Hormone therapy does not modify emotion-induced brain activity in older women

Sex hormones have actions in brain regions important for emotion, including the amygdala and prefrontal cortex. Previous studies have shown that cyclic sex hormones and hormone therapy after menopause modify responses to emotional events. Thus, this study examined whether hormone therapy modified emotion-induced brain activity in older women. Functional magnetic resonance imaging (fMRI), behavioral ratings (valence and arousal), and recognition memory were used to assess responses to emotionally laden scenes in older women currently using hormone therapy (HT) and women not currently using hormone therapy (NONE). We hypothesized that hormones would affect the amount or persistence of emotion-induced brain activity in the amygdala and ventrolateral prefrontal cortex (VLPFC). However, hormone therapy did not affect brain activity with the exception that NONE women showed a modest increase over time in amygdala activity to positive scenes. Hormone therapy did not affect behavioral ratings or memory for emotional scenes. The results were similar when women were regrouped based on whether they had ever used hormone therapy versus had never used hormone therapy. These results suggest that hormone therapy does not modify emotion-induced brain activity, or its persistence, in older women.

Health status, mood, and cognition in experimentally induced subclinical thyrotoxicosis

OBJECTIVE

Our objective was to determine whether subclinical thyrotoxicosis alters health status, mood, and/or cognitive function.

DESIGN

This was a double-blinded, randomized, cross-over study of usual dose l-T(4) (euthyroid arm) vs. higher dose l-T(4) (subclinical thyrotoxicosis arm) in hypothyroid subjects.

PATIENTS

A total of 33 hypothyroid subjects receiving l-T(4) were included in the study.

MEASUREMENTS

Subjects underwent measurements of health status, mood, and cognition: Short Form 36 (SF-36); Profile of Mood States (POMS); and tests of declarative memory (Paragraph Recall, Complex Figure), working memory (N-Back, Subject Ordered Pointing, and Digit Span Backwards), and motor learning (Pursuit Rotor). These were repeated after 12 wk on each of the study arms.

RESULTS

Mean TSH levels decreased from 2.15 to 0.17 mU/liter on the subclinical thyrotoxicosis arm (P < 0.0001), with normal mean free T(4) and free T(3) levels. The SF-36 physical component summary and general health subscale were slightly worse during the subclinical thyrotoxicosis arm, whereas the mental health subscale was marginally improved. The POMS confusion, depression, and tension subscales were improved during the subclinical thyrotoxicosis arm. Motor learning was better during the subclinical thyrotoxicosis arm, whereas declarative and working memory measures did not change. This improvement was related to changes in the SF-36 physical component summary and POMS tension subscales and free T(3) levels.

CONCLUSIONS

We found slightly impaired physical health status but improvements in measures of mental health and mood in l-T(4) treated hypothyroid subjects when subclinical thyrotoxicosis was induced in a blinded, randomized fashion. Motor learning was also improved. These findings suggest that thyroid hormone directly affects brain areas responsible for affect and motor function.

Estrogen modifies arousal but not memory for emotional events in older women

Emotional arousal and the affective content of events influence memory. These effects shift with age such that older people find negative information less arousing and remember proportionately more positive events compared to the young. The emotional enhancement of memory is mediated by medial temporal lobe limbic structures and the prefrontal cortex, which are both affected by sex hormones. We examined whether hormone use (estrogen or estrogen and progesterone) in older women modulated perceptions of valence and arousal, and subsequent memory for emotional images or stories. Their performance was compared to younger women. Hormone use in older women resulted in higher arousal for negative images and stories but memory was not affected. We hypothesize that estrogen modifies the influence of the amygdala and the prefrontal cortex on emotion, but that age-related changes in the hippocampus prevent the enhancement of emotional memory in older women.

Health status, mood, and cognition in experimentally induced subclinical hypothyroidism

OBJECTIVE

The objective of the study was to determine whether subclinical hypothyroidism causes decrements in health status, mood, and/or cognitive function.

