Schulz Lab

The Schulz Lab (Kalynn Schulz, PI) is interested in how environmental events shape the developing nervous system and adult behavior. In particular, we use rodent models to investigate the mechanisms by which developmental stress exposure confers risk for mental illness.

Sensitive Periods Of Development

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The prenatal period and adolescence are two phases of development consistently linked with adult psychiatric illness. For example, when a woman experiences extreme stress during pregnancy, her offspring have an increased risk for psychiatric problems such as anxiety, depression, and schizophrenia[1-3]. In contrast, adolescence is the time when many psychiatric illnesses tend to emerge[4]. However, the relationship between adolescent development and psychiatric illness remains poorly understood. Therefore, an overarching goal of our laboratory is to understand how the timing of stress exposure across development determines brain and behavioral development.

Nicotinic Acetylcholine Receptors (nAChRs) and Mental Illness

Structure of  nicotinic acetylcholine receptors (nAChRs).

Structure of  nicotinic acetylcholine receptors (nAChRs).

Nicotinic receptor dysfunction is common across many mental illnesses[5, 6]. Nicotine activates nicotinic acetylcholine receptors in the same way as the endogenous neurotransmitter acetylcholine. Rates of smoking are significantly higher amongst depressed, anxious, and schizophrenic individuals compared to the general population[7], suggesting individuals may be “self-medicating” to alleviate some of their symptoms. In support of this possibility, nicotine has anxiolytic actions in humans[7], and nicotine also ameliorates sensory gating attentional deficits in schizophrenia patients[8]. There are several nicotinic receptor subtypes, and the two most widely found in the brain and implicated in psychiatric disorders are the high affinity nicotinic alpha4 beta2 receptors and the low affinity nicotinic alpha7 receptors[9]. Animal studies demonstrate that alpha7 or alpha4 beta2 nicotinic receptor activation facilitates memory performance in a variety of testing paradigms[10, 11]. There is also evidence to suggest that disrupting the balance of hippocampal alpha7 and alpha4 beta2 receptor activity alters memory function in rats[10, 11]. In addition, both alpha7 and alpha4 beta2 hippocampal receptors have been shown to influence anxiety and depressive-like behaviors in rodents[12]. Taken together, these data suggest that alpha7 and alpha4 beta2 nicotinic receptors in the hippocampus play a key role in both cognitive and affective behavioral function.

Representative coronal section depicting a-BTX binding in the hippocampus of a rat. a-BTX selectively binds to alpha7 nAChRs, allowing for quantification of alpha7 receptors in the brain.

Representative coronal section depicting a-BTX binding in the hippocampus of a rat. a-BTX selectively binds to alpha7 nAChRs, allowing for quantification of alpha7 receptors in the brain.

Representative coronal section depicting epibatadine binding in the hippocampus of a rat. Epibatadine selectively binds to alpha4 beta2 nAChRs, allowing for quantification of these receptors in the brain.

Representative coronal section depicting epibatadine binding in the hippocampus of a rat. Epibatadine selectively binds to alpha4 beta2 nAChRs, allowing for quantification of these receptors in the brain.

Prenatal Stress, Behavior, and nAChRs

Behavioral effects of prenatal stress

Prenatal stress has wide-ranging effects on the behavior of rodents. Dozens of published papers demonstrate that prenatal stress increases anxiety and depressive-related behaviors, and decrease memory function. Interestingly, these effects tend to be sexually dimorphic in nature. In our laboratory, we observe prenatal stress-induced increases in anxiety-related behaviors in females but not in males, and decreased memory function in males but not in females[13]. 

Adapted from Schulz et al. 2011. Prenatal stress has sex-specific effects on the behavior of rodents in adulthood. For anxiety-related behavior in the elevated zero, prenatal stress increases anxiety (as indexed by decreased time in open areas of the zero maze) in females but not in males. In contrast, memory performance (assessed via novel object task)  is impaired in males but not females.

Adapted from Schulz et al. 2011. Prenatal stress has sex-specific effects on the behavior of rodents in adulthood. For anxiety-related behavior in the elevated zero, prenatal stress increases anxiety (as indexed by decreased time in open areas of the zero maze) in females but not in males. In contrast, memory performance (assessed via novel object task)  is impaired in males but not females.

We assess anxiety-related behaviors using the elevated zero maze. There are open and closed areas of the zero. The open areas are anxiety-provoking for rodents. As such, more time in the open area = decreased anxiety.

We assess anxiety-related behaviors using the elevated zero maze. There are open and closed areas of the zero. The open areas are anxiety-provoking for rodents. As such, more time in the open area = decreased anxiety.

We use a spatial variant of the novel object recognition task to assess memory function. A rat is placed into an arena with two identical objects, allowed to explore for 5 min, and then returned to the home cage. One hour later, the rat is placed back into the test arena with the same objects, but one of the objects has changed locations within the arena. Rats have a natural interest in novelty, so if the rat remembers the previous spatial configuration of objects, he/she will investigate the object in a new locataion more than the object in the stationary location. If a rat explores both object locations equally, this suggests it doesn't remember the original spatial location.

