Selective Serotonin Reuptake Inhibitor (SSRI) treatment of early postnatal mice reverses their prenatal stress-induced brain dysfunction

In paper citation: (Ishiwata, Shiga & Okado, 2005).

The last review that I read about SSRIs in development talked about their paradoxical effects, and the long-term damage that they can cause. This paper comes in from a completely different angle and looks at the benefits of SSRIs immediately after birth. I have to say that I am simply fascinated at the extent to which SSRIs seem to affect development.

Important background:

• Serotonin concentration and synaptic density in the hippocampus, as well as spatial learning ability are reduced after prenatal stress (Hayashi, et al., 1998)
• 5HT and noradrenaline (NA) are involved in the regulation of mineralocorticoid (MR) and glucocorticoid (GR) mRNA expression (Seckl & Fink, 1992)
• SSRIs suppress HPA axis activity, decrease CRF mRNA expression and increase neurogenesis in the hippocampus of adult rodents.
• There were five groups in this study:
• Mice from non-stressed mothers, no SSRI treatment (C)
• Mice from non-stressed mothers with SSRI treatment from 1-3 weeks (CS)
• Mice from stressed mothers with no SSRI treatment (S)
• Mice from stressed mothers with SSRI treatment from 1-3 weeks (SS)
• Mice from stressed mothers who received SSRIs at 6-8 weeks of age (L-SS)

The new findings from this paper:

• Corticosterone levels:
• Mice from group S had 21% higher circulating corticosterone after restraint stress at week 3.
• Mice from group SS had corticosterone concentrations similar to controls.
• Monoamine concentrations:
• Mice from group SS and CS had significantly higher levels of serotonin (5-HT) than controls at postnatal week 3 and 6 by about 30% in the control treated mice and 60% in the stressed treated mice. 
• The 5-HT metabolite, 5HIAA was elevated in S mice compared to C mice. 
• Thus the 5-HT turnover rate was markedly elevated (77% greater) compared to controls. 
• Dendritic spine and synapse density:
• At week 3, spine density at the stratum radiatum in the S mice was 21% less than the control mice.
• At week 3, the SS mice had significantly more spines than S mice and resembled the control mice.
• At week 9, the S mice had 19% less spine and synapse density than controls.
• At week 9, the SS mice looked like normal mice.
• The mice with later SSRI treatment increased their spine density by 10%, but this was not significant.
• Spatial learning:
• C, CS, and SS mice all performed equally well at the Morris Water maze, but the S and LSS mice had learning impairments at the second and third exposure to the maze. These two groups also showed impairments at the reversal. 

Further information:

• Neonatal handling also reverses prenatal stress-induced behavioral deficits (Wakshlak & Weinstock, 1990).
• Chronic tianeptine treatment also reverses immobility time in the forced swim task (Morley-Fletcher, et al., 2003) *I'm surprised that this wasn't mentioned in the animal model overview.
• Hippocampal glucocorticoids are reduced in prenatally stressed animals, which is not what you would expect at first for cell death (Szuran, et al., 2000).
• The age of the rat may account for its stress response differences between prenatally stressed rats and controls (McCormick et al., 1995). 
• The first 3 postnatal weeks are very important for the development of the HPA axis. The concentration of GR in the rat hippocampus is low during week 1, then increases to adult values (Olpe & McEwen, 1976; Clayton, et al., 1977). The HPA axis reached adult levels of functionality by postnatal week 3. 

Remaining questions:

What happens to mice from stressed mothers who are raised by surrogates? Is it the mother's glucocorticoid levels that programs these mice or is it the mother's caregiving behaviors?

What happens to female rats who are in the same paradigm?

How did they get monoamine concentrations from both week 3 and week 6? Did they just plow through mice?

If mice postnatal week 0- postnatal week 2 correlate to the third trimester of primate births, could SSRI therapy actually help reverse learning impairments if administered acutely and early?

Listening to Prozac but hearing placebo: A meta-analysis of antidepressant medication

In paper citation (Kirsch & Sapirstein, 1998)

This paper specifically looks at the effects of the placebo in placebo-controlled drug studies treating depression. This analysis only includes drug studies before 1995 and therefore misses most of the modern drugs prescribed today. However, Kirsch and Sapirstein's results are really shocking. They find that in drug studies, the placebo group improves in proportion to the effectiveness of the drug. The correlation between the placebo response and the drug response is r=.90, p<.001 and the placebo response is 75% of the drug response. So if the drug response in a sertraline drug trial was 2.0, the placebo response in that trial would be around 1.5. These numbers were slightly higher for active placebos... side effects actually may convince people that they are receiving full treatment, and therefore cause them to expect a better response. This is also interesting in light of the more modern Turner and colleagues meta-analysis, which found that 49% of FDA approved clinical trials show no significant difference between placebo and antidepressant trials. Perhaps both the experimental and control patients are improving in proportion to the expected efficacy of the drug, and so only the most effective drugs will come out ahead of their placebos.

