Raphe Lesions Research Articles

Differential effects of medial, central and basolateral amygdaloid lesions on four models of experimentally-induced aggression in rats

To clarify whether various nuclei of the amygdaloid complex play different roles in aggressive behavior including muricide, 4 types of aggression were experimentally induced in rats. These include olfactory bulbectomy (OB rats), midbrain raphe lesions (Raphe rats), administration of Δ 9-tetrahydrocannabinol (THC rats) and long-term isolation (Iso rats). Rats which exhibited muricide following these treatments were subjected to bilateral lesions of either the medial (AME), central (ACE) or basolateral (ABL) amygdaloid nuclei. Both muricide and hyperemotionality in the OB rat were markedly inhibited by AME lesions. Those of the Iso and THC rats were moderately inhibited. However, in the Raphe rat, aggressive behavior was not inhibited by AME lesions. Furthermore, ACE or ABL lesions caused no significant changes in all 4 models of aggression. These results suggest that the AME plays a facilitatory role in aggression of OB, Iso and THC rats, but aggression in Raphe rat is independent of amygdaloid activity.

Effects of locus coeruleus stimulation on muricide in olfactory bulbectomized and raphe lesioned rats.

In order to elucidate the role of central monoamines in muricide of the rat, the effects of electrical stimulation of the locus coeruleus (LC) were investigated on two types of muricide induced by olfactory bulbectomy (OB rats) and midbrain raphe lesions (raphe rats). Muricide was inhibited in 71.4% of the OB rats by bilateral LC stimulation and in 26.7% by unilateral stimulation. Even in the rat in which muricide was not inhibited following LC stimulation, muricide was almost invariably suppressed by LC stimulation after pretreatment with pargyline. The antimuricidal effect of LC stimulation was partially blocked by administration of propranolol, but not by phenoxybenzamine. In contrast, muricide was inhibited by bilateral LC stimulation in 44.4% of the raphe rats, but this effect was not potentiated by pretreatment with pargyline. On the other hand, muricide was not significantly inhibited by either dorsal raphe or medial raphe stimulation in any OB rats. These results suggest that noradrenaline plays a more important role in inhibiting muricide in OB rats than in raphe rats.

Pharmacological evidence that serotonergic stimulation of prolactin secretion is mediated via the dorsal raphe nucleus.

Administration of the serotonin-releasing drug DL-p-chloroamphetamine (PCA) to rats caused a dose-dependent increase in plasma prolactin levels. The effect was maximal 2 h after administration. The effect of PCA was prevented by prior administration of the serotonin synthesis inhibitor p-chlorophenylalanine-methyl ester (PCPA). PCPA pretreatment did not prevent the increase in plasma prolactin levels after administration of the serotonin agonist quipazine which is consistent with a postsynaptic receptor interaction of quipazine. To determine which serotonergic neurons are involved, the prolactin responses to PCA were determined in rats sustaining lesions of the dorsal or median raphe nuclei. The lesions were produced in desmethylimipramine-pretreated rats by local injections of 5,7-dihydroxytryptamine (5,7-DHT) 2 weeks prior to the PCA challenge. In rats with dorsal raphe lesions, the effect of PCA on prolactin secretion was significantly attenuated. In contrast, median raphe lesions did not prevent the effect of PCA on plasma prolactin levels. In summary, these data support the hypothesis that release of serotonin increases prolactin secretion. In addition, these data suggest that serotonergic neurons in the dorsal raphe nucleus are part of a neural pathway which can mediate increases in prolactin secretion.

A radioautographic and immunocytochemical study of the GABA systems of the habenula complex in the rat

Radioautography of [ 3H]GABA accumulation and immunocytochemistry of glutamate decarboxylase have been used to study anatomically and morphologically the GABA system of the rat habenular (Hb) complex. Radioautographic visualisation of GABA specific neurons show a very high innervation of the complex including both stria medullaris (SM), the habenular commissure and the periventricular thalamic fibers (FPVT). A massive labeled fiber system in the SM appears to divide into two branches when it reaches the Hb nuclei: a part of fibers continue their course dorsally to the nuclei up to the habenular commissure; other fibers enter the Hb lateralis or run along the ventral Hb medialis at the level of FPVT. The staining is markedly diminished in the entire complex in response to SM lesions. In the Hb lateralis, the radioautographic-positive reaction is mainly bound to labeled fibers or axonal varicosities. However GAD immunocytochemistry reveals some GAD-positive cell bodies in the ventro-median portion of the nucleus. In the Hb medialis the radioautographic and immunocytochemical staining is observed in the neuropile between the unlabeled large cell bodies. In the subependymal layer bundles of processes are strongly labeled and form a continual strain behind the unlabeled ependymocytes. Three types of reactive terminals have been differentiated based on size and shape of vesicles. Some of them are exclusively characterized by clear round vesicles and probably have their origin in the septum. Others contain clear vesicles and some large dense-cored vesicles and disappear after mesencephalic Raphe lesions or 5,7-dihydroxytryptamine treatment. They could correspond to terminals of raphe neurons with a double potentiality GABA and 5HT. The last exhibit mainly a dense population of large dark-cored granules similar to the ones found in neurosecretory nerve endings. However numerous fibers morphologically similar to the reactive fibers are unlabeled.

