Specificity of 6-hydroxydopamine induced degeneration of central monoamine neurones: an electron and fluorescence microscopic study with special reference to intracerebral injection on the nigro-striatal dopamine system

Electrical stimulation of mesencephalic cell groups (A9-A10) produces monosynaptic excitatory potentials in rat frontal cortex

Electrical stimulation of the ventral tegmental area and substantia nigra produces monosynaptic and polysynaptic excitatory postsynaptic potentials in rat frontal neurons that can be recorded intracellularly. The electrophysiological characteristics of the monosynaptic responses and the possibility that dopamine (DA) mediates these events are discussed.

6-Hydroxydopamine induces degenerative changes in innervation of the rat pituitary gland

Administration of 6-hydroxydopamine to adult male rats by peripheral injections induces degenerative changes in nerve terminals innervating cells of the pituitary intermediate lobe. Additional animals were treated with 5-hydroxydopamine, which produced images of nerve profiles containing vesicles with electron-dense centers, indicative of uptake of the false catecholamine (CA) neurotransmitter. Endocrine cells showed cytologic evidence of activation of synthetic and secretory compartments. The ultrastructural observations suggest that innervation to opiomelanocortin cells is sensitive to a CA-specific neurotoxin and strengthens the hypothesis that CA-containing fibers play a role in intermediate lobe neuroregulation.

Amine accumulation in behavioural pathology

When nigro-striatal and meso-cortical neurons degenerate there is a loss of dopamine in the terminal fields and an accumulation of amines in the axons of these systems as they traverse the hypothalamus through the medial forebrain bundle. Traditional lines of thought have attributed the occurrence of motor and consummatory deficits which occur after dopamine neuron degeneration to the loss of functional dopamine neurotransmitter in the terminal fields. However, we have hypothesized that hypothalamic amine accumulation represents an area of brain tissue where processes such as neurotransmitter release, ephaptic transmission or local axon swelling may be affecting adjacent neurons and may thereby participate in the production of behavioural deficits. There is a considerable amount of evidence from studies on both peripheral and central catecholamine-containing neurons indicating that when their axons degenerate a release of functional neurotransmitter can occur. Information from neuropharmacological studies indicates that several drugs which facilitate behavioural recovery from dopamine-depleting lesions may do so by affecting amine release or receptor sensitivity near areas of accumulation rather than depleted terminal fields. We conclude that amine accumulation is a component of dopamine neuron degeneration which should be considered when assessing the role of the central catecholamine systems in the control of various behavioural and physiological processes.

Microspectrofluorometric characterization of amine accumulation proximal to lateral hypothalamic lesions

Microspectrofluorometry was employed to identify the spectral characteristics of the formaldehyde-induced fluorophore derived from amine accumulation proximal to the site of 6-hydroxydopamine injection or radiofrequency lesions in the lateral hypothalamus of Sprague-Dawley rats. The excitation and emission spectra of the accumulation were consistent with that of catecholamines in models subjected to similar formaldehyde treatment. These results indicate that while biochemical assay technique may not permit the quantification of amine accumulations, these areas do in fact represent degeneration associated increases in catecholamines which may be of functional significance.

Catecholamine-blocking drugs injected at sites of amine accumulation reverse catecholamine degeneration associated deficits

It has been hypothesized that catecholamine (CA) accumulation in the axons of degenerating neurons may represent areas of functional neurotransmitter, and may be producing some of the consummatory and locomotory deficits which occur after central CA-depleting lesions. To test this hypothesis further, haloperidol (0.5 microliter of a 7 nM sol.), propranolol (0.5 microliter of a 175 nM sol.) or isotonic saline (0.5 microliter) were injected 1.5 h, 24 h and 48 h after the injection of 6-hydroxydopamine (6-OHDA; 2 microliter of 8 micrograms/microliters) into the lateral hypothalamus (LH) of Sprague-Dawley rats to determine if the hypothermia, motor impairment and consummatory deficits could be reversed. Although haloperidol injection significantly enhanced the hypothermia seen 1.5 h after 6-OHDA injection, open field performance and consummatory responses were significantly improved after haloperidol was injected into the LH where accumulation is known to occur. Three consecutive days of intracerebral haloperidol treatment produced a recovery of body weight regulation lasting for 6 days. Treatment with propranolol enhanced open field performance 1 day after 6-OHDA injection but failed to enhance recovery of consummatory behaviour and body weight control. These results suggest that CA released from areas of accumulation act on adjacent CA receptors to participate in the production of behavioural deficits previously attributed only to the loss of functional neurotransmitter in terminal fields in the forebrain.

Cytoarchitectonics of substantia nigra grafts: a light and electron microscopic study of immunocytochemically identified dopaminergic neurons and fibrous astrocytes

Maturation of dopaminergic (DA) neurons and astroglia was studied in transplants of the substantia nigra grown for up to 7 months in the brain of rats. The investigation had three specific aims. The first was to observe effects of different transplant positions on the longevity of DA neurons. Second, the grafts were examined for changes of synaptic interactions and associations between DA neurons and astroglia. Third, an answer was sought to the question whether transplanted DA neurons migrate into the adjacent host brain. The grafts were taken from the ventral mesencephalon of rat embryos of different ages (day 14 to 18 of gestation) and placed into the cerebral cortex, tectum, cerebellum, or ventricles of newborn host animals. Following different times of survival the immunocytochemical localization of tyrosine hydroxylase (TH) and of glia filament protein (GFA) in the transplants were observed. In all of the transplantation sites, except for one, neurons of different morphologies that contained TH were found in the grafts. The cerebellar white matter of the host brain failed to support the long-term survival of DA neurons. The overall structure of mature substantia nigra grafts had some resemblance to intact substantia nigra (SN). On the ultrastructural level, it was found that morphological expression of some immature features of DA neurons, such as glial sheaths, somatic spines, and lack of oligodendroglia, persisted in mature grafts. Specific associations of DA neurons and astroglia in the grafts suggested that the cytoarchitectonic appearance of a given brain region may be related to the existence of particular neuron glia relationships. In contrast to intact SN, transplants revealed deficiencies in unlabeled pleomorphic boutons and contained some TH-immunoreactive terminals. Migration of DA neurons and their processes into the adjacent host brain was rarely observed.

