Enhancement of rapid eye movement sleep in the rat by actions at A1 and A2a adenosine receptor subtypes with a differential sensitivity to atropine

The adenosine agonist cyclohexaladenosine injected into the medial pontine reticular formation of the rat induces a long-lasting increase in rapid eye movement sleep. To investigate the adenosine receptor-subtype(s) mediating this effect, the dose-response relationships for increasing rapid eye movement sleep by two highly selective adenosine receptor agonists were compared. Rats were surgically prepared for chronic sleep recording and bilateral guide cannulae were aimed at medial sites in the caudal, oral pontine reticular formation. Injections were made unilaterally in 60 nl volumes within 1 h after lights-on. The adenosine agonists used were A1-selective cyclohexaladenosine (10(-6)-10(-4) M) and A2a-selective CGS 21680 (10(-7)-10(-3) M). Each animal also received a series of three, paired-consecutive injections of the muscarinic receptor antagonist atropine (4x10(-3) M) followed by the lowest effective dose of each agonist or saline as control. The A2a receptor agonist, CGS 21680, was one order of magnitude more potent than the A1 receptor agonist, cyclohexaladenosine, in inducing rapid eye movement sleep increases. Preinjection of atropine at a dose that did not itself affect rapid eye movement sleep resulted in antagonism of CGS 21680, but not cyclohexaladenosine-induced rapid eye movement sleep. The differential sensitivity of these ligands to antagonism by atropine supports the conclusion that both A1 and A2a adenosine receptor subtypes in the reticular formation subserve agonist-induced rapid eye movement sleep and that they do so by independent mechanisms. The A2a mechanism requires the cholinergic system and may act through the increased release of acetylcholine. The A1 mechanism operates at a different locus possibly through an inhibition of GABA neurotransmission.

Food restriction-like effects of dietary dehydroepiandrosterone. Hypothalamic neurotransmitters and metabolites in male C57BL/6 and (C57BL/6 x DBA/2)F1 mice

Dehydroepiandrosterone (DHEA) is a precursor of sex hormones in mammals. Dietary DHEA serves to prevent or inhibit various diseases and also lengthens life spans of animals. Moreover, dietary DHEA inhibits food intake in certain strains of mice. We administered DHEA (0.45% w/w of food) to C57BL/6 (B6) and (B6 x DBA/2)F1 (BDF1) mice for 5 weeks. Food intake was inhibited in both strains of mice during the first week. Thereafter, B6, but not BDF1, mice consumed less food. Because hypothalamic serotonin and/or dopamine regulate appetite, satiety and other behaviors, the hypothesis tested was that hypothalamic concentration of serotonin, dopamine and/or their metabolites are affected differentially in B6 and BDF1 mice fed DHEA. In another study, mice were fed the AIN-76A diet with or without DHEA for 1 and 7 days or were pair-fed to DHEA-fed mice for 7 days. On Day 1 of DHEA feeding (acute effects) hypothalamic levels of serotonin, dopamine, and metabolites were unchanged in B6 mice, but levels of dopamine were increased and levels of dopamine metabolites were decreased in BDF1 mice. On Day 7 of DHEA feeding, levels of serotonin were increased in BDF1 but not B6 mice. On Day 7 of pair-feeding there were decreased levels of hypothalamic dopamine metabolites in BDF1 but not B6 mice. Paraventricular nuclei of BDF1 mice had decreased levels of serotonin but not of dopamine in all groups. Serum levels of DHEA and its metabolite, 5-androstene-3beta,17beta-diol, correlated significantly only with serotonin concentrations in BDF1 mice. The salient findings of these experiments are that DHEA inhibits food intake to a greater extent in B6 than in BDF1 mice. However, alterations of hypothalamic neurotransmitters were greater in BDF1 than in B6 mice. Because BDF1 and B6 mice share B6 genes, relevant gene(s) derived from DBA/2 mice might mediate the different responses detected.

Ponto-geniculo-occipital-wave suppression amplifies lateral geniculate nucleus cell-size changes in monocularly deprived kittens

