Superior Cervical Ganglionectomized Research Articles

Circadian Regulation of IOP Rhythm by Dual Pathways of Glucocorticoids and the Sympathetic Nervous System.

PurposeElevated IOP can cause the development of glaucoma. The circadian rhythm of IOP depends on the dynamics of the aqueous humor and is synchronized with the circadian rhythm pacemaker, that is, the suprachiasmatic nucleus. The suprachiasmatic nucleus resets peripheral clocks via sympathetic nerves or adrenal glucocorticoids. However, the detailed mechanisms underlying IOP rhythmicity remain unclear. The purpose of this study was to verify this regulatory pathway.MethodsAdrenalectomy and/or superior cervical ganglionectomy were performed in C57BL/6J mice. Their IOP rhythms were measured under light/dark cycle and constant dark conditions. Ocular administration of corticosterone or norepinephrine was also performed. Localization of adrenergic receptors, glucocorticoid receptors, and clock proteins Bmal1 and Per1 were analyzed using immunohistochemistry. Period2::luciferase rhythms in the cultured iris/ciliary bodies of adrenalectomized and/or superior cervical ganglionectomized mice were monitored to evaluate the effect of the procedures on the local clock. The IOP rhythm of retina and ciliary epithelium-specific Bmal1 knockout mice were measured to determine the significance of the local clock.ResultsAdrenalectomy and superior cervical ganglionectomy disrupted IOP rhythms and the circadian clock in the iris/ciliary body cultures. Instillation of corticosterone and norepinephrine restored the IOP rhythm. β2-Adrenergic receptors, glucocorticoid receptors, and clock proteins were strongly expressed within the nonpigmented epithelia of the ciliary body. However, tissue-specific Bmal1 knock-out mice maintained their IOP rhythm.ConclusionsThese findings suggest direct driving of the IOP rhythm by the suprachiasmatic nucleus, via the dual corticosterone and norepinephrine pathway, but not the ciliary clock, which may be useful for chronotherapy of glaucoma.

Effect of pinealectomy, superior cervical ganglionectomy, or melatonin treatment on 24-hour rhythms in ornithine decarboxylase and tyrosine hydroxylase activities of rat spleen.

Diurnal variations in splenic ornithine decarboxylase and tyrosine hydroxylase activities were examined in rats subjected to pinealectomy, bilateral superior cervical ganglionectomy, or their respective sham operations. Rats were treated with Freund's complete adjuvant or its vehicle 2 days before sacrifice. After immunization, splenic ornithine decarboxylase activity was augmented 5-6-fold. In both immunized and nonimmunized sham-operated rats, significant diurnal variations in ornithine decarboxylase activity were detectable, with a maximum at early morning, acrophases after Cosinor analysis varying from 0845 to 1048h. In pinealectomized or superior cervical ganglionectomized, immunized rats, ornithine decarboxylase activity attained values 22-27% lower than those of immunized sham-operated controls, while amplitude decreased significantly by 27-30%. Administration of melatonin (30 microg/animal s.c. at late evening for 11 days in immunized rats) significantly augmented mesor levels of splenic ornithine decarboxylase activity and increased the amplitude of the diurnal rhythm both in pinealectomized and in superior cervical ganglionectomized rats. Melatonin treatment also augmented rhythm mesor in immunized, sham-ganglionectomized rats, as well as rhythm amplitude in immunized and nonimmunized, sham-ganglionectomized rats. Splenic tyrosine hydroxylase activity attained its maximum at late afternoon and early night, with acrophases varying from 1800 to 2023h. Immunization significantly increased mesor values of splenic tyrosine hydroxylase activity, whereas neither pinealectomy nor superior cervical ganglionectomy affected circadian rhythm parameters. Melatonin treatment augmented mesor values of tyrosine hydroxylase rhythm and increased its amplitude in pinealectomized, ganglionectomized, or sham-operated rats. The results are compatible with the view that the pineal gland plays a role in circadian changes of immune responsiveness in rat spleen via an immunopotentiating effect of melatonin on splenic cell proliferation.

