D.E. Redmond

II. New evidence for a locus coeruleus-norepinephrine connection with anxiety

Abstract The hypothesis that brain noradrenergic systems have a broad biological function which is related to human fear or anxiety is reviewed. Data from studies of the function of the nucleus locus coereleus in non-human primates are presented in the context of recent anatomical, physiological, pharmacological, and animal behavioral experiments. Implications are suggested for the treatment of anxiety, drug addictions, pain, and psychosomatic diseases.

Benzodiazepines attenuate single unit activity in the locus coeruleus

Abstract Several classes of anxiolytic compounds have the common effect of decreasing the firing of noradrenergic neurons or attenuating the post- synaptic effects of noradrenergic activity. In order to determine whether the benzodiazepines, the most widely used anxiolytics, also decrease noradrenergic activity, the effect of acute intravenous injections of diazepam (0.1–2.0 mg/kg) and chlordiazepoxide (0.5–4.0 mg/kg) were administered to anesthetized rats while spontaneous activity of single neurons in the principal noradrenergic nucleus, the locus coeruleus, was recorded. Diazepam and chlordiazepoxide decreased spontaneous single unit activity in the locus coeruleus at relatively low doses. This net effect on noradrenergic systems is consistent with the actions of several classes of nonbenzodiazepine anxiolytics, and with the involvement of noradrenergic systems in the neural mechanisms of anxiety.

Spontaneous Blink Rates Correlate with Dopamine Levels in the Caudate Nucleus of MPTP-Treated Monkeys

Previous studies have suggested a dopaminergic regulation of eye blink rates in human and nonhuman primates. Blockade of either dopamine (DA) D1 or DA D2 receptors or DA depletion induced by the dopaminergic neurotoxin MPTP both decrease spontaneous eye blink rates in monkeys. MPTP-induced decreases in blink rates can be reversed by administration of the full efficacy D1 agonist dihydrexidine, which has also been found to have dramatic antiparkinsonian effects in MPTP-treated animals. Increases in blink rates can also be induced by D1 and D2 agonists in normal animals. In the current study, we have investigated whether blink rates correlate with concentrations of DA or HVA and/or HVA:DA ratios in specific brain regions in MPTP-treated monkeys. Furthermore, the potential relationship between the severity of behavioral indices of parkinsonism and blink rates were examined. We found that (1) blink rates significantly correlate positively with concentration of DA and inversely with HVA:DA ratios in the rostral portion of the ventromedial body of the caudate nucleus (CD), but not other subcortical regions, and (2) that severity of parkinsonism was inversely correlated with blink rate. These data support a dopaminergic regulation of blink rate and suggest that the ventromedial region of the body of the CD may be critically involved in regulation of blink rate.

Symptomatic and asymptomatic 1 -methyl-4-phenyl-1,2,3,6-tetrahydropyridinetreated primates: Biochemical changes in striatal regions

Administration of the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, to primates produces an excellent behavioral model of idiopathic Parkinsons disease. In the vervet monkey, regional biochemical differences in the striatum of two 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated groups were examined one to two months after treatment and compared with controls; one group displayed no observable gross motor abnormalities after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment (asymptomatic), whereas the other group became markedly parkinsonian (symptomatic). In both 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated groups massive depletions of dopamine and homovanillic acid concentrations were observed in the striatum; generally, dopamine losses in the symptomatic group (greater than 95%) were greater than in the asymptomatic group (greater than 75%). However, in striatum, a marked heterogeneity in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine susceptibility was found; certain striatal regions having 99% depletion of dopamine even in asymptomatic monkeys. Overall, in ventromedial regions of striatum the losses of dopamine and homovanillic acid concentrations were less than in dorsolateral regions at the same coronal level. There was a significant negative correlation between control homovanillic acid/dopamine ratios and susceptibility of examined regions to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity. Unlike idiopathic, but similar to postencephalitic, Parkinsons disease, dopamine and homovanillic acid levels in caudate nucleus were not spared relative to putamen; in fact, in the asymptomatic group caudate nucleus dopamine and homovanillic acid concentrations were depleted to a greater extent than in putamen.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma and cerebrospinal fluid 3-methoxy-4-hydroxyphenylethylene glycol (MHPG) as indices of brain norepinephrine metabolism in primates