EFFECTS OF LOCUS COERULEUS STIMULATION ON MURICIDE IN OLFACTORY BULBECTOMIZED AND RAPHE LESIONED RATS

In order to elucidate the role of central monoamines in muricide of the rat, the effects of electrical stimulation of the locus coeruleus (LC) were investigated on two types of muricide induced by olfactory bulbectomy (OB rats) and midbrain raphe lesions (raphe rats). Muricide was inhibited in 71.4% of the OB rats by bilateral LC stimulation and in 26.7% by unilateral stimulation. Even in the rat in which muricide was not inhibited following LC stimulation, muricide was almost invariably suppressed by LC stimulation after pretreatment with pargyline. The antimuricidal effect of LC stimulation was partially blocked by administration of propranolol, but not by phenoxy-benzamine. In contrast, muricide was inhibited by bilateral LC stimulation in 44.4% of the raphe rats, but this effect was not potentiated by pretreatment with pargyline. On the other hand, muricide was not significantly inhibited by either dorsal raphe or medial raphe stimulation in any OB rats. These results suggest that noradrenaline plays a more important role in inhibiting muricide in OB rats than in raphe rats.

Ingestive behaviors of rats with electrolytic median raphe lesions maintained on a food deprivation schedule

The current study examines the effects of electrolytic median raphe lesions on the feeding and drinking behaviors of rats maintained on a 23-hr food deprivation schedule. Measurement of food intake during the feeding period indicated no difference between the two groups but lesioned animals showed significantly more spillage than controls. Furthermore, measurement of water intakes indicated that median raphe lesioned rats consume significantly less water than controls in the absence of food and come to ingest virtually all of their daily fluid intake during the feeding period. Additionally, rats with lesions of this nucleus take significantly more drinks during the feeding period, often punctuating their meal with short draughts. Since similar behaviors are seen following the destruction of certain hypothalamic and limbic nuclei anatomically related to the median raphe, it is possible that these syndromes share an anatomical basis.

Shock-induced suppression of drinking following electrolytic median raphe lesions

Electrolytic lesions of the median raphe nucleus in rats were found to attenuate the suppression of drinking produced by noncontingent footshock presented in an environment in which the rats had been trained to drink. Standard passive avoidance of an electrified drinking tube, however, was not altered, demonstrating that, under some circumstances, animals with raphe lesions are capable of showing normal inhibition of a reinforced response. It is suggested that these results may reflect an impairment in the attention paid to less salient aspects of the stimulus environment.

Effect of brain serotonin level on induced hippocampal paroxysmal activity in rats

Experiments were performed to study the involvement of brain 5-HT in an experimental model of epilepsy induced by repeated electrical stimulation of the dorsal hippocampus of rats. The experiments included: (1) systemic injections of 5-hydroxytryptophan (5-HTP) and p-chlorophenylalanine (pCPA) and (2) electrolytic lesions of the midbrain raphe nuclei. The pCPA group showed a significant increase while animals which received systemic injections of 5-HTP showed a great reduction in the electrographic seizure activity. Although several reports have shown that midbrain raphe lesions do not modify the 0pileptic susceptibility, we observed a clear enhancement in the epileptiform activity in lesioned animals. The results presented here support the view that serotonergic systems may exert a tonic inhibitory effect on hippocampal epileptic activity.

