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Biomedical subjects

R L Lloyd

Publications and source records attributed to R L Lloyd.

At least 19 recordsLinked to original sources
PubMed2001

Antidepressant effects of thyrotropin-releasing hormone analogues using a rodent model of depression.

The antidepressant potential of two naturally occurring analogues of thyrotropin-releasing hormone (TRH), pGLU-GLU-PRO-NH2 (EEP) and pGLU-PHE-PRO-NH2 (EFP), were examined using a rodent model of antidepressant efficacy. The Porsolt Swim Test was used to assay the antidepressant properties of these two peptides. Both analogues of TRH produced significant antidepressant effects, with EEP producing the stronger response. No effect of EEP upon triiodothyronine (T3) was observed at the dosage used. EFP, which has previously been demonstrated to crossreact with the TRH receptor, significantly increased serum T3. Since an effect upon T3 was only observed in the weaker of the two compounds, these data suggest that the behavioral effect of EEP was not secondary to stimulation of thyroid hormone. Additionally, the differential behavioral response to the two compounds suggests a degree of sequence specificity in the ability of TRH-like tripeptides to produce an antidepressant effect.

Animals↗
PubMed2000

How to break even on an acquired primary care network.

Challenged by declining revenues, hospitals are taking steps to improve the financial performance of hospital-owned primary care group practices. Although some hospitals are divesting themselves of their group practices, others are attempting turn-around strategies to help them break even on their investment. Ensuring that expenses do not exceed revenues in a primary care network can be achieved by implementing initiatives on network-wide and practice site levels and may require draconian measures. By setting a financial target of break-even, primary care practices can experience dramatic improvements.

Decision Making, Organizational↗
PubMed1999

TRH in therapeutic vs. nontherapeutic seizures: affective and motor functions.

We have modeled some aspects of electroconvulsive therapy (ECT) in rats. In addition to sham-treated controls, one group received two electroconvulsive (ECS) current-doses at grand mal seizure threshold. Two more groups received three additional ECSs at two higher current-doses. Only the two suprathreshold groups showed significant antidepressant (AD) effects in the forced-swim test, but all three seizure groups showed significant increases in TRH and related peptides in anterior cortex (AC), pyriform cortex (PYR), amygdala/entorhinal cortex (AY), and hippocampus (HC). In motor cortex (MC), TRH appeared to be increased only in the lower dose suprathreshold ECS condition. No condition increased TRH in striatum (STR). These results fell short of directly implicating limbic TRH in AD effects, but in HC, MC, and STR, correlations of peptide levels with individual swim scores raise the possibility that this peptidergic system might be involved in motor as well as affective functions. Other peptides related to TRH might also be implicated in affective regulation and antidepressant effects.

Affect↗
PubMed1997

Electroconvulsive seizures increase levels of PS4, the TRH-enhancing peptide [prepro-TRH(160-169)], in rat brain.

We report the development of a radioimmunoassay for prepro-TRH(160-169) (PS4), a thyrotropin-releasing hormone (TRH) enhancing peptide, and its use in characterizing the effect of electroconvulsive seizures on the levels of this peptide in various brain regions of male Wistar rats. We found that electroconvulsive seizures significantly elevated the PS4 levels in hippocampus, amygdala, pyriform (olfactory) cortex, and anterior cortex but not in striatum, motor cortex, locus ceruleus, or ventral lateral medulla. The levels of PS4 were highly correlated with the corresponding TRH (p-Glu-His-Pro-NH2) and TRH-Gly (p-Glu-His-Pro-Gly) levels in hippocampus, amygdala, and pyriform cortex, consistent with the prepro-TRH source of all of these peptides. The PS4 levels in hippocampus and amygdala were significantly correlated with the immobility time in the Porsolt forced swim test, an established animal model for antidepressant effects. The PS4 levels in peripheral blood, hypothalamus, anterior cortex, amygdala, and eyes increased severalfold at 20 min following intracisternal injection of 228 microg of this peptide, suggesting that it readily crosses the blood-brain barrier. The pituitary levels of PS4 and TRH-Gly, on the other hand, were decreased within 20 min by intracisternal PS4, suggesting PS4 stimulated the release of prepro-TRH peptides from the pituitary. Fresh rat and human serum rapidly degraded PS4, indicating that it may act primarily as a paracrine modulator of TRH effects in pituitary, brain, and reproductive system.

