuronal number. These data indicate important interactions between nutrition, brain stem physiology, and age that are potentially relevant to understanding 5-HT deficiency in the sudden infant death syndrome.     

Effects on breathing of carotid body denervation in neonatal piglets.

The purpose of these studies was to test the hypothesis that carotid chemoreceptor activity is necessary for postnatal maturation of the ventilatory control system. By using a lateral surgical access, 17 piglets were carotid body denervated (CBD) and 14 were sham denervated at 3-25 days of age. After surgery, there was no irregular breathing in any group. There was no significant hypoventilation when CBD was performed at less than 5 days of age (n = 5) and only a mild (arterial PCO(2) 5 Torr; P < 0.05) to moderate, transient (arterial PCO(2) 8 Torr; P < 0.5) hypoventilation in piglets denervated at 10-15 (n = 6) and 20-25 (n = 6) days of age, respectively. Three weeks after surgery, both breathing of a hypoxic gas mixture and jugular venous NaCN injections elicited a hyperpnea in the CBD piglets that was attenuated compared with that in sham CBD piglets. In the CBD piglets, there was no response to injections of NaCN in the carotid arteries, but there was a response to NaCN injected into the proximal descending aorta, suggesting the residual peripheral chemosensitivity was of aortic origin. Carotid chemoreceptor-intact piglets had carotid and aortic NaCN chemosensitivity by 2 days of age. The carotid response persisted for the 40 days of the study, but the aortic reflex persisted only until approximately 8 days of age. We conclude that 1) the major effect of CBD per se in neonatal piglets is age-dependent hypoventilation and 2) there is a high degree of plasticity in peripheral chemosensitivity in neonates that may contribute to minimizing the changes in breathing after CBD.     

Muscimol dialysis in the rostral ventral medulla reduced the CO(2) response in awake and sleeping piglets.

Some victims of sudden infant death syndrome have arcuate nucleus abnormalities. The arcuate nucleus may be homologous with ventral medullary structures in the cat known to be involved in the control of breathing and the response to systemic hypercapnia. We refer to putative arcuate homologues in the piglet collectively as the rostral ventral medulla (RVM). We inhibited the RVM in awake and sleeping, chronically instrumented piglets by microdialysis of the GABA(A) receptor agonist muscimol. Muscimol dialysis (10 and 40 mM) had no effect on eupnea but caused a significant reduction in the response to hypercapnia during both wakefulness (34.8 +/- 8.7 and 30.7 +/- 10.1%, respectively) and sleep (36.7 +/- 6.7 and 49.5 +/- 8.9%, respectively). The effect of muscimol on the CO(2) response was entirely via a reduction in tidal volume and appeared to be greater during non-rapid-eye-movement sleep. We conclude that the piglet RVM contains neurons of importance in the response to systemic CO(2) during both wakefulness and non-rapid-eye-movement sleep. We hypothesize that dysfunction of homologous regions in the human infant could lead to impaired ability to respond to hypercapnia, particularly during sleep, which could potentially be involved in the pathogenesis of sudden infant death syndrome.     

Dissociation of the plasticity of 5-HT1A sites and 5-HT transporter sites

To study the early effects of neonatal 5,7-dihydroxytryptamine lesions on 5-hydroxytryptamine_1A (5-HT_1A) receptors, we measured regional [³H]8-OH-DPAT-labeled 5-HT_1A sites in binding assays and compared them to our previous studies of [³H]paroxetine-labeled 5-HT transporter sites during the first month in the same rats. While there were significant time- and dose-dependent effects of 5,7-DHT on 5-HT transporter sites, there were no significant changes in 5-HT_1A sites in cortex, hippocampus, diencephalon, brainstem, cerebellum, or spinal cord. 5,7-DHT lesions also did not alter the K_i of Gpp(NH)p at brainstem 5-HT_1A sites or the K_i of 5-HT in cortex or brainstem in the presence or absence of GTPS or Gpp(NH)p. There were significant regional differences between the density of 5-HT_1A sites and 5-HT transporter sites. The ontogeny of brainstem 5-HT_1A sites was a pattern of increases until three weeks postnatal, and 5,7-DHT lesions did not alter the ontogeny of 5-HT_1A sites. These data suggest differential plasticity of 5-HT_1A and 5-HT transporter binding sites during the first month after neonatal 5,7-DHT lesions.     