Tyrosine hydroxylase activity in peripherally denervated rat pineal gland

The presence of tyrosine hydroxylase (TH) in the rat pineal gland was studied using a combination of immunochemical and biochemical methods. In superior cervical ganglionectomized (SCGx) animals and in isolated pineals incubated for 72 h, both TH immunoreactive (TH-IR) fibers and TH biochemical activity were still present but reduced. Conversely, in dispersed pinealocytes incubated for only 24 h we were unable to detect either TH activity or TH-positive cells. Since in the pineal gland of intact rats total 3-methoxy-4-hydroxy phenylglycol (MHPG) was undetectable, and only traces of norepinephrine (NE) were present in the pineal of ganglionectomized animals, the results suggest a central pinealopetal catecholaminergic pathway which could use dopamine as a neurotransmitter.

Changes in ovine pineal gland neuron-specific enolase immunoreactivity following bilateral, but not unilateral, superior cervical ganglionectomy.

Pineal gland tissue from control and from unilaterally or bilaterally superior cervical ganglionectomized (SCGX) sheep was found to contain neuron-specific enolase immunoreactive cells and nerve fibers. Morphological characteristics of pineal cells exhibiting immunoreactivity indicated that they were predominantly pinealocytes, while other cell types were nonimmunoreactive. Whereas bilateral SCGX resulted in a reduction in the size, and possibly number, of immunoreactive cells in the pineal, unilateral denervation did not result in any significant effects when compared with control pineals. Concomitant with the reduction in immunoreactivity in bilaterally denervated pineals was a significant increase in the volume of interstitial space, but not the number of nonimmunoreactive cells. These results suggest that sympathetic nerve fibers innervating the pineal of unilaterally sympathectomized sheep exhibited a degree of neural plasticity that resulted in denervated pinealocytes being reinnervated by remaining intact nerve terminals, thus preventing the occurrence of degenerative changes normally associated with complete loss of neural input through bilateral denervation. The fact that in unilaterally denervated sheep neither left nor right SCGX produced any discernible effects in either half of the pineal indicates that nerve fibers from each of the ganglia cross over to innervate the contralateral as well as the ipsilateral pineal half. In the stalk of the pineal an extensive network of immunoreactive nerve fibers was found in both the caudal and habenular commissures, and occasionally these fibers were observed to enter the body of both intact and sympathetically denervated pineals. This latter result suggests that the sympathetic innervation enters the pineal over its surface and not via the stalk.

Evidence that interferon-γ alters pineal metabolism both indirectly via sympathetic nerves and directly on the pinealocytes

1. 1. Interferon-γ (IFN-γ) has been shown to suppress N-acetyltransferase (NAT) activity in cultured rat pineal glands when stimulated with isoproterenol (ISO). 2. 2. Conversely, IFN-γ has also been shown to increase the melatonin content of the rat pineal gland in organ culture. 3. 3. Circumstantial evidence leads to a hypothesis that the NAT suppressive effect may be due to the action of IFN-γ on the sympathetic nerve terminals. 4. 4. To test this hypothesis, pineal glands from intact (INT) and superior cervical ganglionectomized (SCGX) rats, which had been operated 5 days earlier, were cultured with either ISO or ISO + IFN-γ. 5. 5. The concentration of ISO was 10 −8 M and that of IFN-γ was 300 antiviral units/ml. 6. 6. The pineals were incubated for a total period of 5.5 hr, after which the activities of NAT and hydroxyindole- O-methyltransferase (HIOMT) and the levels of melatonin and cAMP were estimated. 7. 7. Suppression of NAT by IFN-γ was observed in the pineals from INT rats, but not in those from SCGX animals. 8. 8. IFN-γ significantly enhanced melatonin levels over those in ISO-stimulated pineals and culture media from the SCGX animals, but not from the INT animals. 9. 9. IFN-γ treatment had no effect on either the HIOMT activity or cAMP levels. 10. 10. The results indicate that the IFN-γ-induced NAT suppression requires the integrity of the sympathetic nerve terminals and the IFN-γ-induced enhancement of melatonin production is accomplished through its direct action on pinealocytes.

