Degenerative processes after punctate intracerebral administration of 6-hydroxydopamine

Characterization of a new low-dose 6-hydroxydopamine model of Parkinson's disease in rat

Intrastriatal administration of 6-hydroxydopamine (6-OHDA) induces partial degeneration of the nigrostriatal pathway, mimicking the pathology of Parkinson's disease (PD). Setting up the partial lesion model can be challenging because a number of experimental settings can be altered. This study compares seven experimental settings in a single study on d-amphetamine-induced rotations, tyrosine hydroxylase (TH)-positive neurites in the striatum, dopamine transporter (DAT)-positive neurites in the striatum, and TH-positive cells in the substantia nigra pars compacta (SNpc) in rats. Moreover, we validate a new algorithm for estimating the number of TH-positive cells. We show that the behavior and immunoreactivity vary greatly depending on the injection settings, and we categorize the lesions as progressive, stable, or regressive based on d-amphetamine-induced rotations. The rotation behavior correlated with the degree of the lesion, analyzed by immunohistochemistry; the largest lesions were in the progressive group, and the smallest lesions were in the regressive group. We establish a new low-dose partial 6-OHDA lesion model in which a total of 6 μg was distributed evenly to three sites in the striatum at a 10° angle. The administration of low-dose 6-OHDA produced stable and reliable rotation behavior and induced partial loss of striatal TH-positive and DAT-positive neurites and TH-positive cells in the SNpc. This model is highly suitable for neurorestoration studies in the search for new therapies for PD, and the new algorithm increases the efficacy for estimating the number of dopamine neurons. This study can be extremely useful for laboratories setting up the partial 6-OHDA model.

Astroglial and microglial reaction after a partial nigrostriatal degeneration induced by the striatal injection of different doses of 6-hydroxydopamine

Astroglial and microglial activation was analyzed in adult male Wistar rats after a unilateral striatal injection of different doses (8, 4 and 1 micrograms) of 6-hydroxydopamine (6-OHDA). Control animals received the injection of the same volume of the solvent. The rotational behavior was registered by a rotometer 24 and 72 hours, 7, 10, 14 and 22 days after lesion. Following, animals were sacrificed and the tyrosine hydroxylase (TH) positive dopamine cells, the glial fibrillary acidic protein (GFAP) immunolabeled astrocytes and the OX42 immunoreactive microglia were visualized by mean of immunohistochemistry and quantified by stereologic method employing the optical disector and the point intercepts. The apomorphine (0.5 mg/kg)-induced circling behavior was seen only after 8 micrograms of 6-OHDA from 72 hours postlesion until sacrifice. Decreases of the TH immunoreactive terminals and cell bodies were found in the sampled fields of the striatum and pars compacta of the substantia nigra (SNc), respectively, after 8 and 4 micrograms of 6-OHDA. The GFAP immunohistochemistry revealed increases in the number/density of astroglial cells in the ipsilateral neostriatum (137% of control) and ipsilateral SNc (83% of control) and also in the volumeal fraction of the astroglial processes in the ipsilateral neostriatum (30% of control) and ipsilateral SNc (38% of control) in the rats with higher dose of the neurotoxin. Increases in the number of OX42 microglial labeled profiles and in the volumeal fraction of microglial processes were found in the ipsilateral neostriatum (67% and 27%, respectively, of control) and ipsilateral SNc (100% and 50%, respectively, of control) in the 8 micrograms 6-OHDA injected rats. These results suggest that the retrograde degeneration induced by a intrastriatal injection of a small dose of the 6-OHDA leads to an astroglial and microglial reaction in the nigrostriatal dopamine pathway. The interaction between activated glial cells may be involved in the wounding and repair events in the partial lesioned nigrostriatal system as well as in the paracrine responses to surviving dopamine neurons.