We have previously shown that during the post-natal critical period of development of the cat visual system, 1 week of instrumental rapid eye movement (REM) sleep deprivation (IRSD) during 2 weeks of monocular deprivation (MD) results in significant amplification of the effects of solely the 2-week MD on cell-size in the binocular segment of the lateral geniculate nucleus (LGN) [36,40]. In this study, we examined whether elimination of ponto-geniculo-occipital (PGO)-wave phasic activity in the LGN during REM sleep (REMS), rather than suppression of all REMS state-related activity, would similarly yield enhanced plasticity effects on cell-size in LGN. PGO-activity was eliminated in LGN by bilateral pontomesencephalic lesions [8,32]. This method of removing phasic activation at the level of the LGN preserved sleep and wake proportions as well as the tonic activities (low voltage, fast frequency ECoG and low amplitude EMG) that characterize REM sleep. The lesions were performed in kittens on post-natal day 42, at the end of the first week of the 2-week period of MD, the same age when IRSD was started in the earlier study. LGN interlaminar cell-size disparity increased in the PGO-wave-suppressed animals as it had in behaviorally REM sleep-deprived animals. Smaller A1/A-interlaminar ratios reflect the increased disparity effect in both the REM sleep- and PGO-suppressed groups compared to animals subjected to MD-alone. With IRSD, the effect was achieved because the occluded eye-related, LGN A1-lamina cells tended to be smaller relative to their size after MD-alone, whereas after PGO-suppressing lesions, the A1-lamina cells retained their size and the non-occluded eye-related, A-lamina cells tended to be larger than after MD-alone. Despite this difference, for which several possible explanations are offered, these A1/A-interlaminar ratio data indicate that in conjunction either with suppression of the whole of the REMS state or selective removal of REM sleep phasic activity at the LGN, altered visual input evokes more LGN cell plasticity during the developmental period than it would otherwise. These data further support involvement of the REM sleep state in reducing susceptibility to plasticity changes and undesirable variability in the course of normative CNS growth and maturation.

REM sleep deprivation in monocularly occluded kittens reduces the size of cells in LGN monocular segment

STUDY OBJECTIVES

In this study, we test the hypothesis that when REM-state activation (which impinges upon all lateral geniculate nucleus laminae irrespective of stimulating eye) is deprived, the monocular segment (MS) that is cut off from visual input and also deprived of REM-state activation will exhibit smaller cells, owing to the loss of extrinsic as well as intrinsic activation.

DESIGN

We carried out a study comparing soma sizes in the MSs of kittens subjected to monocular deprivation (MD) + REM deprivation (RD) to two age-matched nonRD groups, MD ONLYs and MD MOMS (MD kittens living in their home cages).

MEASUREMENTS AND RESULTS

Perikaryal outlines of 100 cells in each of the bilateral MSs were measured. As predicted, mean cell size in the MS connected to the patched eye of MD + RD kittens, but in neither of the control groups, was significantly smaller than in the MS afferented by the nonpatched eye. One-way ANOVAs comparing MS cell-size means from the same sides across groups were also significant, but the two MSs showed different results on post hoc tests. The ordering of MS cell-size means correlated significantly with a measure that aggregates the sources of activation reaching a particular MS and their durations.

CONCLUSIONS

These results reveal that removal of REM-state activation during CNS development amplifies the plasticity processes generated when normal visual afferentation to central visual areas is interrupted. Our findings in the MS of the LGN indicate that during the usual operation of REM sleep, central visual-sensory sites receive intrinsic activation that, in the visual system, is additive and complementary to the stimulation obtained from extrinsic sources. In the course of early development, normative symmetrical activation of central visual areas during REM sleep may counterbalance plasticity changes caused either by absent or aberrant sensory stimulation.

The neurotoxin 1-methyl-4-phenylpyridinium is sequestered within neurons that contain the vesicular monoamine transporter

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine produces a parkinsonian syndrome in man and experimental animals. The toxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, 1-methyl-4-phenylpyridinium, exhibits high-affinity uptake by plasma membrane monoamine transporters and also by the vesicular monoamine transporter. Using autoradiographic and immunohistochemical methods in mice, we demonstrate the accumulation of [3H]1-methyl-4-phenylpyridinium within neurons that contain the vesicular monoamine transporter, following systemic administration of [3H]1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Within 1-24 h following the intraperitoneal administration of 10 microg/kg of [3H]1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, [3H]1-methyl-4-phenylpyridine labelling was found within such regions as the locus coeruleus, dorsal, medial, and pallidal raphe nuclei, substantia nigra pars compacta, ventral tegmental area, and paraventricular nucleus of the hypothalamus. These regions all contain monoaminergic somata as defined by immunohistochemical staining with an antibody against the vesicular monoamine transporter. There was a positive relationship between the density of [3H]1-methyl-4-phenylpyridinium label and the density of vesicular monoamine transporter immunoreactivity: the highest densities of both were found in the locus coeruleus and lowest densities in the midbrain dopaminergic neurons. In addition, [3H]1-methyl-4-phenylpyridinium labelling was detected in the bed nucleus of the stria terminalis and paraventricular nucleus of the thalamus, which also contained vesicular monoamine transporter immunoreactive nerve terminals. The present data indicate that low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine cause a significant accumulation of 1-methyl-4-phenylpyridinium within monoaminergic somata in parallel with the amount of vesicular monoamine transporter in the neuron. Since nuclei with intense labelling are not damaged by doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine that are toxic to midbrain dopaminergic neurons, these data are consistent with the hypothesis that sequestration of 1-methyl-4-phenylpyridinium within monoaminergic synaptic vesicles can protect the neurons from degeneration caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.