Furthermore, the authors compared the effect of taking a placebo pill to receiving no treatment while on a wait-list for psychotherapy trials. For the people on wait-lists, or receiving no placebo treatment at all, their depression scores worsened overall during the course of the study. This shows that the placebo pill is more effective than no treatment.

My remaining questions actually involve the rating scales of depression. It could be that different research centers treat their patients more holistically, and that is why the scores are so well correlated, but it could also be that people respond to the depression interviews in a rote manner. For example, if I know the symptoms of depression, and I want to be a good research subject, I may describe my pre-treatment symptoms in a way so that the doctor will give me the quick fix and treat me with an antidepressant. Then when the doctor asks me follow ups, I also know what improvement should look like, and I've been looking out for that in my daily life, and so I focus on the improvement for my follow up questionnaire. Whether the drug has actually improved my mood is hard to tell, because I started by looking for symptoms to describe to my doctor, and then I started looking for improvements to tell to my doctor. Thus the placebo effect.

Does anyone else think that is totally plausible? I guess Kirsch & Sapirstein would, but they do not mention it in their discussion. In cases of mild to moderate depression, I would like to see a study that looks at various types of placebos to see what works best. Inert substances should be better for our bodies in the long run, and especially useful for pregnant mothers who desire treatment for mood disorders.

Selective Publication of Antidepressant Trials and its Influence on Apparent Efficacy

In paper citation (Turner, et al., 2008).

In groundbreaking work, Turner and his colleagues invoked the freedom of information act to "check up" on the efficacy of antidepressants. Basically, the majority of studies with negative or questionable results about the efficacy of an antidepressant versus a placebo never get published and therefore do not have a chance to influence people's mentality about the efficacy of antidepressant drugs.

Basically, among the published literature, 94% of antidepressant trials conducted are positive. However, among the FDA registered clinical trials of antidepressants, only 51% of antidepressant trials are positive. This gives us great pause for consideration as pharmaceuticals make billions of dollars a year on these drugs.

I personally would trust the FDA effect sizes now that they are out. The effect size compares the difference in means between the control and the placebo group at the end of the treatment period divided by the pooled standard deviation.

The overall effect size was .31 for the modern antidepressants.

Sleep Disturbance Associated with an enhanced Orexinergic system induced by chronic treatment with paroxetine and milnacipran

In paper citation (Rahmadi, et al., 2011).

Mice treated with the SSRI paroxetine 10mg/kg or SNRI milancipran (30mg/kg) had their sleep recorded on day 7 and their orexinergic receptor and mRNA for orexinergic receptors quantified on day 28. Both antidepressants significantly decreased total sleep time and decreased total NREM sleep. OX1R and OX2R mRNA expression significantly increased in the hypothalamus of animals on antidepressants, as did the H1R and histidine decarboxylase mRNA expression in the frontal cortex.

Paroxetine still has an affinity for the H1R receptor of .0045*10^-7/equilibrium dissociation constant, which may be blockading the H1R receptor and thus upregulating it (Richelson, 1996). Richelson did not have the binding affinity for milnacipran in his paper.

Histidine decarboxylase is involved in the synthesis of new histamines, so the blockade of H1R receptors might promote this increased synthesis, and thus increased mRNA expression in the frontal cortex.

Orexins are synthesized in the lateral hypothalamus, so the increase in Orexinergic receptor mRNA expression might indicate that little orexin is making it back to the hypothalamus for use in a feedback mechanism. The orexins might be binding in wake-promoting areas and getting metabolized there. Increasing total orexins should increase a person's wakefulness.

New Perspectives on the Neurodevelopmental effects of SSRIs

In paper citation: (Homberg, Schubert, & Gaspar, 2009)

This paper is a review article and therefore is mostly just a collection of useful facts. I will leave citations to be looked up using the paper.

Introduction

• Selective serotonin reuptake inhibitors inhibit the function of the serotonin transporter (5HTT), which is responsible for the high affinity reuptake of serotonin.
• The 5HTT has only one gene and is an identical protein in the peripheral and central nervous system, making it hard to target.
• 10-16% of pregnant women are depressed; 25% of these women continue SSRI use through their pregnancy and another .5% of these women start taking SSRIs while pregnant.
• The SSRIs reach the fetus through the placenta and the newborn through breastmilk. 
• Perinatal administration of SSRIs causes anxiety and depression-like behaviors in rodents (the SSRI paradox)

The SSRI paradox

• In adults the chronic use of SSRIs:
• decrease anxiety/depression
• decrease REM sleep
• cause cardiodepression and vasodilation
• In contrast, perinatal exposure to SSRIs:
• increases anxiety/depression
• increases REM sleep
• blunts pain responses
• improves spatial learning
• increases cocaine-induced conditioned place preference
• causes dilated cardiomyopathy

It is important to note that functional brain maturity at postnatal day 12&13 in rodents are most similar to the day of birth in primates. 