Relationship between sensorimotor neglect and the specificity, degree and locus of mesotelencephalic dopaminergic cell loss following 6-hydroxydopamine

The involvement of cell groups within the dopaminergic mesotelencephalic system in the development of the sensorimotor neglect syndrome was re-evaluated in two ways. Firstly, dopaminergic specificity of the neglect was further established by studying the relationship between nomifensine protection of dopamine cells against 6-hydroxydopamine damage and the degree of neglect which resulted. The sensorimotor neglect syndrome which developed following injection of 6-hydroxydopamine was diminished by concomitant treatment with nomifensine in parallel with the degree of protection afforded the dopaminergic cells. Non-specific damage produced by 6-hydroxydopamine was unaltered by nomifensine. Secondly, the role in sensorimotor neglect of both total cell damage, and damage to regional sub-classes of dopaminergic cells was considered. It was found that the extent of the resulting neglect was correlated with the overall damage to the substantia nigra and ventral tegmental area, rather than to any individual region within this dopaminergic system. There was a threshold, involving destruction of approximately one third of the system, below which no neglect syndrome developed. Certain regions, including the ventral tegmental area (VTA), showed a higher partial correlation with the extent of neglect than other regions. While specific lesioning of the A8 or A10 dopaminergic neurons is probably insufficient to produce a neglect syndrome, damage to these areas potentiates the severity of the neglect produced by nigrostriatal lesions. It appears that the involvement of the individual subclasses of the mesotelencephalic dopaminergic neurons in the neglect syndrome is more widespread than previously thought.

The masking of amine accumulation by catecholamine depletion

6-Hydroxydopamine (2 microliter of 8 micrograms/microliter) was injected bilaterally into the lateral hypothalamus of male Sprague-Dawley rats to produce depletion of forebrain terminal fields and an accumulation of amines proximal to the site of injection. Two additional groups of animals were injected with either vehicle or were food and water intake-matched to those receiving 6-hydroxydopamine. Motor performance, food and water intake and body weight were measured in all animals for 2 days before and 6 days after injection. Animals were then sacrificed and brain tissue was prepared for biochemical assay or fluorescence histochemistry. The area of hypothalamic tissue proximal to 6-hydroxydopamine injection, that which contains the amine accumulation, was sectioned from the surrounding tissue with a biopsy punch and assayed for noradrenaline and dopamine content. The nucleus caudatus-putamen, basomedial hypothalamus, and tissue containing the olfactory tubercle and accumbens nucleus were also assayed. Fluorescent histochemical examination of tissue showed that in addition to the depletion of catecholamines in various terminal fields there was also an increase in the fluorescent amine accumulation proximal to the injection site in the impaired animals. This accumulation was not detected with the biochemical assay and is probably due to the occurrence of a masking effect by adjacent depletions. A significant rise in noradrenaline levels was seen in the basomedial hypothalamus of intake-matched controls. However, this too was not detected in 6-OHDA-treated animals and was probably due to masking by adjacent depletions in these areas.(ABSTRACT TRUNCATED AT 250 WORDS)

A role for amine accumulation in the syndrome of ingestive deficits following lateral hypothalamic lesions

Lesions of the lateral hypothalamus produce ascending catecholamine neuron degeneration which results in terminal depletion and proximal accumulation above the lesions. The occurrence of deficits in ingestive behaviour has been attributed traditionally to the loss of functional dopamine neurotransmitter in the terminal fields. However, release of functional amines may occur in the lateral hypothalamus at areas of accumulation, to produce at least some of the behavioural symptoms characterizing the lateral hypothalamic syndrome. Recovery from behavioural deficits as a result of various pharmacological treatments, after dopamine-depleting lesions, may be mediated by changes in amine release or modified sensitivity of receptors affected by released amines. We conclude that amine accumulation should be considered when interpreting experiments implicating central catecholamine systems in the control of consumatory behaviour and the regulation of body weight.

Effect of nomifensine on the toxicity of 6-hydroxydopamine for mesotelencephalic dopamine neurons

The ability of nomifensine to protect the dopaminergic cells of the substantia nigra and ventral tegmental areas against 6-hydroxydopamine-induced destruction was evaluated. Nomifensine at high doses (20 mg/kg, i.p.) protected the cells from the effects of low amounts of 6-hydroxydopamine (2 micrograms) injected intracerebrally. This protective effect was markedly decreased with an increased amount of 6-hydroxydopamine (8 micrograms), or by lower doses of nomifensine (6.7 mg/kg). These doses of nomifensine are higher than those required to protect dopaminergic nerve terminals.

Sensorimotor impairment and elevated levels of dopamine metabolites in the neostriatum occur rapidly after intranigral injection of 6-hydroxydopamine or gamma-hydroxybutyrate in awake rats

The unilateral injection of 6-hydroxydopamine (8 micrograms) into the ventral tegmental area of awake rats produced a rapidly developing and irreversible sensory neglect to contralateral tactile stimuli. This neglect developed in a caudal to rostral direction on the affected body surface and coincided with significant elevation in the concentrations of dopamine and two of its metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the ipsilateral neostriatum. The unilateral injection of procaine or gamma-hydroxybutyric acid (GHB) into the substantia nigra of awake animals also produced a contralateral neglect that developed in a caudal to rostral direction, but the behavioral effect of these drugs diminished within 1 hr. Concentrations of dopamine, dihydroxyphenylacetic acid and homovanillic acid in the neostriatum were markedly elevated during continuous infusions of procaine or gamma-hydroxybutyric acid. The extent of sensory neglect and changes in dopamine metabolism in the neostriatum varied according to the amount of gamma-hydroxybutyric acid injected into the nigra and according to the proximity of injections of gamma-hydroxybutyric acid to the pars compacta. The rapid onset of sensory neglect following microinjections of 6-hydroxydopamine, procaine or gamma-hydroxybutyric acid is consistent with the ability of each of these drugs to block the conduction of impulses in mesostriatal neurons and suggests that concomitant increases in levels of dopamine, dihydroxyphenylacetic acid and homovanillic acid in the neostriatum resulted from decreases in the release of dopamine coupled with increased synthesis of dopamine. These findings also indicate that the catabolism of dopamine to dihydroxyphenylacetic acid or homovanillic acid may originate intraneuronally, without prior release of dopamine and its recapture by mesostriatal terminals, if the flow of impulses in this pathway has been blocked.