Pineal Gland Transplants into the Cerebral Hemisphere of Newborn Rats: A Study of the Blood Brain Barrier and Innervation

Pineal glands from neonatal (0-1 day) Long-Evans black-hooded rats were transplanted into the cerebral hemispheres of litter mates for periods of 1 to 5.5 months. Grafts exhibited differentiated pinealocytes that were intensely immunoreactive for serotonin. Transplant vasculature was permeable to endogenous IgG, comprised fenestrated endothelia with wide pericapillary spaces typical of in situ glands, and had a volume density intermediate to that of surrounding cortex and in situ pineals. Along the periphery, transplant capillaries tended to have continuous endothelia similar to those of host cortex. This peripheral zone was impermeable to endogenous IgG and appeared to increase in size in older grafts. The presence of noradrenergic-like fibers within the perivascular compartment suggested that transplants were innervated by peripheral sympathetic neurons from the superior cervical ganglia. In animals which had been superior cervical ganglionectomized, noradrenergic-like fibers were absent or degenerating. Neural regulation of transplant metabolic activity was suggested by the increased frequency of pinealocyte synaptic ribbons in denervated grafts. These findings are consistent with the hypothesis that factors from both graft and host influence vasculature physiology and differentiation in neural transplants. Furthermore, grafts appeared to receive appropriate neural input from the peripheral sympathetic system.

Long-term reproductive cycles in rams after pinealectomy or superior cervical ganglionectomy

Long-term cycles in diameter of the testes, colouration of the sexual skin and plasma concentrations of testosterone, FSH and prolactin were monitored in groups of pinealectomized (PINX), superior cervical ganglionectomized (SCGX), and control Soay rams living near Edinburgh (56 degrees N). In Exp. 1, PINX, SCGX and control rams were kept outside for 4 years, and well defined seasonal cycles in each of the reproductive parameters were evident in all 3 groups (e.g. testosterone cycle length assessed by sine-wave analysis: 12.08 +/- 0.17, 12.39 +/- 0.14 and 12.15 +/- 0.10 months for PINX, SCGX and control rams respectively). Qualitative differences, however, were apparent between the groups in the timing and amplitude of the reproductive cycle. The seasonal peak in reproductive function occurred from July to September in the PINX and SCGX rams, some 2 months earlier in the year than in controls, while the amplitude of the cycle was less marked in the PINX and SCGX rams. There were no significant differences between the experimental groups in the seasonal cycle in the plasma concentrations of prolactin. In Exp. 2, SCGX and control rams were kept indoors under an artificial environment with a 32-week light cycle and constant nutrition for 4 years. Compared to the controls, in which the reproductive changes were synchronized to the driving light cycle, the SCGX rams showed poorly defined reproductive cycles of lower amplitude and longer period (e.g. testosterone cycle length: 57.8 +/- 6.1 and 32.1 +/- 0.2 weeks for SCGX and control rams, respectively). There was evidence of a cycle in some of the reproductive parameters in the SCGX rams with a period close to 32 weeks during the second half of the study (e.g. testosterone cycle 32.4 +/- 0.8 weeks), which was taken to indicate social induction from the neighbouring control rams. In two further short-term experiments, SCGX rams showed a decline in testicular activity in response to receiving a restricted diet (60% of controls) and an increase in testosterone secretion in response to exposure to oestrous ewes. The overall results illustrate that PINX and SCGX rams can generate long-term synchronized cycles in pituitary and testicular activity. The animals are apparently unable to respond to changes in daylength due to the loss of the functional pineal gland but they remain competent to respond to other environmental cues such as changes in nutrition, temperature and social factors.(ABSTRACT TRUNCATED AT 250 WORDS)

A seasonal pineal peptide rhythm persists in superior cervical ganglionectomized rats

Neurohypophyseal peptide hormone activity is present in the pineal gland of mammals, and varies over a seasonal cycle. Pineal peptide levels, measured by arginine vasotocin (AVT) radioimmunoassay, increase dramatically for a brief time during August each year. The manner in which this cycle is regulated is as yet unknown. Input to the pineal from sympathetic axons arising in the superior cervical ganglia (SCG) is essential for the generation and regulation of the circadian rhythm in melatonin synthesis, and is the only pathway known to regulate pineal biochemical processes. It was of interest then to determine the impact of the SCG on the seasonal peptide cycle. Levels of pineal arginine vasotocin immunoactivity (iAVT) were monitored during August, 1984, in rats which had been superior cervical ganglionectomized (SCGX), in sham-operated and intact controls (L:D 12:12), and in rats subjected to L:D 22:2. The results indicate that SCGX does not abolish the seasonal cycle, but may influence the timing of the iAVT peak. Inhibition of pineal melatonin synthesis by exposure of rats to L:D 22:2 did not mimic the phase delay seen with SCGX, but did cause a significant increase in the amplitude of the August iAVT activity peak.