The effects of stimulation and lesion of raphe nuclei on luteinizing hormone release in estrogen-progesterone-treated ovariectomized rats

A study was made of the effects of electrochemically stimulating (ECS) and destroying the midbrain dorsal and median raphe nuclei on the estrogen-progesterone- (EP) induced surge of pituitary LH release in ovariectomized rats. ECS and lesions were produced simultaneously with anodal direct current through a chronically implanted stimulation-lesion electrode. Blood for LH assay was collected through a chronic intra-atrial cannula positioned on the day of first treatment with progesterone. ECS of the raphe nuclei exerted a strong inhibition of the LH surge when compared with sham stimulation. On the second EP treatment the onset of the LH surge was advanced both in sham-stimulated animals and in rats with raphe lesions resulting from the anodal direct current of the initial ECS. It was suggested that this apparent facilitation of the LH surge on the second EP treatment was the result of reduced stress or an altered hormonal milieu and not a consequence of destroying the raphe nuclei. The results confirm in a chronic preparation that stimulation of raphe nuclei depresses the EP-induced LH surge and that subsequently in the absence of the raphe nuclei the LH response to EP treatment is apparently normal.

Aromatic L-amino acid decarboxylase in rat corpus striatum: implications for action of L-dopa in parkinsonism.

We studied the distribution of aromatic L-amino acid decarboxylase (AAAD) activity in striatal compartments of rats. After near-total destruction of nigrostriatal dopaminergic neurons, 15 to 20% of the initial enzyme activity remained. Striatal enzyme activity remained unchanged after destruction of serotoninergic terminals by electrolytic raphe lesions. Combined raphe-nigrostriatal lesions or nigrostriatal lesions alone produced similar decreases in striatal decarboxylase. Intrastriatal injection of kainic acid (which selectively destroys striatal interneurons and efferent neurons and also induces marked glial proliferation) reduced activity by 20%. Only 7% of initial striatal activity (perhaps localized in capillaries) remained after combined nigrostriatal-kainic acid lesions. These findings indicate that after degeneration of dopaminergic terminals, striatal interneurons and efferent neurons, but not serotonergic terminals of glia, contain an important fraction of the residual AAAD. This compartment may be the site of enzymatic conversion of exogenous L-dopa to dopamine in the parkinsonian striatum.

Effect of morphine on circling behaviour in rats with 6-hydroxydopamine striatal lesions and electrolesions of the raphe nucleus

Morphine antagonized d-amphetamine circling in rats which had received unilateral 6-OHDA lesions of the striatum but failed to reduce the circling in rats with both a unilateral 6-OHDA striatal lesion and a raphe (5-HT) lesion. Naloxone precipitated withdrawal of morphine tolerant rats greatly enhanced d-amphetamine circling when the rats had a 6-OHDA lesion but not when both 6-OHDA and raphe lesions were present. It is concluded that 5-HT is necessary for the morphine-induced inhibition of the circling. The effect of morphine tolerance and naloxone precipitated withdrawal on brain 5-HT function was investigated using a putative 5-HT rotation model in which both dopamine and a 5-HT agonist were administered to rats with an asymmetrical medial raphe lesion. The findings suggest that chronic treatment with morphine increases striatal 5-HT function.

Time-course of alterations in morphine-induced analgesia and nociceptive threshold following medullary raphe lesions

Electrolytic lesions which included major portions of the nucleus raphe magnus produced alterations in nociceptive threshold and morphine-induced analgesia. These effects were highly dependent on the time at which measurements were made following the lesioning procedure. Seven days or less after placement of the lesions there was a pronounced decrease in nociceptive threshold, but no effect on the capacity of morphine to induce antinociception. However, the nociceptive threshold exhibited recovery by 21–28 days, during which time there was a gradual, but profound, decrease in the capacity of morphine to induce analgesia. At longer times after the placement of lesions (28–35 days), the nociceptive threshold, assessed using the tail-flick test, became elevated concomitant with a recovery of morphine's analgesic potency. The differential time course of the lesion-induced attenuation of morphine analgesia and decrease in nociceptive threshold suggests that these effects result from the destruction of separate neuronal systems. Thus, the lesion-induced decrease in nociceptive threshold probably results from destruction of raphespinal serotonergic neurons while the attenuation of morphine analgesia is most likely an indirect result of damage to non-serotoninergic raphe-spinal neurons. Finally, the failure of acute raphe lesions to alter morphine analgesia indicates that the neurons found in the raphe magnus are not directly involved in mediating the antinociceptive actions of opiates.