Amplitude and phase relations of electrocortical waves regulated by transhypothalamic dopaminergic neurones: a test for a linear theory

We have previously proposed that electrocortical activity (EEG) arises as a manifestation of linear waves generated by resonance among telencephalic neurones, and that this activity is controlled in part by ascending neurones from the brain-stem, which regulate the damping of each resonance. The present experiments focus on a specific class of ascending neurones, the mesotelencephalic dopaminergic cells, because these cells are thought to mediate important psychological effects, and are conveniently subject to selective lesion. A critical test of the theory is undertaken, by performing selective unilateral lesion, assessing the changes in the power spectrum of the EEG attributable to lesion, and determining whether the changes in phase of the EEG correspond to that predicted from the changes in power. Results support the theory, although the model order applicable in these experiments in inadequate. The consequences of these findings for automata theory, linear network theory and their application to mammalian brains are briefly discussed.

Changes in body weight and food-related behaviour induced by destruction of the ventral or dorsal noradrenergic bundle in the rat

Three experiments contrasted the effects of 6-hydroxydopamine-induced lesions of the ventral noradrenergic and dorsal noradrenergic projections, predominantly to hypothalamus and cortex, respectively, upon body weight changes and food-related behaviour in the rat. In general, ventral noradrenergic bundle lesions enhanced weight gain and these effects were exaggerated by the provision of palatable cheese to the standard chow diet. In contrast, lesions of the dorsal noradrenergic bundle produced minor changes in body weight. Associated with the effects of ventral noradrenergic bundle lesions were hyperphagia, enhanced suppression of intake of food adulterated with quinine, (at high concentration), a small attenuation of food neophobia, and enhanced acquisition, but not performance, of the eating response to tail-pinch stimulation. These ventral noradrenergic bundle lesions failed to alter basal activity levels, amphetamine anorexia or the diurnal pattern of eating or activity. In contrast, lesions of the dorsal noradrenergic bundle did not produce either hyperphagia or enhanced rejection of food adulterated with quinine. However, there was a strong attenuation of food neophobia and a retarded acquisition (but unimpaired performance) of eating in response to tail-pinch stimulation. The results are discussed in connection with previous studies of ventral and dorsal noradrenergic bundle lesions, with the effects of ventromedial hypothalamic lesions and with the underlying behavioural and physiological processes that mediate these contrasting effects of different neuroanatomical patterns of central noradrenaline depletion.

Distribution of tritium label in the neonate rat brain following intracisternal or subcutaneous administration of [3H]6-OHDA. An autoradiographic study

The present report describes the distribution of tritium label after injection of newborn rats with [3H]6-hydroxydopamine ([3H]6-OHDA). The animals were injected either intracisternally (i.c.) or subcutaneously (s.c.), with or without pretreatment with nomifensine, which blocks the high-affinity uptake of both noradrenaline (NA) and dopamine (DA), and sacrificed at intervals from 40 min to 24 h post-injection (p.i.). In i.c. injected animals, tritium label is demonstrable as early as 40 min p.i. in neurons of all known NA and DA cell groups. In NA neurons, it is taken up into cell body, dendrites, preterminal and terminal axons. The intensity of neuronal labeling is highest within the first 4 h p.i. and decreases in most neurons with longer postinjection intervals. A significant proportion of both NA and DA neurons degenerate beginning 6 h p.i., the majority show morphological signs of the axon reaction 24 h p.i. Uptake of [3H]6-OHDA into serotonergic and non-catecholaminergic neurons is not demonstrable. [3H]6-OHDA is accumulated by the following extraneuronal cells of the CNS: ependymal cells, epithelial cells of the choroid plexus, subependymal macrophages, smooth muscle cells in the wall of large intraparenchymal blood vessels, meningeal cells and glial cells. The time course of accumulation and disappearance of the label varies among these extraneuronal elements. The meningeal cells show the highest labeling intensity and degenerate within 24 h p.i. After pretreatment of the animals with nomifensine, the uptake of [3H]6-OHDA into NA and DA neurons is totally blocked; by contrast uptake of the labeled drug into extraneuronal cells is not prevented. These findings show that [3H]6-OHDA is not only accumulated by neurons possessing the high-affinity uptake for NA or DA, but by numerous other, extraneuronal cells which also participate in the metabolism of catecholamines.

Acetylcholinesterase associated with dopaminergic innervation of the neostriatum: histochemical observations of a heterogeneous distribution

Unilateral injections of 6-hydroxydopamine that damaged the mesotelencephalic dopaminergic projection resulted in decreased acetylcholinesterase (AChE) staining in the ipsilateral neostriatum. This reduction, which was most apparent in the posterior and medial anterior neostriatum, occurred in rats killed 3 days or more after the 6-hydroxydopamine injection. No hemispheric asymmetries of AChE staining were found in the medial nucleus accumbens septi, olfactory tubercle or amygdala. Thus, some of the AChE in the neostriatum appears to be localized to its dopaminergic innervation; however, the enzyme may be heterogeneously distributed throughout this structure's dopaminergic afferent fibers. AChE seems not to be associated with dopaminergic axons innervating the limbic forebrain.