Involvement of melatonin in the seasonal changes of the gonadal function and prolactin secretion in female goats.

Ovarian cyclicity in the goat continues under short days (8L: 16D), while it ceases for 150-200 days under long days (16L: 8D). During the anovulatory period under long days, prolactin secretion is enhanced. Experiments were conducted to investigate the role of the pineal gland in the photoperiodic control of the gonadal function and prolactin secretion in the goat. Firstly, the effects of the abolition of the diurnal change in melatonin secretion on the photoperiodic responses of the gonadal axis and prolactin secretion were examined. Female Saanen goats, reared under short days (8L:16D, 22 +/- 2 degrees C) for 5 months, were bilaterally superior cervical ganglionectomized (SCGX) to denervate their pineal gland. One month after surgery, both SCGX and intact control goats were divided into two groups. Animals in group 1 were maintained under short days and those in group 2 were transferred to long days (16L:8D). In group 1, both SCGX and intact goats ovulated periodically and basal plasma levels of prolactin were maintained throughout the day. In intact controls, exposure to long days blocked ovulation and increased prolactin secretion for the first 150-200 days of exposure. The animals became photorefractory after this time; ovulation recurred and prolactin secretion was suppressed. The continuous melatonin secretion appeared simultaneously with the photorefractoriness. Superior cervical ganglionectomy abolished or weakened the suppression of gonadal axis and eliminated the increase in prolactin secretion induced by the exposure to long days in intact animals. Secondly, the effect of melatonin replacement by timed melatonin infusion on prolactin secretion was examined in SCGX goats to establish that the effect of SCGX could be ascribed to the abolition of the diurnal change in melatonin. Ovariectomized SCGX Shiba goats (n = 5) were infused with melatonin (20 micrograms/h, s.c.) daily for 8 h (the long-day-type infusion) and for 16 h (the short-day-type infusion) to mimic the nocturnal profiles of plasma melatonin under long days and short days, respectively. The long-day-type melatonin infusion for 9 days accelerated prolactin secretion, inducing a nocturnal rise in plasma prolactin; this was comparable to that observed in intact controls under long days. On the other hand, by the short-day-type infusion, the plasma prolactin concentrations were maintained at a low level throughout the day as were observed in intact goats under short days. The prevailing photoperiod appeared to have no distinct effect on these prolactin responses to exogenous melatonin, which were indistinguishable under long and short days.(ABSTRACT TRUNCATED AT 400 WORDS)

Pinealectomy or Superior Cervical Ganglionectomy do not Alter Reproduction in the Wolf (Canis Lupus)

Twelve wolves (6 male and 6 female) were used to study the role of the pineal in photoperiodic mediation of seasonal reproduction. Eight wolves were pinealectomized (PNX) or sham-pinealectomized (S-PNX) at 5 mo of age, and 4 were superior cervical ganglionectomized (SCGX) at 16 mo of age (2 males and 2 females per treatment). All attained puberty at the species-typical time, during their second breeding season, except 2 SCGX males that did not survive. Reproductive cycles of an additional male that was SCGX as an adult and the PNX and S-PNX wolves, followed for a minimum of 3 yr, did not differ from each other or from those of unoperated colony wolves on measures of serum testosterone and luteinizing hormone for males, or of serum estradiol and progesterone for females. Nor was the range of dates for ovulation different for treated vs. untreated females. Surgical transection of the olfactory tracts of 1 male and 1 female PNX wolf, inducing anosmia to control for the possibility of pheromonally synchronized cycles, also failed to alter the seasonality of these reproductive parameters. These results do not conform to the model of pineal mediation of sexual cycles for photoperiod-sensitive species. In spite of evidence for photoperiod influence, the wolf apparently relies on a system other than the pineal for seasonal control of reproduction.

Norepinephrine or isoproterenol stimulation of pineal N-acetyltransferase activity and melatonin content in the Syrian hamster is restricted to the second half of the daily dark phase.