Cellular Targets of SSRIs during development

• At mid gestation (E11) the 5HTT gene is first expressed in the raphe nucleus.
• At birth, the 5HTT gene is expressed in many regions of the frontal cortex.
• 5HTT expression in non-serotonergic neurons ends rapidly during during the second postnatal week.
• Repression of 5HTT expression is controlled by circulating hormones, such as thyroid, that peak in postnatal life.

Signalling Pathways of 5HT

• 5HT1B receptors are similar to the 5HTT and regulate activity dependent axon-remodelling by controlling glutamate release and cyclic AMP production. This in turn is involved in the production of netrins and ephrins. This could result in an altered brain topography.
• 5HTT regulates 5HT levels and thus determine the activation of pre and post synaptic 5HT receptors. 

Lessons from rodent behavioral studies

Embryonic exposure to SSRIs:

• increased neonatal mortality
• reduced body weight
• reduced the receptor density of 5HT2A/2C 
• reduced expression of 5HT and 5HTT
• resulted in depression-like symptoms during adulthood
• reduced exploratory behavior and increased anxiety-related phenotype
• reduced aggression
• reduced sexual behavior
• increased REM sleep and anhedonia
• blunted thermal and tactile responses
• delayed motor development
• improved spatial learning
• reduced impulsivity
• kept the rats from swimming on a forced swim test
• increased sensitivity to cocaine-seeking behaviors

Genetic vs. Pharmacological models of 5HTT downregulation

• 5HT1A affected in knockout mice, but not in mice treated with SSRIs neonatally
• Cognitive effects seem similar, but not enough testing has been done to be sure.

Neuroanatomical differences in rodents with perinatal SSRI exposure:

• Somatosensory cortex:
• treated rats have thinned terminal clusters and altered dendritic organization in the spiny stellate neurons in layer 4 barrel cortex
• rats have impaired transmission of tactile information in the somatosensory cortex, but do not lose their tactile skills completely
• structural organization of thalamocortical innervations perturbed
• Corticolimbic circuit
• The dorsal raphe nucleus, mPFC and amygdala make up this serotonergic circuit
• in knockout rodents, the PFC and amygdala have pyramidal cells with abnormally increased branching and  abnormally increased dendritic spine density

In humans

• Humans carrying the short allelic variant of the 5HTT promoter have reduced circulating 5HTT in their blood. These people show increased stress responsivity as newborns, and increased amygdala activity as adults.
• This allele also modulates the antidepressant effects of SSRIs.

Sleep-wake effects of meta-chlorophenyl piperazine and mianserin in the behaviorally depressed rat

In paper citation: (Mavanji, Meti, & Datta, 2002)

All rats in this paper were made depressed using neonatal clomipramine treatments. All rats were male. Controls were treated with saline, but handled in the same manner.

The new findings from this paper are:

1. REM sleep onset latency is significantly shorter in depressed rats than in controls. Rats spend ~25% less time in SWS before their first REM cycle.
2. The total number of REM sleep episodes is significantly (~2X) higher in depressed rats than in controls.
3. The total amount of REM sleep in depressed rats is significantly more than controls (>2X more REM).
4. mCPP, a serotonin agonist, decreased the total amount of REM sleep in the depressed rats by decreasing the total number of REM sleep episodes and increasing the REM sleep onset latency.
5. mianserin, a SSRI, decreased the total amount of REM sleep in the depressed rats by decreasing the total number of REM sleep episodes. 

Other important information:

• REM sleep deprivation in humans alleviates symptoms of depression (Vogel et al., 1975).
• REM sleep deprivation in rats normalizes deficits in sexual activity and aggression, which are symptoms of rat depression (Vogel et al., 1990).
• mCPP is known to increase serotonin release (Bauman et al., 1993) and reduce REM sleep in humans ( Lawlor et al., 1991).
• Clomipramine treated rats have less serotonin in their brain than control rats (Mavanji & Meti, 1999).
• Serotonin inhibits REM sleep (McCarley, 1982) and so serotonin agonists reduce REM sleep (Quattrochi et al., 1992; Stickgold et al., 1993)
• mCPP normally reduces REM in the controls if it is injected systemically because it inhibits acetylcholine release (Vizi et al., 1981) It didn't in this case because it was injected  ICV.
• Mianserin typically reduces REM in both depressive patients and normal subjects (Mendlewicz et al., 1995; Tormey et al., 1980).

Remaining questions:

• How does the clomipramine rat model work? Would this still be the case in social stress depressed rats, or learned helplessness rats?
• The CLI+mianserin group seemed to have low wakefulness and high SWS in my opinion. I'm surprised that it didn't come out significant.