DESIGN

This was a double-blinded, randomized, crossover study of usual dose l-thyroxine (L-T4) (euthyroid arm) vs. lower dose L-T4 (subclinical hypothyroid arm) in hypothyroid subjects.

PATIENTS

Nineteen subjects on L-T4 therapy for primary hypothyroidism participated in the study.

MEASUREMENTS

Subjects underwent measurements of health status, mood, and cognition using validated instruments: Short Form 36, Profile of Mood States, and tests of declarative memory (paragraph recall, complex figure), working memory (N-back, subject ordered pointing, digit span backward), and motor learning (pursuit rotor). The same measures were repeated after 12 wk on each of the study arms.

RESULTS

Mean TSH levels increased to 17 mU/liter on the subclinical hypothyroid arm (P < 0.0001). Mean free T4 and free T3 levels remained within the normal range. The Profile of Mood States fatigue subscale and Short Form 36 general health subscale were slightly worse during the subclinical hypothyroid arm. Measures of working memory (N-back, subject ordered pointing) were worse during the subclinical hypothyroid arm. These differences did not depend on mood or health status but were related to changes in free T4 or free T3 levels. There were no decrements in declarative memory or motor learning.

CONCLUSIONS

We found mild decrements in health status and mood in L-T4-treated hypothyroid subjects when subclinical hypothyroidism was induced in a blinded, randomized fashion. More importantly, there were independent decrements in working memory, which suggests that subclinical hypothyroidism specifically impacts brain areas responsible for working memory.

The role of androgens in cognition and brain aging in men

Losses of working and long-term memory are hallmarks of human aging and may signal impending neurodegenerative disease. The maintenance of neural elements in brain systems that support memory, such as synapse formation in prefrontal cortex and hippocampus, are critical for cognitive health in aging. This paper reviews the biological basis for androgens as neuroprotectants or neuromodulators in aging and the importance of androgens on the brain systems important for memory. We relate biological effects to cognitive outcomes in elderly men under a variety of androgen conditions. In brief, androgen deprivation causes significant loss of synapses in the hippocampus in rodent and nonhuman primates, increases amyloid deposition in human and rodent models and causes changes in neurotransmission in prefrontal cortex in rodent models. Recent work suggests that these changes modify age-related cognitive loss, particularly to memory in men. In addition, the conversion of testosterone to its androgen metabolites or to estradiol may play a special role in the preservation of memory in aging. This paper reviews discrepancies between studies using animal models and studies of human cognition, and suggests new directions that are likely to be fruitful in the future for understanding the role of androgens in brain aging. This review suggests that studies of low androgen levels in older men may not index the same biological mechanisms and behavioral effects as the studies of gonadectomy in animal models.

Context processing in older adults: evidence for a theory relating cognitive control to neurobiology in healthy aging

A theory of cognitive aging is presented in which healthy older adults are hypothesized to suffer from disturbances in the processing of context that impair cognitive control function across multiple domains, including attention, inhibition, and working memory. These cognitive disturbances are postulated to be directly related to age-related decline in the function of the dopamine (DA) system in the prefrontal cortex (PFC). A connectionist computational model is described that implements specific mechanisms for the role of DA and PFC in context processing. The behavioral predictions of the model were tested in a large sample of older (N = 81) and young (N = 175) adults performing variants of a simple cognitive control task that placed differential demands on context processing. Older adults exhibited both performance decrements and, counterintuitively, performance improvements that are in close agreement with model predictions.

Selective preservation and degeneration within the prefrontal cortex in aging and Alzheimer disease

BACKGROUND

The prefrontal cortex (PFC) is a heterogeneous cortical structure that supports higher cognitive functions, including working memory and verbal abilities. The PFC is vulnerable to neurodegeneration with healthy aging and Alzheimer disease (AD).