Seven experiments were performed to investigate the sensitivity of the hamster pineal gland to exogenously administered norepinephrine (NE). In these studies NE (1 mg/kg) administration was preceded (10 min earlier) by the injection of the catecholamine uptake inhibitor desmethylimipramine (DMI; 5 mg/kg). When DMI and NE were given at night, the hamsters were exposed to light to depress pineal N-acetyltransferase activity and melatonin values to low levels; the drugs were then given 20 (DMI) and 30 (NE) min later, and the subsequent changes in pineal N-acetyltransferase and melatonin were monitored. The combination of DMI and NE administration anytime during the normal light period or during the first 4 h of the normal dark period failed to stimulate either pineal N-acetyltransferase activity or melatonin levels. Conversely, DMI followed by NE (injected either intraperitoneally or subcutaneously) in the second half of the dark phase typically stimulated pineal melatonin production. Likewise, the NE agonist isoproterenol promoted pineal melatonin production only in the latter half of the dark phase. If hamsters were exposed to continual light at night or if they were superior cervical ganglionectomized, a procedure which sympathetically denervates the pineal gland, the stimulatory effect of NE on melatonin production was significantly suppressed. Thus, the hamster pineal gland is sensitive to NE only during the latter half of the normal dark period and both darkness and an intact sympathetic innervation to the pineal gland are required for the gland to develop maximal sensitivity to the catecholamine. Also, the hamster pineal seems not to exhibit a supersensitivity response to NE following a period of reduced exposure to the catecholamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Superior cervical ganglionectomy prevents gonadal regression and increased plasma prolactin concentrations induced by long days in goats.

The effects of the abolition of the diurnal change in melatonin secretion on the photoperiodic response of the gonadal axis and prolactin secretion to long days were examined in female goats. Female Saanen goats, reared under short-day conditions (8 h light: 16 h darkness; lights on at 05.00 h) at 22 +/- 2 degrees C for 5 months, were bilaterally superior cervical ganglionectomized (SCGX). One month after surgery, both SCGX and intact control goats were divided into two groups. Animals in group 1 were maintained under short days and those in group 2 moved to long days (16 h light: 8 h darkness; lights on at 05.00 h). In group 1, both SCGX and intact goats ovulated periodically and basal plasma prolactin levels were maintained throughout the day. In intact controls, exposure to long days suppressed ovulation and increased prolactin secretion for the first 150-200 days of exposure. The animals became photorefractory after this time; ovulation recurred and prolactin secretion returned to basal levels. Superior cervical ganglionectomy abolished or weakened the suppression of gonadal function and eliminated the increase in prolactin secretion induced by exposure to long days in the intact controls. These results suggest that the pattern of melatonin secretion under long days is necessary to induce the photoperiodic response of gonadal function and prolactin secretion to long days and that, under natural conditions, melatonin regulates the seasonal changes in gonadal function and prolactin secretion by mediating the effect of long days.

Ocular effects of a relatively selective alpha 2 agonist (UK-14, 304-18) in cats, rabbits and monkeys.

UK-14, 304-18 (UK), a relatively selective alpha 2-agonist, was examined for its effects on intraocular pressure (IOP) and pupil diameter (PD) in rabbits, cats and monkeys and on noradrenergic function in the cat nictitating membrane (CNM) preparation. Topical, unilateral administration of UK (0.0005-0.5 mg) produced dose-dependent decreases in IOP and pupil size in normal, unanesthetized rabbits, cats and monkeys. The ocular hypotensive effect of UK in the ipsilateral eye was delayed relative to the contralateral eye in all three species; UK produced an initial transient ocular hypertension in rabbits which was abolished by surgical transection of three major extraocular muscles. Mean arterial blood pressure in rabbits was not affected by 0.005 mg UK topically. The ocular hypotensive and miotic effects of UK were attenuated in superior cervical ganglionectomized (SX) cats and rabbits. Intra-arterially administered UK (0.33, 1.0, 3.3 and 10 micrograms) produced dose-related systemic hypotension and inhibition of contractions of the CNM elicited by electrically stimulating the pre- and postganglionic sympathetic trunks in the urethane/chloralose anesthetized cat. This inhibition was reversed and prevented by 300 micrograms rauwolscine but not by 300 micrograms domperidone. UK also enhanced the contractile response of the CNM to injected norepinephrine (10 micrograms). UK suppressed ocular hypertension induced by water loading and IOP recovery rate following hypertonic saline infusion in rabbits suggesting that aqueous flow was inhibited. These results indicate that UK lowers IOP, in part, by suppressing sympathetic neuronal function which causes a reduction in aqueous flow.