The neurotoxin MPTP causes degeneration of specific nucleus A8, A9 and A10 dopaminergic neurons in the mouse

The neurotoxin MPTP has been used to create an animal model of Parkinson's disease in the mouse, in part, because it causes a significant loss of dopaminergic neurons in the substantia nigra (nucleus A9). The purpose of the present study was to determine whether MPTP also causes degeneration of midbrain dopaminergic neurons in nuclei A8 and A10 in the mouse, as occurs in humans with Parkinson's disease. Two commonly used strains of mice were used: FVB/N and C57BL/6. MPTP was administered in cumulative doses of 50-300 mg/kg. Seven days later, dopamine concentrations were measured in the striatum using high performance liquid chromatography, and midbrain dopaminergic neurons were identified using an antibody against tyrosine hydroxylase. The cell locations were mapped with a computer imaging system. In the FVB/N strain, there was a dose-dependent decrease in striatal dopamine concentrations. Although the highest dose (300 mg/kg) caused an 86% reduction in striatal dopamine concentrations, there was only a moderate and non-significant loss of midbrain dopaminergic neurons. In the C57BL/6 strain, however, a high dose of MPTP (240 mg/kg) caused a significant reduction in both striatal dopamine concentrations (95%), and midbrain dopaminergic cells; 69% loss of nucleus A8 cells, 75% loss of nucleus A9 cells, and in nucleus A10 subnuclei there was 42% loss of ventral tegmental area cells, 55% loss of interfascicular nucleus cells, and no loss of cells in the central linear nucleus. These data (1) provide further evidence for differential susceptibility to MPTP toxicity among different mouse strains, (2) indicate that a significant depletion of striatal dopamine is not necessarily due to degeneration of midbrain dopaminergic neurons, (3) provide the precise locations of midbrain dopaminergic cells that are vulnerable to MPTP, which will aid future studies that seek to determine the mechanism/s by which-MPTP selectively destroys only certain midbrain dopaminergic neurons, and (4) indicate that MPTP produces midbrain dopaminergic neuronal degeneration in the same nuclei in the C57BL16 mouse that degenerate in humans with Parkinson's disease.

Rapid eye movement sleep deprivation in kittens amplifies LGN cell-size disparity induced by monocular deprivation

The abundance of rapid eye movement (REM) sleep in the neonatal mammal and its subsequent decline in the course of development, as well as the dramatic and widespread enhancement of CNS activity during REM sleep, led us to propose that this state plays a functional role in the normative physiological and structural maturation of the brain [54]. When, after 1 week of monocular deprivation (MD), a second week of MD was coupled with behavioral deprivation of REM sleep, the structural alteration in the visual system provoked by MD alone (interlaminar relay cell-size disparity in the lateral geniculate nucleus (LGN) was amplified. With the addition of REM deprivation during MD, the LGN cells connected to the surgically patched eye, which are smaller than normal after MD, became even smaller, whereas the LGN cells receiving input from the seeing eye, which display compensatory hypertrophy after MD, grew even larger. We believe that the interlaminar disparity effect widened because during REM deprivation, the already vision-compromised LGN cells associated with the patched eye also lose the ascending brainstem activation reaching them during the REM state. Loss of the two main sources of 'afference' by these LGN cells permits their seeing-eye LGN counterparts to gain even greater advantage in the competition for synaptic connections in cortex, which is reflected in the relative soma sizes of the LGN relay cells. It is likely that the relatively abundant REM state in early maturation provides symmetric stimulation to all LGN relay cells, irrespective of eye of innervation. The symmetric activation propagated from brainstem to LGN acts to 'buffer' abnormal, asymmetric visual input and, thereby diminishes the extreme, asymmetric structural alteration that results from MD in the absence of REM sleep. We conclude that REM sleep-generated CNS discharge in development has the effect of 'protecting' the CNS against excessive plasticity changes. This is consistent with the possibility that REM sleep plays a role in the genetically programmed processes that direct normative brain development.