Dopaminergic innervation and inhibition of ciliary movement in the ciliated epithelium of frog palatine mucosa

The effect of dopamine on ciliary movement and the existence of dopamine-containing cells in the ciliated epithelium of frog palatine mucosa were investigated pharmacologically and by means of electron and fluorescence microscopy, respectively. Ciliary movement was suppressed markedly when the perfusion medium contained 10(-6) M dopamine, thereby indicating that dopamine has a suppressive effect on ciliary movement. Electron microscopy revealed at least two types of granule-containing (GC) cells, type 1 cells containing small spherical granular vesicles (about 100-150 nm in diameter) and type 2 cells containing elongated dense granules (about 150 X 250 nm in diameter). One hour after systemic administration of dihydroxyphenylalanine-[3H(G)] [( 3H]DOPA), a large number of silver grains appeared only in type 2 GC cells, thus indicating that type 2 cells are catecholamine-storing. Blue-green fluorescent cells were detected in the ciliated epithelium. On microspectrofluorometry, catecholamine fluorescence in the cells showed a main excitation and emission maxima at 415 and 480 nm, respectively. When the fluorescent cells were exposed to HCl vapor for several s, the excitation peak shifted to 380 nm and this peak was unchanged after treatment for an additional 5 min. It may be considered that these fluorescent cells contain dopamine and correspond to type 2 GC cells. A possible functional relationship between regulation of ciliary movement and dopamine-containing cells was also discussed.

Deficits in locomotor behaviour and motor performance after central 6-hydroxydopamine or peripheral L-DOPA

Intracerebral injections of 6-hydroxydopamine (6-OHDA) which produce deficits in locomotor behaviour and motor performance cause localized accumulation of monoamines as well as depletion of central catecholamines (CA). To determine whether the localized increases in monoamines could be contributing to the behavioural deficits seen after intracerebral 6-OHDA injection, the behavioural and biochemical effects of peripherally administered L-DOPA were compared to those which occurred after central injections of 6-OHDA. Forty-five minutes after the injection of 40 mg/kg of L-DOPA, in animals pretreated with 50 mg/kg of R04-4602, the ability to step down, to retract a limb and to ambulate were significantly impaired. Locomotor behaviour and body temperature of L-DOPA-injected animals were similar to those displayed by animals receiving intracerebral injections of 6-OHDA. Fluorescent histochemical and biochemical assessment of diencephalic and telencephalic CA revealed that depletion of CA was not related to the severity of the motor deficits which occurred, but that increased diencephalic CA were present in impaired animals injected with either 6-OHDA or L-DOPA. These findings support the contention that increased CA in degenerating hypothalamic neurones may contribute to behavioural deficits seen after the injection of 6-OHDA.

The cytology of dopaminergic and nondopaminergic neurons in the substantia nigra and ventral tegmental area of the rat: a light- and electron-microscopic study

The results of this study support the conclusion that dopaminergic cells can be distinguished from non-dopaminergic cells, at both the light- and electron-microscopic level, by cytological features, and particularly by the pattern of Nissl substance. In both the substantia nigra and the ventral tegmental area, two main categories of cell type can be identified in Nissl preparations: (1) dark-staining, basophilic cells with large masses of Nissl substance and (2) light-staining cells with more translucent cytoplasm. The following findings provide evidence that the basophilic cells of both substantia nigra and ventral tegmental area are the dopaminergic cells. (1) There is a good correlation between the topographic distribution of basophilic cells and that of dopaminergic cells mapped by both histofluorescence and immunohistochemical methods. (2) After unilateral destruction of the dopaminergic neurons by intracerebral injection of 6-hydroxydopamine in the dopaminergic pathway, the basophilic cells in the substantia nigra and ventral tegmental area disappeared on the lesion side, while the lighter-staining cells appeared unaffected. (3) In normal rats, and in rats with unilateral 6-hydroxydopamine lesions, intraventricular injection of [3H]norepinephrine was used for specific labeling of dopaminergic neurons. In autoradiograms of semithin sections, such labeling was observed only in dark-staining and not in light-staining cells, and in cases of unilateral 6-hydroxydopamine lesion was totally absent on the lesion side. Electron-microscopy showed much of the cytoplasm of the basophilic dopaminergic cells to be densely filled with free ribosomes associated with large, well organized complexes of rough endoplasmic reticulum. The cytoplasm of the light, non-dopaminergic cells contains only sparse free ribosomes and small, widely spaced aggregates of rough endoplasmic reticulum. Both cell types occur in a similar variety of size and shape.

Role of ventral mesencephalic reticular formation and related noradrenergic and serotonergic bundles in turning behaviour as investigated by means of kainate, 6-hydroxydopamine and 5,7-dihydroxytryptamine lesions

A unilateral kainate (KA) infusion (2 x 0.15 micrograms, 2 x 0.25 micrograms) in the ventral mesencephalic reticular formation (MRF) resulted in spontaneous contraversive turning lasting only a few days. Upon challenge with apomorphine (0.5 mg/kg s.c.) or amphetamine (5 mg/kg i.p.) the contraversive turning could be reinstated. The incidence, as well as the intensity, of the drug-induced response decreased over the 45 days of observation. KA infused in the ventral MRF induced typical lesions after doses of 2 x 0.15 micrograms but resulted in demyelination after 2 x 0.25 micrograms. These lesions failed to reduce noradrenaline (NA), serotonin (5 HT) or dopamine (DA) in various forebrain areas. Unilateral lesion of ascending NA projections by 6-OHDA infusion (4 micrograms) within the NA bundles coursing in the mesencephalon or near the locus coeruleus, failed to induce motor asymmetries. Unilateral selective lesion of the ventral NA bundle by local 6-OHDA (2 micrograms) infusion also failed to induce motor asymmetries, either spontaneously or in response to dopaminergic drugs. Unilateral lesion of ascending 5-HT projections by the tegmental infusion of 5,7-dihydroxytryptamine (10 micrograms) also failed to induce motor asymmetries in response to dopaminergic drugs but resulted in contraversive circling in response to 5-hydroxytryptophan. These data indicate that intrinsic neurones of the ventral MRF play a role in turning behaviour and exclude, in contrast with previous studies, a role of NA or 5-HT projections in the contraversive turning responses to DA receptor agonists obtained after lesions of the ventral MRF.

