Endogenous opiates: 1979(1)

Alzheimer's disease through the eye of a mouse. Acceptance lecture for the 2001 Gayle A. Olson and Richard D. Olson prize

There is now ample evidence that beta-amyloid proteins decrease memory. The SAMP8 mouse (P8) develops an early decline in the ability to learn and to retain new information. The studies reviewed here suggest that this is due to overproduction of beta-amyloid. Both antibodies to beta-amyloid and specific antisense to the amyloid precursor protein reverse these deficits in the P8 mouse. This antisense can cross the blood brain barrier. It is hypothesized that the overproduction of beta-amyloid leads to a decline in Delta(9) desaturase activity with an alteration in membrane fatty acids. This results in altered membrane mobility leading to a decline in neurotransmitter activity and a decreased release of acetylcholine. This decreased cholinergic activity results in a decreased ability of the P8 mouse to learn and retain new information.

The Tyr-MIF-1 family of peptides

A review of research on the Tyr-MIF-1 family of peptides is presented with emphasis on Tyr-MIF-1 and its structure, passage through the blood-brain barrier, and both opiate antagonist and agonist properties. Family members MIF-1, Tyr-W-MIF-1 and Tyr-K-MIF-1 are also included.

Hippocampal and cortical opioid receptor binding: changes related to the hibernation state

In vitro opioid receptor binding in the dorsal hippocampal formation and parietal cortex was surveyed in ground squirrels (Citellus lateralis) in the contrasting physiological states of hibernation and euthermia (i.e. not hibernating). Computer-assisted autoradiographic analysis of coronal sections incubated with [3H]dihydromorphine (DMH; 4 nM) revealed statistically significant reductions in specific opioid binding associated with hibernation. In the dorsal hippocampal formation of hibernating animals, binding in the stratum radiatum of CA3, hilus of the dentate gyrus and molecular layer of the dentate gyrus exhibited decreases up to 34% compared to euthermic animals. The stratum radiatum of CA3 exhibited the smallest decrease overall. DHM binding in parietal cortex displayed significant hibernation-related reductions, although they were not uniformly observed across all laminae at the 3 different brain levels examined. These experiments present evidence of changes in brain opioid binding related to the mammalian state of hibernation. The results suggest that changes in opioid receptor binding during hibernation may contribute to the earlier reported apparent failure of morphine physical dependence to develop during hibernation.

Central nervous system effects of peptides, 1980-1985: a cross-listing of peptides and their central actions from the first six years of the journal Peptides

A tabular synopsis is presented for articles concerned with the effects of peptides on the central nervous system that appeared in the journal Peptides from 1980-1985. A table arranged alphabetically by peptide and one arranged by effects, both listing routes of injection, species, direction of change, and qualifying notes, provides easy cross-referencing of peptides and their effects. Over 80 peptides and over 135 effects are listed. The list of peptides includes, but is not limited to: ACTH, angiotensin, bombesin, bradykinin, calcitonin, casomorphin, CCK, ceruletide, CGRP, CRF, dermorphin, DSIP, dynorphin, endorphins, enkephalins, GRF, gastrin, LHRH, litorin, metkephamid, MIF-l, motilin, MSH, NPY, NT, oxytocin, ranatensin, sauvagine, substances P and K, somatostatin, TRH, VIP, vasopressin, and vasotocin. The list of effects includes, but is not limited to: aggression, alcohol, analgesia, attention, avoidance, behavior, cardiovascular regulation, catalepsy, conditioned behavior, convulsions, dopamine binding and metabolism, discrimination, drinking, EEG, exploration, feeding, fever, gastric secretion, GI motility, grooming, learning, locomotor behavior, mating, memory, neuronal activity, open field, operant behavior, rearing, respiration, satiety, scratching, seizure, sleep, stereotypy, temperature, thermoregulation and tolerance.

Antagonism of brain opioid peptide action reduces hibernation bout duration

The effect of continuous intracerebroventricular (i.c.v.) administration of naloxone on the duration of individual bouts of hibernation was investigated in the golden-mantled ground squirrel (Citellus lateralis). Following entrance into hibernation, naloxone was continuously administered by an osmotic minipump at a rate of 1 microliter/h through a chronically implanted unilateral i.c.v. cannula guide. Naloxone (1, 5 and 7.5 micrograms/microliter) produced a dose-dependent reduction in hibernation bout duration ranging from 1 to 4 days (13.9-62.3% of expected bout duration). These data suggest that selected endogenous opioid system neurons may contribute to the CNS maintenance of the hibernating state and, consequently, to the overall conservation of energy in this species.