Integrity of the mesocortical dopaminergic system is necessary for complete expression of in vivo hippocampal-prefrontal cortex long-term potentiation

The prefrontal cortex receives dopaminergic inputs from the ventral tegmental area and excitatory inputs from the hippocampus. Both afferent pathways target in close proximity dendritic spines of pyramidal cells in layer V-VI of the prefrontal cortex. In view of the prominent role of dopamine in cognitive functions we examined the effects of ventral tegmental area stimulation on the induction of long-term potentiation in the hippocampal-prefrontal cortex pathway of anesthetized rats. Stimulation of the ventral tegmental area at a frequency known to evoke dopamine overflow in the prefrontal cortex produces a long-lasting enhancement of the magnitude of the hippocampal-prefrontal cortex long-term potentiation. The role of dopamine was further examined by investigating the effects of prefrontocortical dopamine depletion induced by an electrolytic ventral tegmental area lesion. A significant correlation (r = 0.8; P < 0.001; n = 14) was obtained between cortical dopamine levels and cortical long-term potentiation amplitude, a depletion of more than 50% of cortical levels corresponding to a dramatic decrease in hippocampal-prefrontal cortex long-term potentiation. However, a recovery to normal long-term potentiation was observed 1 h after tetanic stimulation. In contrast to the effects on long-term potentiation, ventral tegmental area stimulation, when applied at low or high frequency, decreases the amplitude of the hippocampal-prefrontal cortex postsynaptic synaptic response. The present study demonstrates the importance of the integrity of the mesocortical dopaminergic system for long-term potentiation to occur in the hippocampal-prefrontal cortex pathway and suggests a frequency-dependent effect of dopamine on hippocampal-prefrontal cortex transmission.

Differential response of striatal dopamine and muscarinic cholinergic receptor subtypes to the loss of dopamine. I. Effects of intranigral or intracerebroventricular 6-hydroxydopamine lesions of the mesostriatal dopamine system

Quantitative autoradiography was utilized to examine the response of the dopamine (DA) and muscarinic cholinergic system within the striatum to lesions of the mesostriatal DA system following intranigral 6-hydroxydopamine (6-OHDA) injections. In addition, the response of DA system was examined in the striatum of animals treated with low, medium, or high doses of 6-OHDA made intracerebroventricularly (icv). Three weeks following removal of the mesostriatal DA fibers with intranigral 6-OHDA, there was an almost complete depletion of DA and [3H]mazindol binding throughout the striatum. The resulting increase in D2 receptors labeled with [3H]spiroperidol (27%) was most evident in the lateral striatum and topographically correlated with an increase in choline uptake sites labeled with [3H]hemicholinium-3 (20%). There was a smaller but significant decrease in D1 receptors labeled with [3H]SCH 23390 (15-18%) that was not topographically related to changes in [3H]spiroperidol or [3H]hemicholinium-3 binding. All doses of icv 6-OHDA produced a significant loss of DA and of [3H]mazindol binding as compared to vehicle injections that was more pronounced in the medial than in the lateral striatum. No increase in D1 receptors was observed with any dose of 6-OHDA and greater than 90% loss of DA and [3H]mazindol resulted in an increase in D2 receptors in the lateral striatum and a reduction in D1 receptors in the dorsal striatum. These data are consistent with the evidence that there is independent regulation of the two subtypes of the DA receptor. Moreover, the distribution and regulation of the subtypes of the muscarinic receptor were independent. Muscarinic M2 receptors ([3H]N-methylscopolamine in presence of excess pirenzepine) showed a lateral to medial gradient (highest laterally) that was related to the pattern of choline uptake sites and D2 receptors. Loss of DA resulted in a reduction in M2 receptors (24-30%) that was correlated with the increase in choline uptake sites. In contrast, M1 ([3H]pirenzepine) receptors showed a reverse gradient from the M2 receptor and a smaller reduction following loss of DA.