Uptake and retention of [3H]adrenaline by central monoaminergic neurons: a light- and electron-microscope radioautographic study after intraventricular administration in the rat

Paraventricular and paracisternal regions of adult rat central nervous system were investigated by light- and electron-microscope radioautography after intraventricular administration of tritiated adrenaline. In tissue primarily fixed by glutaraldehyde perfusion and post-fixed by immersion in osmium tetroxide, there were no aggregates of silver grains indicative of intraneuronal accumulation of the tracer, except over perivascular nerve terminals at the base of the brain. In contrast, when both fixation and postfixation were carried out by rapid vascular perfusion, preferentially labeled nerve cell bodies and axonal varicosities (i.e. terminals) were detected in various anatomical areas known to contain dopaminergic and/or noradrenergic neurons. Serotoninergic axonal varicosities in the supraependymal plexus and subcommissural organ, as well as a small group of nerve cell bodies of undetermined chemical identity in the n. paraventricularis thalami were also found to be labeled. Addition of a ten-fold higher concentration of non-radioactive serotonin to the solution of [3H]adrenaline suppressed the reactivity in the subcommissural organ and the supraependymal plexus but had no such effect elsewhere in brain. Lesioning of the nigrostriatal dopaminergic system with 6-hydroxydopamine prior to [3H]adrenaline injection eradicated axon terminal labeling in the ipsilateral neostriatum. Electron-microscopic examination of [3H]adrenaline-labeled varicosities in the neostriatum, lateral septum, arcuate nucleus and median eminence extended earlier observations on the ultrastructure of the catecholaminergic innervation of these regions. It was concluded that both dopaminergic and noradrenergic neurons as well as certain serotonin-containing axon terminals can take up and retain [3H]adrenaline, although they probably have lesser affinity for this amine than for their own transmitter. Due to the fact that presumptive adrenergic neurons are intermingled with dopaminergic and noradrenergic elements, further work will be needed to determine to which extent they also contributed to [3H]adrenaline uptake in the present experimental conditions.

Distribution of dopamine in 35 subregions of the rat caudate-putamen: a high performance liquid chromatography with electrochemical detection analysis

Topographical variations in the endogenous content of dopamine were studied in the rat caudate-putamen. For this purpose, a high performance liquid chromatography with electrochemical detection procedure for the determination of norepinephrine, epinephrine and dopamine in nervous tissue samples is described. Tissue preparation required only homogenization in acidic solution and centrifugation prior to application to the chromatograph. Detection limits in the low picogram range were found for the catecholamines separated. This assay was used in combination with a micropunch dissection technique. The performance of this analytical technique is illustrated by the detailed mapping of dopamine content in 35 subregions of the rat caudate-putamen. The distribution of dopamine varies along the major axis of the nucleus.

The behavioural effects of intrahypothalamic multistage versus single injections of 6-hydroxydopamine

16 micrograms of 6-hydroxydopamine were injected bilaterally into the lateral hypothalamus of male Sprague-Dawley rats in either a single injection or in a series of multistage injections over a period of 75 days. While the single injection produced behavioural deficits typical of those seen following catecholamine depletion of the forebrain, the behaviour of animals injected incrementally with the same dose was indistinguishable from that of controls. Fluorescent histochemical assessment revealed that the animals in the multistage injection group, the behaviourally unimpaired, suffered more severe depletion of forebrain catecholamines than those in the single-stage injection group. Accumulation of amines proximal to the site of drug injection was extensive only in those animals displaying behavioural deficits, that is, the group with the lesser amount of forebrain catecholamine depletion. It is suggested that the severity of deficits in consummatory and motor behaviour occurring after hypothalamic trauma is determined by a lesion's effectiveness in producing amine accumulation rather than catecholamine depletion.

Overeating after midbrain 6-hydroxydopamine: prevention by central injection of selective catecholamine reuptake blockers

Earlier research from this laboratory showed that 6-hydroxydopamine (6-OHDA) injected into the ventral midbrain of rats causes overeating and the gradual development of obesity in association with extensive depletion of forebrain norepinephrine. It was proposed that depletion of norepinephrine or epinephrine was the cause of the behavioral abnormality. This was questioned on the basis of experiments showing that 6-OHDA can cause non-selective lesions and also that non-selective neurotoxins can cause hyperphagia. To help resolve this question, the present experiments used 191 rats in 28 groups to test 3 doses of 6-OHDA and 3 different pretreatments with reuptake blockers, amphetamine, desmethylimipramine and benztropine. The result of midbrain 6-OHDA alone was hyperphagia that was highly correlated with the dose. Pretreatment with intraperitoneal desmethylimipramine (DMI) caused gastric distress, and systemic amphetamine caused delayed overeating, but these unwanted side effects were avoided by injecting the drugs directly into the midbrain 15 min before the 6-OHDA. DMI and amphetamine partially prevented catecholamine depletion in the forebrain and totally prevented subsequent hyperphagia and obesity. Benztropine prevented dopamine depletion, but had no effect on hyperphagia. We conclude that some of the neurons protected by local injection of amphetamine and DMI are probably norepinephrine or epinephrine fibers that ascend through the ventral midbrain and have as one of their functions the inhibition of food intake. These neurons could also play a role in the control of body weight.

Plasticity of neostriatal dopamine receptors after nigrostriatal injury: relationship to recovery of sensorimotor functions and behavioral supersensitivity

Rats given unilateral injections of 6-OHDA along the course of the mesotelencephalic dopaminergic projection show impairments in contralateral sensorimotor functions from which they often recover. Such rats also display an enhanced sensitivity to DA receptor stimulants, e.g. apomorphine, as revealed by contralateral turning, and an increased binding of neuroleptic compounds (e.g. [3H]spiroperidol) to the denervated striatum. This research examines the relationship of these receptor changes to both behavioral supersensitivity and recovery of sensorimotor functions by quantifying the time course of each phenomenon after injury. The supersensitivity to apomorphine and the behavioral recovery developed with a similar time course after injury, being evident within 1.5-3 days and reaching nearly maximal levels by 2 weeks postoperatively. A significant increase in in vivo [3H]spiroperidol binding to the denervated striatum occurred by 4 days postoperatively, and the magnitude of this change increased linearly during the first postoperative month. In contrast, the in vitro binding of this ligand to membranes of the denervated striatum was not increased until 3 weeks after the lesion. The results suggest that a proliferation of DA receptors may contribute to the pharmacological supersensitivity and the recovery of function, and that these early receptor changes may be revealed with greater sensitivity using in vivo binding techniques.