Amino Acid Sequence↗
PubMed1994

TRH gene products are implicated in the antidepressant mechanisms of seizures.

1. After a series of electroconvulsive seizures, levels of TRH-Gly (the immediate precursor of TRH) in four limbic regions correlate significantly and highly with increased swimming in the forced-swim test model of antidepressant efficacy. Only in hippocampus did TRH itself correlate with swimming. 2. After ECS, limbic forebrain regions differ in the relationship of TRH to its precursor peptides. This probably results from differences in the coordination of induction of TRH-processing enzymes, as well as differences in the level of prepro-TRH following seizures. 3. Sprague-Dawley rats that are partially kindled with corneal stimulation swim less in the forced-swim test, opposite to the effect seen with antidepressant agents. 4. Pyriform cortex is unique among the four limbic regions examined in showing decreased amounts of the TRH precursor following swim/stress. 5. Combining ECS with the forced-swim test of antidepressant effects creates a useful model for studying the involvement of TRH and its precursor peptides in both the antidepressant and anticonvulsant effects of controlled therapeutic seizures in the treatment of major depressive disorders. Regional differences between the effects of pinnate and corneal ECS on peptides and behavior support the idea that corneal ECS is a better model than pinnate ECS for human bitemporal ECT. 6. Together with recent results in other laboratories, our results suggest that a series of generalized seizures results in prolonged and increased release and action of TRH in limbic forebrain.

Animals↗
PubMed1991

Delta activity from amygdala in squirrel monkeys (Saimiri sciureus): influence of social and environmental context.

A previous study reported that power in the delta band of the amygdala is selectively elevated when primates are exposed to affectively ladened stimuli (Kling, Steklis, & Deutsch, 1979). Radiotelemetric recordings suggested that this elevation was greatest when the animal was confronted with conspecific behaviors that could be interpreted as "ambiguous." In the present study, a specific elevation of delta activity was observed when the animal was placed in an environment in which uncued shock had previously been received, in relation to environments in which shock had always been cued. This occurred even though the conditioned stimulus or unconditioned stimulus (or both) was not presented. A specific elevation in delta activity also occurred when a conspecific was present, in relation to when the animal was alone. Finally, recordings in an environment in which shock training had previously occurred showed a striking lateralization of delta activity in the right amygdala but not in the cortex. At other times, no lateralization was observed.

Affect↗
PubMed1990

Antagonism of the hypothermic effect of clozapine in mice by centrally-active alpha 2-adrenergic antagonists and alpha 1-adrenergic agonists.

Hypothermia induced by either clozapine or clonidine in mice was blocked by the alpha 2-adrenergic antagonists yohimbine, idazoxan, CH-38083, SKF 86466, and L-657,743. These effects were dose related, and the ID50 values for inhibition of clozapine- or clonidine-induced hypothermia were fairly comparable. The order of potency for blocking clonidine-induced hypothermia was: L-657,743 greater than CH-38083 greater than yohimbine greater than idazoxan greater than SKF 86466. A very similar blockade hierarchy for clozapine-induced hypothermia was observed, with the order of the two most effective compounds being reversed. Hypothermia induced by either compound was not blocked by the peripherally-acting, selective alpha 2-adrenergic antagonist, L-659,066, indicating that blockade by the other compounds occurred centrally. The centrally-acting, alpha 1-adrenergic agonists St 587, cirazoline, and SKF 89748 were very effective in blocking the response to clozapine, but ineffective in antagonizing clonidine-induced hypothermia. The ED50 values for the blockade of this response to clozapine, however, did not correlate with their reported potencies in stimulating either peripheral or central alpha 1-adrenergic receptors. This indicates that clozapine-induced hypothermia in mice is not a suitable model for evaluating the properties of central alpha 1-adrenergic compounds. Moreover, since the clonidine-induced hypothermia is not influenced by alpha 1-adrenergic agonists, this paradigm is preferable to clozapine-induced hypothermia in the assessment of alpha 2-adrenergic antagonism The ability of alpha 2-adrenergic antagonists to block clozapine-induced hypothermia may result from the central overflow of norepinephrine, which is known to be brought about by this group of compounds.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Agonists↗
PubMed1989

