Microinjection Of Morphine Research Articles

Reinforcing effects of brain microinjections of morphine revealed by conditioned place preference

The previously documented place conditioning paradigm 25 was used to study the reinforcing effects of cerebral microinjections of morphine. Rats with implanted cannulae experienced place conditioning procedures, involving morphine administration into the IV (0.5 or 10 μg), III (10 μg) or lateral (0.5–10 μg) ventricles. Positive reinforcement, indicated by a significant preference for the place paired with morphine compared to the place similarly paired with control treatment, was seen in rats given 10 μg morphine into the lateral ventricle. The rats given 10 μg into the III ventricle also showed a preference, but the effect was not statistically significant. Positive reinforcement was subsequently demonstrated with morphine microinjections (10 μg) into the lateral hypothalamus, periaqueductal gray or nucleus accumbens. No clear preferences were produced by morphine injections into the caudate-putamen, amygdala or nucleus ambiguus. Following the final place conditioning test, rats were re-administered the treatment dose and analgesia and body temperature were measured. All three sites associated with reinforcement evidenced hyperthermia, but only the periaqueductal gray evidenced a short-latency analgesia. Sites with null place conditioning were not associated with any major behavioral effects. Using (+) and (−)-morphine (10 μg), it was demonstrated that only the active (−)-stereoisomer was effective in producing place preferences after injection into the periaqueductal gray. It was concluded that morphine administered directly into parts of the rat brain can produce place conditioning similar to that seen after systematically administered morphine 25. Morphine-produced place preference is not related to the acute depressant aspects of morphine, but may be related to the stimulant aspects.

Failure of spinal cord serotonin depletion to alter analgesia elicited from the periaqueductal gray

The effects of spinal cord serotonin depletion or combined serotonin/norepinephrine depletion on analgesia elicited by electrical stimulation of, or morphine microinjection into, the periaqueductal gray, were tested. Spinal cord serotonin was depleted by intrathecal injection of 5,7-dihydroxytryptamine (5,7-DHT), preceded by systemic desipramine, while 5,7-DHT alone was used to deplete both norepinephrine and serotonin. Selective serotonin depletion had no effect on analgesia induced by either method at 24 h, 1 week, or 2 weeks after treatment. Depletion of both monoamines had no effect on stimulation produced analgesia 24 h and one week after treatment, but produced a slight attenuation 2 and 3 weeks after treatment. In contrast, depletion of both monoamines drastically attenuated morphine analgesia 24 h after treatment. The results are discussed in relation to multiple pain inhibitory pathways.

Inhibition of spinal neurons by microinjection of morphine and focal stimulation in the mesencephalon of the cat

Inhibition of spinal neurons by microinjection of morphine and focal stimulation in the mesencephalon of the cat

A spinal opioid synapse mediates the interaction of spinal and brain stem sites in morphine analgesia

The interaction of spinal and brain stem opiate-sensitive sites was investigated using microinjection of morphine and naloxone into the fourth ventricle and lumbar subarachnoid space of the rat. Depending on the order of administration, spinal naloxone either partially or completely blocked the effect of ventricular morphine on both a spinal nociceptive reflex (tail-flick) and a complex nociceptive behavior (‘pain-induced’ vocalization). This suggests that the antinociceptive effects of ventricular morphine involve an endogenous opioid link at the level of the spinal cord.

Lesion in nucleus reticularis gigantocellularis: effect on the antinociception produced by micro-injection of morphine and focal electrical stimulation in the periaqueductal gray matter

The effect of bilateral electrolytic lesions in the nucleus reticularis gigantocellularis (NGC) on the antinociceptive efficacy of morphine and electrical stimulation applied in the periaqueductal central gray matter (PAG) was investigated. Antinociception, evaluated by standard hot plate and tail-flick analgesiometric tests, was reliably produced by morphine (5 μg) and focal electrical stimulation (40–200 μA) administered in the PAG of rats via chronic indwelling cannula/electrode assemblies. Subsequent to the initial antinociceptive testing, bilateral electrolytic lesions were introduced in the NGC and the antinociceptive efficacy of morphine and stimulation in the PAG was again evaluated. Lesions in the NGC prevented the expression of the antinociception produced by the microinjection of morphine in the PAG whereas the antinociception resulting from electrical stimulation in the PAG was unaffected. Further, lesions in the NGC did not alter baseline (control) nociceptive thresholds in either analgesiometric test. These results provide additional support for involvement of the NGC in morphine-induced antinociception and, in addition, suggest that the NGC is not essential to a tonically-active inhibitory system or to the antinociception produced by focal electrical stimulation in the PAG.