Histofluorescence analysis of several systems of catecholaminergic nerve fibres within the rat neostriatum revealed by either restricted lesions of the substantia nigra or gamma-hydroxybutyrate

The glyoxylic acid fluorescence technique was applied to the study of catecholamine fibres in the caudate-putamen (neostriatum) of control and experimental adult rats. Cryostat or vibratome sectioning procedures were used; in the last case, either incubations of brain slices in gamma-methyl-noradrenaline or pre-treatment of animals with gamma-hydroxybutyrate were performed, in order to increase the intensity of fluorescence. In control animals and in the contralateral side of rats lesioned in the substantia nigra, the fluorescence of the dense plexus of dopamine nerve fibres appeared under the form of densely packed varicosities. However, some regions differed from the ordinary fluorescence of the neostriatum by their stronger intensity and more visible varicosities. They were located principally in the ventro-medial regions bordering either the nucleus accumbens, the dorsal nucleus interstitialis striae terminalis and the ventricle in the anterior part, or the amygdala, the globus pallidus and the ventricle in the posterior part. Moreover, islands of stronger fluorescence also were observed in the head of the caudate-putamen along the dorsal and lateral corpus callosum, as well as scattered in the central region. These particular neostriatal structures might correspond to a separate system of ascending dopamine nerve fibres. Therefore, restricted electrolytic lesions of the substantia nigra pars compacta were undertaken in order to study the morphology of the remaining catecholaminergic fibres in the ipsilateral neostriatum. In largely denervated areas, different types of fluorescent axons were evident. Presumed noradrenergic nerve fibres characterized by a very coarse appearance and closed varicosities were rare. They contrasted markedly with numerous delicate fibres which might belong to several dopaminergic systems. Both first types exhibited long, clearly visible intervaricose segments and ovoid triangular varicosities. The second type, which was thicker and more strongly fluorescent, probably formed the islands observed in unlesioned striata. The third type had very closed, small spherical varicosities and poorly fluorescent intervaricose segments. Dopamine nerve fibres of the same morphology were described previously in the neocortex [43,44] and the possibility of a common origin for nerve fibres of the same type is discussed. When rats were treated with the anaesthetic gamma-hydroxybutyrate, all the dopamine nerve fibres appeared to develop a strong fluorescence within the neostriatum, but more fluorescent islands were always visible. Additionally, some swollen fluorescent fibres were seen; these could be abnormal dopamine fibres whose metabolism had been pathologically altered by the drug.

Acquisition and extinction of continuously and partially reinforced running in rats with lesions of the dorsal noradrenergic bundle

Local injection of 6-hydroxydopamine was used to selectively destroy the dorsal ascending noradrenergic bundle (DB) in rats. Two lesion procedures were used, differing in the extent of depletion of forebrain noradrenaline they produced (greater than 90% or 77%). In Experiments 1-3 the rats were run in a straight alley for food reward on continuous (CR) or partial (PR) reinforcement schedules. The smaller lesion reduced and the larger lesion eliminated the partial reinforcement acquisition effect (i.e. the faster start and run speeds produced by PR during training) and the partial reinforcement extinction effect (PREE, i.e. the greater resistance to extinction produced by PR training); these changes were due to altered performance only in the PR condition. Abolition of the PREE by the larger DB lesion occurred with 50 acquisition trials, but with 100 trials the lesion had no effect. In Experiment 4 rats were run in a double runway with food reward on CR in the second goal box, and on CR, PR or without reinforcement in the first. The larger lesion again eliminated the PREE in the first runway, but did not block the frustration effect in the second runway (i.e. the faster speeds observed in the PR condition after non-reward than after reward in the first goal box). These results are consistent with the hypothesis that DB lesions alter behavioural responses to signals of non-reward, but not to non-reward itself. They cannot be predicted from two other hypotheses: that the DB mediates responses to reward or that it subserves selective attention. Since septal and hippocampal, but not amygdalar, lesions have been reported to produced similar behavioural changes, it is proposed that the critical DB projection for the effects observed in these experiments is to the septo-hippocampal system.

Dopamine agonist-induced restoration of drinking in response to hypertonic saline in adipsic dopamine denervated rats

Bilateral 6-hydroxydopamine lesions of the ascending dopamine neurones of the nigro-striatal bundle or bilateral electrolytic lesions of the lateral hypothalamus cause a syndrome of aphagia and adipsia. Rats with such lesions do not drink in response to hypertonic saline which causes thirst in intact animals. However, the systemic administration of the direct dopamine receptor agonists apomorphine, piribedil and lergotrile restored drinking in response to hypertonic saline in 6-hydroxydopamine treated rats but not in rats with electrolytic lesions of the lateral hypothalamus. Amphetamine and beta-phenylethylamine failed to restore drinking in response to hypertonic saline in either group of lesioned rats which suggests that these drugs may act indirectly on the dopaminergic system. The restoration of drinking model suggests that dopamine may have a permissive function in thirst, and, in addition, appears to represent a useful test for the screening of new drugs for a direct dopamine receptor stimulating action.