The relationship between MHPG concentration in several brain areas, cisternal CSF and plasma was examined in 26 vervet monkeys. Free MHPG was measured by gas chromatography-mass spectrometry using deuterated MHPG as internal standard. In animals with or without treatment with drugs that alter norepinephrine metabolism, highly significant correlations were found in concentrations of MHPG between the various brain areas, between plasma and CSF, between plasma and brain areas and between CSF and brain areas. The concentration of MHPG in CSF was higher than in plasma and with the exception of occipital cortex, all brain regions contained a higher concentration of MHPG than CSF. This study supports the notion that free MHPG concentrations in plasma and cisternal CSF are useful indices of central noradrenergic activity.

Excretion of catecholamine metabolites following intraventricular injection of 6-hydroxydopamine in the Macaca speciosa☆

Abstract Seven non-human primates ( Macaca speciosa ) were stereotaxically implanted with Kopf cannulae with the tip being placed at the junction of the lateral and third ventricles. Following a recovery period, 2 24-hr baseline urine specimens were collected from each animal. 4 of the animals were given intraventricular (i. vent.) injections of 1, 2, 4 and 8 mg of 6-hydroxy-dopamineṡHBr (6-OH-DAṡHBr) at 12-hr intervals ( in 1 ml of artifical CSF) and 7 days later a final injection of 16 mg of 6-OH-DAṡHBr. 3 control animals were given artificial CSF + equimolar NaBr injections on a similar schedule. Following the i. vent. injections 24-hr urine specimens were collected at periodic intervals. Urines were assayed for normetanephrine (NM), metanephrine (M), 3-methoxy-4-hydroxy-mandelic acid (VMA), and 3-methoxy-4-hydroxyphenylglycol (MHPG). All animals were sacrificed 16 days after the final i. vent. injections and 14 areas of brain, adrenal gland, heart, and thoracic sympathetic chain were removed and assayed for norepinephrine (NE). It has been found that it is possible with this schedule of injection of 6-OH-DA to produce animals which have significantly reduced levels of brain NE (70% depletion) without decreasing NE in tissues outside the CNS. Such experimental animal preparations should be of particular use in studies in which a separation of peripheral from central noradrenergic systems is desirable. No differences in the excretion of NM, M, VMA, and MHPG between baseline and post-injection periods were found in those animals which were injected with artificial CSF only. In all animals which were given intraventricular 6-OH-DA and in which there was a decrement in brain NE without a depletion of NE in tissues outside the central nervous system, there was a significant decrement in urinary MHPG between the baseline and post-injection periods while no differences in the excretion of NM, M, or VMA were found. Based upon these data calculations were made which suggest that a significant fraction of urinary MHPG has its origin in metabolism of NE in brain.

Effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on catecholamines and metabolites in primate brain and CSF

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administration is able to produce nigrostriatal damage and motor disabilities in primates similar to those seen in Parkinsons disease. Two months after MPTP treatment in African Green monkeys, significant depletions of dopamine (DA) and/or homovanillic acid (HVA) were found in the dorsal ventral tegmental area, and septum, but not in the ventral part of the ventral tegmental area or nucleus accumbens. However, DA losses were greater at all examined sites in the striatum. In putamen and caudate nucleus the decreases in DA and HVA appeared more marked dorsolaterally than ventromedially. After MPTP treatment the ratio HVA/DA was elevated in the septum and all striatal regions; in the striatum the increases in ratio were greater in the dorsolateral than in the ventromedial samples. NE concentration was not significantly altered by MPTP in the mesolimbic system. In control animals the HVA concentration and the ratio HVA/DA were higher in the putamen than in the caudate nucleus. A longitudinal study showed that CSF HVA and 3-methoxy-4-hydroxyphenylglycol were reduced by MPTP and remained below baseline level for 12 months after MPTP treatment. This biochemical study indicates that in the monkey MPTP is able to induce selective damage within both the nigrostriatal and mesolimbic DA systems.

