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D C German

Publications and source records attributed to D C German.

99 records · Page 6Linked to original sources
PubMed1976

Responses of primate locus coeruleus and subcoeruleus neurons to stimulation at reinforcing brain sites and to natural reinforcers.

In alert rhesus monkeys the activity of 64-neurons was recorded in the locus coeruleus and subcoeruleus region, collectively referred to as coeruleus (C) neurons. C neurons were identified physiologically by antidromic activation from electrodes in the medial forebrain bundle (MFB) and medial septal nucleus which sustained intracranial self-stimulation (ICSS) behavior, and/or anatomically by their proximity to microlesions at unit recording sites. The following results were obtained: (1) the current intensity that supported the highest rate of MFB and septal ICSS was similar to the current intensity for evoking antidromic responses in C neurons; (2) stimulation in the vicinity of the dopaminergic neurons of nucleus A10 did not activate C neurons; (3) C neurons were antidromically activated by ipsilateral and contralateral MFB shocks; (4) the C axons had slow estimated conduction velocities (1-5 m/sec), and a mean neural refractory period of 0.8 msec; (5) the behaviorally determined refractory period for MFB ICSS was also approximately 0.8 msec; and (6) mean firing rates while the monkey sat quietly were 15 +/- 2 Hz (S.D.) for subcoeruleus cells and 5 +/- 3 Hz for locus coeruleus cells, and activity of most cells changed negligibly during operant responding for apple-sauce reinforcement. These results suggest that the reinforcing effects of ICSS may be mediated by activation of coeruleus cells, but that these cells do not appear to be strongly involved in operant responding for natural reinforcers.

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PubMed1975

Locus ceruleus in rhesus monkey (Macaca mulatta): a combined histochemical fluorescence, Nissl and silver study.

The locus ceruleus (LC) of the rhesus monkey (Macaca mulatta) was investigated using the histochemical fluorescence method and Nissl and ammoniacal silver stains. Caudally, a few fluorescent cells were observed in the lateral wall of the ventriculus quartus near the velum medullaris superior. Rostrally, the fluorescent cells were compactly clustered and reached their greatest density medial and, to a lesser extent, lateral to the tractus mesencephalicus n. trigemini at the level of the decussation of the nervus trochlearis. In the most rostral plane, fluorescent cells were more diffusely scattered ventral and medial to the pedunculus cerebellaris superior with a few cells situated near the nervus trochlearis. Nissl staining of tissue previously used for histochemical fluorescence showed that fluorescent cells were largely found in a region labelled LC in two rhesus monkey brain atlases and erroneously labelled nucleus tractus mesencephalicus n. trigemini in one brain atlas. Ammoniacal silver staining resulted in a dense accumulation of silver granules in the cells found to display a positive reaction for monoamines. The silver stains therefore offer an alternative to the histochemical fluorescence method for identifying the monoamine-containing LC neurons.

Ammonia↗
PubMed1973

Directionality of rewarding impulses within the medial forebrain bundle self-stimulation system of the rat.

Self-stimulation performance of rats was tested with conditioning pulses to the anterior preoptic area of the medial forebrain bundle followed at various intervals by test pulses to the contralateral posterior hypothalamic area of this bundle. Alternatively, conditioning pulses were delivered through the posterior electrode and test pulses were sent through the anterior electrode. The animals' performance in these two test sequences was indicative of (i) synaptic facilitation and (ii) a posterior convergence site of "self-stimulation impulses" in the medial forebrain bundle.

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PubMedDate not supplied

Functional and reactive hyperemia are unaltered by homocysteine in conscious dogs.