Non-dopaminergic nigrostriatal pathway

The nigrostriatal projection was studied with a retrograde tracing method (Evans blue, EB) combined with a technique for dopamine histofluorescence. The study, realized in control rats and in animals with 6-hydroxydopamine-induced lesions of the dopaminergic pathway, yielded the following results. (1) In 3 control rats injected with 0.1 microliter of a 10% solution of EB in the center of the caudate-putamen 1 mm anterior to the globus pallidus, 96% of all substantia nigra neurons retrogradely labelled with the dye contained dopamine fluorescence. The remaining ones (average 350 per brain) were devoid of dopamine fluorescence and predominantly found in the posterior 75% of the substantia nigra. These last cells were confined to the upper-half of the pars reticulata. (2) In a series of 6 animals, the cytotoxic agent 6-hydroxydopamine was injected in various locations in the vicinity of either the substantia nigra or the nigrostriatal tract 12--15 days prior to the injections of 0.1 microliter of EB in the same striatal locations as in the controls. Despite a reduction of up to 85% in the number of dopaminergic cell bodies, the substantia nigra of these rats contained the same average number of EB-labelled neurons devoid of dopamine fluorescence. (3) Eight rats received smaller injections (0.1 microliter) of EB in various striatal sites and in two further cases such injections were placed in the globus pallidus to determine more accurately the anatomical location of the dopamine-negative nigral neurons retrogradely labelled with the dye. Following the striatal injections, these cells were found mostly in the upper-half of the pars reticulata and were arranged in longitudinal oriented clusters whose mediolateral location depended on the striatal injection site. Following the pallidal injections, retrogradely labelled neurons devoid of dopamine fluorescence were found in greater numbers and were located in all areas of the pars reticulata. The possibility of retrograde labelling of some nigrothalamic neurons was not entirely ruled out in these two cases. (4) Finally 6 rats received 0.1 microliter injections of EB in various parts of the parietal cortex. In these cases the substantia nigra did not contain any EB-positive dopamine-negative neurons. These results are interpreted as evidence in support of the existence of a topographically organized non-dopaminergic nigrostriatal projection.

Neurophysiology and neuropharmacology of cardiovascular regulation and stress

Evidence has accumulated over the past several years indicating that environmental factors can have a substantial influence on cardiovascular dynamics. It has been hypothesized by many investigators that through these influence environmental stressors may be important to the etiology and maintenance of cardiovascular diseases. Since the nervous system is intimately involved in the regulation of cardiovascular function it may be assumed that environmental influences on cardiovascular dynamics are to a large extent mediated by the nervous system. This assumption is supported by the literature reviewed which indicates that there are many nervous system nuclei and neurotransmitter systems involved in the regulation of cardiovascular dynamics which are also involved in an organisms adjustment to environmental stressors. The conclusion is reached that further multidisciplinary research will reveal underlying neurophysiological and neuropharmacological mechanisms responsible for stress induced cardiovascular disease and lead to new methods of treatment.

Male rat sexual behavior compared after 6-OHDA and electrolytic lesions in the dorsal NA bundle region of the midbrain

Forebrain catecholamine depletion and midbrain histological damage in adult male rats were investigated as a function of 6-hydroxydopamine dosage in the range 4 microgram in 2 microliter to 8 micrograms in 4 microliter, stereotaxically injected at 0.43 microliter/min bilaterally in the region of the ascending dorsal noradrenaline bundle of the locus coeruleus, without and with a 30-60 min earlier 25 mg/kg intraperitoneal dose of desmethylimipramine (DMI). Sexual behavior of the male rat was compared for treatment with 4 microgram in 2 microliter 6-OHDA, without and with 25 mg/kg protective dose of DMI, and alternatively for 1 mA 30 sec bilateral electrolytic lesions at the same location. For the behaviorally tested rats receiving 6-OHDA treatment, cortical noradrenaline was depleted to 17% and to 81% of control, without and with DMI, respectively. Hypothalamic NA was depleted to 60% and 102% (no depletion), respectively. Caudate dopamine depletion did not reach significance at P = 0.05. For rats with electrolytic lesions cortical NA was depleted to 46% of control and caudate dopamine was not depleted. For the electrolytically lesioned rats, the first 3 post-ejaculatory intervals decreased by an average of 24%, while the 1 h ejaculatory frequency increased by 17%, which confirms a prior finding. However, no measured sexual behavioral effects were observed with 6-OHDA. Thus, interrupting the dorsal noradrenaline bundle has not been shown to have any effect on sexual behavior in the male rat.

Electrophysiological evidence for non-dopaminergic mesocortical and mesolimbic neurons in the rat

The neurons located in the ventromedial tegmentum (VMT) and projecting either to the frontal cortex, to the septum or to the nucleus accumbens were identified by the antidromic activation method in normal rats and in animals whose dopaminergic (DA) systems had been previously lesioned by microinjections of 6-hydroxydopamine (6-OHDA). Two groups of VMT neurons innervating each structure could be distinguished. The first group (group S) are slow conducting neurons whose number is reduced in 6-OHDA lesioned rats and which may correspond to A10 DA neurons. The second group (group F) are fast conducting neurons which are resistant to 6-OHDA treatment and therefore probably non-DA VMT cells.

Non-dopamine containing efferents of substantia nigra: the pathway to the lower brain stem

In animals pretreated with 6-hydroxydopamine, the descending efferent connections of the substantia nigra are restricted to a bilateral projection to the superior colliculus and a pathway which stops in the dorso-lateral reticular formation of the pons.

Pars compacta of the substantia nigra modulates motor activity but is not involved importantly in regulating food and water intake

Precise, bilateral radio-frequency lesions of pars compacta of the substantia nigra in rats resulted in the immediate and sustained appearance of hyperactivity, but such lesions did not produce significant alterations in food or water intake. These behavioral effects were correlated with considerable, histochemically assessed loss of dopamine terminals in the caudate-putamen complex, but dopamine innervation in nucleus accumbens and other forebrain areas was only slightly affected. The magnitude of motor activity increase was positively correlated with the degree of pars compacta involvement. Animals with lesions in the median raphe and adjacent reticular formation also displayed chronic hyperactivity. In contrast to rats receiving discrete radio-frequency lesions of pars compacta, animals with bilateral mesencephalic ablations produced by 6-hydroxydopamine (6-OHDA, 8 micrograms/4 microliters or 4 micrograms/2 microliters in combination with desipramine pretreatment) displayed poverty of movement. Furthermore, significant, dose-dependent decrements in food and water intake were seen after 6-OHDA. The nonselective component of such lesions was frequently large and irregular in shape. Occasional ablations produced by this neurotoxin, however, appeared more selective in that damage was confined primarily to pars compacta. Nonetheless, the best correlate of aphagia and adipsia associated with 6-OHDA treatment was lesion size, regardless of the extent of pars compacta or other nigral involvement. We conclude that aphagia and adipsia concomitant to 6-OHDA lesions of the substantia nigra results from the incidental destruction of extra-nigral systems. Virtually complete, but precise, lesions of pars compacta do not produce aphagia and adipsia. While our results are consistent with the notion that the substantia nigra serves an important role in the regulation of motor activity, they provide no support for the conjecture that it is importantly involved in mediating ingestive behaviors.