Participation of microRNA 124-CREB pathway: a parallel memory enhancing mechanism of standardised extract of Bacopa monniera (BESEB CDRI-08)

Bacosides, the effective component of standardised leaf extract of Bacopa monniera (BESEB CDRI-08) has been reported to have memory enhancing effect. Our previous reports suggested that BESEB CDRI-08 (BME) improves memory in postnatal rats by enhancing serotonin [5-hydroxytryptamine (5-HT)] metabolism, its transportation and subsequently activates 5-HT(3A) receptor during hippocampus-dependent learning. In this study, we examine whether the up-regulated 5-HT(3A) receptor activity by BME modulate microRNA 124-CREB pathway to enhance synaptic plasticity. Wistar rat pups received single dose of vehicle solution (0.5?% gum acacia?+?0.9?% saline)/BME (80?mg/kg)/mCPBG (10?mg/kg)/BME?+?mCPBG during the postnatal days (PND) 15-29. On PND 30, individuals were trained at brightness discrimination task and 24?h later, they were tested on the task. The BME treated group exhibited significantly lower percentage of errors during retention than acquisition. In addition, pre-miR-124 expression in hippocampus was significantly down-regulated in the BME and mCPBG?+?BME treated groups combined with a significant increase in the plasticity related genes, cAMP response element-binding protein, its phosphorylation and postsynaptic density protein 95. Our results suggest that this may be one of the mechanisms of bacosides present in BME for the memory enhancement.     

Time course of expression and function of the serotonin transporter in the neonatal rat's primary somatosensory cortex

Immunocytochemical and autoradiographic techniques were employed to determine the time course of expression of the serotonin (5-HT) transporter (SERT) on thalamocortical afferents in the rat's primary somatosensory cortex (S-I), and to correlate this expression to the transient vibrissae-related patterning of 5-HT immunostaining previously described. In additional in vivo and in vitro experiments, 5-HT and 3 H-5-HT were applied directly to the cortices of untreated and 5,7-dihydroxytryptamine-treated (5,7-DHT) rats in order to determine the period during which SERT functions on thalamocortical axons to take up 5-HT. In postnatal rats, SERT immunohistochemistry revealed a somatotopic patterning in S-I that persisted until P-15, which is 6 days after the disappearance of the vibrissae-related 5-HT immunostaining. 3 H-citalopram autoradiography revealed a vibrissae-related pattern in layer IV of S-I until at least P-30. Following destruction of raphe-cortical afferents with 5,7-DHT on the day of birth, this binding pattern remained visible until at least P-25, indicating that SERT located on thalamocortical axons is responsible for the 3 H-citalopram patterning observed in S-I. Tissue from 5,7-DHT-treated rats that had 5-HT applied directly to their cortices revealed a normal vibrissae-related pattern of 5-HT immunostaining in S-I at P-7 and P-11 but only a faint pattern at P-13 and none at P-14. In addition, 3 H-5-HT injected directly into S-I labeled layer IV barrels at P-6 and P-12 but not at P-18. The results of these experiments demonstrate that SERT is expressed by thalamocortical afferents and remains functional long after the vibrissae-related 5-HT immunostaining in cortex disappears.     

Age-dependent metabolic effects of repeated hypoxemia in piglets

The aim of this study was to determine whether repeated exposure to hypoxemia would modify the response to hypoxemia during maturation. We exposed piglets to three 1-h cycles of hypoxemia (PaO2 = 30 to 35 mmHg; 1 mmHg = 133.3 Pa) at 1 week (n = 9), 2-3 weeks (n = 10), and 4-5 weeks of age (n = 10). O2 consumption (V(O2)) and CO2 production (V(CO2)) were measured, and alveolar ventilation (V(A)) was derived from V(CO2) and PaCO2. Levels of lactic acid (lactate) and serum catecholamines were also measured. With hypoxemia, time had a significant effect on V(O2) and body temperature in an age-dependent fashion: that is, whereas the 1 week group and the 4-5 week group showed both variables decreasing over time, the 2-3 week group showed no drop in V(O2) and a small increase in body temperature over time. Lactate levels increased with hypoxemia in all animals during the first exposure. However, with repeated exposures to hypoxemia, only the 2-3 week group continued to increase its lactate levels. Furthermore, the changes in lactate levels paralleled the changes in epinephrine levels with hypoxemia. We found, too, that although V(A) increased significantly with hypoxemia in all animals, this change was not modified by age or repeated exposures. No significant effects of age or repeated exposures were found in the cardiovascular response to hypoxemia. We concluded that, from a metabolic viewpoint, after repeated exposures to hypoxemia the 2-3 week animals responded differently.     