OBJECTIVE

We used volumetric magnetic resonance imaging to determine whether any region within the PFC is more vulnerable to deterioration with late aging or AD.

METHODS

Volumetric analysis of PFC regions was performed on younger healthy elderly subjects (n = 26; 14 men and 12 women [mean age, 71.7 years] for aging analysis; 12 men and 14 women [mean age, 71.4 years] for AD analysis), oldest healthy elderly (OHE) subjects (n = 22 [11 men and 11 women]; mean age, 88.9 years), and patients with AD (n = 22 [12 men and 10 women]; mean age, 69.8 years).

RESULTS

The OHE subjects had less PFC white matter than did young healthy elderly subjects. The orbital region was selectively preserved relative to other PFC regions in the OHE subjects. Subjects with AD had less total PFC gray matter than did age-matched healthy subjects and significantly less volume in the inferior PFC region only.

CONCLUSIONS

Orbital PFC is selectively preserved in OHE subjects. In contrast, degeneration within the PFC with AD is most prominent in the inferior PFC region. Thus, degeneration within the PFC has a regionally distinct pattern in healthy aging and AD.

Informants' knowledge of reproductive history and estrogen replacement

BACKGROUND

There has been much interest in assessing estrogen use in healthy older women and those with Alzheimer's disease. However, data for the women with Alzheimer's disease must be obtained from an informant. The aim of this study was to better understand what informants are likely to know about reproductive history and estrogen use.

METHODS

Reproductive history data from informants of Alzheimer's patients were modeled by comparing responses from 40 cognitively healthy older women with that of a designated informant. The designated informants were similar in demographics to informants for patients with Alzheimer's disease.

RESULTS

Informant data regarding reproductive history was likely to be accurate, when known. However, 30% of the subjects did not identify an informant who had personal knowledge of them. Of those informants who had personal knowledge of the subject, accuracy for those who reported that they knew the information varied depending on the aspect of reproductive history assessed (age of menarche, 29%; age of menopause, 20%; pregnancies, 63%; live births, 92%; hysterectomy, 92%; and postmenopausal estrogen use, 82%). Daughters served as the most likely and most accurate informants in this study.

CONCLUSION

This study demonstrates that information obtained from informants for patients with Alzheimer's disease is likely to be accurate for some but not all aspects of reproductive history. Of concern for such studies will be the 30% of patients who do not have an informant with personal knowledge about them.

Sex steroids modify working memory

In the last ten years, numerous mechanisms by which sex steroids modify cortical function have been described. For example, estrogen replacement improves verbal memory in women, and animal studies have shown effects of estrogen on hippocampal synaptogenesis and function. Little is known about sex steroid effects on other aspects of memory, such as frontal lobe-mediated working memory. We examined the relationships between working memory and sex steroid concentrations and whether sex steroid supplementation would modify age-related loss of working memory in older men and women. Before hormone supplementation, working memory, tested with the Subject Ordered Pointing Test (SOP), was worse in older subjects than younger subjects, and there was no evidence of gender differences at either age. Testosterone supplementation improved working memory in older men, but a similar enhancement of working memory was not found in older women supplemented with estrogen. In men, testosterone and estrogen effects were reciprocal - with better working memory related to a higher testosterone to estrogen ratio. These results suggest that sex steroids can modulate working memory in men and can act as modulators of cognition throughout life.

Sex differences in prefrontal volume with aging and Alzheimer's disease

We used volumetric magnetic resonance imaging to examine sex differences in prefrontal tissue volumes of healthy aged and patients with Alzheimer's disease (AD). Healthy subjects had greater total prefrontal volume than AD, and men had greater total prefrontal volume than women (ps < or = 0.02). This was true for both gray and white matter volumes. There were no interactions between group and sex for total prefrontal volume. An exploratory analysis of each group suggested that sex differences in both gray and white matter in healthy aging are not sustained in AD.