Involvement of noradrenergic system in a remarkably rapid tongue clonus produced by acute hypnotic doses of ethanol in Fischer F344 rats.

Ethanol (2.95 g/kg, IP) eliminated the righting reflex and induced vigorous tongue clonus spontaneously or following tactile tongue stimulation in Fischer F344 rats. Responses normally lasted 30-60 min, and was reinstated by tactile stimulation in those cases where it subsided quickly. Sub-hypnotic (1.95 g/kg) or high (3.95 g/kg) doses failed to elicit clonus, even after tactile stimulation. A lipophilic alpha 1-adrenergic agonist (St 587) promptly initiated tongue clonus in rats treated with a 3.95 g/kg dose of ethanol. Prazosin, a selective alpha 1-adrenergic antagonist, blocked clonus, while the dopamine selective antagonist pimozide failed to modify this response. We infer an alpha 1-adrenergic effect in which norepinephrine is released by ethanol.

Animals↗
PubMed1987

Aging reduces somatosensory responsiveness of caudate neurons in the awake cat.

Neuronal activity was recorded in 7 awake cats (3 animals 11-15 years and 4 animals 1-3 years of age) to determine if the ability of caudate neurons to process facial somatosensory information was impaired in aged animals. Proportionately fewer neurons responded to somatosensory stimuli and facial receptive fields were larger in the aged cats. In addition, proportionately fewer caudate neurons responded to cortical activation, there were fewer excitatory responses and spontaneous firing decreasing in aged cats. These results provide additional evidence that excitability of caudate neurons is reduced in aged cats.

Action Potentials↗
PubMed1987

Neurophysiological alterations in caudate neurons in aged cats.

These neurophysiological studies provide information on the alterations in functional capacity of neurons in the aging caudate nucleus (Cd) of the cat. The major finding is that there is a marked loss of excitation in the Cd during the aging process. This loss is most apparent in animals 11-14 years of age but is demonstrable in animals 6-7 years of age. Extracellular recording techniques were used to test the ability of Cd neurons to respond to activation of two of their major inputs, the precruciate cortex (CX) and the substantia nigra (SN). Types of responses that were evoked in both 1-3- and 11-14-year groups were similar and consisted of excitation, excitation followed by inhibition of action potentials or inhibition alone without preceding excitation. The frequency of occurrence of these responses was altered in the aged animals when either input was stimulated. In 1-3-year-old cats CX stimulation evoked initially excitatory responses in 75% of the cells tested while in 11-14-year-old cats excitatory responses occurred in 62% of the cells. When the SN was stimulated the decrease in initial excitation was greater (69% in 1-3- vs 35% in 11-14-year groups). In all aged animals but not in 1-3-year-old cats stimulation thresholds were higher (39-79%) for evoking excitatory responses than for evoking inhibitory responses. In order to assess synaptic security, the ability of Cd neurons to respond to iterative stimulation was determined. Distributions of the minimum interval necessary to evoke two excitatory responses were constructed. There was a marked increase in the proportion of longer intervals in the aged animals indicating that the synaptic response was less secure. There was a tendency for more of the responses in aged animals to have shorter latencies. This result was probably due to loss of less secure longer latency responses that are mediated via multisynaptic pathways. These findings indicate that there are functional changes in a population of Cd neurons in aged cats that impair their ability to process information.