The neurotoxin MPTP increases calbindin-D28k levels in mouse midbrain dopaminergic neurons

The calcium-binding protein calbindin-D28k (CALB) has been localized in high concentrations in several neuronal populations within the central nervous system (CNS) and is believed to act as an intracellular calcium (Ca2+) buffer. There has been much interest and speculation concerning its potential neuroprotective function. However, there is little direct evidence linking CALB content of individual neurons to Ca2+ buffering ability, resistance to Ca(2+)-mediated excitotoxicity, or vulnerability to Ca(2+)-mediated degeneration. It is necessary to demonstrate these relationships on a cellular level so that more definitive conclusions can be made. We have utilized immunocytochemical and Western blot techniques to determine whether cellular CALB content is altered in the nucleus A10 dopaminergic region of the midbrain following administration of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Our data demonstrate a significant increase in the CALB content of nucleus A10 neurons (up to 227 +/- 23% above control) 3 and 6 h after MPTP treatment. CALB elevation demonstrated both time and dosage dependence as 6-h groups exhibited larger increases than 3-h groups, and a 60 mg/kg dosage induced a larger increase than a 20 mg/kg dosage. These data support the hypothesis that MPTP is neurotoxic by causing increases in free intracellular Ca2+ and that increased CALB in the midbrain dopaminergic neurons is a protective response to elevated intracellular free Ca2+.

A functional role for REM sleep in brain maturation

The biological function of REM sleep is defined in terms of the functions of neural processes that selectively operate during the REM sleep state. The high amounts of REM sleep expressed by the young during a period of central nervous system plasticity suggest that one function of REM sleep is in development. The phenomenon of activity-dependent development has been clearly shown to be one mechanism by which early sensory experience can affect the course of neural development. Activity-dependent development may be a ubiquitous process in brain maturation by which activity in one brain region can influence the developmental course of other regions. We hypothesize an ontogenetic function of REM sleep; namely, the widespread control of neuronal activity exerted by specific REM sleep processes help to direct brain maturation through activity-dependent developmental mechanisms. Preliminary tests of the hypothesis have been conducted in the developing feline visual system, which has long been known to incorporate information derived from visual experience in establishing neuronal connectivity. We find that suppression of REM sleep processes by an instrumental REM deprivation procedure results in a significant enhancement of the effects of altered visual experience by monocular occlusion. Bilateral brainstem lesions that selectively block the occurrence of ponto-geniculo-occipital (PGO) waves are sufficient to produce similar results. These data indicate that the propagation of phasic influences during REM sleep interacts with other processes subserving neural development. This source of influence appears not to derive from the environment but rather stems from an intrinsic source of genetic origin. Examination of the neural activity associated with PGO waves in the lateral geniculate nucleus reveals a distribution of facilitatory influence markedly different from that induced by visual experience. We conclude that REM sleep directs the course of brain maturation in early life through the control of neural activity.

Opioid receptors in midbrain dopaminergic regions of the rat. I. Mu receptor autoradiography

Several lines of evidence indicate that an interaction exists between opioid peptides and midbrain dopaminergic neurons. The purpose of this study was to map and quantify the density of the mu opioid receptor subtype relative to the location of the dopaminergic (DA) neurons in the retrorubral field (nucleus A8), substantia nigra (nucleus A9), and ventral tegmental area and related nuclei (nucleus A10) in the rat. Sections through the rostral-caudal extent of the midbrain were stained with an antibody against tyrosine hydroxylase, as a DA cell marker, and comparable sections were processed for in vitro receptor autoradiography using the mu-selective ligand, 3H-Tyr-D-Ala-N-MePhe-Gyl-ol enkephalin. In the nucleus A8 region, there were low levels of mu binding. In the rostral portion of nucleus A9, there was prominent mu binding both in the ventral pars compacta, which contains numerous DA neurons, and in regions that correspond to the location of the DA dendrites which project ventrally into the underlying substantia nigra pars reticulata. In the caudal portion of nucleus A9, mu binding was greatest in the substantia nigra pars reticulata, but also in the same region that contains DA neurons. In nucleus A10, mu receptor densities differed depending upon the nucleus A10 subdivision, and the rostral-caudal position in the nucleus. Low receptor densities were observed in rostral portions of the ventral tegmental area and interfascicular nucleus, and there was negligible binding in the parabrachial pigmented nucleus and paranigral nucleus at the level of the interpeduncular nucleus; all regions where there are high densities of DA somata. Mu binding was relatively high in the central linear nucleus, and in the dorsal and medial divisions of the medial terminal nucleus of the accessory optic system, which has been shown to contain DA dendrites. These data indicate that mu opioid receptors are located in certain regions occupied by all three midbrain DA nuclei, but in a highly heterogeneous fashion.