Time course of expression and function of the serotonin transporter in the neonatal rat's primary somatosensory cortex

Immunocytochemical and autoradiographic techniques were employed to determine the time course of expression of the serotonin (5-HT) transporter (SERT) on thalamocortical afferents in the rat's primary somatosensory cortex (S-I), and to correlate this expression to the transient vibrissae-related patterning of 5-HT immunostaining previously described. In additional in vivo and in vitro experiments, 5-HT and 3H-5-HT were applied directly to the cortices of untreated and 5,7-dihydroxytryptamine-treated (5,7-DHT) rats in order to determine the period during which SERT functions on thalamocortical axons to take up 5-HT. In postnatal rats, SERT immunohistochemistry revealed a somatotopic patterning in S-I that persisted until P-15, which is 6 days after the disappearance of the vibrissae-related 5-HT immunostaining. 3H-citalopram autoradiography revealed a vibrissae-related pattern in layer IV of S-I until at least P-30. Following destruction of raphe-cortical afferents with 5,7-DHT on the day of birth, this binding pattern remained visible until at least P-25, indicating that SERT located on thalamocortical axons is responsible for the 3H-citalopram patterning observed in S-I. Tissue from 5,7-DHT-treated rats that had 5-HT applied directly to their cortices revealed a normal vibrissae-related pattern of 5-HT immunostaining in S-I at P-7 and P-11 but only a faint pattern at P-13 and none at P-14. In addition, 3H-5-HT injected directly into S-I labeled layer IV barrels at P-6 and P-12 but not at P-18. The results of these experiments demonstrate that SERT is expressed by thalamocortical afferents and remains functional long after the vibrissae-related 5-HT immunostaining in cortex disappears.     

Gasping and autoresuscitation in the developing rat: effect of antecedent intermittent hypoxia.

Gasping is a critically important mechanism for autoresuscitation and survival during extreme tissue hypoxia. Evidence of antecedent hypoxia in sudden infant death syndrome suggests that intermittently occurring hypoxic episodes may modify gasping and autoresuscitation. To examine this issue, an intermittent hypoxia (IH) profile consisting of alternating room air and 10% O(2)-balance N(2) every 90 s was applied to pregnant Sprague-Dawley rats (IHRA; n = 50) and to pups after a normal pregnancy (RAIH; n = 50) as well as to control pups (RARA; n = 50). At postnatal day 5, pups were exposed to 95% N(2)-5% CO(2), and gasping and the ability to autoresuscitate were assessed. Compared with RARA, IHRA- and RAIH-exposed pups had a reduced number of gasps, decreased overall gasp duration, and were less likely to autoresuscitate on introduction of room air to the breathing mixture during the last phase of gasping (P < 0.001 vs. RARA). We conclude that both prenatal and early postnatal IH adversely affect gasping and related survival mechanisms.     

Postnatal changes in regional blood flow during cold-induced shivering in sow-reared piglets.

To determine whether newborn pigs are able to display adequate cardiovascular adjustments favouring shivering thermogenesis in skeletal muscles soon after birth, regional blood flow and fractional distribution of cardiac output were determined in 1-day-old (n = 6) and 5-day-old (n = 6) conscious piglets at thermal neutrality and during cold exposure, using coloured microspheres. Five-day-old piglets stayed with the sow before the experiment. The cold challenge was designed to induce a similar increase (approximately +90%) in heat production at both ages. Skeletal muscle blood flow increased with both age (p < 0.05) and cold exposure (p < 0.001), with the effect of cold being more pronounced in 5-day-old piglets than in 1-day-old piglets (+60%, p < 0.05). The difference between individual muscles increased with age, with fractional blood flow being 41% higher in rhomboideus than in longissimus thoracis muscle during cold exposure in 5-day-old piglets (p < 0.05). Cardiac output was similar at both ages and increased by 23% in the cold (p < 0.001). At 1 day of age, there was no redistribution of cardiac output among the internal organs during the cold challenge, while at 5 days of age, the increase in muscle fractional blood flow was associated with a reduction (p < 0.05) in the fraction of cardiac output reaching the skin (-24%), the small intestine (-21%), and the liver (-20%). In conclusion, these results suggest that there is a rapid postnatal improvement of cardiovascular adjustments favouring blood perfusion and probably heat production during cold-induced shivering in the most oxidative muscles studied. This cardiovascular response may play a role in the postnatal enhancement of thermoregulation in piglets.     