Feeding induced by opiates injected into the paraventricular hypothalamus

Injection of morphine or d-ala-2-met-5-enkephalinamide (DALA) into the paraventricular nucleus of the hypothalamus (PVN) produced a dose dependent increase in feeding in rats. DALA increased feeding within 45 minutes; morphine within 90 minutes. Naloxone injected into the PVN diminished the effect. DALA increased water intake only when food was available, suggesting the primary effect was on feeding. In summary, an enkephalin analogue induced feeding, and an opiate receptor blocker attenuated it; therefore the PVN may contain opiate receptors that facilitate feeding.

Opiates and classical conditioning: selective abolition of conditioned responses by activation of opiate receptors within the central nervous system

It has previously been shown that opiates produce selective abolition of aversively motivated classically conditioned responses in the rabbit. The experiments reported here show that these effects are mediated by specific activation of opiate receptors within the central nervous system in that this central activation is both necessary and sufficient to produce opiate-induced abolition of conditioned responding. Further characterization suggests that selective activation through opiate-mu-receptor interactions within the periaqueductal gray/periventricular region of the fourth ventricle may be critical in mediating this abolition.

Effect of naloxone and D-met2-pro5-enkephalinamide treatment on the DNA synthesis in the developing rat brain

Effects of a single dose of naloxone and of D-Met2-Pro5-enkephalinamide on the DNA synthesis in the forebrain, hypothalamus and cerebellum of 11 day old female rats were studied. As an index of DNA synthesis the rate of incorporation of 3H-thymidine into DNA was measured 30 min after a sc. injection of 40 muCi/100 g b.w.. A time dependent effect of naloxone administration on cerebral DNA synthesis was observed. In the forebrain at 1 and 3 hrs after naloxone injection an increased rate of 3H-thymidine incorporation into DNA was found followed by a marked decrease at 9 and 12 hrs. The effect in the hypothalamus was similar but the initial increase at 1 hr was absent. On cerebellar DNA synthesis naloxone had no effect. The administration of D-Met2-Pro5-enkephalinamide resulted in a marked reduction in the labelling of cerebral and hypothalamic DNA between 1 to 12 hrs. Except a decrease at 1 hr no effect was found in the cerebellum.

Selective, naloxone-reversible morphine depression of learned behavioral and hippocampal responses

Morphine administered intravenously causes immediate and complete abolition of a simple learned response (classically conditioned nictitating membrane extension in rabbit) and of the associated learning-induced increase in hippocampal neuron activity. Both effects are completely reversed by low doses of naloxone. Morphine has no effect at all on behavioral performance of the unconditioned reflex response.

Interaction of acute and chronic stress with respiration: modification by naloxone

Rats exposed to inescapable foot shock displayed an increase in respiratory rate, tidal volume and minute volume. Naloxone HCl (5 mg/kg, SC) potentiated the foot shock-induced increase in ventilation. Inhalation of high (5% and 10%) concentrations of carbon dioxide enhanced the stimulation of ventilation observed in both the acute stressed animals and the acute stress-naloxone treated group. Chronic daily foot shock sessions (11 days) attenuated the respiratory stimulation produced by acute foot shock and the potentiation induced by naloxone. The appearance of foot shock-induced stimulation of respiration paralleled the production of acute foot shock-induced analgesia. On the other hand, chronic foot shock attenuated both stress-related analgesia and respiratory stimulation. These results strongly suggest stress can influence respiratory function through activation or release of the endogenous opioids. It is postulated that the endorphinergic system functions as a compensatory system which prevents excessive stimulation of respiration by stress.

Dynorphin (1-13): analgesia, hypothermia, cross-tolerance with morphine and beta-endorphin

Intracerebroventricular administration of 20, 40 and 60 nmol of dynorphin (1-13) produced analgesia, as assessed by flinch/jump response to footshock, and hypothermia in the rat. Rats developed tolerance to both the analgesic and thermic effects of the 20 nmol dose of dynorphin. Dynorphin and beta-endorphin showed cross-tolerance with respect to their analgesic but not their thermic effects. Dynorphin and morphine also produced cross-tolerant analgesic effects. Naloxone (10 mg/kg, IP) completely blocked the barrel rolling produced by 20 nmol dynorphin but did not alter its analgesic or thermic effects.

Endogenous opiates: 1980

Vast amounts of research have been done that have attempted to delineate the pharmacological and physiological effects of the endogenous opiate peptides. A great deal of knowledge has also been accumulated in a limited time span concerning the types and locations of the opiate receptors and peptides, as well as their functions. In 1980, reports were made concerning the effects of these peptides on analgesia, on tolerance and dependence, on activity, on learning and memory, on schizophrenia and other types of emotional disturbances, and on physiological responses such as eating and drinking, cardiovascular responses, and sexual function. Additional understanding was also gained concerning their interactions with neurotransmitters, other neuropeptides, and hormones. These and other studies published only in 1980 are reviewed in this paper, which is the third of an annual series.