Opioid receptors in midbrain dopaminergic regions of the rat. II. Kappa and delta receptor autoradiography

Opiates and opioid peptides are known to influence the dopaminergic (DA) neurons in the midbrain. The purpose of this study was to map and quantify the density of kappa and delta opioid receptor subtypes in the retrorubral field, substantia nigra, and ventral tegmental area and related nuclei, which contain DA nuclei A8, A9, and A10, respectively. Sections through the rostral-caudal extent of the rat midbrain were stained with an antibody against tyrosine hydroxylase, as a DA cell marker, and comparable sections were processed for in vitro receptor autoradiography using the kappa-selective ligand, U-69593, and the delta-selective ligand, D-Pen2, D-Pen5-enkephalin. In general, both kappa and delta ligands exhibited low levels of specific binding in regions occupied by the midbrain DA neurons. Kappa binding (4-8 fmol/mg tissue) was high throughout the rostral-caudal extent of the substantia nigra, in rostral portions of the ventral tegmental area, and in the nucleus paranigralis; low binding occurred in the retrorubral field and central linear nucleus raphe. Delta binding (6-18 fmol/mg tissue) was high in the caudal portion of the substantia nigra pars reticulata, and in the medial terminal nucleus of the accessory optic system (a region previously shown to contain DA dendrites). The kappa and delta receptor binding is heterogeneously distributed in regions occupied by midbrain dopaminergic neurons, and several fold lower than the binding of mu opioid receptors in the same brain regions.

Increased midbrain dopaminergic cell activity following 2'CH3-MPTP-induced dopaminergic cell loss: an in vitro electrophysiological study

Several days after the administration of 1-methyl-4-(2'-methylphenyl)-1,2,3,6-tetrahydropyridine (2'CH3-MPTP) to the BALB/cJ mouse there is a loss of midbrain dopaminergic neurons, a reduction of forebrain dopamine (DA) content, and an elevation in forebrain DA turnover. The purpose of the present study was to determine whether the increase in forebrain DA turnover is related to an increase in dopaminergic neuronal activity. In vitro extracellular single unit recordings were made from midbrain dopaminergic neurons in the substantia nigra pars compacta (nucleus A9) and ventral tegmental area (nucleus A10) of BALB/cJ mice. The experimental animals were treated intraperitoneally with 40, 50 or 55 mg/kg 2'CH3-MPTP and killed 7-15 days later. Forebrain DA concentrations were decreased below control values by the two higher toxin doses in the caudate-putamen (67% and 78%, respectively), but not in the nucleus accumbens. DA turnover increased more than 2-fold in the caudate-putamen, but was unchanged in the nucleus accumbens. Nucleus A9 cells, in the 2'CH3-MPTP-treated animals, exhibited a 3-fold increase in the number of spontaneously active cells, and an 84% increase in basal firing rates. There was also a positive correlation between the A9 cell firing rates, and the DA turnover in the striatum of the toxin-treated mice. Nucleus A10 cells, in the 2'CH3-MPTP-treated animals, exhibited neither changes in number of spontaneously active cells nor changes in firing rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Sleep state-specific neuronal activity in rat dorsal lateral geniculate nucleus is not altered by local serotonin and norepinephrine depletion

The relay cells in dorsal lateral geniculate nucleus (dLGN) represent one among many populations of neurons throughout the neuraxis that display systematic alteration of spontaneous rate and pattern of discharge concurrent with change in state of arousal. Both noradrenergic (NE) and serotonergic (5-HT) systems innervate dLGN and are implicated in sleep-wake control mechanisms. Our study was designed to test the influence of these systems upon sleep state-related multiple unit activity in the dLGN. Two monoamine neurotoxins, 5,7-dihydroxytryptamine and 6-hydroxydopamine, were injected locally into dLGN to destroy NE and 5HT afferents individually and in combination. In three separate treatment groups, mean monoamine concentrations in dLGN were reduced in relation to the contralateral, vehicle-injected, control dLGN to: 1) NE-17%, 5HT-14%; 2) NE-46%, 5HT-28%, and 3) NE-6%, 5HT-77%. In no case was chronic sleep state-related cell activity in dLGN significantly altered. We conclude that afferent monoaminergic inputs are not critically related to the mechanisms underlying normative shifts in sleep state-related neuronal activity in dLGN.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonian syndrome in Macaca fascicularis: which midbrain dopaminergic neurons are lost?

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) produces, in both human and non-human primates, a syndrome very similar to idiopathic Parkinson's disease. The syndrome is associated with degeneration of the dopamine-containing neurons in the substantia nigra, many of which project to the neostriatum. The purpose of the present study was to quantify the regional distribution of midbrain dopamine neurons remaining after MPTP administration to the monkey (Macaca fascicularis) and to develop alternative procedures for maintaining the normal nutrition in MPTP-treated animals. Three monkeys were treated with MPTP and three served as controls. Representative sections were examined from rostral to caudal through the midbrain dopamine cell nuclei and the location of every tyrosine hydroxylase-containing cell was entered into a computer. Midbrain dopamine neuronal cell loss ranged from 36-78%, being most extensive in the two monkeys which exhibited the most severe parkinsonian syndrome. The greatest cell loss (46-93%) occurred in the substantia nigra pars compacta, or nucleus A9, and the loss was primarily in the ventral portion of the nucleus. Contrary to most previous reports, however, there was also a loss of cells in the ventral tegmental area (28-57%) and ventral reticular formation (33-87%), corresponding to nuclei A10 and A8, respectively. Since neuroanatomical tracing studies have shown that the dorsal and lateral portions of the striatum (areas showing the greatest dopamine depletion after MPTP) receive input from cells in the ventral A9 and from cells in the A8 and A10 areas, the present data suggest that MPTP preferentially destroys dopamine cells that project to the striatum (i.e. the mesostriatal cells).