The purpose of this study was to test the hypothesis that L-homocysteine thiolactone (L-HCTL), through its reaction with adenosine to form S-adenosylhomocysteine, may modulate myocardial functional and reactive hyperemic responses. Reactive hyperemic responses to 10-sec occlusions or 400-msec diastolic occlusions of the circumflex coronary artery and functional hyperemic responses to ventricular extra-activations were studied in a chronic heart-blocked dog preparation during a control period and following L-HCTL (40 mg/kg). In two additional dogs multiple venous blood samples and left ventricular myocardial biopsies were obtained following L-HCTL to measure changes in plasma homocysteine and tissue S-adenosylhomocysteine. Despite a 75-fold increase in peak plasma homocysteine and a 26-fold increase in tissue S-adenosylhomocysteine, L-HCTL did not alter myocardial functional and reactive hyperemic responses. The rapid increase in myocardial S-adenosylhomocysteine confirmed cellular entry of homocysteine and its reaction with endogenous adenosine. The failure of L-HCTL to alter functional and reactive hyperemic responses suggests that either such treatment does not affect myocardial release of adenosine or that adenosine is not an important regulator of coronary flow.

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PubMedDate not supplied

Differences in norepinephrine and dopamine neurotransmitter storage systems.

Low doses of d-amphetamine (d-AMP) produced a 50% or greater decrease in the firing rates of both dopamine (DA) neurons (substantia nigra zone compacta) and norepinephrine (NE) neurons (locus coeruleus). However, pretreatment with the tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (alpha-MT) blocked the d-AMP-induced reduction in DA neuron firing rate, but had no effect on the d-AMP-induced reduction in NE cell firing rate. Similarly, alpha-MT administered subsequent to d-AMP readily reversed the d-AMP-induced decrease in the firing rates of DA cells, but caused no significant reversal in NE cell firing rates. These electrophysiological findings, in conjunction with biochemical and behavioral data, support the hypothesis that there is a difference in the DA and NE neurotransmitter storage mechanism. In the DA neuron, there appears to be a slow transfer between stored and readily-releasable (newly synthesized) amine pools so that, following synthesis inhibition, there is little DA available for release. However, in the NE neuron, there is a more rapid mobilization of stored amine to readily releasable sites, such that d-AMP continues to cause the release of NE even though synthesis of transmitter is blocked.

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PubMedDate not supplied

Mesostriatal projections in BALB/c and CBA mice: a quantitative retrograde neuroanatomical tracing study.

A major portion of the midbrain dopamine (DA)-containing neurons project to the striatum and make up the mesostriatal DA system. The purpose of the present experiment was to map the location and quantify the density of mesostriatal neurons within two inbred mouse strains (BALB/c and CBA) known to possess different numbers of midbrain DA neurons. Computer-assisted reconstructions were made of both the wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) striatal injection site and the retrogradely labeled midbrain cells. There was no strain differences in the major source or topographical pattern of innervation of the striatum from the midbrain cellular regions. Even following small striatal injections, the labeled midbrain cells were found throughout most of the rostrocaudal extent of the midbrain DA nuclei; some labeled cells were found within the substantia nigra, the ventral tegmental area and the adjacent retrorubral field. Although the BALB/c strain has 20-25% more midbrain DA neurons than the CBA, given comparable striatal injection volumes, there was no significant difference in the number of HRP-filled mesostriatal neurons between the two mouse strains. These data suggest that the mesostriatal neurons give rise to comparable axonal branching within the striatum in the two mouse strains.

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PubMedDate not supplied

Factors affecting access to menopause information.

OBJECTIVE: As female life expectancy increases, women spend a greater proportion of their life in menopause. Menopausal women may benefit from preventive treatments, such as hormone replacement therapy, and are more likely to use medical treatments if they have access to information about menopause. The purpose of this study was to identify women's needs with respect to learning about menopause. DESIGN: A 20-question survey was administered anonymously to 116 women during outreach programs. Data were separated and evaluated by race and level of education. RESULTS: A significant association was found between access to information about menopause and both race and education level. Being African American or having less than a college education was associated with a twofold risk (p < 0.01) for not having a source of menopause information. A significant relationship was found between a woman's rating of her current knowledge of menopause and access to source of information (p = 0.03); women who did not have an information source felt the least knowledgeable about the subject. Women varied in the ways in which they are comfortable with learning about menopause. Different groups of women seemed to prefer different methods of learning about menopause. CONCLUSIONS: Both level of education and race are associated with a woman's ability to obtain information about menopause. To enhance women's understanding of health during menopause, information must be readily available. This information should be presented to women through educational programs that are designed to meet the needs of varied groups of adult women.

Adult↗