The ocular effects of xylazine in rabbits, cats, and monkeys.

Xylazine is an agent frequently used in combination with ketamine to anesthetize rabbits. Xylazine is also related pharmacologically to clonidine, a relatively selective alpha 2-agonist. In the present studies, xylazine was examined for its effects on intraocular pressure (IOP) and pupil diameter (PD) in rabbits, cats and monkeys and on noradrenergic function in the cat nictitating membrane (CNM) preparation. Topical and unilateral administration of xylazine (1.0 mg) lowered IOP bilaterally in normal, unanesthetized rabbits, cats and monkeys and caused unilateral miosis in rabbits and cats. These ocular effects of xylazine were attenuated in superior cervical ganglionectomized (SX) cats and rabbits. In addition, intra-arterially administered xylazine (10, 33 and 100 micrograms) produced dose-related inhibition of contractions of the CNM elicited by electrically stimulating the pre- and postganglionic sympathetic trunks without altering the response to i.a. norepinephrine (10 micrograms). These data suggest that ocular effects of xylazine are mediated, in part, by alteration of sympathetic neuron function. Xylazine suppressed ocular hypertension induced by water loading and IOP recovery rate following hypertonic saline infusion in rabbits suggesting that aqueous flow was inhibited. Topical pretreatment with 0.05 mg of timolol caused potentiation of the ocular hypotensive response to 0.05 mg of xylazine in rabbits. These results indicate that xylazine lowers IOP, in part, by suppressing sympathetic neuronal function which causes a reduction in aqueous flow. The augmented response to timolol and xylazine, as compared with either agent alone, suggests a rational basis for combining a prejunctionally active agent with a postjunctionally active one.

Endogenous opioids and the control of seasonal LH secretion in Soay rams.

Soay rams were treated with naloxone and/or morphine at different stages of their annual reproductive cycle to study the role of endogenous opioid peptides in the control of pulsatile LH secretion. The responses in intact rams were compared with those shown by pinealectomized (PNX) or superior cervical ganglionectomized (SCGX) rams which had a different annual testicular cycle. Naloxone (4-6 mg/kg i.v.) given to intact rams at four times of the year induced significant increases in LH pulse frequency in the breeding season in September and December, but minimal responses in the non-breeding season in June. Similar treatments given to PNX or SCGX rams induced good responses in March, June and September and the poorest response in December; the different seasonal pattern between the intact and PNX/SCGX rams was correlated with differences in the timing of their testicular cycles. Morphine (1 mg/kg i.v.) induced a significant decrease in LH pulse frequency when given to intact rams in October, but no significant effects were observed when morphine was given to sexually inactive rams in early July. Naloxone (1 mg/kg i.v.) given concurrently with morphine in October reversed the suppressive effect and resulted in an actual increase in LH pulse frequency above pretreatment levels. Morphine-treated rams showed normal LH responses to injections of LH-releasing hormone (LHRH) indicating that the site of opiate inhibition was on hypothalamic LHRH secretion rather than on pituitary LH release. Chronic treatment of intact and PNX rams with naloxone (1 mg/kg every 4 h for 7 days) in April and October produced the expected acute increase in LH pulse frequency in the intact rams in October, and at both times of year in the PNX rams, however there was no sustained increase in LH secretion in response to chronic naloxone in any of the treatment groups. The response to the second naloxone injection was much reduced and was absent after 3 days; responsiveness to naloxone was restored within 2 days of stopping the chronic treatment. The overall results indicate that endogenous opioid mechanism is involved in the tonic inhibition of LH secretion and that this mechanism is most active in the breeding season when both naloxone and morphine have marked effects on pulsatile release of LH. Regulation of endogenous opioids in the hypothalamus may be part of the mechanism by which environmental factors modulate steroid negative-feedback control of LHRH and thus LH secretion in seasonally breeding mammals.

Induction of early rutting in male red deer (Cervus elaphus) by melatonin and its dependence on LHRH.