Morphine administration in the amygdala or periaqueductal central gray depress serum levels of luteinizing hormone

The ability of morphine to depress serum levels of luteinizing hormone (LH) directly at extrahypothalamic sites was examined in male rats with guide cannulae implanted bilaterally in either the amygdala or the periaqueductal central gray (PAG). While no alterations in serum levels of LH in blood sampled via a chronic jugular catheter were observed following the microinjection of morphine, naloxone or artificial CSF in the amygdala or the PAG of intact males, serum levels of LH were significantly depressed in castrated rats following intracranial administration of morphine bilaterally in the cortical amygdala or the PAG. The intracranial administration of naloxone bilaterally in the PAG likewise significantly elevated serum levels of LH in castrated rats. These data further establish the amygdala and the PAG as extrahypothalamic sites which can directly mediate the opiate-induced effects on LH.

Release of Prolactin in Response to Microinjection of Morphine into Mesencephalic Dorsal Raphe Nucleus

Blood samples were collected via jugular catheters from ovariectomized rats at 10-min intervals for 1 h before and 2 h after microinjection of 0.5 microliter of either saline vehicle or morphine sulfate (10 micrograms) into the dorsal raphe nucleus (DRN) or adjacent periaqueductal gray by means of chronically-implanted guide cannulae. Prolactin was measured by radioimmunoassay, and mean preinjection and mean postinjection values were compared for each rat (t test) as well as for each treatment group (paired t test). Neither saline in DRN nor morphine in the surrounding periaqueductal gray significantly altered circulating prolactin. A significant rise in prolactin was observed following injection of morphine into DRN. This effect of morphine was prevented by pretreatment of the animals with the narcotic antagonist naltrexone (10 mg/kg i.v.), indicating the involvement of opiate receptors. These results indicate that DRN is one site at which systemically-administered morphine might act, and suggest the possibility of participation of this mechanism in modulation of prolactin release by endogenous opioids.

Effects of morphine and naloxone on the responses to noxious stimulation of neurones in the nucleus reticularis paragigantocellularis

Studies were made of the effects of morphine and naloxone applied by microiontophoresis to neurones in the nucleus reticularis paragigantocellularis (NRPG) of the rat. The baseline firing rate of the majority of cells was unaffected but where effects were seen large currents of morphine (150 nA) tended to be excitant but smaller currents (50 nA) to be depressant. Both types of response were blocked by naloxone. The responses of neurones to noxious and non-noxious stimulation of the hind limb were compared. Sixty-nine per cent of the cells responded to noxious stimulation and 2% to non-noxious stimuli. Although 50 nA of morphine or naloxone had little effect on the firing rate of cells, these agents influenced their responses to noxious stimulation. The response of 52% of the cells was potentiated by morphine and inhibited by naloxone. The opposite occurred with 28% of the cells examined. With a sample of 7 cells levorphanol mimicked the actions of morphine and dextrorphan did not. As cells in the NRPG are predominantly affected by noxious stimuli, are very sensitive to morphine and others have shown that stimulation and microinjection of morphine cause analgesia, it is possible that this nucleus forms part of a negative feedback loop mediating analgesia.

Effects of midbrain, bulbar and combined morphine microinjections and systemic injections on orofacial nociception and rostral trigeminal stimulation: independent midbrain and bulbar opiate analgesia systems?

Microinjections of 0.35 μg and 0.7 μg morphine were made into rat nucleus reticularis paragigantocellularis and ventral central gray respectively. When injected simultaneously, the analgesic effect on orofacial thermal pain was significantly greater than the effect of either injection alone, suggesting a summation mechanism for the two sites. No microinjection affected the threshold for aversive response to main sensory trigeminal nuclear stimulation. This threshold was, however, profoundly elevated by 10 mg/kg systemic injection.

The participation of substantia nigra zona compacta and zona reticulata neurons in morphine suppression of caudate spontaneous neuronal activities in the rat

Spontaneous, unitary activity from the caudate nucleus, substantia nigra zona reticulata and zona compacta were recorded extracellularly from lightly anesthetized rats. Intravenous injection of morphine (5 mg/kg) produced a depression of both caudate and reticulata discharges with a concomitant increase in the compacta activities. These effects were reversed by naloxone (1 mg/kg, i.v.). Microinjection of morphine (25, 50, and 100 μg) directly into the substantia nigra zona compacta induced a naloxone-reversible depression of caudate activity. Direct nigral application of strychnine (5 μg), a glycine antagonist, resulted in a moderate decrease in caudate activity and an increase in compacta discharges, but no appreciable effect on the reticulata neurons. Morphine (5 mg/kg, i.v.) further enhanced the strychnine effects on both caudate and compacta cells, while depressing the reticulata neurons. These results suggest that morphine may suppress caudate spontaneous activity via an activation of the nigrostriatal neurons and an inactivation of a novel striatonigral pathway. The latter may incorporate the reticulata neurons, which may exert a tonic inhibition on the compacta cells, possibly using glycine as the putative neurotransmitter.