Effects of injection mechanics, pH of infusate and 6-hydroxydopamine on cerebromicrovascular permeability in rats

The effects of altering the rate, manner and vehicle used for intracerebral injection upon microvascular permeability were studied in Sprague-Dawley rats employing horseradish peroxidase histochemistry. The volume of vehicle delivered and the site of intracerebral injection were kept constant. In comparison to continuous infusion, vascular permeability was significantly greater following manual (intermittent) injections; however, no differences were found when the infusion rate was decreased 10-fold. Use of a buffered vehicle (Hanks' balanced salt solution) with pH adjusted to 7.4, in contrast to the more commonly used non-buffered vehicle (saline-ascorbate), resulted in significant reductions in permeability. The apparent influence of the agent 6-hydroxydopamine (6-OHDA) on changes in vascular permeability was found to vary depending on the type and pH of the vehicle used for injection. Significantly greater permeability resulted with saline-ascorbate (pH 3.1) as the vehicle when compared to Hanks' balanced salt solution (pH 7.4). Changes in vascular permeability can therefore be produced by varying mechanical and vehicular factors which, in the case of 6-OHDA, far outweigh previously reported permeability changes specifically attributed to this neurotoxin.

Effects of the noradrenaline neurotoxin N-2-chloroethyl-N-ethyl-2-bromo-benzylamine hydrochloride (DSP4) on the blood-brain barrier. An experimental study in the mouse using protein tracer and density determination techniques

Cerebral microvessels receive a noradrenergic innervation originating from the locus coeruleus. Previously, many studies have tried to elucidate the role of the central noradrenergic innervation on the blood-brain barrier (BBB). Many of them are based on chemical destruction of the innervation by local injection of 6-hydroxydopamine (6-OHDA) or physical injury to the locus coeruleus. Such methods are not selective and the results reported are contradictory. We have treated mice with a single i.p. injection of the compound, N-2-chloroethyl-N-ethyl-2-bromo-benzylamine hydrochloride (DSP4). This substance induces a selective noradrenaline depletion and, unlike 6-OHDA, it can pass into the brain after an i.p. injection. The animals were allowed to survive for 6 h to 60 days and the BBB was investigated with i.v.-injected horseradish peroxidase (HRP). Brain density values were also determined to find out of edema developed. The light microscopic distribution of HRP in the brain of DSP4-treated animals did not differ from that in control mice, i.e., there were no signs of increased BBB permeability to this protein tracer caused by DSP4. Density determinations revealed statistically significant reduced values in cerebrum (P less than 0.005) and rhombencephalon (cerebellum) (P less than 0.0005) of animals given 100 mg/kg body wt. of DSP4 indicating development of edema. A minor drop in density of the rhombencephalon (cerebellum) (P less than 0.05 at 48 h) and of the cerebrum (statistically not significant) appeared when 50 mg/kg body wt. of DSP4 was injected.(ABSTRACT TRUNCATED AT 250 WORDS)

Norepinephrinergic reinnervation of cat occipital cortex following localized lesions with 6-hydroxydopamine

We studied biochemical and morphological changes in central catecholamine (CA) terminals in the kitten visual cortex following direct infusion with 4 mM 6-hydroxydopamine (6-OHDA) for a week. Two zones may be distinguished within the cortical area affected by 6-OHDA (a radius of approximately 10 mm). In the primary lesion zone (a radius of approximately 5 mm) near the center of the 6-OHDA infusion, excluding an area of non-specific damage left by cannulation (a radius of less than 1.5 mm), we found: (1) absence of fluorescent CA terminals by histochemistry; (2) very low desipramine-sensitive uptake of tritiated norepinephrine (NE) by cortical slices (desipramine-resistant NE uptake stayed high); (3) a 50% increase in beta-adrenoreceptor binding sites by densitometry of light microscopic autoradiograms; and (4) low levels (less than 20% of control) of endogenous NE and low to moderate levels (10-70%) of endogenous dopamine (DA). In the surrounding zone (about 5-10 mm from the infusion center), however, none of the above changes were observed, except for a moderate to substantial reduction (50-80% of control) in endogenous NE and a small (10-20%) reduction in endogenous DA. Within two weeks after the end of the cortical 6-OHDA infusion, the dimensions of the cortical area devoid of CA terminals became substantially smaller than those found earlier. Fluorescent CA terminals were seen virtually everywhere in the cortex by 4 weeks, including the scar left by placement of the infusion cannula. In 24 weeks CA terminals in the occipital cortex appeared close to normal in density as well as in fluorescence intensity. Biochemical assays also revealed the recovery trend of CA contents. A steady increase in the NE content was obtained in the surrounding zone, with the stronger trend at its periphery, eventually attaining full recovery in 23 weeks. The recovery was slow in the primary lesion zone, especially near the infusion center, though there was a continual increase in endogenous DA toward control even at the infusion center.