Effects of raphe lesions on circadian ACTH, corticosterone and motor activity rhythms in free-running blinded rats

Blinded female rats underwent additional midbrain raphe lesions, in order to explore the role of the raphe in the organization of endogenous circadian rhythms for ACTH, corticosterone (B) and motor activity (MA). Amplitudes and mean levels of rhythms were depressed for ACTH and MA, with persistent free-running circadian periodicity for MA and, in several rats, for ACTH and B as well. Other rats exhibited split circadian and ultradian rhythmicity for ACTH and B, whereas others again displayed no detectable ACTH rhythmicity. These results are discussed in the light of the structure of circadian pacemaker systems.

The role of central serotonergic mechanisms on head-twitch and backward locomotion induced by hallucinogenic drugs

Head-twitch induced by lysergic acid diethylamide, mescaline and 2,5-dimethoxy-4-methylamphetamine (DOM) was significantly increased by medial raphe (m-R) lesions, but dorsal raphe (d-R) lesions did not produce any changes. Hallucinogen-induced head-twitch was inhibited by methysergide and tended to be increased by PCPA. These results suggest that 5-HT receptors innervated with the ascending 5-HT pathway originating in the m-R play a vital role in the manifestation of hallucinogen-induced head-twitch. That is, increase of head-twitch is ascribed to supersensitivity of 5-HT receptors. On the other hand, DOM-induced backward locomotion was inhibited by m-R or both dorsal and medial raphe lesions and methysergide, and was reversed to forward locomotion, differently from the hallucinogen-induced head-twitch. A reversion of backward locomotion was not obtained with d-R lesions or PCPA treatment.

Actions of tetrahydronorharmane (tetrahydro-β-carboline) on 5-hydroxytryptamine and dopamine mediated mechanisms

The activity of 5-hydroxytryptamine (5-HT) or dopamine (DA) containing neurones of rats was blocked either by neurotoxic agents [ p-chlorophenylalanine ( p-CPA), 6-hydroxydopamine (6-OHDA)], or thermolytic lesions (raphe nuclei, medial forebrain bundle). To assess the effect of the various pretreatments on 5-HT-dependent mechanisms, the hyperactivity-syndrome-test was used. 5-Hydroxytryptophan as well as tetrahydronorharmane (THN) evoked the syndrome in a dose-dependent manner. Combined treatment led to a potentiation of the effects of the single drugs. Lesions of the raphe nuclei reduced the THN-elicited activity syndrome. 6-OHDA had no effect under the same conditions. Injection of 300 mg/kg p-CPA caused a shift to the left of the THN-curve. Following two doses of p-CPA on consecutive days, THN induced a cataleptic syndrome. To assess DA-dependent mechanisms, apomorphine-evoked stereotyped behaviour was used. Pre-treatment with 2 × 300 mg/kg p-CPA as well as lesions of the raphe nuclei reduced the compulsive licking. Thus, the integrity of 5-HT-containing neurones is obviously required for the action of apomorphine. Licking movements were diminished by THN. Pretreatment with 6-OHDA strengthened this action of THN. The effect can be explained by an inhibition of postsynaptic dopaminergic receptors by THN which is not modulated by the stimulating action of 5-HT neurones on DA-containing cells after their destruction by 6-OHDA. The ffect of p-CPA pretreatment and raphe lesions on apomorphine-induced licking was neutralized by THN and this was interpreted as a direct postsynaptic stimulation of 5-HT-receptors.

Effects of raphe magnus and raphe pallidus lesions on morphine-induced analgesia and spinal cord monoamines

These studies examined the role of bulbospinal serotonin-containing neurons found in the nucleus raphe magnus and nucleus raphe pallidus in the mediation of morphine-induced antinociception. Lesions were made using both electrolytic coagulation and the axon-sparing technique of monosodium-L-glutamate injection to ascertain whether the effects following lesions in the area of the medullary raphe nuclei are due to destruction of neuronal perikarya or fibers passing near these nuclei. These studies revealed that lesions of both the raphe magnus and raphe pallidus resulted in decreased nociceptive thresholds and attenuation of morphine-induced analgesia. Such effects were observed regardless of the lesioning method used, which suggests that destruction of neurons in these nuclei was responsible for lesion-induced effects. In addition, lesion-induced changes in spinal cord serotonin content and morphine analgesia were significantly correlated which lends support to the conclusion that the bulbospinal serotonin systems are necessary for the mediation of morphine effects. Furthermore, no correlation was observed between changes in spinal cord norepinephrine content and morphine analgesia. This observation suggests that lesion-induced damage to bulbospinal noradrenergic fibers which pass near the midline does not contribute to the attenuation of morphine analgesia resulting from raphe lesions.