Action Potentials↗
PubMed1987

Slow wave changes in amygdala to visual, auditory, and social stimuli following lesions of the inferior temporal cortex in squirrel monkey (Saimiri sciureus).

Radiotelemetry of slow wave activity of the amygdala was recorded under a variety of conditions. Power, and the percentage of power in the delta band, increased in response to stimulation. Recordings of monkey vocalizations and slides of ethologically relevant, natural objects produced a greater increase in power than did control stimuli. The responses to auditory stimuli increased when these stimuli were presented in an unrestrained, group setting, yet the responses to the vocalizations remained greater than those following control stimuli. Both the natural auditory and visual stimuli produced a reliable hierarchy with regard to the magnitude of response. Following lesions of inferior temporal cortex, these two hierarchies are disrupted, especially in the auditory domain. Further, these same stimuli, when presented after the lesion, produced a decrease, rather than an increase, in power. Nevertheless, the power recorded from the natural stimuli was still greater than that recorded from control stimuli in that the former produced less of a decrease in power, following the lesion, than did the latter. These data, in conjunction with a parallel report on evoked potentials in the amygdala, before and after cortical lesions, lead us to conclude that sensory information, particularly auditory, available to the amygdala, following the lesion, is substantially the same, and that it is the interpretation of this information, by the amygdala, which is altered by the cortical lesion.

Amygdala↗
PubMed1987

Differential effects of inferior temporal cortex lesions upon visual and auditory-evoked potentials in the amygdala of the squirrel monkey (Saimiri sciureus).

Visual-evoked potentials (VEPs) and auditory-evoked potentials (AEPs) were elicited from amygdala nuclei and inferior temporal (IT) cortex in chaired, alert squirrel monkeys to diffuse flash and click stimuli. VEPs were recorded from electrodes placed in basalis lateralis amygdalae (BLA) and basalis medialis amygdalae (BMA) while AEPs could also be obtained from additional electrode sites in basalis accessorius medialis (BAM), centralis amygdalae (CeA), and lateralis amygdalae (LA). The amygdala-evoked potentials resulting from stimulation of the two modalities were similar in terms of component configuration. AEPs recorded from the IT cortex had shorter latencies than the amygdala VEPs that were recorded. Both modalities of stimulation elicited potentials with shorter onset latencies in the amygdala than those recorded from the surface of IT cortex. Bilateral ablation of the IT cortex eliminated VEPs recorded from the BMA but not the BLA amygdala region. AEPs recorded from BMA as well as other amygdala areas were not consistently affected by these IT cortical ablations.

Amygdala↗
PubMed1978

Origin of the neocortically monitored theta rhythm in the curarized rat.

An array of epidural electrodes was acutely implanted in locally anesthetized, curarized rats in order to map the surface distribution of rhythmic slow activity (RSA) which appears within the neocortex. Peak amplitudes (of about 122 muV) were centered over the dorsal hippocampus outline. A laminar profile of RSA recorded within the neocortex indicated no shifts in phase relative to a homotopic, epidural electrode. RSA increased slightly in amplitude (mean increase = 53%) at the deepest level or neocortex, but it did not approximate an amplitude peak or null within the neocortex. Multiple-unit activities within the neocortex were not phase-locked to RSA. On the other hand, all of these manifestations of an RSA generator were observed as electrodes passed into the dorsal hippocampus. A unilateral cortical spreading depression (CSD) treatment, which markedly attenuated barbiturate spindles in all subjects (N = 10), usually (N = 7 of 10) had no effect on the neocortically monitored RSA. Dissociations between depressed and non-depressed hemispheres, and between neocortical and hippocampal RSA, were obtained in some subjects during CSD. However, concurrent dissociations were also apparent between recording sites within the hippocampus. It is concluded that the neocortical RSA of rats is passively spread from the underlying hippocampus, and dissociations in neocortical and hippocampal RSA in the rat are secondary to changes in the organization of multiple generators of hippocampal RSA.

Animals↗