Further studies on the neurochemical specificity of 6-hydroxydopamine as compared to radiofrequency lesions

Despite the large volume of literature during the past 15 years addressing the problem concerning the neurochemical specificity of 6-hydroxydopamine (6-OHDA), there is still disagreement over this issue. While some claim that the catecholamine-specific effects of this drug can be maximized by controlling the dose injected, others claim that all doses of 6-OHDA produce non-specific damage (NSD), thereby contraindicating its use in experimental paradigms. In the present study, we examined the degree of neurochemical specificity of 6-OHDA by comparing the volume of proximal accumulation to that of NSD, produced by 6-OHDA (2 microliter of 8 micrograms/microliter) or radiofrequency (RF) lesions (60 degrees C for 50 s and 45 degrees C for 30 s), placed in the medial forebrain bundle. The volume of NSD and accumulation produced by 6-OHDA was significantly less than that produced by large RF lesions which had a similar effect on the gross behaviour of albino rats. Smaller RF lesions produced similar volumes of NSD but less amine accumulation than did 6-OHDA, and did so without affecting normal behaviour. The ratio of NSD to accumulation in 6-OHDA treated rats was 3/1, while large and small RF lesions produced a NSD/accumulation ratio of 15/1. The present study introduces a novel method of determining the degree of neurochemical specificity which can be achieved with 6-OHDA and reveals that it is several magnitudes more neurochemically specific than RF lesions.

The amine accumulation-producing capacity of 6-hydroxydopamine and its neurochemical specificity

There was considerable research during the 1970's addressing the problem of the neurospecificity of 6-hydroxydopamine (6-OHDA). Despite the numerous attempts to define the criteria governing the use of this drug in experimental paradigms, some believed that specific damage to catecholamine (CA)-containing neurones could be achieved only by controlling the dose injected, while others claimed that the neurotoxic effect that this drug had on non-CA systems was so severe that it contraindicated its use experimentally. The issue still remains unresolved. In the present study, we examined the degree of neurochemical specificity produced by 6-OHDA or radiofrequency (RF) lesions by comparing the quantity of amine accumulation to the amount of physical damage at the lesion site (termed non-specific damage, NSD) which each technique produced. The volume of NSD produced by 6-OHDA (2 microliter of 8 micrograms/ul) was significantly less than that produced by large RF lesions (60 degrees C for 50 sec) both of which has a similar effect on the regulation of short term body weight. Both types of lesions produced similar quantities of amine accumulation. Smaller RF lesions (45 degrees C for 30 sec) produced the same amount of NSD as did 6-OHDA but significantly less amine accumulation and had no effect on body weight regulation. The ratio of NSD to amine accumulation in 6-OHDA treated rats was 3/1 while large and small RF lesions produced a NSD/accumulation ratio of 15/1. The present results reveal that the neurochemical specificity of 6-OHDA is several magnitudes greater than with RF lesions, when using the criteria as defined in the present experiment.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the selective noradrenergic neurotoxin DSP4 on cerebellar Purkinje neuron electrophysiology

The effect of the adrenergic neurotoxin DSP4 on cerebellar electrophysiology was studied in the rat. DSP4, administered parenterally, depleted cerebellar norepinephrine by 76%. The depressant response of cerebellar Purkinje neurons to phencyclidine, a drug which acts on adrenergic presynaptic terminals to release NE, was markedly reduced after DSP4 pretreatment. In contrast with 6OHDA, which increased firing rates of the Purkinje cells, DSP4 did not change the rate or pattern of Purkinje cell discharge. Taken together these results suggest that DSP4 may be a valuable tool for studying central adrenergic pathways, but that this drug has properties which differ from 6OHDA.