Prefrontal gray and white matter volumes in healthy aging and Alzheimer disease

OBJECTIVES

To quantify the contribution of gray and white matter volumes to total prefrontal volume in healthy aging. To determine if prefrontal tissue volumes distinguish healthy aging from Alzheimer disease (AD).

DESIGN

Volumes of total prefrontal cortex, prefrontal gray matter, and prefrontal white matter were compared among young healthy elderly (YHE) (n = 14; mean age, 70 years), old healthy elderly (OHE) (n = 14; mean age, 90 years), and subjects with AD (n = 14; mean age, 70 years) by analysis of variance. Additionally, Pearson correlations were performed between volumes and age.

RESULTS

Old healthy elderly and subjects with AD had significantly less total prefrontal volume (approximately 15% less in both groups) and prefrontal white matter volume (approximately 30% less and 20% less in the OHE and AD groups, respectively) than YHE, but there were no differences between the OHE and AD groups. There was a significant difference in gray-white matter volume ratio with OHE having a higher ratio than YHE. Subjects with AD did not differ from YHE or OHE in this ratio. There were significant negative correlations between age and total prefrontal volume and age and prefrontal white matter volume in the healthy subjects.

CONCLUSIONS

In the very old, the decline of white matter volume is disproportionately greater than the decline of gray matter volume. In subjects with AD both gray and white matter loss contribute to the decline of prefrontal volume. This is demonstrated by the gray-white matter ratio that does not differ between YHE and subjects with AD. Thus, it is likely that AD is different from accelerated aging.

Formula supplementation with long-chain polyunsaturated fatty acids: are there developmental benefits?

OBJECTIVE

To evaluate the developmental outcomes of children who participated in an augmented randomized clinical trial of supplementing a standard infant formula with long-chain polyunsaturated fatty acids.

DESIGN

Randomized clinical trial, augmented with a nonrandomized human milk comparison group. There were three randomized formula groups: standard formula, standard formula containing docosahexaenoic acid (DHA), and standard formula containing DHA and arachidonic acid.

SETTING

Three clinical sites serving diverse populations: Kansas City, MO; Portland, OR; and Seattle, WA.

PARTICIPANTS

A total of 274 healthy full-term infants were enrolled in the infant-feeding protocol; of these, 197 (72%) participated in assessments of developmental outcome. Formula Supplements. In the randomized trial, one group received a standard formula, another group received a formula that had been supplemented with DHA from fish oil, and a third group received a formula supplemented with both DHA and arachidonic acid from an egg phospholipid.

OUTCOME MEASURES

Mental and Motor Scales of the Bayley Scales of Infant Development at 12 months of age; vocabulary and gesture communication scores from the MacArthur Communicative Development Inventories at 14 months of age.

RESULTS

There were no statistically significant differences for either the Bayley Mental Scale or the Bayley Motor Scale, neither when the analysis was restricted to the three randomized formula groups nor when the analysis included all four groups. However, the DHA formula group had significantly lower scores on two of the MacArthur scales: the DHA group scored lower than the nonrandomized human milk comparison group on the Vocabulary Comprehension Scale, and the DHA group scored lower than the randomized control formula group on the Vocabulary Production Scale. Moreover, additional analyses both in the formula groups and in the human milk comparison group found significant negative correlations between DHA levels and vocabulary outcomes.

CONCLUSION

We believe that additional research should be undertaken before the introduction of these supplements into standard infant formulas.

Estrogen and sequential movement

Normal movement depends in part on the brain's ability to produce and use dopamine, which regulates basal ganglia function. Behavioral, neuroanatomical, and neurophysiological data suggest that the basal ganglia are critical for the performance of sequential movement. Dopaminergic function is modulated by estrogen in animals and in humans. To test the hypothesis that estrogen modulates sequential movement, this study measured the reaction time (RT) and movement time (MT) of 15 women and 10 men in a choice RT task with sequential responses. Higher levels of estradiol in women's blood were associated with faster total movement time (RT plus MT). Testosterone levels in women's blood were not associated with keypressing performance. Hormone levels in men's blood were unrelated to keypressing performance. These results suggest that women's motor performance was affected by hormone levels, and that estrogen may interact with dopaminergic function in women.