Regulation of Pain Sensitivity in the Central Nervous System

Nociceptive information may be inhibited by stimulation of opiate receptors located presynaptically on primary afferent neurons. Sensory signals entering the spinal cord inhibit nociceptive signals by a non-opioid "gate" mechanism. Descending systems also modulate pain sensitivity at the spinal level. The descending 5-hydroxytryptamine (5-HT) system has a tonic inhibitory function, with diurnal fluctuations in intensity. The strong analgesic effects of electrical stimulation and morphine microinjections in certain brainstem structures is probably mediated by other descending systems. The ascending 5-HT system may influence the results of some complex tests for pain sensitivity by altering e.g. emotionality and habituation rate. Acupuncture analgesia involves opioid systems. In high frequency electroacupuncture and transcutaneous nerve stimulation, a non-opioid "gate" mechanism may predominate. Acute stress may produce analgesia by opioid as well as non-opioid mechanisms. The control of pain sensitivity is influenced by learning (e.g. biofeedback techniques and social factors), and may be affected in depression, mania and schizophrenia.

The effect of intracerebroventricular injections of morphine on vasopressin release in the rat.

1. An investigation was carried out to determine the effect of intracerebroventricular (I.C.V.) micro-injections of morphine on vasopressin (AVP) release in the urethane-anaesthetized rat. 2. Plasma AVP levels at different time intervals, following I.C.V. injection of 10-150 microgram morphine, were measured by radioimmunoassay. The effect of I.C.V. micro-injections of morphine on urine outflow was also studied in a group of water-loaded rats. 3. The vasopressin response to I.C.V. micro-injections of morphine was both dose- and time-dependent. High dose of 50 and 150 microgram morphine produced short latency stimulation of AVP release, followed by a fall. The low dose of 10 microgram morphine produced only a long latency inhibition. The most consistent response of I.C.V. injection of morphine was an inhibition of release. 4. Both stimulatory and inhibitory effects of morphine on vasopressin release were naloxone reversible and stereospecific. 5. I.C.V. micro-injections of morphine produced a dose-dependent rise in mean arterial blood pressure of short latency. Naloxone (0.5 mg/kg) completely abolished the rise seen with 10 microgram morphine and diminished the rise with 50 microgram. 6. Doses of 10 and 50 microgram morphine injected I.C.V. produced an immediate antidiuresis in water-loaded rats under urethane anaesthesia. 7. The vasopressin response to I.C.V. micro-injections of morphine is independent of the effects on the cardiovascular system and may involve different opiate receptor populations. The results also suggest the possibility that opiate receptors with different affinities for morphine may be responsible for the stimulatory and inhibitory effects of morphine on vasopressin release.

Functional properties of neurons in cat trigeminal subnucleus caudalis (medullary dorsal horn). II. Modulation of responses to noxious and nonnoxious stimuli by periaqueductal gray, nucleus raphe magnus, cerebral cortex, and afferent influences, and effect of naloxone.

Functional properties of neurons in cat trigeminal subnucleus caudalis (medullary dorsal horn). II. Modulation of responses to noxious and nonnoxious stimuli by periaqueductal gray, nucleus raphe magnus, cerebral cortex, and afferent influences, and effect of naloxone.

Effect of dorsal raphe stimulation or microinjection of morphine into central gray on brain-stimulation induced escape

Effect of dorsal raphe stimulation or microinjection of morphine into central gray on brain-stimulation induced escape

Récepteurs de l’opium et sommeil

In the rabbit, microinjections of DSIP (delta-sleep peptide) at optimal doses in the median thalamus, periaqueductal gray matter (22.5 nmol), and nucleus of the tractus solitarius (15.0 nmol) produce slow-wave sleep with abundant recruiting spindles. As is seen with morphine, this effect is blocked by naloxone (160 micrograms intracerebrally; i.c.). At least in the rabbit, DSIP is probably a neurotransmitter or a neuromodulator of the bulbothalamic system inducing slow-wave sleep and particularly recruiting spindles. It is likely to restore slow-wave sleep after supraoptimal awakening i.c. microinjections of morphine.