Release of endogenous serotonin from "encéphale isolé" cats. II - Correlations with raphe neuronal activity and sleep and wakefulness

The discharge pattern of single neurons localized in raphe nuclei dorsalis and centralis superior was recorded in "encéphale isolé" cats, during sleep and wakefulness episodes occurring spontaneously or triggered by vago-aortic stimulation. In both nuclei, a similar and progressive decrease in frequency of discharges is generally observed during shifts between wakefulness, the transitional phase of sleep and paradoxical sleep. In addition, the release of serotonin (5-HT) has been studied with push-pull cannulae (caudate nucleus level) and superfusion techniques (cortical associative area) in relation to the different stages of consciousness. The results showed a clear diminution of endogenous 5-HT released during spontaneously occurring or vago-aortic triggered sleep.     

Effects of imipramine and serotonin-2 agonists and antagonists on serotonin-2 and beta-adrenergic receptors following noradrenergic or serotonergic denervation

The effects of chronic (14 day) administration of the tricyclic antidepressant imipramine, the serotonin-2 (5-HT2) antagonist ketanserin, and the serotonin agonist quipazine on 5-HT2 receptor binding parameters and 5-HT2-mediated behavior were examined in rats with or without prior serotonergic denervation [via 5,7-dihydroxytryptamine (5,7-DHT)] or noradrenergic denervation [via N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4)]. Chronic administration of imipramine, ketanserin, or quipazine produced a marked reduction in the number of 5-HT2 binding sites which was accompanied by reductions in the 5-HT2-mediated quipazine-induced head shake response. In animals receiving DSP4 or 5,7-DHT lesions and continuous vehicle treatment, beta-adrenergic receptor binding sites were significantly up-regulated while 5-HT2 receptor binding sites did not change. Imipramine normalized the lesion-induced increases in beta-adrenergic binding observed in DSP4 and 5,7-DHT-lesioned rats but failed to down-regulate beta-adrenergic binding sites below non-lesioned control levels. Chronic imipramine, ketanserin, and quipazine reduced quipazine-induced head shakes and down-regulated 5-HT2 binding sites in rats with noradrenergic denervation. While imipramine, ketanserin, and quipazine all down-regulated 5-HT2 binding sites in animals with serotonergic denervation, only imipramine's ability to reduce quipazine-induced head shakes was attenuated in 5,7-DHT-lesioned rats. The present results suggest that imipramine-induced down-regulation of 5-HT2 receptors may not involve presynaptic 5-HT mechanisms, and imipramine-induced alterations in 5-HT2 sensitivity as reflected in the quipazine-induced head shake may, in part, be influenced by beta-adrenergic receptors.     

Are 5-HT receptors involved in the sprouting of serotoninergic terminals following neonatal 5,7-dihydroxytryptamine treatment in the rat?

The neonatal administration of 5,7-dihydroxytryptamine to rats (100 mg kg^?1 s.c. on the 1st and 2nd day after birth) resulted in marked reductions in serotoninergic presynaptic markers ([³H]-5-HT synaptosomal uptake, tryptophan hydroxylase activity and endogenous 5-HT content) in various forebrain areas, particularly the cerebral cortex and the hippocampus. In contrast, this treatment produced an increased outgrowth of serotoninergic terminals in the brain stem as judged by the significant increments of these presynaptic markers in this region. Both in the hippocampus and the brain stem, these 5,7-dihydroxytryptamine-induced changes in serotoninergic innervation were associated with a transient increase in 5-HT-sensitive adenylate cyclase activity. No significant alteration of the specific high affinity binding of [³H]-5-HT to synaptosomal membranes from various brain regions was detected in 5,7-dihydroxytryptamine-treated rats for at least the first postnatal month.The chronic blockade of 5-HT receptors by metergoline (5 mg kg^?1 day^?1 from day 3 to day 22 after birth) altered neither the changes in presynaptic markers nor the evolution of [³H]-5-HT high affinity binding in 5,7-dihydroxytryptamine-treated rats.These findings further illustrate that the high affinity binding sites for [³H]-5-HT do not correspond to postsynaptic 5-HT receptors coupled to adenylate cyclase in the rat brain. Apparently, 5-HT receptors play no role in the increased outgrowth of serotoninergic systems in the brain stem following neonatal 5,7-dihydroxy-tryptamine treatment.     