We use a spatial variant of the novel object recognition task to assess memory function. A rat is placed into an arena with two identical objects, allowed to explore for 5 min, and then returned to the home cage. One hour later, the rat is placed back into the test arena with the same objects, but one of the objects has changed locations within the arena. Rats have a natural interest in novelty, so if the rat remembers the previous spatial configuration of objects, he/she will investigate the object in a new locataion more than the object in the stationary location. If a rat explores both object locations equally, this suggests it doesn't remember the original spatial location.

Effects of prenatal stress on nAChRs

The mechanisms by which prenatal stress alters emotional and memory function appear to be complex and to involve a number of neurotransmitter systems. However, the effects of prenatal stress on the brain cholinergic system has received very little attention, despite the importance of this system for both emotional and memory function. We recently demonstrated that prenatal stress significantly increases hippocampal alpha4 beta2 receptor levels in adulthood, suggesting that prenatal stress disrupts normal cholinergic signaling[13].In contrast, the effects of prenatal stress on alpha7 receptors were more subtle. Specifically, prenatal stress increased alpha7 nAChRs in the dentate gyrus of females. These sex-specific effects of prenatal stress may contribute to the sex-specific nature of behavioral impairments caused by prenatal stress.

Adapted from Schulz et al., 2013, Developmental Neurobiology. Prenatal stress significantly increased alpha4 beta2 nAChRs in both sexes across all subregions of the hippocampus analyzed. 

Adapted from Schulz et al., 2013, Developmental Neurobiology. Prenatal stress significantly increased alpha4 beta2 nAChRs in both sexes across all subregions of the hippocampus analyzed. 

Adapted from Schulz et al., 2013, Developmental Neurobiology.  Prenatal stress increased alpha7 nAChRs in the subregions of the dentate gyrus in females but not in males.

Adapted from Schulz et al., 2013, Developmental Neurobiology.  Prenatal stress increased alpha7 nAChRs in the subregions of the dentate gyrus in females but not in males.

Choline as a Stress Intervention

Choline is an essential nutrient and an important structural component of all cell membranes. Therefore, a women's need for choline increases during pregnacy because the fetus requires high choline levels to build new cells. Although choline is abundant in protein-rich foods such as eggs, meats, and beans, about 25% of women do not meet the recommended levels of choline during pregnancy[14], and are consequently at a 4-fold greater risk of having a child with neural tube defects. Interestingly, choline is also a neurotransmitter in the brain and acts directly on the nAChRs that are altered by prenatal stress. As such, we tested whether perinatal dietary choline supplementation counteracts the detrimental effects of prenatal stress. Specifically, we fed stressed and nonstressed dams a choline-supplemented or control diet during pregnancy and lactation, and measured anxiety-related behaviors in adulthood.

Pregnant dams experienced stress procedures during the last week of gestation, or were left undisturbed (control). Half of all stressed and nonstressed dams were fed a choline-supplemented diet during pregnancy and through lactation (postnatal day 21), whereas the other half of dams were fed control chow (normative choline levels). Offspring were weaned at 21 days of age, and all animals were fed the control chow for the remainder of the experiment. In adulthood, animals were tested for anxiety-related behavior in the elevated zero maze, and memory function using the novel object recognition task.

Pregnant dams experienced stress procedures during the last week of gestation, or were left undisturbed (control). Half of all stressed and nonstressed dams were fed a choline-supplemented diet during pregnancy and through lactation (postnatal day 21), whereas the other half of dams were fed control chow (normative choline levels). Offspring were weaned at 21 days of age, and all animals were fed the control chow for the remainder of the experiment. In adulthood, animals were tested for anxiety-related behavior in the elevated zero maze, and memory function using the novel object recognition task.

Adapted from Schulz et al., 2013, Behavioural Brain Research. The effects of prenatal stress (PS) and perinatal choline on female anxiety-related behaviors and male spatial memory. (A) Perinatal choline supplementation ameliorates the effects of PS on adult anxiety-related behaviors in females but not males (male data not shown). (B) Perinatal choline supplementation ameliorates the effects of PS on adult spatial memory function in adult males but not females (female data not shown).

Adapted from Schulz et al., 2013, Behavioural Brain Research. The effects of prenatal stress (PS) and perinatal choline on female anxiety-related behaviors and male spatial memory. (A) Perinatal choline supplementation ameliorates the effects of PS on adult anxiety-related behaviors in females but not males (male data not shown). (B) Perinatal choline supplementation ameliorates the effects of PS on adult spatial memory function in adult males but not females (female data not shown).

Current Projects

Effects of prenatal stress on hypothalamic nAChRs

Prenatal stress is associated with reproductive dysfunctions in offspring including mating behavior, sexual orientation, female fertility, and female fecundity. Nicotinic acetylcholine receptors (nAChR) in the hypothalamus regulate these same processes, but whether the effects of prenatal stress on reproductive function are mediated by altered nicotinic acetylcholine receptors is not known. Given that prenatal stress alters levels of nAChRs in other brain regions, we are testing the hypothesis that maternal stress alters the development of hypothalamic alpha7 nicotinic acetylcholine receptor levels in offspring. 