A method for concurrent local intracranial drug infusion and electrophysiological recording

A method employing a cannula-guidetube system with attached electrodes is described that permits infusions into discrete brain areas and simultaneous recording of multiunits or single units. This method can be used to determine the immediate local effects of drug infusion, and also to acquire electrophysiological feedback information in the process of placement and identification of cell populations at the injection site.

Serotonergic inhibition of the dorsal lateral geniculate nucleus

Electrophysiological studies were conducted on chloral hydrate-anesthetized rats to determine if the dorsal raphe nucleus (DR) exerts an inhibitory influence upon the dorsal lateral geniculate nucleus (dLGN), and if this inhibition is mediated by the release of serotonin (5-HT). Conditioning stimuli presented to the DR 100-400 ms before an optic tract (OT) shock significantly lowered the amplitude of OT shock-elicited, postsynaptic, field potentials of less than 3 ms latency. Rare, long-latency, field potentials (greater than 5 ms) were diminished in amplitude when preconditioning intervals were less than 15 ms. Six days after intracerebral injection of the 5-HT neurotoxin, 5,7-dihydroxytryptamine (8 micrograms), into the dLGN, significant reductions were observed in 5-HT and 5-hydroxyindole acetic acid in the dLGN. Field potentials recorded on the sixth day in indoleamine-depleted dLGN were significantly less inhibited by DR preconditioning. Intracerebral injections of a control solution neither altered monoamine levels nor the degree of inhibition by DR preconditioning. These data provide further evidence that inhibition of dLGN by DR is mediated by release of 5-HT.

The laminar distribution of glutamate decarboxylase and choline acetyltransferase in the adult and developing visual cortex of the rat

The activities of choline acetyltransferase and glutamate decarboxylase were measured in individual layers of the adult and developing rat visual cortex. In the adult, the level of choline acetyltransferase activity was highest in layer V followed by layers I, II & III, IV and VI. These measurements are in complete agreement with recent immunohistochemical observations in the same cortical area. Glutamate decarboxylase activity was highest in layer IV and declined significantly in the more superficial and deeper layers. The activities of both enzymes were low during the first postnatal week but increased dramatically between days 8 and 18. Choline acetyltransferase activity in all layers demonstrated a more gradual rise to adult levels from day 18 onward, while glutamate decarboxylase activity reached adult levels by day 24 in all layers, except layer IV, which showed a continuous increase to adulthood. The functional role of the differences in the laminar distribution of these enzymes remains unknown.

Met-enkephalin levels in midbrain dopamine regions of inbred mouse strains which differ in the number of dopamine neurons

The Met-enkephalin content in tissue micropunches of the substantia nigra zona compacta, ventral tegmental area and the caudate nucleus in BALB/c and CBA mouse strains was measured by radioimmunoassay. The CBA strain had significantly higher Met-enkephalin levels in all 3 regions than the BALB/c strain. These differences should be taken into account when relating the intensity of dopamine-induced behaviors to the number of dopamine neurons.

Activation of specific central dopamine pathways: locomotion and footshock

The present study examined whether neostriatal monoamine biochemistry was activated in a bilaterally symmetrical fashion during a non-lateralized forward locomotor task, and whether specific midbrain dopamine (DA) neuronal systems were influenced selectively by specific behavioral tasks. Monoamine concentrations (DA, serotonin and their metabolites) were measured, using high pressure liquid chromatography, in the neostriatum, nucleus accumbens, and medial prefrontal cortex in rats that were either induced to walk forward in a motorized rotating wheel (two speeds) or were exposed to footshock stress (two shock intensities). Our results demonstrate that during locomotor behavior there is an increase in neostriatal DA metabolism, but not in serotonin metabolism. Furthermore, the increase in DA metabolism was found: (a) in both right and left neostriatal nuclei, but with significantly less asymmetry than occurred in non-locomoting control rats; and (b) within the neostriatum at both speeds and also in the nucleus accumbens at the higher speed. Locomotion had no effect on DA metabolism in the prefrontal cortex. With both shock intensities there was increased DA metabolism in the prefrontal cortex, whereas during the low shock intensity there was also an increased DA metabolism in the nucleus accumbens. At the high level of footshock, which evoked jumping and running escape behavior, there was also an increase in neostriatal DA metabolism. These data indicate that a non-lateralized forward locomotor task activates DA metabolism primarily in the less metabolically active hemisphere. Secondly, we found that specific subgroups of midbrain DA neurons can be selectively activated by specific behavioral tasks.