Intracerebral 6-hydroxydopamine produces extensive damage to the blood-brain barrier in rats

Extensive extravasation of intravenously administered horseradish peroxidase (HRP) was observed in rat brains infused intranigrally with 8 microgram/4 microliter or 4 microgram/2 microliter 6-hydroxydopamine (6-OHDA), suggesting that the cytotoxin produced widespread alterations in the integrity of the blood-brain barrier. Such damage was dose-dependent and occurred in the mesencephalon around the cannula tip, along the cannula tract, and in the cerebral cortex. The extent of HRP extravasation diminished as a function of increasing time after 6-OHDA administration. These findings indicate that alterations in blood-brain barrier permeability may contribute to the constellation of dysfunctions and possible recovery of function following intranigral infusions of the cytotoxin.

Partial lesions of the dopaminergic nigrostriatal system in rat brain: biochemical characterization

Various doses of 6-hydroxydopamine injected into the rat substantia nigra produced partial, dose-dependent lesions of the dopaminergic nigrostriatal tract. The resulting reduction in striatal dopamine concentrations and tyrosine hydroxylase activities tended to be proportional, allowing these measurements to serve as indices for lesion severity in any particular animal. Lesions destroying two-thirds or more of the nigrostriatal neurons accelerated dopamine's synthesis in, and release from, surviving neurons, as indicated by increased striatal levels of the dopamine metabolites dihydroxyphenylacetic acid and homovanillic acid. Formation of these metabolites was also enhanced in dendrites of dopaminergic neurons in the substantia nigra. Supersensitivity of striatal postsynaptic receptors, as judged by induction of rotational behavior after apomorphine or L-DOPA administration, occurred when 90% or more of the nigrostriatal neurons had been destroyed. In contrast, rotational behavior could be induced by amphetamine in animals with only 50% of these neurons destroyed.

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.

Preservation of binocularity after monocular deprivation in the striate cortex of kittens treated with 6-hydroxydopamine

The results of single unit recordings from Area 17 of monocularly deprived kittens were compared with similar ones from littermates who had been monocularly lid-sutured for the same period of time, but who had in addition been given intraventricular injections of 6-hydroxydopamine (6-OHDA) to deplete brain catecholamines. This visual cortices of all catecholamine-depleted kittens showed high proportions of binocular neurons, in contrast to the control group, a majority of whose visual cortical neurons were driven exclusively by the non-deprived eye. Preservation of binocularity in 6-OHDA-treated kittens was dose-related. Even after a 1 to 2-week period of lidsuture which reduced binocularity to 20% in controls, normal proportions of binocular neurons (greater than 75%) were preserved if the cumulative dose had been 10 mg 6-OHDA or more. The density of single neurons sampled from electrode tracks through the cortex of drug-treated kittens was high and did not differ significantly from controls. Neurons were isolated every 100 micron on the average. There was some indication that the drug's effect in preventing an ocular dominance shift disappears by six weeks following cessation of 6-OHDA treatment. This reversal of the physiological effects in cortex is preceded by recovery from the behavioral manifestations of 6-OHDA treatments. Binocularity was only slightly increased in a kitten who received large doses of 6-OHDA after a period of monocular deprivation. This observation, together with control recordings from normal kittens and adults treated with 6-OHDA, indicates that the direct effects of 6-OHDA on cortical neurons' response properties play a minor role in comparison to its effects in reducing the sensitivity of the cortex to monocular deprivation. The overwhelming majority of cortical neurons in 6-OHDA-treated kittens remained normal in receptive field properties after a period of monocular deprivation. These data support the hypothesis that catecholamines are required for the maintenance of visual cortical plasticity during the critical period.

GABA receptor binding in rat striatum: localization and effects of denervation

Intrastriatal injection of 2 microgram of kainic acid, a conformationally restricted analogue of glutamate, causes degeneration of GABAergic neurons intrinsic to the striatum while sparing axons of extrinsic neurons terminating in or passing through the region. From 2 to 15 days after striatal lesion with kainate, the sodium-independent binding of [3H]-psi-aminobutyric acid (GABA) to striatal membranes is increased 200% above that of control. Differences in the amount of endogenous GABA contaminating the membrane preparations do not account for the increased receptor binding. Scatchard analysis reveals an increased affinity of the GABA receptor in the kainate-lesioned striatum with no change in the number of binding sites. The subcellular distribution of the receptor as well as the sensitivity of the receptor to several agonists and antagonists is unchanged by the kainate lesion. Ablation of the nigrostriatal dopaminergic pathway by nigral injection of 8 microgram of 6-hydroxydopamine reduces by 22% the specific binding of [3H]GABA in the ipsilateral striatum and attenuates by 33% the increase in GABA receptor binding produced by the striatal kainate lesion. These studies demonstrate that (1) the sodium independent binding sites for GABA in striatum are localized on axons of extrinsic neurons, and (2) the affinity of these receptors for GABA increases in response to GABAergic denervation.