Septal elicitation of hippocampal theta rhythm after localized de-afferentation of serotoninergic fibers

Previous experiments using serotonin antagonists and electrolytic raphe lesions suggest that the serotonergic input to the hippocampus inhibits low frequencey (< Hz) theta rhythm in the rat, whereas experiments using raphe stimulation suggest facilitation. The present experiments employed neurotoxic lesions of the serotonergic input to the hippocampus in an attempt to reproduce the effects of systemically administered antagonists. If the septal area is stimulated at frequencies between 6 and 10 Hz in the rat, the threshold current for driving hippocampal theta is minimum at 7.7 Hz. Systemic blockage of serotonergic synapses has been shown to shift this minimum to 6.9 Hz. In the present experiments, neurotoxic lesions were made with injections of 5,7-dihydroxytryptamine into the cingulum bundle, fornix or both. The observed effect depended on the loss of serotonin in the hippocampus, rather than the site of injection, and extensive depletion shifted the minimum to 6.9 Hz. These results indicate that the fornix and cingulum serotonergic inputs to the hippocampus are functionally homogenous, at least with respect to this response; and that the effects of systemic manipulation of serotonin systems on the septal elicitation of hippocampal theta rhythm may be attributed to changes in these two inputs.

Effects of serotonergic lesions on investigatory responding by rats in a holeboard

Both the frequency and the typical durations of nose pokes by rats (male Sprague-Dawleys) into holes in the floor during a 24-min session in a holeboard were markedly increased by electrolytic lesions of the median raphe nucleus, and only slightly increased by lesions of the dorsal raphe nucleus. The raphe lesion-induced augmentation of holeboard responding was evident both 5 and 21 days after surgery, although a significant attenuation of the effect was found in the latter test. These lesions reduced hippocampal and striatal serotonin, respectively. However, comparable depletions of forebrain serotonin produced by infusions of the neurotoxin, 5,7-dihydroxytryptamine, into the lateral ventricle (100 μg/10 μl), the hippocampus (45 μg/4.5 μl each side), or the median raphe nucleus (3 μg/0.3 μl) had no significant effect on behavior in the holeboard. Furthermore, the neurotoxin was ineffective in affecting holeboard responding in the same animals in which hyperreactivity was demonstrable in a tactile startle test. These results suggest that the effects of electrolytic raphe lesions on behavioral measures of reactivity are better related to depletions of forebrain serotonin than are the effects of these lesions on measures of activity or investigatory behavior. An additional experiment demonstrates that the reductions in holeboard responding produced by either the hallucinogen, d-lysergic acid diethylamide (100 μg/kg), or the dopaminergic agonist, apomorphine (1.0 mg/kg), are unaltered by either electrolytic or neurotoxic lesions of the ascending serotonergic pathways. Therefore, the effects of these drugs on investigatory responses in a holeboard appear to be independent of their effects on central serotonergic systems.

The effect of raphe lesion on sleep in the rat

The midbrain raphe nuclei (nucleus raphe dorsalis and nucleus raphe medialis) were destroyed by electrocoaggulation in rats. On the first few days following the lesion, a marked hyperactivity was observed in lesioned animals as well as in shame-operated controls. Between the 5th and 36th days after the lesion, sleep patterns did not differ either qualitatively or quantitatively from the shame-operated and intact controls. The forebrain 5-HT level was reduced to 33.85%. It is concluded, that in rats restoration of the sleep system after the destruction of midbrain raphe nuclei is extremely rapid and effective. 5-HT seems to play an important role in this restored sleep system even though the forebrain 5-HT content was still markedly reduced.

The effects of electrolytic median raphe lesions on two measures of latent inhibition

This study investigates the effects of median raphe lesions on the ability of conditioned stimulus preexposure to impair the acquisition of a shuttlebox avoidance and a taste aversion task. Control rats, who were exposed to the conditioned stimulus prior to its signaling of shock, were impaired relative to nonpreexposed controls in the subsequent acquisition of a shuttlebox avoidance response. In contrast, the performance of rats with median raphe lesions was not affected by preexposure to the conditioned stimulus. Using a taste aversion paradigm, however, lesioned and control subjects showed similar fluid intakes of a flavored solution following a 7-day preexposure period prior to pairing with illness. It is suggested that the appearance of latent inhibition in median raphe-lesioned rats may depend on the saliency of the conditioned stimulus.