Sex differences in the corpus callosum with aging

The present study examined sex differences in the area and age-related atrophy of the corpus callosum (CC) of 76 healthy elderly subjects using magnetic resonance imaging. The cerebellum and pons served as noncortical control structures. CC area and its subregions were also related to cognitive performance. Women had a slightly larger posterior sector of the CC than men. Women but not men showed age-related atrophy of the anterior and middle sectors of the CC but not the posterior sector. Cerebellum and pons size was similar in men and women, and neither showed age-related atrophy. CC area was related to visual memory in women but not men; no other significant cognitive to structure area relationships were found. These findings show that selective age related atrophy of the CC differs in men and women late in life.

Atrophy of the corpus callosum in Alzheimer's disease versus healthy aging

OBJECTIVE

To investigate the specificity of atrophic changes in the corpus callosum (CC) compared with the cerebellum and pons in patients with Alzheimer Disease (AD), healthy elderly subjects (HE), and a sample of prospectively studied subjects who have developed cognitive decline or "incipient dementia" (ID).

DESIGN

Cross-sectional comparison by age using quantitative MRI.

SETTING

Ambulatory research unit.

PARTICIPANTS

Sixty HE subjects (mean age 78.2 years; range 66-95), 20 ID subjects (mean age 88.1 years; range 78-98) and 39 AD subjects (mean age 72.2 years; range 52-91) were enrolled in longitudinal studies of healthy aging or AD. The population was selected for optimal health; all were examined to exclude medical, neurological and psychiatric illness.

MEASUREMENTS

Brain atrophy by quantitative MRI.

RESULTS

AD subjects had smaller CC than HE or ID subjects, who did not differ from each other. All three sectors of the CC were smaller in AD than in HE or ID subjects. The cross sectional area of the cerebellum and pons did not differ between groups. HE and ID subjects showed a significant decline in CC size with age. No age-related decline was found for AD subjects. The regional atrophy of the CC in AD subjects was significantly related to cognitive function but not to disease duration.

CONCLUSIONS

Atrophy of the CC differentiates HE and ID from AD subjects and tracks the cognitive decline of this disease. In addition, optimally healthy subjects show an age-related decline in callosum size. The atrophy is specific to the CC, a cortical projection system, and does not occur in cerebellum or pons.

Asymmetrical memory decline in normal aging and dementia

We assessed whether age-associated memory impairments and the memory impairment of Alzheimer's disease (AD) is comparable in the verbal and nonverbal domains. Subjects incidentally learned the identity and location of a group of objects and later verbally recalled the objects as well as recalling their previous spatial location. Comparison subject (younger subjects for experiment 1, and older subjects for experiment 2) were tested after retention intervals that equated their performance with that of the index subjects. We found that memory does not change uniformly with age. Verbal memory is more affected than nonverbal memory. This asymmetrical pattern is a feature of normal aging and does not appear to be due to a degenerative process such as Alzheimer's disease.

Testosterone influences spatial cognition in older men

Testosterone plays a role in the organization of behavior during development. The authors examined whether testosterone could play a maintenance role in behavior as well. In a double-blind manner, verbal and visual memory, spatial cognition, motor speed, cognitive flexibility, and mood in a group of healthy older men who were supplemented for 3 months with testosterone were assessed. The increase in testosterone levels to 150% of baseline levels resulted in a significant enhancement of spatial cognition, but no change in any other cognitive domain was found. Testosterone supplementation influenced the endogenous production of estradiol, and estradiol was found to have an inverse relationship to spatial cognitive performance. These results suggest that testosterone supplementation can modify spatial cognition in older men; however, it is likely that this occurs through testosterone's influence on estrogen.