Striatal lesions with kainic acid: neurochemical characteristics

Stereotaxic injection of 2.5 microng of kainic acid, a rigid analogue of glutamate into the rat striatum caused a 70% reduction in the striatum of the cholinergic parameters, choline acetyltransferase, acetylcholine and synaptosomal uptake of choline and a similar reduction in the GABAergic parameters, glutamic acid decarboxylase, psi-aminobutyric acid (GABA) and synaptosomal uptake of GABA. In contrast, the striatal content of dopamine and the synaptosomal uptake of dopamine were unchanged, and the activity of tyrosine hydroxylase was significantly increased. Significant changes in the activity of neurotransmitter synthesizing enzymes were demonstrable within 6h after injection of 2.5 microng of kainic acid and maximal effects occurred at 48h; the activities of choline acetyltransferase and glutamic acid decarboxylase remained depressed up to 21 days after injection. The kinetic characteristics of striatal tyrosine hydroxylase were altered 48h after injection with a two-fold increase in the Vmax for tyrosine and a three-fold reduction in Km for the pteridine cofactor. In contrast to the effects of kainic acid, the injection of copper sulfate, a non-specific toxin, caused a proportionate reduction in the dopaminergic as well as the cholinergic and GABAergic presynaptic markers. The kainate lesion caused an 85% decrement in the activity of dopamine-sensitive adenylate cyclase, a 40% reduction in the specific binding of [3H]quinuclidinyl benzilate and a 195% increase in the specific binding of [3H]GABA in the striatum. The morphology of the kainate injected striatum was markedly altered with nearly a complete loss of intrinsic neurons, increased number of glial cells but intact internal capsule fibers. Intracerebral injection of nanomolar quantities of kainic acid appears to cause degeneration of neurons with cell bodies near the injection site while sparing axons terminating in or passing through the region.

Regulatory deficits after surgical transections of three components of the MFB: correlation with regional amine depletions

Parasagittal knife cuts along the lateral border of the diencephalon (PS), coronal cuts across the lateral (LMFB) or medial (MMFB) components of the medial forebrain bundle reproduce most of the persisting deficits in responding to glucoprivic and hydrational challenges that characterize rats with lateral hypothalamic lesions or intracranial injections of 6-hydroxydopamine (60HDA). Each of these cuts produced a differnet pattern of regulatory deficits, suggesting that individual components of the LH syndrome may be mediated by different neural substrates. This interpretation is supported by the results of our correlational analysis of the relationships between specific behavioral and biochemical effects of our cuts. For example, feeding responses to insulin were reliably correlated with striatal DA concentrations but feeding responses to 2-deoxy-d-glucose (2DG) were not. Water intake during periods of food deprivation was reliably correlated with striatal DA but water intake after an experimental osmotic challenge was not. Only one of the common persisting deficits (impaired feeding response to peripheral injections of insulin) was positively correlated with the duration of aphagia and adipsia.

Effects on hypothalamic and telencephalic NE and 5-HT of tegmental knife cuts that produce hyperphagia or hyperdipsia in the rat

Knife cuts in the coronal plane through various aspects of the midbrain tegmentum produced hyperphagia, hyperdipsia, or no effect on ingestive behavior. All of the cuts significantly depleted NE and 5-HT from hypothalamus and forebrain. The brains of hyperphagic or hyperdipsic animals did not differ from those of normophagic and normodipsic animals with respect to hypothalamic NE or 5-HT or telencephalic NE. Both hyperphagic and hyperdipsic animals had significantly lower concentrations of 5-HT in forebrain than rats which sustained similar cuts in the tegmentum which did not affect ingestive behavior.