Terminal degeneration demonstrated by the Fink-Heimer method following lateral ventricular injection of 6-hydroxydopamine

Degenerating terminals were mapped by the Fink-Heimer method after lateral or fourth ventricular administration of 6-hydroxydopamine (60OHDA). This method marks dopaminergic terminals and has the advantage that noradrenergic terminals are not stained. Fink-Heimer stained degeneratig terminals were seen bilaterally in specific patterns in many nuclei known to have a dopaminergic innervation: neostriatum, nucleus accumbens, olfactory tubercle, the dorsolateral and ventral parts of the bed nucleus of the stria terminalis, laterla septal nucleus, amygdala, and layers II-III of anterior cingulate cortex. Detailed maps are provided of the dopaminergic innervation in the bed nucleus of the atria terminalis in relatin to the cytoarchitectural subdivisions of this nucleus. A Fink-Heimer stained field was discovered in the lateral parabrachial nucleus, suggesting the presence of a previously unreported dopaminergic innervation of this nucleus. It was also noted that nonspecific degeneration near the injection site was much worse after lateral ventricle than after fourth ventricle injection.

Selective retrograde labeling indicating the transmitter of neuronal pathways

A number of tritiated transmitter related compounds-amino acids and biogenic amines-were injected into the rat caudoputamen or substantia nigra in order to test (1) for the occurence of autoradiographic perikaryal labeling, (2) for a selectivity of perikaryal labeling relating certain compounds to certain pathways, and (3) for the relation of perikaryal labeling to known transmitter specificitites of the systems involved. Perikaryal labeling was observed after injection of some but not all of the substances used and was best explained by retrograde labeling in pathways projecting to the injection sites. Six hours after injection of high concentrations of tritiated transmitter into the terminal area, perikaryal labeling was observed: (A) in substantial nigra compacta (A9), A10 (rostral) and A8 (all heavy), and in n. raphe dorsalis (light) after [3H]-dopamine and [3H]-norepinephrine injection into caudoputamen; (B) same pattern as in A, but heavy in n. raphe dorsalis after [3H]-serotonin injection into caudoputamen; perikaryal labeling absent in cortex and thalamus after injection of substances mentioned in A and B; (C) only in substantia nigra compacta (minimally) after [3H]-GABA injection into caudoputamen; (D) in cerebral cortex and thalamus but not in substantia nigra, A10, A8, nor in n. raphe dorsalis after injection of [3H]-D-aspartate into caudoputamen; (E) in the rat caudoputamen but not in n. raphe dorsalis after [3H]-GABA injection into substantia nigra; (F) in n. raphe dorsalis but not in caudoputamen after [3H]-serotonin into substantia nigra. These results indicated, indeed, a certain selectivity-partly related to transmitter specificity-for perikaryal labeling patterns. As a method, transmitter specific retrograde tracing could be useful in pathways with dopamine-, serotonin-, and GABA-mediated synaptic transmission.

Electrophysiological identification of mesencephalic ventromedial tegmental (VMT) neurons projecting to the frontal cortex, septum and nucleus accumbens

The electrophysiological properties of neurons located in the mesencephalic ventromedial tegmentum (VMT) and the organization of the efferents of these neurons to the frontal cortex, the septum, the nucleus accumbens and the head of the striatum were studied in ketamine-anesthetized rats. The projections of the VMT cells were determined through use of the antidromic activation method. Our results show that VMT projections to different target areas originate mainly from different VMT neurons. However, in some cases single VMT neurons were found to send axon collaterals to two different areas. Three branching patterns were observed: septum-cortex, septum--nucleus accumbens and septum--striatum. The occasional observation of temporally distinct antodromic responses from a single area was considered to result from activation of different branches of the arborizing axon. The distribution of antidromic response latencies for VMT projections to each structure is discussed in relation to the question of dopaminergic versus non-dopaminergic mesolimbic and mesocortical systems.

Immune lesions of central noradrenergic neurons produced by antibodies to dopamine-beta-hydroxylase

(1) Intraventricular injection of antibodies to dopamine-beta-hydroxylase (DBH) caused degeneration of central noradrenergic nerve terminals in rats and guinea-pigs. In rats it was necessary to infuse exogenous complement in the form of guinea-pig serum together with the anti-DBH, whereas in guinea-pigs the anti-DBH was effective on its own. Control animals were infused with equivalent amounts of non-immune serum and complement and showed no signs of degeneration other than in the region of the needle tract. (2) There was a loss of varicosities in most terminal fields of the noradrenergic projections and swollen distorted axons were seen in both ascending and descending noradrenergic pathways. Noradrenergic cell bodies in the locus coeruleus and subcoeruleus appeared unaffected. No histochemical changes were observed in dopaminergic neurons. (3) The ultrastructural changes in degenerating axons that were first identifided by fluorescence histochemistry included swelling, vacuolation, accumulation of dense cored vesicles, lysosome-like bodies and smooth membranous sacs. The surrounding neuropil appeared normal. (4) There was a significant depletion of noradrenaline in all regions of the rat brain ranging from 20% in the hypothalamus to 80% in the neocortex. Dopamine concentrations were unaffected. (5) These observations provide a new approach to the production of selective lesions in specific neurotransmitter pathways that could be extended to non-adrenergic neurones. They may also be useful as a model for the study of autoimmune diseases of the nervous system.