Eight red deer stags, 2 control, 3 control-immunized (i.e. a low titre of LHRH antibodies after active immunization 2 years earlier) and 3 superior cervical ganglionectomized, were given a s.c. implant of melatonin in May at the nadir of the sexual cycle; 5 other stags remained untreated. All the melatonin-treated animals shed the velvet-like skin from the antlers in June or July at least 1 month before the untreated controls, and had an early increase in blood plasma testosterone concentrations. The treated stags were also precocious in the development of rutting behaviour, although this inductive effect was blocked dramatically in the control-immunized stags after a booster immunization against LHRH; these animals failed to show any further reproductive development and cast their antlers. It is concluded that continuous exposure to melatonin in early summer will induce premature seasonal testicular development, an effect dependent on the secretion of LHRH, and similar to that produced by exposure to short daylengths.

Distribution of substance P neurons in the epithalamus of the rat: an immunohistochemical investigation.

Substance P (SP) immunoreactivity was studied in the epithalamus of intact and superior cervical ganglionectomized female rats by using the peroxidase-antiperoxidase immunocytochemical technique. Cells containing immunoreactive SP were located in the medial habenula, and SP fibers were observed in the lateral habenula, habenular commissure, pineal stalk, and the pineal organ. Bilateral removal of the superior cervical ganglia did not affect the immunocytochemical staining of SP-containing cells and fibers 15-30 days later. It is suggested that habenular neurons containing SP send projections into the pineal organ of the rat.

Effect of superior cervical ganglionectomy on the ultrastructure of the pinealocyte in the cotton rat ( Sigmodon hispidus)

The ultrastructure of pinealocytes was examined morphometrically in superior cervical ganglionectomized and sham-operated cotton rats. Following denervation, the pinealocytes decreased in size. Reduced areas of the nucleoli, Golgi apparatus, granular endoplasmic reticulum, mitochondria, and vacuoles containing a flocculent material as well as a decreased number of dense-core vesicles were noted. In contrast, the numbers of “synaptic” ribbons and ribbon fields increased. The nature of ultrastructural changes observed in the cotton rat pinealocyte after sympathectomy may indicate a diminution of the presumptive secretory processes of this cell. The presence of a small number of myelinated and unmyelinated axons in the pineal gland of the cotton rat following superior cervical ganglionectomy suggests that the sympathetic nerve fibers from the superior cervical ganglia do not comprise the only source of innervation to the pineal. Additionally, the presence of striated muscle fibers has been observed in the present study in the pineal gland of the cotton rat which heretofore has not been reported in this species.

Amphetamine-induced increases in pineal gland N-acetyltransferase activity: Effects of denervation and/or adrenalectomy

1. 1. d-Amphetamine injections in intact rats increase activity of the pineal gland enzyme, N-acetyltransferase (NAT). 2. 2. The NAT elevation may be mediated in part by the ability of amphetamine to enhance the release, and block the reuptake, of norepinephrine from post-ganglionic sympathetic nerves onto pineal gland β-noradrenoceptors. 3. 3. However, catacholamines released from cells other than those directly innervating the pineal gland may also increase NAT activity following systemic amphetamine injections, inasmuch as the enzyme responses of superior cervical ganglionectomized, adrenalectomized, or combined ganglionectomized-adrenalectomized animals were greatly potentiated following the drug.

Studies on pineal melatonin levels in a diurnal species, the eastern chipmunk (Tamias striatus): effects of light at night, propranolol administration or superior cervical ganglionectomy.

Five experiments were carried out on the control of melatonin levels in the pineal gland of a diurnal species, the Eastern chipmunk (Tamias striatus). We confirmed that the exposure of chipmunks of fluorescent white light of 3,981-4,304 lux during the normal dark period does not prevent the rise in pineal melatonin levels normally associated with darkness. Also, the administration of propranolol (20 mg/kg) at 8 p.m. did not block the rise in pineal melatonin in animals exposed to either dark or light at night. Similarly, if chipmunks received propranolol 4 hours into the dark phase, pineal melatonin levels were not depressed 2 hours later. When animals were superior cervical ganglionectomized, however, the pineal content of melatonin remained low regardless of whether animals were exposed to darkness or light at night. The exposure of chipmunks acutely to light at midnight (4 hours after darkness onset) had only a slight depressive effect on pineal melatonin 30 min later; by comparison, when chipmunks were acutely exposed to light at 3 a.m. (7 hours after darkness onset) daytime pineal melatonin levels were reached within 15 min after light onset. These findings in a diurnal species, The Eastern chipmunk, differ markedly when compared to previously reported observations on nocturnal laboratory rodents.