Efficient transduction of non-human primate motor neurons after intramuscular delivery of recombinant AAV serotype 6

Retrograde transport of viral vectors in the rodent spinal cord provides a powerful means to administer a therapeutic transgene from the innervated musculature. With the aim of scaling up this approach to non-human primates, we have injected recombinant adeno-associated vectors (rAAV) serotype 6 expressing enhanced green fluorescent protein (eGFP) into the gastrocnemius muscle of African green monkeys to determine whether this results in efficient transgene delivery to lumbar motor neurons. Cells expressing eGFP were observed across more than 1 cm of the spinal cord 4 weeks after intramuscular injection, reaching more than half of motor neurons in some cross-sections. Furthermore, quantitative PCR on the spinal cord tissue confirmed that eGFP expression within motor neurons was due to bona fide retrograde transport of the vector genome from the muscle. Although infiltrations of macrophages and lymphocytes were observed in the rAAV2/6-injected muscle, there was no detectable immune response within the transduced region of the spinal cord. These findings imply that retrograde delivery of rAAV serotype 6 in a primate species constitutes a non-invasive and robust approach to transduce motor neurons, a crucial target cell population in neurodegenerative disorders, such as amyotrophic lateral sclerosis and spinal muscular atrophy.

Homovanillic acid concentrations in brain, CSF and plasma as indicators of central dopamine function in primates

In a large number (91) of vervet monkeys, correlation coefficients were determined between homovanillic acid (HVA) concentrations in four brain areas. Significant correlations existed between dorsal frontal cortex and orbital frontal cortex and between putamen and caudate nucleus. However, no significant correlations existed between either cortical area and the basal ganglia areas. Correlations were tested between CSF and plasma HVA and between these fluids and brain regions. The only significant relationship found was between CSF and dorsal frontal cortex, after possible treatment effects were statistically removed. The assumption that primate CSF HVA concentration necessarily reflects basal ganglia HVA concentration is questioned and furthermore, the results suggest that HVA from cortex contributes significantly to that in cisternal CSF. Raw plasma HVA measurements (even when uninfluenced by diet or anesthetic) appear to be of limited value in gauging central dopamine metabolism and turnover.

Altered frontal cortical dopaminergic transmission in monkeys after subchronic phencyclidine exposure: involvement in frontostriatal cognitive deficits.

Long-term exposure to the psychotomimetic drug phencyclidine produces prefrontal cortical cognitive and dopaminergic dysfunction in rats and monkeys, effects possibly relevant to the frontal cortical impairments of schizophrenia. In the present study, the effects of subchronic phencyclidine administration (0.3 mg/kg twice-daily for 14 days) on monoamine systems in the monkey brain were examined and related to cognitive performance on an object retrieval/detour task, which has been linked with frontostriatal function. Long-term (14 days) administration of phencyclidine resulted in a marked and persistent reduction in dopamine utilization in the frontal cortex. Moreover, the degree of cognitive impairment in phencyclidine-treated monkeys correlated significantly with the magnitude of dopaminergic inhibition within the dorsolateral prefrontal cortex and prelimbic cortex. No specific correlation was measured for dopamine utilization in other cortical regions or for indices of serotonin transmission in any brain region. These data show that repeated exposure to phencyclidine reduces prefrontal cortical dopamine transmission, and this inhibition of dopaminergic function is associated with performance impairments on a task sensitive to frontostriatal cognitive dysfunction. Thus, the cognitive deficits of phencyclidine-treated monkeys, as in schizophrenia, appear to be mediated, in part, by reduced dopaminergic function in specific subregions of the frontal cortex.