Complex figure recall in the elderly: a deficit in memory or constructional strategy?

Spatial memory declines with age. This study investigated the hypothesis that the decline in spatial memory in the elderly is due to a dysfunction in frontal lobe-mediated planning and organization. The copy and recall ability of 49 elderly subjects and 20 younger subjects was assessed using the Rey-Osterrieth Figure. In addition, the manner of construction, (e.g., the order that each line was produced) was compared between groups. Despite comparable performance with the younger subjects when copying the figure, older subjects performed significantly worse than younger subjects when asked to reproduce the figure from memory. However, this was not due to the organizational strategies they used while copying the figure. They constructed the figure in the same manner as the younger subjects. Therefore, the spatial memory deficits in the elderly are not due to an abnormal organizational strategy. These results are discussed in relation to those of patients with frontal lobe damage and preliminary data from subjects with mild dementia.

Memory for the temporal order of events in patients with frontal lobe lesions and amnesic patients

Patients with frontal lobe lesions, amnesic patients with Korsakoff's syndrome, other (non-Korsakoff) amnesic patients, and control subjects were given tests of memory for temporal order. In the first experiment, subjects were presented with a list of 15 words and then asked to reproduce the list order from a random array of the words. In the second experiment, they were asked to arrange in chronological order a random display of 15 factual events that occurred between 1941 and 1985. In both experiments, patients with frontal lobe lesions were impaired in placing the items in the correct temporal order, despite normal item memory (i.e. normal recall and recognition memory for the words and facts). The two groups of amnesic patients exhibited impaired memory for temporal order as well as impaired item memory. Patients with Korsakoff's syndrome exhibited poorer temporal order memory than the other amnesic patients, despite similar levels of item memory. These findings demonstrate that patients with frontal lobe lesions have difficulty organizing information temporally. Patients with Korsakoff's syndrome, who have both diencephalic and frontal damage, have memory impairment together with a disproportionate deficit in memory for temporal order.

Source memory impairment in patients with frontal lobe lesions

In two experiments, we investigated memory for recently learned facts and memory for the source of the facts (i.e. where and when the facts were learned) in patients with frontal lobe lesions, age-matched elderly control subjects, and younger subjects. In both experiments, patients with frontal lobe lesions recalled as many facts as their age-matched subjects and the younger subjects, but they frequently attributed facts to incorrect sources. In the second experiment, both patients with frontal lobe lesions and their age-matched subjects committed more source errors than younger subjects. These findings suggest that the frontal lobes may play a special role in associating facts to the context in which they were learned. The results are also discussed in the light of the source memory impairment that occurs in amnesic patients.

Cognitive impairment following frontal lobe damage and its relevance to human amnesia

Whether frontal lobe pathology can account for some of the cognitive impairment observed in amnesic patients with Korsakoff's syndrome was investigated. Various cognitive and memory tests were given to patients with circumscribed frontal lobe lesions, patients with Korsakoff's syndrome, non-Korsakoff amnesic patients, and control Ss. Patients with frontal lobe lesions were not amnesic. Nevertheless they exhibited 2 deficits that were also exhibited by patients with Korsakoff's syndrome but not by other amnesic patients: (a) impairment on the Wisconsin Card Sorting Test and (b) impairment on the Initiation and Preservation subscale of the Dementia Rating Scale. Thus, frontal lobe pathology can explain some of the cognitive deficits observed in patients with Korsakoff's syndrome.

Early language development in infants with cortical and subcortical perinatal brain injury

To understand better the cognitive sequelae of mild perinatal brain injury, we studied three groups of high-risk infants, using the Early Language Milestone Scale (ELM Scale). Premature infants with Grades I and II intraventricular hemorrhages (IVH) were delayed on the expressive but not the receptive subscale of the ELM Scale. Mildly asphyxiated full-term infants were slightly delayed on both the expressive and receptive subscales. Premature infants without IVH performed the same as the normal sample on which the scale was based. Although normal intellectual functioning has been reported in infants with Grade I-II IVH, this study demonstrates early specific deficits in expressive language in these children. These results are discussed in relation to localization of language in the adult brain, and the influence of subcortical structures on development and maturation of the cortex.