Characterization of human pulmonary endocrine cells maintained in vitro

Endocrine cells located in the epithelium of human fetal airways contain the amine, 5-hydroxytryptamine (5HT), and the peptide, bombesin (BOM), but difficulties in studying these cells experimentally have slowed progress in understanding their functional roles. This investigation describes an in vitro method to maintain pulmonary neuroendocrine cells (PNEC) in organ culture. Bronchial trees from human fetal lungs were dissected free of adherent blood vessels and lung tissue. Explants of the airways were placed in culture dishes containing defined tissue culture medium for five days. Using indirect immunofluorescence, 5HT- and BOM-like immunoreactive cells were observed both in nonincubated airways and in explants maintained for five days in organ culture. The number of 5HT-immunoreactive cells/0.1 mm2 of airway epithelium was not significantly different in the two groups, although there was a significant reduction in 5HT content measured by HPLC after the five-day culture period. The diameter of dense core vesicles and the number of dense core vesicles/micron2 of endocrine cell cytoplasm in cultures were not significantly different from non-incubated controls. Treatment of the explants with the 5HT-synthesis inhibitor p-chlorophenylalanine resulted in a significant reduction both in the number of 5HT-containing cells/0.1 mm2 of airway epithelium and in the 5HT content. These results demonstrate that both 5HT and BOM content in endocrine cells of explants from human fetal airways can be well maintained in organ culture for at least 5 days and that they are responsive to pharmacologic inhibition of 5HT synthesis.

The monoaminergic innervation of the rat visual cortex

The intracortical distribution of monoamines, noradrenaline (NA) and serotonin (5-HT), was examined in the visual cortex of the rat with high pressure liquid chromatography (h.p.l.c.) and radioautography. H.p.l.c. measurements showed the densities of both amines to be highest in layer I. The concentration of NA varied considerably in all other layers while the 5-HT concentration decreased with increasing distance from the pial surface. The morphological characteristics of the monoaminergic axon-terminals in the cerebral cortex has been the subject of controversy in recent years. We have used radioautography following topical or intraventricular administration of tritiated amines to examine the ultrastructural features of these terminals in the visual cortex of the rat. Systematic analysis of single sections revealed that more than one-half of the terminals labelled with tritiated NA or 5-HT formed typical synaptic contacts (mostly type I) with dendritic shafts or spines.

Effects of zoxazolamine and related centrally acting muscle relaxants on nigrostriatal dopaminergic neurons

The effects of zoxazolamine (ZOX) and related centrally acting muscle relaxants on striatal dopamine (DA) metabolism and turnover, and substantia nigra zona compacta DA neuronal impulse flow were studied in rats. ZOX, chlorzoxazone and mephenesin, but not meprobamate, chloral hydrate, diazepam, pentobarbital, ethanol or dantrolene, decreased striatal DA metabolism without affecting striatal DA concentrations. More specifically, ZOX, as a representative muscle relaxant, was shown to decrease striatal DA turnover without directly affecting DA synthesis, catabolism, reuptake, or release. ZOX decreased nigral DA neuronal firing rates and dramatically decreased firing rate variability (normally many of the cells fire with bursting firing patterns but after ZOX the cells often fired with a very regular pacemaker-like firing pattern). ZOX and related centrally acting muscle relaxants appear to decrease striatal DA turnover by decreasing both neuronal firing rate and firing rate variability. The possible relationships between DA neuronal activity and muscle tone are discussed.

Naloxone antagonism of stress-induced augmentation of frontal cortex dopamine metabolism

Foot shock stress selectively elevates dopamine metabolism in the medial frontal cortex but not nucleus accumbens or caudate nucleus. Pretreatment with a low dose of naloxone, an opiate antagonist, reversed the elevation in medial frontal cortex dopamine metabolism observed after foot shock. These data support the hypothesis that the stress-induced release of endogenous opioids cause an excitation of mesocortical dopamine neurons.