Prostaglandins and control of breathing in newborn piglets

To investigate the possible role of prostaglandins in regulation of postnatal breathing, phrenic neural activity (PMO) was recorded as an index of breathing in 42 anesthetized, paralyzed piglets less than 30 days of age (weight 2.4 +/- 0.2 kg, age 9.9 +/- 1.5 days) who were mechanically ventilated with 100% O2 at a fixed tidal volume (8-10 ml/kg). End-tidal CO2 was held constant by an electronic servocontroller which adjusted ventilator rate; ventilator rate was monitored as an index of CO2 production. Rectal temperature was maintained at 39.0 +/- 0.2 degrees C. The effects on PMO of intravenous and brain ventricular injections of NaCl and agents active in the prostaglandin cascade were compared. Intravenous (0.25-1.0 mg/kg, n = 9) and brain (5-33 micrograms/kg, n = 6) indomethacin, a cyclooxygenase inhibitor, doubled PMO within 30 min. Intravenous (1-10 micrograms/kg, n = 6) and brain (1-40 micrograms/kg, n = 6) prostaglandin E1 inhibited PMO by one-half at 10 and 30 min.     

Serotonin fiber innervation of cerebellar cell suspensions intraparenchymally grafted to the cerebellum ofpcd mutant mice

One aspect of integration of implanted neurons into the neuronal circuitry of a defective host brain is the re-establishment of a host-to-graft afferent innervation. We addressed this issue by using the adult cerebellum of Purkinje cell degeneration (pcd) mutant mice, which lack virtually all Purkinje cells after postnatal day (P) 45. Purkinje cells constitute one of the cerebellar cell types being innervated by axons of raphé serotonin (5-HT) neurons. In normal mice, 5-HT-immunoreactive fibers are distributed to all cerebellar folia. Following Purkinje cell loss inpcd mice, cerebellar 5-HT-immunoreactive fibers persist. Cerebellar cell suspensions were prepared from embryonic day (E) 11–13 normal mouse embryos and were intraparenchymally grafted into the cerebellum ofpcd mutants either directly or after pre-treatment with 5, 7-dihydroxytryptamine (5,7-DHT) to selectively remove 5-HT cells of donor origin. The state of Purkinje cells and 5-HT axons was monitored in alternate sections by 28-kDa Ca²⁺-binding protein (CaBP) and 5-HT immunocytochemistry, respectively. Serotonin-immunoreactive axons were seen in the grafts from 5 to 32 days after transplantation. In some of the grafts which had not been pre-treated with 5,7-DHT, a small number of 5-HT-immunoreactive cell bodies was found, indicating that part of the 5-HT fiber innervation of the graft could actually derive from donor cells. On the other hand, in grafts pre-treated with 5,7-DHT, no 5-HT cell bodies were seen in the grafted cerebellum; 5-HT fibre innervation of the grafts occurred, but it appeared to be slightly less robust compared to situations of co-grafted 5-HT cell bodies. These findings suggest that host 5-HT fibers are able to provide afferent innervation to donor cerebellar tissue; the presence of co-grafted 5-HT cells may augment such an innervation.Special issue dedicated to Dr. Morris H. Aprison.     

Rat hypothalamic noradrenaline levels following midbrain raphé nuclei lesions

Electrolytic lesions of the median and dorsal raphé nuclei resulted in statistically significant reductions in rat hypothalamic noradrenaline which were observed 1 or 2 days after lesioning, while no changes were observed 7 or 14 days after lesioning. The short term (1-2 days) raphé nuclei lesions produced no changes in hypothalamic 5-hydroxytryptamine or a small reduction in 5-hydroxyindole acetic acid while the expected marked reductions were observed after 7 days. The reduction in hypothalamic noradrenaline observed after short term raphé nuclei lesions suggests the existence of a positive feedback loop between 5-hydroxytryptamine neurons and noradrenaline terminals in the hypothalamus.