Seizures triggered by blinking in a non-photosensitive epileptic

An epileptic girl with Lennox-Gastaut syndrome had seizures triggered specifically by blinking, but not by other eye movements or by photic stimulation. Electrographic and clinical seizures were most reliably precipitated by repetitive blinking produced voluntarily on command, by reflex blinking on corneal stimulation, or by psychogenic triggers of blinking such as social stress or cognitive effort.

Cell degeneration in early development of the forebrain and cerebellum

The hippocampus, dentate gyrus, cerebellum, amygdala and caudate were examined for degenerating cells in normal neonatal hamsters. Each structure was studied from postnatal day 5 (P5) to P 10. The cerebellum was also studied on P 12. This time span was chosen to coincide with cessation of migration and establishment of connectivity in these structures. Substantial numbers of pycnotic cells were found in all structures except the dentate gyrus. The timing and amount of cell death varied between structures. Both the caudate nucleus and the amygdala showed greater cell losses in their peripheral margins than in their centers. The deep half of the internal granule cell layer of the cerebellum showed greater cell loss than the superficial half on all postnatal days studied.

Polygenic and single-gene determination of responses to ethanol in BXD/Ty recombinant inbred mouse strains

Male mice of parent inbred strains C57BL/6J and DBA/2J, and mice from several of the BXD/Ty Recombinant Inbred (RI) strains derived from the cross of the parent inbred strains were tested for responsiveness to ethanol. Separate groups of mice from these strains were characterized for sensitivity to ethanol's effects to increase activity in an open field and to induce ambulatory ataxia in the grid test. The strain distribution pattern of the RI strains indicated polygenic control of both responses to ethanol. Other mice from this battery were tested for acceptance of an ethanol solution, a measure related to preference drinking. This trait may be substantially influenced by a single gene. Mice were then rendered physically dependent on ethanol through inhalation of ethanol vapor for three days. Severity of handling-induced convulsions was used to index the severity of the ethanol withdrawal syndrome. The distribution of the RI strains indicated possible influence of a major gene on ethanol withdrawal severity.

Tolerance to ethanol hypothermia in inbred mice: genotypic correlations with behavioral responses

Hypothermia was studied 5 min before, and 30 and 60 min after intraperitoneal administration of ethanol (3 g/kg) in 20 inbred strains of mice. Ethanol was given daily for 8 days, and temperatures were taken on Days 1, 3, 5, and 8. Tolerance was indexed by the reduction in hypothermia over days. There were large strain differences in baseline temperature, the hypothermic effect of ethanol, and in development of tolerance to hypothermia. Some strains of mice (DBA/1J, DBA/2N, MA/MyJ, and PL/J) did not develop tolerance to the hypothermic effect of ethanol. Initial sensitivity to the hypothermic effect of ethanol was significantly genetically correlated with tolerance development, indicating control of these responses by common genes. Ethanol-induced changes in activity and ataxia, as well as blood ethanol concentrations, were also assessed. Although there were significant strain differences in activity reduction, ataxia, blood-ethanol concentrations, and changes in these parameters during the course of chronic treatment, none of these variables could explain the genetic differences in hypothermic sensitivity and tolerance.

Classical conditioning of kindled seizures

As a model of reflex epilepsy, rats were classically conditioned to show paroxysmal spike activity to an auditory stimulus. A tone stimulus was paired with seizures induced by kindling. After repeated pairings, paroxysmal discharges were elicited at tone onset. The duration of the tone, proximity to the stimulation, and the number of pairings appeared to be important in the conditioning process.