Dopamine in plasma of lateral and medial hypophysial portal vessels: evidence for regional variation in the release of hypothalamic dopamine into hypophysial portal blood

The plasma concentrations of dopamine in blood from hypophysial portal vessels in various locations on the pituitary stalk were evaluated in diestrous rats. It was found that the mean concentration of dopamine in blood from lateral hypophysial portal vessels, which contain the venous effluent of the lateral median eminence, was significantly less (P less than 0.005) than that in blood from medial portal vessels, which contain the venous effluent of the medial median eminence [1.59 +/- (SE) 0.23 ng/ml vs. 3.12 +/- 0.48 ng/ml]. The mean plasma concentration of dopamine in blood of lateral portal vessels and of medial portal vessels was at least 20-40 times greater than that in arterial blood of these animals. It was calculated that the rate of release of hypothalamic dopamine was 174 +/- 38 pg/h into a medial portal vessel and 73 +/- 15 pg/h into a lateral portal vessel. The mean plasma concentration of norepinephrine or epinephrine in blood from a medial portal vessel was not different from that from a lateral portal vessel. To address the issue of whether the rate of release of dopamine into a medial portal vessel and into a lateral portal vessel was correlated with the rate of synthesis of dopamine in discrete regions of the median eminence, the concentration of L-dihydroxyphenylalanine (DOPA), the precursor of dopamine, was evaluated in lateral and medial segments of the median eminence of diestrous rats treated with 3-hydroxybenzylhydrazine, an inhibitor of DOPA decarboxylase activity. The concentration of DOPA was similar in the medial and lateral segments of the median eminence, suggesting that the rate of synthesis of dopamine did not account for the difference in the rate of release of dopamine into portal blood. The finding of different concentrations of dopamine in blood from various hypophysial portal vessels may be important in view of the heterogenous perfusion of the pars distalis with hypophysial portal blood. We suggest that topographic differences may exist in the release of PRL by cells of the pituitary gland as a consequence of uneven concentrations of dopamine in portal blood perfusing the lactotropes.

The development of glutamic acid decarboxylase in the visual cortex and the dorsal lateral geniculate nucleus of the rat

The activity of the enzyme glutamic acid decarboxylase was measured in the visual cortex and the dorsal lateral geniculate nucleus of the rat at several postnatal ages. The results suggest that the developmental pattern of glutamic acid decarboxylase is reflected in the morphology of the neurons which presumably contain the enzyme.

Discrete regional analysis of norepinephrine, dopamine, choline acetyltransferase and glutamic acid decarboxylase in the brain of the newborn and pubescent monkey

A method is described for the removal of discrete areas of the monkey brain. A detailed mapping of norepinephrine, dopamine, choline acetyltransferase and glutamic acid decarboxylase in the newborn and pubescent monkey brain is presented.

Differential sensitivity of hypothalamic dopaminergic and noradrenergic neurones to pharmacological manipulation

The effects of apomorphine (Apo), haloperidol (Hal), reserpine, phenyoxybenzamine, oxotremorine and scopolamine on hypothalamic caatecholamines and metabolites were assessed. All these drugs, except Apo, significantly changed the hypothalamic concentration of 3-methoxy-4-hydroxyphenylglycol (MHPG), thus suggesting parallel changes in noradrenaline (NA) metabolism and turnover. Hal increased MHPG, an effect which was reversed by Apo pretreatment. Oxotremorine and scopolamine respectively increased and decreased MHPG, reserpine decreased NA and increased MHPG. Phenoxybenzamine increased MHPG without altering NA concentrations. Dopamine and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were not changed by Apo and Hal, but were influenced by the other drugs. These results indicate that NA in the hypothalamus is influenced by both cholinergic and dopaminergic events occurring in the brain and that dopaminergic neurones in this organ are different in their biochemical and pharmacological characteristics from neurones present in other central and peripheral systems.

Substance P afferents from the habenula innervate the dorsal raphe nucleus

The lateral habenula nuclei of the diencephalon innervate the median and dorsal raphe nuclei of the brainstem. Habenula lesions lead to decreased substance P levels in the dorsal but not median raphe within 24 hours. From this data, we propose a peptidergic innervation of the dorsal raphe nucleus by the habenula nuclei.

A longitudinal study of bioelectric activity in the pre- and post-hatch chick

A technique for embryonic implantation and the subsequent recording of electrocortical, neck muscle, and ocular activity continously from the 20th day of incubation through hatching and the first few days thereafter is demonstrated. The embryonic maturation of the EEG, with a characteristic muscle burst pattern heralding hatching was found, supporting previous reports obtained with acute preparations. The technique for injection into the chorioallantoic membrane (CAM) vessels or direct deposition onto the CAM is also described. The usefulness of the embryonic neurophysiological implantation coupled with the injection at specific stages of development is discusses as an approach to the understanding of the parameters of the maturation of the sleep-wakefulness cycle, neurochemistry, and behavior.

Gamma-butyrolactone sleep: A 24-hour rhythm paralleling normal sleep in the rat and CNS amine changes

The duration of sleep induced by a fixed dose of gamma-butyrolactone (GBL) (350 mg/kg, IP) FOllows the normal circadian sleep pattern of rats. GBL sleep duration is maximal at 1800 hr and minimal at 0600 hr. CNS amine changes are not extensive, but when normal sleep is anticipated, GBL treatment increases dopamine and serotonin levels and decreases norepinephrine levels.