Opiate receptors and sleep. II. Effects of micro-injection of ethyl alcohol and pentobarbital in the median thalamus, periaqueductal gray matter and nucleus of the tractus solitarius of the rabbit (author's transl)

There is an analogy between sleep EEGs produced by microinjections of morphine in the bulbo-mesencephalo-thalamic recruiting system and EEGs seen during anesthetic-induced sleep. Many studies in the last 10 years have claimed cross-tolerance and cross-dependence between opiates and ethyl alcohol. Opiates, ethyl alcohol and pentobarbital have many common metabolic actions in the central nervous system. Like morphine, microinjections of optimal equimolar doses of ethyl alcohol and pentobarbital in the bulbo-mesencephalo-thalamic sleep-inducing system of the rabbit produce sleep EEGs with abundant fast activity, which is blocked by naloxone (2 mg/kg i.v.) or by microinjections (160 micrograms) into the same structures. However, there is neither binding nor displacement by naloxone of ethyl alcohol or pentobarbital from the opiate receptor. It is thus probable that, via an as yet unknown mechanism, ethyl alcohol and pentobarbital promote the release of endorphins or peptides, which are specific ligands of all or some opiate receptors.

Effects of intracerebral administration of atropine and morphine on the caudate stimulation-induced caudate spindle in rats.

The electrical stimulation of the caudate nucleus could induce a caudate spindle in the rat as in case of the cat and monkey. The spindle was enhanced by atropine (3-10 mg/kg, i.v.) or morphine (3-10 mg/kg, i.v.) and the effect of these drugs were completely abolished by eserine (0.3 mg/kg, i.v.), but not by methysergide (1 mg/kg, i.v.), PCPA (400 mg/kg, i.p. for 3 days) or reserpine (3 mg/kg, i.p. for 2 days). An intraventricular injection of atropine (5-10 microgram/rat) or morphine (10 microgram/rat) exerted a facilitatory action on the spindle, while an intrathalamic and intracaudate injection of atropine (5-50 microgram/rat) showed a suppressive action. The spindle was also markedly enhanced by the microinjection of atropine (15-30 microgram/rat) or morphine (30 microgram/rat) into the reticular formation, and these actions were completely antagonized by eserine (0.3 mg/kg i.v.), but only partially by methysergide (4 microgram/rat, intraventricular administration.) These results suggest that the cholinergic system may play an important role in the regulation of the caudate spindle.

Effects of focal electrical stimulation and morphine microinjection in the periaqueductal gray of the rat mesencephalon on neuronal activity in the medullary reticular formation

Neurons in the medullary reticular formation (MRF; nucleus reticularis gigantocellularis and nucleus reticularis paragigantocellularis) were evaluated for their involvement in the analgesia produced by focal electrical stimulation and microinjection of morphine into the periaqueductal gray region (PAG) of the rat mesencephalon. Analgesia-producing PAG stimulation altered the spontaneous activity of 80% of the neurons in the MRF (both excitation and inhibition were observed) and inhibited the noxious-evoked excitation of 75% of MRF neurons. Microinjection of morphine into the PAG also increased (50%) and decreased (17%) the spontaneous activity of MRF units and inhibited the noxious-evoked excitation of 47% of MRF neurons. These effects were specific for analgesia produced by the PAG manipulations and were partially reversed by naloxone. The role of the MRF in PAG-induced analgesias and the degree of overlap in neuronal systems influenced by intracranial morphine and electrical stimulation is discussed.

Regional distribution of a novel analgesic dipeptide kyotorphin (Tyr-Arg) in the rat brain and spinal cord

Using high performance liquid chromatography, we measured kyotorphin content in discrete regions of the rat brain and spinal cord in an attempt to clarify its physiological significance. Higher concentrations of the dipeptide were found in the midbrain, pons plus medulla oblongata and dorsal cord, which are the most sensitive sites for the microinjection of morphine and/or electrical stimulation-induced analgesia. Kyotorphin may play a physiological role in pain control in the central nervous system.

Depressant and excitant effects of intraspinal microinjections of morphine and methionine-enkephalin in the cat

The effects of intraspinal microinjections of morphine (10 μg) and methionine-enkephalin (Met-enkephalin) (5 μg) on the C-fiber and polysynaptic reflexes in the acute decerebrate low spinal cat were investigated. Microinjected into the dorsal horn, morphine and Met-enkephalin depressed the nociceptive C-fiber reflex (CFR) without altering the short latency polysynaptic reflex. Microinjected into the ventral horn, morphine and Met-enkephalin facilitated the C-fiber and polysynaptic reflexes. Pretreatment of the cats with intravenous naltrexone (2 mg/kg) antagonized the depressant effects produced by dorsal horn intraspinal microinjections of morphine and Met-enkephalin. The excitant effects of ventral horn microinjections of morphine were not antagonized by naltrexone (2 mg/kg). These results support a hypothesis that the analgesic effects of morphine at the spinal cord level are due to interactions with opiate receptors in the dorsal horn.