Effects of prenatal stress on basolateral amygdala nAChRs

Both human and animal studies demstrate that prenatal stress impacts basolateral amygdala (BLA) development. For example, higher maternal cortisol concentrations in early gestation are associated with larger right amygdala volumes in girls at 7 years of age[15]. Furthermore, early gestational cortisol levels are associated with affective problems in girls, suggesting that this association might be mediated, in part, by the larger right amygdala volume [15]. In rodents, the offspring of prenatally stressed Sprague-Dawley dams have smaller BLA nuclei volumes, smaller BLA anterior/posterior lengths, and decreased numbers of neurons and glial cells in the brain[16]. Given that PS impacts overall BLA development, and nicotinic receptors in the BLA are important for many of the behaviors impaired by PS, we hypothesize that PS will also alter levels of nAChRs in the BLA.  

Prenatal programming of the effects of adolescent stress?

From the standpoint of sensitive periods of brain development, and individual’s previous stressful experiences may alter the course of brain development in a manner that confers increased risk, or even resilience, to the impact of subsequent stressors. Although both prenatal and adolescent stress are associated with increased risk of mental illness[1-3], whether prenatal stress exposure increases sensitivity to stress during adolescence is not known. Preclinical rodent models have enormous potential for elucidating the relationships between the timing of stress exposure across development and dysfunction. Therefore, we are currently testing the hypothesis that early stress exposure modifies the behavioral impact of stress during adolescence. This hypothesis predicts that the combined effects of prenatal and adolescent stress on behavioral function will be greater than the isolated effects of stress during either time period.

References

1.            Walker, E., V. Mittal, and K. Tessner, Stress and the hypothalamic pituitary adrenal axis in the developmental course of schizophrenia. Annual Review of Clinical Psychology, 2008. 4: p. 189-216.

2.            Walker, E., et al., Schizophrenia: Etiology and course. Annual Review of Psychology, 2004. 55: p. 401-430.

3.            Walker, E.F., Z. Sabuwalla, and R. Huot, Pubertal neuromaturation, stress sensitivity, and psychopathology. Development and Psychopathology, 2004. 16(4): p. 807-824.

4.            Steinberg, L., et al., The study of developmental psychopathology in adolescence: integrating affective neuroscience with the study of context, in Handbook of Developmental Psychopathology, D. Cicchetti, Editor 2005, John Wiley & Sons: New York, NY.

5.            Newhouse, P., A. Singh, and A. Potter, Nicotine and nicotinic receptor involvement in neuropsychiatric disorders. Current Topics in Medicinal Chemistry, 2004. 4(3): p. 267-282.

6.            Singh, A., A. Potter, and P. Newhouse, Nicotinic acetylcholine receptor system and neuropsychiatric disorders. Idrugs, 2004. 7(12): p. 1096-1103.

7.            Araki, H., K. Suemaru, and Y. Gomita, Neuronal nicotinic receptor and psychiatric disorders: Functional and behavioral effects of nicotine. Japanese Journal of Pharmacology, 2002. 88(2): p. 133-138.

8.            Martin, L.F. and R. Freedman, Schizophrenia and the alpha 7 nicotinic acetylcholine receptor, in Integrating the Neurobiology of Schizophrenia2007. p. 225-246.

9.            Adams, C.E. and K.E. Stevens, Evidence for a role of nicotinic acetylcholine receptors in schizophrenia. Frontiers in Bioscience, 2007. 12: p. 4755-4772.

10.         Graef, S., et al., Cholinergic receptor subtypes and their role in cognition, emotion, and vigilance control: An overview of preclinical and clinical findings. Psychopharmacology, 2011. 215(2): p. 205-229.

11.         Levin, E.D., F.J. McClernon, and A.H. Rezvani, Nicotinic effects on cognitive function: behavioral characterization, pharmacological specification, and anatomic localization. Psychopharmacology, 2006. 184(3-4): p. 523-539.

12.         Mineur, Y.S. and M.R. Picciotto, Nicotine receptors and depression: revisiting and revising the cholinergic hypothesis. Trends in Pharmacological Sciences, 2010. 31(12): p. 580-586.

13.         Schulz, K.M., et al., Maternal stress during pregnancy causes sex-specific alterations in offspring memory performance, social interactions, indices of anxiety, and body mass. Physiology & Behavior, 2011. 104(2): p. 340-7.

14.         Zeisel, S.H. and K.A. da Costa, Choline: an essential nutrient for public health. Nutrition Reviews, 2009. 67(11): p. 615-623.

15.         Buss, C., et al., Maternal cortisol over the course of pregnancy and subsequent child amygdala and hippocampus volumes and affective problems. Proc Natl Acad Sci U S A, 2012. 109(20): p. E1312-9.

16.         Kraszpulski, M., P.A. Dickerson, and A.K. Salm, Prenatal stress affects the developmental trajectory of the rat amygdala. Stress, 2006. 9(2): p. 85-95.